Many electronics circuits and projects for learning in simple ways.

Dual adjustable power supply circuit diagram using 7805 and 7905

The top cheap a Dual adjustable power supply circuit diagram. It can adjust the dc voltage with +5V to +25V and -5V to -25V at current 1 amp, using LM7805 and LM7905. It is suited for testing the linear ICs only by the OP-AMP and very easy.

Introducing
When you want Dual power supply Variable Regulator is simple. I recommend to make 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. This circuit can provide 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 players. 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.

The 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.

Dual adjustable power supply circuit diagram using 7805 and 7905

-The transformer-T1 converts voltage AC 220V(or 120V for friends in the USA) reduce to DC 25V.The diodes D1 through D4 will rectifier the voltage from ACV to DCV. The Both positive and negative voltage flow to mix with 0V point or center taps of T1.

Then, the  DC pulse will flow to  2 capacitors C1, C2  to filter the current, that is smooth up.
Next, 3 capacitors C3, C4, and C8  will  protect a oscillated  between IC1 and IC2

Next, the main of the 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 volts 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 damaged.

For example the voltage from external large capacitors etc. but if there is the bad voltage in 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.

 

Keep Reading: 0-60V Dual Variable power supply

 

How to build it
This project uses a few electronic parts and detail. I think that we can solder all equipment onto the perforated board. Thus saving costs and reducing time to build up. And you can make the PCB as Figure 2. It is the Copper layout of this project. And, Figure 3 is components layout

actual-size-Single-sided-pcb-layout
Figure 2 Actual-size, Single-sided PCB layout

the-components-layout-of-dual-regulator-power-supply-lm7805-lm7905
Figure 3 The components layout

You should put a low on their devices, such as diodes, resistors etc, then put them up high.

You may mount the VR1 and VR2 on the face of this power supply to easy the voltage adjustment.

We should mount the IC1 and IC2 on the heat sink to aid cooling. Be careful about the polarity of the circuit, capacitors, and diodes to correct place.

Because the DC regulator IC is a high current 1 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 is the positive, negative and ground terminals.

If you want to adjust 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. Then, we measure output voltage need is +5 V and -5V. Next, Adjust in the opposite direction to the highest resistance. The output voltage will up to of 25V or highest.

You may mark voltage levels on the face completely. You should use a transformer at full current (2A up) because it is the heart.

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.

This Post Has 9 Comments

  1. are the two terminals(terminal A and B) of the VR1 and VR2 are shorted??
    Thank you for your early reply

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

  3. 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. 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.
    Thanks for your feedback.
    Yes short terminal of VR1,VR2.
    And you can use 18V CT 18V transformer for output 5V to 20V.

  6. Hi,

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

    Thanks

  7. 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.

  8. Are the diodes D5 and D7 essencial for the correct functioning of the circuit?

  9. what will happen if + positive supply terminal and – negative supply terminal shorted means what will happen.Any protection like short circuit protection is there or not?

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