Electronics Project Circuts

LEDs IN SERIES & PARALLEL

<span style="font-family: Arial; font-size: x-small;"><span style="font-family: Arial; font-size: x-small;"><b><span style="color: blue; font-family: Arial; font-size: medium;">LEDs IN SERIES <br />
  </span></b><span style="font-family: Trebuchet MS; font-size: x-small;">LEDs can be placed in 
  series providing some features are taken into account. The main item to 
  include is a current-limiting resistor.<br />
  A LED and resistor is called a string. A string can have 1, 2, 3 or more 
  LEDs. <br />
  Three things must be observed:<br />
  1. MAXIMUM CURRENT through each string = 25mA. <br />
  2. The CHARACTERISTIC VOLTAGE-DROP must be known so the correct 
  number of LEDs are used in any string.<br />
  3. A DROPPER RESISTOR must be included for each string.<br />
  The following diagrams show examples of 1-string, 2-strings and 3-strings: 
  </span> <img border="0" height="255" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/Strings-1.gif" width="660" /><span style="font-family: Trebuchet MS; font-size: x-small;"><br />
  <br />
  </span><b><span style="color: blue; font-family: Arial; font-size: medium;">LEDs IN</span></b><span style="font-family: Arial; font-size: x-small;"><b><span style="color: blue; font-family: Arial; font-size: medium;"> 
  PARALLEL</span></b></span><span style="font-family: Trebuchet MS; font-size: x-small;"><br />
  </span><span style="font-family: Trebuchet MS; font-size: x-small;">LEDs <span style="color: red;"><b>
  CANNOT</b></span> be placed in parallel - until you read this: <br />
  LEDs "generate" or "possess" or "create" a voltage across them called 
  the
  </span><span style="font-family: Trebuchet MS; font-size: x-small;">CHARACTERISTIC VOLTAGE-DROP  
  (when they are correctly placed in a circuit). <br />
  This voltage is generated by the type of crystal and is different 
  for each colour as well as the "quality" of the LED (such as 
  high-bright, ultra high-bright etc). This characteristic cannot be 
  altered BUT it does change a very small amount from one LED to another 
  in the same batch. And it does increase slightly as the current 
  increases.<br />
  For instance, it will be different by as much as 0.2v for red LEDs and 
  0.4v for white LEDs from the same batch and will increase by as much as 
  0.5v when the current is increased from a minimum to maximum.<br />
  You can test 100 white LEDs @15mA and measure the CHARACTERISTIC 
  VOLTAGE-DROP to see this range. <br />
  If you get 2 LEDs with identical
  </span><span style="font-family: Trebuchet MS; font-size: x-small;">CHARACTERISTIC VOLTAGE-DROP, 
  and place them in parallel, they will each take the same current. This 
  means 30mA through the current-limiting resistor will be divided into 
  15mA for each LED. <br />
  However if one LED has a higher
  </span><span style="font-family: Trebuchet MS; font-size: x-small;">CHARACTERISTIC VOLTAGE-DROP, 
  it will take less current and the other LED will take considerably more. 
  Thus you have no way to determine the "current-sharing"  in a 
  string of parallel LEDs.  If you put 3 or more LEDs in parallel, 
  one LED will start to take more current and will over-heat and you will 
  get very-rapid LED failure.  As one LED fails, the others will take 
  more current and the rest of the LEDs will start to self-destruct. The 
  reason why they take more current is this: the current-limit resistor 
  will have been designed so that say 60mA will flow when 3 LEDs are in 
  parallel. When one LED fails, the remaining LEDs will take 30mA each. <br />
  Thus <b>LEDs in PARALLEL </b>should be avoided. <br />
  Diagram <span style="color: navy;"><b>A</b></span> below shows two green LEDs 
  in parallel. This will work provided the Characteristic Voltage Drop 
  across each LED is the same. <br />
  In diagram <span style="color: navy;"><b>B</b></span> the Characteristic 
  Voltage Drop is slightly different for the second LED and the first green LED will glow 
  brighter. <br />
  In diagram <span style="color: navy;"><b>C </b></span>the three LEDs have 
  different Characteristic Voltage Drops and the red LED will glow very 
  bright while the other two LEDs will not illuminate. All the current 
  will pass through the red LED and it will be damaged. <br />
  The reason why the red LED will glow very bright is this: It has the 
  lowest Characteristic Voltage Drop and it will create a 1.7v for the three 
  LEDs. The green and orange LEDs will not illuminate at this voltage and 
  thus all the current</span></span><span style="font-family: Trebuchet MS; font-size: x-small;"> 
  from the dropper resistor will flow in the red LED and it will be 
  destroyed. </span><span style="font-family: Arial; font-size: x-small;">
  <span style="font-family: Trebuchet MS; font-size: x-small;"><br />
 </span><img border="0" height="220" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/ParallelLEDs-1.gif" width="600" /></span></span>

LEDs IN SERIES & PARALLEL

LEDs IN SERIES LEDs can be placed in series providing some features are taken into account. The main item to include is a current-l...

Identifying a LED

Sunil Jadhavar LED Projects 7:17 AM

Identifying a LED

A LED does not have a "Positive" or "Negative" lead. It has a lead identified as the "Cathode" or Kathode...

5 channel radio remote control

Sunil Jadhavar 5:27 AM

<b>TX-2B / RX / 2B  5 channel radio remote control.</b><br />

<div style="text-align: justify;">
This article is about a simple 5 channel
 radio remote control circuit based on ICs TX-2B and RX-2B from Silan 
Semiconductors.  TX-2B / RX-2B is a remote encoder decoder pair that can
 be used for remote control applications. TX-2B / RX-2B has five 
channels, wide operating voltage range (from 1.5V to 5V), low stand by 
current (around 10uA), low operating current (2mA), auto power off  
function and requires few external components. The TX-2B / RX-2B was 
originally designed for remote toy car applications, but they can be 
used for any kind of remote switching application.</div>
<br />
<b><span style="font-size: large;">Circuit diagrams and description</span>.</b><br />

<h4>
Remote encoder / transmitter circuit.</h4>
<div class="wp-caption aligncenter" id="attachment_6287" style="width: 1185px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-radio-remote-control-circuit.jpg"><img alt="radio remote control transmitter ciruit" class="size-full wp-image-6287" height="250" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-radio-remote-control-circuit.jpg" title="5 channel radio remote control circuit" width="640" /></a><div class="wp-caption-text">
5 channel redio remote control encoder / transmitter circuit</div>
</div>
<div style="text-align: justify;">
The TX-2B forms the main part of the 
circuit. Push button switches S1 to S5 are used for activating (ON/OFF) 
the corresponding O/P channels in the receiver / decoder circuit. These 
push button switches are interfaced to the built-in latch circuitry of 
the TX-2B. Resistor R7 sets the frequency of the TX-2B’s internal 
oscillator. Resistor R1 and Zener diode D1 forms a simple Zener 
regulator circuit for providing the IC with 3V from the 9V main supply. 
C2 is the filter capacitor while C1 is a noise by-pass capacitor. D2 is 
the power on indicator LED while R6 limits the current through the same 
LED. S1 is the ON/OFF switch. The encoded control signal will be 
available at pin 8 of the IC. The encoded signal available at pin 8 is 
without carrier frequency. This signal is fed to the next stage of the 
circuit which is a radio transmitter. Crystal X1 sets the oscillator 
frequency of the transmitter section. R2 is the biasing resistor for Q1 
while R3 limits the collector current of Q1. The encoded signal is 
coupled to the collector of Q1 through C3 for modulation. Transistor Q2 
and associated components provide further amplification to the modulated
 signal.</div>
<h4 style="text-align: justify;">
Remote receiver / decoder circuit.</h4>
<h4 style="text-align: justify;">
<div class="wp-caption aligncenter" id="attachment_6288" style="width: 910px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-remote-control-receiver.png"><img alt="" class="size-full wp-image-6288" height="457" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-remote-control-receiver.png" title="5 channel remote control receiver" width="640" /></a><div class="wp-caption-text">
5 channel radio remote decoder</div>
</div>
</h4>
<div style="text-align: justify;">
The remote receiver circuit is built 
around the IC RX-2B. The first part of the circuit is a radio receiver 
built around transistor Q1. The received signal is demodulated and fed 
to pin 14 of the IC. Pin 14 is the input of the built in inverter inside
 the IC. R2 sets the frequency of the IC’s internal oscillator. O/P 1 to
 O/5 are the output pins that are activated corresponding to the push 
buttons S1 to S5. Zener diode D1 and resistor R12 forms an elementary 
Zener regulator for supplying the RX-2B with 3V from the 9V main supply.
 C12 is the filter capacitor while R11 is the current limiter for the 
radio receiver section. Diode D2 protects the circuit from accidental 
polarity reversals. C15 is another filter capacitor and C14 is a noise 
by-pass capacitor.</div>
<h3>
Notes.</h3>
<ul>
<li>This circuit can be assembled on a vero board or  a PCB.</li>
<li>Use 9V DC for powering the transmitter / receiver circuits.</li>
<li>Battery is the better option for powering the transmitter / receiver circuit.</li>
<li>If you are using a DC power supply circuit, it must be well regulated and free from any sort of noise.</li>
<li>Both ICs must be mounted on holders.</li>
</ul>
<h4>
Interfacing relay to the RX-2B output.</h4>
<div style="text-align: justify;">
The method for interfacing a relay to 
the output of RX-2B is shown below. When push button switch S1 of the 
transmitter circuit is pressed, pin O/P1 (pin 7 of the RX-2B) goes high.
 This makes the transistor 2N2222 to conduct and the relay is activated.
 The same technique can be applied to other output pins of the RX-2B. 
The relay used here is a 200 ohm type and at 9V supply voltage the load 
current will be 45mA which is fine for 2N2222 whose maximum possible 
collector current is 900mA. When using relays of other ratings this 
point has to be remembered and do not use a relay that consumes a 
current more than the maximum possible collector current of the driver 
transistor.</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_6286" style="width: 422px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/interfacing-relay-to-RX-2B-output.png"><img alt="transistor relay driver" class="size-full wp-image-6286" height="363" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/interfacing-relay-to-RX-2B-output.png" title="interfacing relay to RX-2B output" width="412" /></a><div class="wp-caption-text">
Interfacing relay to the remote decoder</div>
</div>
<table><tbody>
<tr><td>

5 channel radio remote control

TX-2B / RX / 2B 5 channel radio remote control. This article is about a simple 5 channel radio remote control circuit based on ICs TX-2...

Flashing battery monitor

Sunil Jadhavar LED Projects 5:24 AM

<div style="text-align: justify;">
<b>Description.</b></div>
<div style="text-align: justify;">
Here is a simple circuit in which an LED
 will continue flashing as long as the voltage of the battery to be 
monitored is above the set level.The transistors Q1 and Q2 are wired as a
 complementary astable multivibrator.The circuit can operate from  a 
voltage range from 6V to 12V. The voltage level at which LED has to stop
 flashing can be set by adjusting the preset R4.When the battery voltage
 reaches the threshold the flashing frequency decreases and when the 
voltage goes below the threshold the LED becomes OFF.The diode D1 is 
used to compensate the changes in the base emitter voltage of Q1 due to 
temperature changes.</div>
<div style="text-align: justify;">
<b>Circuit diagram with Parts list.</b></div>
<div style="text-align: justify;">
<b><a href="http://www.circuitstoday.com/wp-content/uploads/2009/04/flashing-battery-monitor-circuit.jpg"><img alt="flashing-battery-monitor-circuit" class="alignnone size-full wp-image-846" height="450" src="http://www.circuitstoday.com/wp-content/uploads/2009/04/flashing-battery-monitor-circuit.jpg" title="flashing-battery-monitor-circuit" width="614" /></a><br />
</b></div>
<div style="text-align: justify;">
<b>Notes.</b></div>
<ul>
<li>Assemble the circuit on a general purpose PCB.</li>
<li>Batteries from 6V to 12V can be monitored by this circuit.</li>
<li>The diode D1 must be a Schottky diode.</li>
</ul>

Flashing battery monitor

Description. Here is a simple circuit in which an LED will continue flashing as long as the voltage of the battery to be monitored is a...

Battery charger circuit using L200

Sunil Jadhavar 5:19 AM

<strong>Description.</strong>
<br />
<div align="justify">
A very simple battery charger circuit having reverse 
polarity indication is shown here.The circuit is based on IC L200 . L200
 is a five pin variable voltage voltage regulator IC.The charging 
circuit can be fed by the DC voltage from a bridge rectifier or center 
tapped rectifier.Here the IC L200 keeps the charging voltage 
constant.The charging current is controlled by the parallel combination 
of the resistors R2 & R3.The POT P1 can be used to adjust the 
charging current.This circuit is designed to charge a 12 V lead acid 
battery.The transistor t1,diode D3 and LED are used to make a battery 
reverse indicator.In case the battery is connected in reverse polarity 
,the reverse polarity indicator red LED D5 glows.When the charging 
process is going on the battery charging indicator green LED D4 glows.</div>
<div align="justify">
<br /></div>
<div align="justify">
<br /></div>
<div align="justify">
<strong>Circuit diagram with Parts list.</strong></div>
<div align="justify">
<br /></div>
<div align="justify">
 <a href="http://www.circuitstoday.com/wp-content/uploads/2008/08/battery-charger-circuit-using-l200.JPG" title="battery-charger-circuit-using-l200.JPG"><img alt="battery-charger-circuit-using-l200.JPG" src="http://www.circuitstoday.com/wp-content/uploads/2008/08/battery-charger-circuit-using-l200.JPG" /></a></div>
<div align="justify">
<br /></div>
<div align="justify">
<br /></div>
<div align="justify">
<strong>Notes. </strong></div>
<ul>
<li>The circuit can be assembled on a good quality PCB or common board.</li>
</ul>
<ul>
<li>The values of R2 & R3 can be obtained from the equation,</li>
</ul>
(<strong>R</strong>2//<strong>R</strong>3) =( <strong>V</strong>5-<strong>2</strong>)/(<strong>I</strong>o).<br />

Where <strong>V</strong>5 is  the charging voltage (voltage at pin 5) and <strong>I</strong>o is the charging current.<br />

<ul>
<li>The POT R8 can be used for fine adjustments of charging current.</li>
</ul>
<ul>
<li>If battery is connected in reverse polarity the RED LED will glow.</li>
</ul>
<ul>
<li>When the  charging is going on the GREEN LED will glow.</li>
</ul>
<ul>
<li>The rectified input voltage to the charger can be 18V.</li>
</ul>

Battery charger circuit using L200

Description. A very simple battery charger circuit having reverse polarity indication is shown here.The circuit is based on IC L200 . L2...

Three phase auto changer circuit

Sunil Jadhavar 5:18 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
The circuit given here is designed by Mr.Seetharaman V.S (<a href="mailto:seethasub@hotmail.com">seethasub@hotmail.com</a>) from Chennai.</div>
<div style="text-align: justify;">
<span style="color: grey;"><em><strong>Seetharaman’s comments about the circuit</strong></em></span>: This circuit is a modification of  High & Low voltage cut-off with delay& alarm
 circuit  appeared in Circuits today, which I have tried and found to be
 quite reliable. You can adopt this circuit with small modification. Use
 a transformer with secondary 15 – 0 – 15 AC Volt at 500mA, for 18Volt 
relay operation. Normally any modern electrical / electronic equipment 
can operate with 230 Volt ± 15% AC supply. That is, it can stand normal 
voltage operating range of 195 to 265 Volts. It may misbehave beyond 
this voltage range. You can choose the practical voltage required for 
the low end high cut off to change over to other phase.</div>
<strong>Circuit diagram.</strong><br />

<strong>Connection diagram.</strong><br />

<strong>Notes.</strong><br />

<ul>
<li> Set VR3 for minimum voltage to switch on the relay (Say 195 Volt input).</li>
<li>Set VR1 to switch off the relay above a particular voltage (say 260Volt input).</li>
<li>You can use a 100μF 40 Volts good make in parallel with relay for chatter free operation.</li>
<li>Each Phase you have to use one module as above.</li>
<li>The relay interconnections are shown in the connection diagram above.</li>
<li>T1 can be a 15-015 V secondary, 230V primary, 500mA step down transformer.</li>
</ul>

Three phase auto changer circuit

Description. The circuit given here is designed by Mr.Seetharaman V.S ( seethasub@hotmail.com ) from Chennai. Seetharaman’s comments ab...

LDO regulator / low dropout regulator

Sunil Jadhavar 5:16 AM

<div style="text-align: justify;">
LDO regulator means low dropout 
regulator. An LDO voltage regulator is just a DC linear voltage 
regulator which can be operated with a very small input-output voltage 
differential. This input output voltage differential is called dropout 
voltage. In simple words dropout voltage is the voltage dropped by the 
regulator circuitry alone for its working. For example, an LM2941 LDO 
voltage regulator has a dropout voltage of only around 0.5V, which means
 that in order to get 5 volts at the output you need to input only 5.5 
volts where an ordinary 7805 linear voltage regulator has a dropout 
voltage of around 2V. This means that, in order to get 5V at the output 
of 7805 you need to input at least 7V.</div>
<h3 style="text-align: justify;">
LDO regulator working.</h3>
<div class="wp-caption aligncenter" id="attachment_6066" style="width: 613px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-schematic.png"><img alt="LDO regulator block diagram" class="size-full wp-image-6066" height="414" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-schematic.png" title="LDO regulator schematic" width="603" /></a><div class="wp-caption-text">
Schematic of a LDO regulator</div>
</div>
The image shown above is the schematic of a typical LDO voltage 
regulator. The working principle of LDO regulator is just like that of 
an ordinary linear voltage regulator. The essential components of an LDO
 voltage regulator are a reference voltage source, error amplifier and 
series pass element (BJT or MOSFET). The voltage drop across the series 
pass element is controlled by the error amplifiers output in order to 
control the output voltage. For example, suppose the load current 
decreases and as results the output voltage tends increase. This 
increase in output voltage will increase the error voltage (VERR).The 
output of the error amplifier will increase, making the series pass 
element ( P-Channel MOSFET) less conducting, which results in the 
reduction of the output voltage and the output voltage is brought back 
to the original level.<br />

<div style="text-align: justify;">
As I said above the working of a LDO 
voltage regulator is similar to the working of an ordinary linear 
voltage regulator and the only difference is in the schematic topology 
of their internal circuitry. Ordinary linear regulators (7805, LM117, 
LM317 etc) uses a common collector scheme while the LDO regulators use 
an open collector (termed as open drain if a MOSFET is used as the 
series pass element) scheme.</div>
<h4 style="text-align: justify;">
Common collector scheme.</h4>
<div style="text-align: justify;">
Common collector scheme is one of the 
three basic transistor configurations. Here base is the input terminal, 
emitter is the output, and supply voltage is applied to the collector 
terminal. The series pass transistor inside an ordinary linear voltage 
regulator is wired in this configuration. Fig A shows the common 
collector scheme (also termed as emitter follower scheme).</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_6067" style="width: 674px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/common-collector-and-open-collector-scheme.png"><img alt="emitter follower scheme and open drain scheme" class="size-full wp-image-6067" height="355" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/common-collector-and-open-collector-scheme.png" title="common collector and open collector scheme" width="664" /></a><div class="wp-caption-text">
Common collector and open collector scheme</div>
</div>
<h4 style="text-align: justify;">
Open collector scheme.</h4>
<div style="text-align: justify;">
Many integrated circuits like LDO 
voltage regulators this scheme for wiring the series pass element (BJT 
or MOSFET). The input signal (which comes from the previous stage inside
 the IC) is coupled to the base of the BJT (or gate of the MOSFET), 
collector is left open and it is connected to a pin of the IC while the 
emitter is connected to the IC ground. This configuration makes it easy 
to saturate the series pass element and hence the dropout voltage is 
minimized.Fig B shows the open collector / drain scheme.</div>
<h3 style="text-align: justify;">
Practical LDO regulator circuit.</h3>
<h3 style="text-align: justify;">
<div class="wp-caption aligncenter" id="attachment_6068" style="width: 641px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-using-LM2941.png"><img alt="practical LDO regulator circuit" class="size-full wp-image-6068" height="434" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-using-LM2941.png" title="LDO regulator using LM2941" width="631" /></a><div class="wp-caption-text">
LDO regulator using LM2941</div>
</div>
</h3>
<div style="text-align: justify;">
The circuit shown above is of a 
practical LDO regulator circuit using IC LM2941 from National 
semiconductors. LM2941 is an integrated LDO voltage regulator IC whose 
output can be adjusted. The IC has many good features like thermal 
shutdown, transient protection, short circuit protection etc. The 
reverse polarity protection feature makes this IC very applicable in 
automotive applications. The output voltage can be adjusted from 5V to 
20V and the dropout voltage is 0.5V at 1A output current.<br />
In the circuit the voltage divider network comprising of R1 and R2 sets 
the output voltage. Capacitor C2 is the input filter which is very 
essential if the regulator circuitry is situated away from the 
rectifier+filter module. Capacitor C1 is the output filter while S1 is 
the ON/OFF switch. Resistor R3 is used to ensure the necessary 300mA 
pull up current which is necessary for proper shutdown when the switch 
S1 is made open.</div>
<h3 style="text-align: justify;">
Notes.</h3>
<ul>
<li>The circuit must be assembled on a good quality PCB.</li>
<li>A heat sink is required for application above few hundred milli amps.</li>
<li>Vout = 1.275 ((R1 + R2)/R1)</li>
<li>During calculation select R1=1K and solve for R2.</li>
<li>Selecting R1 = 1K will make the input bias current error of the adj pin negligible.</li>
<li>Reducing the value of C1 below 22uF will induce instabilities and 
also this capacitor must be placed as close as possible to the IC on the
 PCB.</li>
</ul>
<table><tbody>
<tr><td>

LDO regulator / low dropout regulator

LDO regulator means low dropout regulator. An LDO voltage regulator is just a DC linear voltage regulator which can be operated with a ve...

Regulated DC power supply

Sunil Jadhavar 5:14 AM

<b>Regulated DC Power Supply using transistors.</b><br />
<br />

<div style="text-align: justify;">
A low ripple regulated DC power supply 
designed based on transistors is shown here. Such transistor voltage 
regulators are suitable for application where high output current is 
required. Conventional integrated series regulators like 7805 can only 
deliver up to 1A. Additional series pass transistors have to be added to
 the 7805 based regulator circuit for improving their current capacity.</div>
<h3>
Description.</h3>
<div style="text-align: justify;">
The circuit shown below is a basic 
series voltage regulator based on transistors. Transistor Q1 (2N 3054) 
and Q2 (2N 3055) form a darlington pair. Resistor R1 provides the base 
current for Q1 and also keeps the zener diode D2 in the active region. 
The overall working of the circuit can be demonstrated by explaining two
 situations.</div>
<ul>
<li style="text-align: justify;">When the input voltage (output of the 
rectifier section) increases, the output voltage of the regulator (Vout)
 also increases. This increase in Vout decreases the base emitter 
voltage of Q2 because the zener diode D2 is operating in the breakdown 
region and the voltage across it is unchangeable. This decrease in V<sub>BE</sub> increases the collector emitter resistance  of Q2 and so the output voltage (Vout) gets reduced accordingly.</li>
<li style="text-align: justify;">When the output load increases, the output voltage (Vout) gets reduced. This decrease of output voltage (Vout) makes V<sub>BE</sub> of Q2 to decrease. This reduces the collector emitter resistance of Q2 and so the output voltage gets increased accordingly.</li>
</ul>
<h3>
Circuit diagram.
<div class="wp-caption aligncenter" id="attachment_6483" style="width: 849px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/10/regulated-dc-power-supply.png"><img alt="zener regulated dc power supply" class="size-full wp-image-6483" height="327" src="http://www.circuitstoday.com/wp-content/uploads/2011/10/regulated-dc-power-supply.png" title="regulated dc power supply" width="640" /></a><div class="wp-caption-text">
Regulated dc power supply</div>
</div>
</h3>
<h3>
Notes.</h3>
<ul>
<li>If 5A bridge is not available, then make one using 6A6 diodes.</li>
<li>Transistor Q2 requires a heat sink.</li>
<li>An optional 5A fuse can be added in series to the output.</li>
<li>Breakdown voltage of the zener diode D2 must be chosen according to 
the output voltage you need,         and it is according to the 
equation, Vout = Vz – 0.7.</li>
</ul>
<table><tbody>
<tr><td>

Regulated DC power supply

Regulated DC Power Supply using transistors. A low ripple regulated DC power supply designed based on transistors is shown here. Such t...

Transformerless switch mode power supply circuit

Sunil Jadhavar 5:13 AM

<span style="font-size: small;"><b>12V/120mA switch mode power supply circuit.</b></span><br />
<br />

Transformer less switch mode power supplies have become very popular 
these days. The circuit shown below is of a 12V/120mA output, 85 to 230V
 AC input transformerless switch mode power supply using LNK304 IC. 
Applications of a power supply based on this IC includes hand held 
devices, timers, small appliances, LED drivers, industrial gadgets etc.<br />

<div style="text-align: justify;">
LNK304 is a low component count, 
efficient off-line switcher IC that can support buck, buck-boost and 
flyback topologies. The IC has a built in auto start circuit for short 
circuit and open loop fault protection. Other features of LNK304 
includes low temperature variation, thermal shut down,high break down 
voltage, good line & load regulation, high band width , wide input 
voltage range (85 to 230V AC) etc. In general the LNK304 has a better 
performance when compared to the many other discrete buck regulators.</div>
<div style="text-align: justify;">
<br /></div>
<div class="wp-caption aligncenter" id="attachment_6115" style="width: 642px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LNK304-pin-configuration-typical-application.png"><img alt="" class="size-full wp-image-6115" height="294" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LNK304-pin-configuration-typical-application.png" title="LNK304 pin configuration & typical application" width="632" /></a><div class="wp-caption-text">
LNK304 pin configuration and typical application</div>
</div>
<div style="text-align: justify;">
The pin configuration and the typical 
application diagram of LNK304 are shown above. Drain (D) pin the drain 
connection of the built in power MOSFET. The external by pass capacitor 
(0.1uF) is connected to the BYPASS (BP) terminal. FEEDBACK (FB) pin 
controls the switching of the built in power MOSFET. A current above 
than 49uA delivered to this pin will inhibit the switching. The internal
 power MOSFETs source is connected to the SOURCE (S) pin.</div>
<h3 style="text-align: justify;">
LNK304 based switch mode power supply circuit.</h3>
<div class="wp-caption aligncenter" id="attachment_6116" style="width: 972px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/12V-transformerless-switching-power-supply.png"><img alt="12V switch mode power supply" class="size-full wp-image-6116" height="349" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/12V-transformerless-switching-power-supply.png" title="12V transformerless switch mode power supply" width="962" /></a><div class="wp-caption-text">
12V /120 switch mode power supply circuit</div>
</div>
<div style="text-align: justify;">
The circuit diagram of a practical 
12V/120mA transformerless switch mode power supply is shown above. 
Resistor R1, capacitors C1 and C2, diodes D1 and D2 and inductor L1 
forms the input stage. D1 and D2 forms the rectifier section while C1 
and C2 are input filters. Resistor R1 which is a fusible resistor limits
 the inrush current, increases differential mode noise attenuation and 
also serves as an input safety fuse.</div>
<div style="text-align: justify;">
The next stage is the regulator stage 
which consists of IC LNK304, diodes D3 and D4, capacitors C3, C4 and C5,
 resistors R3, R4 and R5 and inductor L2. D3 is the freewheeling diode 
while L2 is the output choke. C5 is the output filter capacitor which 
limits the output ripple voltage to a value as low as possible. The IC 
LNK304 is so configured that the power supply operated in the most 
discontinuous mode and that’s why a fast recovery diode (UF4005) is used
 as the freewheeling diode (D3). UF4005 has a reverse recovery time of 
around 75nS and it is well enough for the given situation.</div>
<div style="text-align: justify;">
The voltage drop across diodes D3 and D4
 are practically same and so the voltage across C4 tracks the output 
voltage and this voltage is picked by the network comprising of 
resistors R2, R3 and is fed to the feedback pin. R2 and R3 sets the 
output voltage and for 12V output the voltage at the feedback pin must 
be 1.65V DC. The circuit attains regulation by skipping the switching 
cycles. When the output voltage rise, the current at the feedback pin 
also rises and when the current rises above the threshold value, 
subsequent cycles are skipped until the current at the feedback pin goes
 below the threshold and thus a constant output voltage is maintained.</div>
<div style="text-align: justify;">
The IC will auto restart if no cycles 
are skipped during a 50mS time period and this limits the maximum output
 power to 6% of the maximum over load power. That’s how over load 
protection is attained. Resistor R4 serves as a small preload which 
nullifies the effects of tracking error.</div>
<h3>
Notes.</h3>
<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>LNK304 is a very high efficiency switching regulator IC that has a hand full of applications.</li>
<li>LNK304 is commonly available in SMD package (DIP is also available) and care must be taken while soldering it.</li>
<li>D1 and D2 are standard 1N4007 silicon rectifier diodes.</li>
<li>D3 (UF4005) is a fast recovery diode.</li>
<li>D4 (1N4005GP) is a glass passivated diode.</li>
<li>C3 can be a ceramic capacitor.</li>
<li>C1,C2 and C4 are polyester capacitors.</li>
<li>C5 can be electrolytic or polyester capacitor.</li>
<li>Voltage ratings of the capacitors are shown in the circuit diagram.</li>
<li>R1 is a fusible, fire proof resistor.</li>
<li>Maximum possible output current is 120mA.</li>
<li>Input voltage range is 85 to 230V AC.</li>
</ul>

Transformerless switch mode power supply circuit

12V/120mA switch mode power supply circuit. Transformer less switch mode power supplies have become very popular these days. The circuit...

10A Adjustable voltage Regulator MSK 5012

Sunil Jadhavar 5:11 AM

<div style="text-align: justify;">
MSK5012 is a highly reliable adjustable 
voltage regulator.Whose output can be programmed using two resistors. 
The regulator has a very low dropout voltage(0.45v @10A  )due to the 
usage of MOSFET with very low Rds (ON) as the internal series pass 
element.The MS5012 has a high level of accuracy and ripple rejection is 
around 45dB. It is available in a 5 pin Sip package that is electrically
 isolated from the internal circuitry. This give us the freedom to fit 
the IC directly to the heat sink and this sort of direct heat sinking 
improves the thermal dissipation.</div>
<h3>
<strong>Description.</strong></h3>
<div style="text-align: justify;">
The output voltage of this circuit is adjustable from 1.3v to 36v DC.Resistors R<sub>1</sub> and R<sub>2</sub> are used for programming the output voltage.For all applications, value of R<sub>2</sub> is fixed to 10K. The relationship between R<sub>1</sub>,R<sub>2</sub> and output voltage Vout is according to the equation R<sub>1</sub>=R<sub>2</sub>(Vout/1.235)-1. C<sub>1</sub>
 is a filter capacitor which is also a part of the gate drive circuit of
 the internal series pass MOSFET. Around three times the input voltage 
will appear across this capacitor and so the its voltage rating must be 
selected accordingly.C<sub>2</sub> is the input filter capacitor while C<sub>3</sub> is the output filter capacitor.</div>
<h3 style="text-align: justify;">
Circuit  diagram.</h3>
<div class="wp-caption aligncenter" id="attachment_6496" style="width: 607px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/10/10A-adjustable-voltage-regulator-MSK5012.png"><img alt="adjustable regulator" class="size-full wp-image-6496" height="329" src="http://www.circuitstoday.com/wp-content/uploads/2011/10/10A-adjustable-voltage-regulator-MSK5012.png" title="10A adjustable voltage regulator MSK5012" width="597" /></a><div class="wp-caption-text">
10A adjustable voltage regulator MSK5012</div>
</div>
<h3>
<strong>Notes.</strong></h3>
<ul>
<li>Input voltage 3v to 36v DC.</li>
<li>Output voltage range 13v to 36v DC.</li>
<li>Typical application of MSK5012 are high efficiency linear 
regulators, constant voltage/current regulators, system power supplies 
etc.</li>
<li>A heat sink with thermal resistance not more than 2.40 <sup>o</sup>C/W must be fitted to the MSK5012.</li>
<li>Resistance R<sub>2</sub> is fixed at 10 K for all applications.</li>
<li>Quiescent current of MSK5012 is around 10mA.</li>
</ul>

10A Adjustable voltage Regulator MSK 5012

MSK5012 is a highly reliable adjustable voltage regulator.Whose output can be programmed using two resistors. The regulator has a very lo...

Battery eliminator circuit

Sunil Jadhavar 5:10 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
Here is the circuit diagram of a battery
 eliminator circuit that can be used as a replacement for 9V PP3 
batteries. The circuit given here can be used to power any device that 
operates from a 9V battery. The transformer T1 steps down the mains 
voltage and bridge D1 performs the job of rectification. Capacitor C1 is
 a filter. IC LM317T is the regulator here. The value of R1, R2 and R3 
are so selected that the output voltage of IC1 will be steady 9 volts.</div>
<div style="text-align: justify;">
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2009/12/battery-eliminator-circuit.png"><img alt="battery eliminator circuit" class="alignleft size-full wp-image-2732" height="263" src="http://www.circuitstoday.com/wp-content/uploads/2009/12/battery-eliminator-circuit.png" title="battery eliminator circuit" width="640" /></a></div>
<strong>Notes.</strong><br />

<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>Transformer T1 can be a 230V primary, 9V secondary, 1.5A step down transformer.</li>
<li>If 1A Bridge is not available, then make one using four 1N 4007 diodes.</li>
<li>Do not connect loads that consume more than 1.5A to this circuit.</li>
<li>A heat sink is recommended for IC1.</li>
</ul>
<table><tbody>
<tr><td>

Battery eliminator circuit

Description. Here is the circuit diagram of a battery eliminator circuit that can be used as a replacement for 9V PP3 batteries. The ci...

Automatic changeover circuit

Sunil Jadhavar 5:10 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
The circuit diagram shown here is of a automatic changeover switch using
 IC LTC4412 from Linear Technologies. This circuit can be used for the 
automatic switchover of a load between a battery and a wall 
adapter.LTC4412 controls an external P-channel MOSFET to create a near 
ideal diode function for power switch over and load sharing. This makes 
the LT4412 an ideal replacement for power supply ORing diodes. A wide 
range of MOSFETs can be driven using the IC and this gives much 
flexibility in terms of load current. The LT4412 also has a bunch of 
good features like reverse battery protection, manual control input, 
MOSFET gate protection clamp etc.</div>
<div style="text-align: justify;">
The diode D1 prevents the reverse flow 
of current to the wall adapter when there is no mains supply. Capacitor 
C1 is the output filter capacitor. Pin 4 of the IC is called the status 
output. When wall adapter input is present the status output pin will be
 high and this can be used to enable another auxiliary P-channel MOSFET 
(not shown in the circuit diagram).<br />
<strong> </strong></div>
<div style="text-align: justify;">
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2010/01/automatic-changeover-circuit.png"><img alt="automatic changeover circuit" class="alignleft size-full wp-image-2931" height="305" src="http://www.circuitstoday.com/wp-content/uploads/2010/01/automatic-changeover-circuit.png" title="automatic changeover circuit" width="517" /></a></div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul>
<li> Assemble the circuit on a good quality PCB.</li>
<li>The wall adapter input can be anything between 3 to 28V DC.</li>
<li>The battery voltage can be anything between 2.5V to 28V.</li>
<li>Do not connect loads that consume more than 2A.</li>
<li>Maximum continuous drain current of Q1 (FDN306P) is 2.5A.</li>
<li>D1 (1N5819 is a 1A Schottky diode.</li>
<li>Q1 (FDN306P) is a P-channel MOSFET.</li>
</ul>

Automatic changeover circuit

Description. The circuit diagram shown here is of a automatic changeover switch using IC LTC4412 from Linear Technologies. This circuit c...

12V battery level indicator circuit (LED bargraph)

Sunil Jadhavar 5:07 AM

<h4>
LM3914.</h4>
<div style="text-align: justify;">
The heart of this circuit is the LM3914 
from national semiconductors. The LM3914 can sense voltage levels and 
can drive a display of 10 LEDs in dot mode or bar mode. The bar mode and
 dot mode can be externally set and more than one ICs can be cascaded 
together to gat an extended display. The IC can operate from a wide 
supply voltage (3V to 25V DC). The brightness of the LEDs can be 
programmed using an external resistor. The LED outputs of LM3914 are TTL
 and CMOS compatible.</div>
<h4>
Description.</h4>
<div style="text-align: justify;">
In the circuit diagram LEDs D1 toD10 
displays the level of the battery in either dot or bargraph mode. 
Resistor R4 connected between pins 6,7 and ground controls the 
brightness of the LEDs. Resistors R1 and POT R2 forms a voltage divider 
network and the POT R2 can be used for calibration.</div>
<div style="text-align: justify;">
The circuit shown here is designed in 
order to monitor between 10.5V to 15V DC. The calibration of the circuit
 can be done as follows. After setting up the circuit connect a 12V DC 
source to the input. Now adjust the 10K POT to get the LED10 glow (in 
dot mode) or LEDs up to 10 glow (in bar mode). Now decrease the voltage 
in steps and at 10.5 volts only LED1 will glow. Switch S1 can be used to
 select between dot mode and bar graph mode. When S1 is closed, pin9 of 
the IC gets connected to the positive supply and bar graph mode gets 
enabled. When switch S1 is open pin9 of the IC gets disconnected to the 
positive supply and the display goes to the dot mode.</div>
<div style="text-align: justify;">
With little modification the circuit can
 be used to monitor other voltage ranges. For this just remove the 
resistor R3 and connect the upper level voltage to the input. Now adjust
 the POT R2 until LED 10 glows (in dot mode). Remove the upper voltage 
level and connect the lower level to the input. Now connect a high value
 POT (say 500K) in the place of R3 and adjust it until LED1 alone glows.
 Now remove the POT, measure the current resistance across it and 
connect a resistor of the same value in the place of R3. The level 
monitor is ready.</div>
<h4>
Circuit diagram of battery level indicator using LM3914.</h4>
<div class="wp-caption aligncenter" id="attachment_7080" style="width: 704px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/11/battery-level-indiactor.png"><img alt="" class="size-full wp-image-7080" height="468" src="http://www.circuitstoday.com/wp-content/uploads/2011/11/battery-level-indiactor.png" title="battery level indiactor" width="640" /></a><br />
<div class="wp-caption-text">
Battery level indicator circuit using LM3914</div>
</div>
<h4>
Cascading two LM3914.</h4>
Two or more LM3914 ICs can be cascaded together to get 
an extended display. The schematic of two LM3914 ICs cacaded together to
 get a 20 LED voltage level indicator is shown below.<br />
<div class="wp-caption aligncenter" id="attachment_7084" style="width: 728px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/11/cascading-two-LM3914.png"><img alt="20 LED voltage level indicator" class="size-full wp-image-7084" height="640" src="http://www.circuitstoday.com/wp-content/uploads/2011/11/cascading-two-LM3914.png" title="cascading two LM3914" width="622" /></a><br />
<div class="wp-caption-text">
Cascading two LM3914</div>
</div>
<h4>
<b>Few other battery level related circuits that you may like.</b></h4>
<div style="text-align: justify;">
1.<i><b>Simple battery level indicator</b></i>
 : This circuit can be used for monitoring the level of 3V batteries. 
The circuit is based on MN13811G from Panasonic. MN13811G is a CMOS 
 voltage detector IC that can be used a variety of voltage monitoring 
applications. In the circuit LED D1 will flash when ever the battery 
voltage drops below 2.4 volts.</div>
<div style="text-align: justify;">
2.<i><b>3 LED battery level indicator</b></i>
 : A 3 LED battery level indicator that can be used for monitoring the 
voltage level of 12V automobile battery is shown here. Three states of 
the battery ie; below 11.5V, between 11.5 and 13.5 and above 13.5 are 
shown by the glowing of LEDs.</div>
<div style="text-align: justify;">
3.<i><b> Flashing battery monitor</b></i>
 : This circuit can be used for monitoring the voltage level of 6 to 12V
 batteries. The circuit is based on transistors and the voltage level at
 which the LED starts flashing can be adjusted by using a potentiometer.</div>
<ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_2_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins>

12V battery level indicator circuit (LED bargraph)

LM3914. The heart of this circuit is the LM3914 from national semiconductors. The LM3914 can sense voltage levels and can drive a displ...

Chager circuit for SMF batteries

Sunil Jadhavar 5:05 AM

<strong>Description.</strong><br />

<div align="justify">
Here is a simple charger circuit for charging 
SMF(sealed maintenance free ) batteries.The charger circuit being 
curernt and voltage regulated,can be safely used to charge SMF batteries
 of 1.2 AH rating.This circuit was actually designed in response to a 
request from a reader.With slight modifications you can use it for 
charging any sort of SMF batteries.</div>
<div align="justify">
The first part of the circuit is the power supply 
made of transformer T1 and diodes D1&D2.The capacitor C1 filters the
 rectifier output .The next part is the section comprising of IC1 and Q1
 which provides the necessary volatge and current regulation.The diode 
D3 prevents ther reverse flow of charge from the battery .</div>
<div align="justify">
<strong>Circuit diagram with parts list.</strong></div>
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/06/smf-battery-charger-circuit.JPG" title="smf-battery-charger-circuit.JPG"><img alt="smf-battery-charger-circuit.JPG" height="314" src="http://www.circuitstoday.com/wp-content/uploads/2008/06/smf-battery-charger-circuit.JPG" width="640" /></a><br />

Notes.<br />

<ul>
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>An ammeter can be conncted in series with the battery to monitor the charging current.</li>
<li>Do not short circuit the charging terminals of the circuit.The circuit doesnot have short circuit protection.</li>
<li>R4 is the component that determines the charging current.Here it is 
set to be 120 mA. R4= (0.6 V/Charging current).By selecting the proper 
value of R4 according to equation, you can charge batteries that require
 different charging currents.</li>
</ul>
<ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_2_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins>

Chager circuit for SMF batteries

Description. Here is a simple charger circuit for charging SMF(sealed maintenance free ) batteries.The charger circuit being curernt an...

Super fast Ni-Cd battery charger

Sunil Jadhavar 5:03 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
<strong>H</strong>ere is  the circuit 
diagram of an effective and super fast Ni-Cd battery charger circuit.The
 circuit is based on the IC MAX 712. The circuit is designed to fast 
charge a Ni-Cd battery at 3oomA. After the fast charging is completed 
the circuit charges the battery in trickle charging mode at 15 mA. Here 
the instant to end fast charging and start trickle charging is sensed by
 dv/dt method as per the data sheet. This method of charging increases 
the charging speed as well as the battery life. The circuit is designed 
strictly as per the data sheet from Maxim and found to be working with 
no flaw.</div>
<div style="text-align: justify;">
<strong>T</strong>he diode D3 toD6 full 
wave rectifies the input supply. The capacitor C4 filters the output of 
the rectifier. The transistor Q1 (SK 100)  with associated components 
forms a series pass for driving the charging battery. The LED indicates 
the fast charging.</div>
<div style="text-align: justify;">
<strong>Circuit diagram with Parts list. </strong></div>
<div class="wp-caption aligncenter" id="attachment_7536" style="width: 625px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/04/Ni-Cd-Battery-CHarger-Circuit-Schematic.jpg"><img alt="Ni-Cd Battery Charger Circuit Diagram" class="size-full wp-image-7536" height="417" src="http://www.circuitstoday.com/wp-content/uploads/2008/04/Ni-Cd-Battery-CHarger-Circuit-Schematic.jpg" title="Ni-Cd Battery Charger Circuit Diagram" width="615" /></a><div class="wp-caption-text">
Ni-Cd Battery Charger Circuit Diagram</div>
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul style="text-align: justify;">
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>Transistor 2N6109 can be also used instead of SK 100.</li>
<li>Do not connect not more than 2 Ni-Cd cells.</li>
<li>If you are using a PCB, it should be well designed and fabricated 
that there are no  unwanted feed back paths existing, which would cause 
oscillations in the circuit.</li>
</ul>

Super fast Ni-Cd battery charger

Description. H ere is the circuit diagram of an effective and super fast Ni-Cd battery charger circuit.The circuit is based on the IC ...