1.2V to 13.4V Variable Power Supply

5,200

81

7

This Variable Power Supply allows you to change voltage depending on your requirement.You can change the voltage from 1.2 Volts to 13.4 Volts. So you can use this variable power supply for powering your projects too.

This variable power supply consists of IC LM317T which allows you to vary voltage.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Circuits Used in Variable Power Supply

Variable Power Supply Consists of following circuits

• Full Wave Rectifier
• 15 Volt Regulator

Step 2: Components Required

Components for 15 Volt Regulator

• 12-0-12 V Transformer
• Gendral Purpose PCB
• Connectors------------3
• 1N5408 Diode---------2
• 2200uf,50V capacitor
• Heat Sink
• IC 7815

• Gendral Purpose PCB
• Connectors-------------3
• 1N4007 Diodes
• IC LM317T
• 10uf,50V capacitor
• 560 ohm Resistor
• 0.1uf ceramic capacitor
• 5K pot

Step 3: Schematic Diagram of Variable Power Supply

I had also attached Schematic File Below

Step 4: Assembling Variable Power Supply

I had soldered the components in Gendral Purpose PCB according to schematic diagram of variable power supply.

Step 6: Operation of 15 Volt Regulator

The 15V Regulator Use 12-0-12 Volt transofrmer.The 12 volt at input of 15V regulator circuit is amplified into 16V by the use of 2200uf capacitor.The capacitor is connected at the output of Full Wave Rectifier.The full wave rectifier is formed by two diodes 1N5408.The full wave rectifier will convert 12V AC into 12V DC.The Voltage at the output of full wave rectifier is 12V.If we add 2200uf capacitor at the output of full wave rectifier in parallel.The 12V is boosted into 16V. This 16 V is given to IC 7815.This IC will regulate 16V into 15V. So you get 15V at the output of 15 Volt Regultor Circuit.

Step 7: Assembling 15V Regulator

I had soldered Components in Gendral Purpose PCB according to schematic diagram of 15Volt Regulator.

Step 9: Operation of Adjustable Voltage Regulator

The adjustable voltage regulator consists of IC LM317T which is designed with resistors to control voltage from 1.2V to 13.4V.We know that PN junction diodes conduct only in forward direction.The two diodes 1N4007 which is used for protection purpose.The 5K Potentiometer is used to vary voltage.The pot is to be fixed with knob for adjusting voltage comfortably.

Step 10: Assembling Adjustable Voltage Regulator

I had soldered the components in gendral purpose PCB according to the schematic Diagram of Adjustable Voltage Regulator.

Step 11: Video

Participated in the
Epilog Contest 8

Recommendations

• Large Motors Class

13,114 Enrolled

7 Discussions

Exactly why did you use a 7815 fixed voltage regulator before the LM317T variable voltage regulator? You could have just eliminated the fixed 15 volt regulator and made the exact same circuit with fewer parts. Just come off the bridge rectifiers and filter that voltage and feed it straight to the LM317T regulator. And you would have had a little larger range of variable voltage as well with less parts. And if you wanted to stop the high side at +15 volts, you could add in a selected resistor with the variable pot for that option easily. Also, your schematic diagram is a little awkward. Most schematics are drawn with positive voltages at the top and grounds and negative voltages on the bottom. And they read left to right. You did that with the first regulator setup, but then swapped them when connecting to the variable regulator. That made it interesting to read. Your circuit will work like you have it, but I don't understand all the extra parts. IDK

4 replies

If you directly connect the full wave rectifier to variable voltage regulator there may be some small ripple voltage exist at the output of LM317.At lm7815 there may be some small ripple.This ripple voltage is eliminate if you connect another voltage regulator that is LM317T.So you get two stage filtering of ripple voltage.So that your output voltage is pure straight line DC with no ripples.

I've built so many power supplies in my days of all types that I can't remember them all now. And I've never had any issue with output ripple with any of them. And that includes fixed and variable regulators as well. And yes I have used Oscilloscopes to verify the ripple figures as well. But to each their own. Nothing wrong with your design other then unneeded extra parts. JMHO

Here is the best example for your question about ripple.Consider Fm transmitter circuit using IC NE555.The fm transmitter is powered by battery to eliminate noise.Because battery source has no ripples.Then if you power the same fm transmitter with transformer power source using voltage regulators there will be so much of noise added.This is because the voltage regulators has small ripple voltage that causes noise in FM transmitters

Input filter capacitors should eliminate any ripple of the rectified AC.

Nice Work! A dc dc converter would be far more efficient though but I like your effort.