Category: Electronics
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In this project I built an analog adjustable power supply capable of delivering approximately 5Amps to the load with maximum voltage of 30V. It also has two positive and negative outputs.

This is an ideal supply to use with your audio amp projects. Because if you have a symmetrical positive and negative voltage you can use it with a very simple push-pull amplifier to get a powerful sound out of your speakers. I should note here that the positive and negative outputs of this power supply can be adjusted independently and if you wanted to use this with your audio amp you can adjust the positive and negative voltages so that they'd be equal.

I myself used it with my audio amp and it worked perfect!


The schematic and PCB designs were done in the Altium Designer 6 software.

Schematics are here.

The AC and GND inputs come from a 3 wire 10:1 transformer which is a big thing because of the high current it should endure.  

As you can see I've used two regulator ICs. LM317 for the positive output and it's compatible negative version LM317 for the negative output.

I've also used two power transistors to amplify the current. If you take a look at the regulators' datasheets you can see that they are capable of delivering the maximum current of 1Amps so we need these two transistors which can deliver our 5Amp current.

I've used a TIP41C as the NPN and it's PNP counterpart TIP42C.

These two are very powerful 65Watt general purpose transistors capable of working with even 6A loads.

Naturally the regulators and power transistors are mounted on heat sinks.

I've even used two fans to cool the power transistors. If you want to work with high power loads you have to consider these fans.

There's a mechanism to prevent the precious power transistors from burning in the case you shortcircuit supply's outputs. I've put two SPDT switches for you to decide whether you want to use this security system or not. One of these switches is for the positive output and the other one is for negative output. 

When the switch is on 0 you'll have a 0.15 ohm resistor series with your load. Now if the load draws some current more than 6 amps ,it creates a voltage drop across this resistor. The three diodes become active and the current is conducted through these diodes and prevent the transistor from being damaged.

Now at 5amps the voltage drop across the resistor would be 5*0.15=0.75. If you want an extreme precision across your load and you don't want to lose this voltage drop you can put the switch to 1. In this case transistor's emitter is connected directly to the load and you won't have any voltage drop but be careful ! If you make a mistake and short the output you'll have to think about a new pair of transistors.  

PCB is here.

As usual if you need the Altium source files you can contact me.

here is a photo of the assembled board: