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Dc variable power supply

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rizwanspirit

rizwanspirit

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(what | which) variable power supply

I want to make a variable dc power supply.and I have transformers having 14.5v or less ac output.please tell me any simple circuit of Variable DC Power Supply.
I have a circuit but it uses transformer of 24 v secondary.The circuit is shown under.
 

circuit for variable dc power supply

it's just a simple bridge circuit with adjustable regulator, the 317 datasheet tell you that minimum differential input to output voltage is 3V, so the circuit is fine, but indeed, maximum voltage you can get from 14V AC is less than the written one in the circuit
 

    rizwanspirit

    rizwanspirit

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You can increase the output using a voltage doubling rectifier.

63_1211910798.gif
 

Hi, I don't know you need which range of DC adjust power (Ex: 0 to 5VDC,...). Because your circuit can be used with lower voltage.
 

I told that i have maximum 14.5v ac secondary transformer so how much maximum volts i can get from this ?
 

check this ...

**broken link removed**

The average DC voltage output from transformer is about 0.9Vpp for full bridge, so your input for LM317 is around 13V
 

    rizwanspirit

    rizwanspirit

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Yes, D1 is always recommended if a short circuit of input voltage (unlikely with a transformer) or backward load from output (very likely in many applications) can occur, D2 would be needed only together with Cadj, both not generally necessary.

By the way, the maximum input voltage with no load is considerably higher than 14 V of course, e. g. 19 or 20 V.
 

By the way, the maximum input voltage with no load is considerably higher than 14 V of course, e. g. 19 or 20 V.[/quote]

yups. that's true...check with your voltmeter for sure....
 

Hi !

You should use a double switch for S1, and a double fuse, to switch off both line of your AC power supply.
If you open S1, T1 is still connected to your ac power supply and isn't protected by your fuse.

Good luck,
 

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