# Dual Variable Regulator power supply 5-25V by LM7805,LM7905

The top cheap dual variable regulated power supply. It can adjust the dc voltage with +5V to +25V and -5V to -25V at current 1 amp, suited for testing the linear ICs only by op-amp and very easy.
Introducing
When you want Dual power supply Variable Regulator be simple. I begs for to advise this circuit, because use the integrated circuit LM7805 and IC 7905. Make have Voltage +5V to +25V and -5V to -25V unless. VR1 for Adjustable + Volt output,VR2 for adjustable -volt output. Still pay current get about 1A enough with general usability. The important factor is you should use Transformer at enough size doesn’t lower 2A and IC all stick let off the heat with.

The DC power supply that has the positive voltage output and negative all in one form, and also can fine output voltage that need much in experiments the Linear ICs, especially op-amp.
Therefore, this power supplies so it is necessary on the experiments table all of those electronic player. Or will be used in the laboratory by various educational institutions. The need is not so bad. Saving money does not need to buy the foreign trade balance.
Building is easy, because the IC regulator 3-pin, Popular Numbers 7805 and 7905 controlled positive voltage and negative voltage respectively, by adjustable output voltage can be between from 5 to 25 volts, both positive and negative independently. Okay let’s see how it works.

### SEE image: 5 volt power supply circuit

How it works
This circuit is shown below.
-The transformer-T1 converts voltage AC 220V(or 120V for friends in USA) reduced to DC 25V.They diode D1-D4 is used to be rectifier to charge from ACV to DCV both positive and negative voltage is compared to the 0V point, or center taps of T1.
– then the dc volt is filtered with two capacitors C1,C2 for the dc current is smooth up.
– Three capacitor C3,C4 and C8 is used for protect a oscillated that may be with IC1 and IC2
– The main of circuit, is two IC1 and IC2 are dc regulator form 3 pin number IC-7805 and IC-7905. Which will be regulated to DC current output are +5 volt and -5 volt respectively.

-When we put VR1 and VR2 into middle leg of IC1 and IC2 to adjust the output voltage.
The diode D5,D6 as act to Prevent the voltage from external backward into ICs, which it may be damage. For example the voltage from a external large capacitors etc. but if there is the bad voltage into this circuit, it will flow through D5,D6 until the end and D7, D8 likewise
When you want to change the voltage higher than 5V, simply adjust the VR1 and VR2, the higher the value the more resistance, the output voltage will increase as well.

How to build it
This project uses a few electronic equipments, and is not very detailed. I think that we can soldering all equipment onto the peforated board. Thus saving costs and reducing time to build up. and you can make the PCB as Figure 2 is Copper layout of this project. and Figure 3 is components layout

Figure 2 Actual-size,Single-sided PCB layout

Figure 3 The components layout

You should put a low before their devices, such as diodes, resistors etc, then put them up high.
– The VR1 and VR2 are mounted on the face of this power supply, to easy the voltage adjustment.
– The IC1 and IC2 should be a little cooler (the heat sink) to aid cooling. Be careful about the polarity of the circuit, capacitors and diodes, must be placed correctly.

Because DC regulator IC is a high current one ampere. Therefore, using the wiring the circuit, so it should be larger than 0.5 square millimeters. To minimize voltage loss in the cable, which will take place on the current lot.
The box of this dc power supply, you can use any plastic box, large enough to contain it, to get comfortable. The terminals output 3-pole connector are the positive, negative and ground terminals.
If you want to fire both positive and negative changes to the VR1 and VR2 together it is variable resistor has a second layer using the same.
Bring it to use
When it is ready, then try to see what voltage changes or not. By adjusting VR1 and VR2 in the direction with the lowest resistance. Measuring output voltage need be +5 V and-5V. Adjusted in the opposite direction to the highest resistance. Will be output voltage of about 25V or higher, little does not matter. Manage marked voltage levels. On the face completely. You should use a transformer at full current because it is the heart.

Note: For some people who want to the circuit easier.

## DC Power Supply 5-22V by IC 7805

Here is circuit DC Power supply Adjustable Voltage 5V to 22V 1A by IC 7805.
It easy to make circuit and low cost too.

## 7 thoughts on “Dual Variable Regulator power supply 5-25V by LM7805,LM7905”

1. Alvin says:

are the two terminals(terminal A and B) of the VR1 and VR2 are shorted??

2. Alvin says:

Hey., I’m just getting 5V-20VDC.., I can’t get the
5V-25VDC..

3. Anthony says:

Hi. I had read this post. Based on the description, the input voltage is 15V DC. I want to create a -5V DC based on this circuit. But I only have 9V DC adaptor with 1A output current. will it produce me a -5V DC too?

4. Saraii Maute says:

if i used a center-tapped 12V 750mA transformer, what else should be replaced in the circuit so it would work just fine? thanks in advance.

5. Hi,Alvin.
Yes short terminal of VR1,VR2.
And you can use 18V CT 18V transformer for output 5V to 20V.

6. Nik S says:

Hi,

I need 30v regulated low amp supply. Can 78xx be pushed to 30 volts.

Thanks

7. Robert S. says:

There seems to be a problem with the design. I tried to build it as shown, but got very narrow range variable output.
*I discovered you need from 150 ohm to 2500 ohm resistor from ADJ leg to OUT leg for both + and -, then you get full range adjustment.
**Also recommended to use 20 turn pots for finer control of output.