12V Dual Power Supply using 7812, 7912

This is a +/- 12v dual power supply circuit diagram using 7812 and 7912. We use an LM7812 voltage regulator IC for +12V and LM7912 for -12V.  This circuit is suitable for a preamplifier tone control with an OP-AMP circuit. It can deliver an output current of not more than 1A.

I will show you, an interesting concept. When we build a small preamplifier circuit. It needs to use a power supply. It requires a low supply current is only 100mA. But It is special that the need for dual voltage in three terminals positive, negative, and ground. So, we use a 12V dual power supply.

How does it work

There are two circuit ideas for you choosing by your work. The first circuit use half-wave rectifier. The second is full-wave rectifier.

Read more 12v power supply circuit using 7812

Low current version

First is a simple circuit below.

+/- 12V dual power supply circuit
If your load uses a low current not more than 300mA. You may use this circuit.

In the circuit, There is an unregulated power supply. Which include S1, F1, T1, D1, D2, C1, C2, C3, and C4. Since they are two rectifier diodes in half-wave rectifier form. You should use the double filter capacitors, C2 and C4. To reduce a ripple voltage.

•  Read also: How to use 7805 voltage regulator

This circuit uses a 300mA transformer AC 15V CT 15V. (30V) When it converts to DCV. This voltage rises up to about 42VDC.  Each input voltage is 21VDC comes to  7812 and 7912. Both IC-regulator keeps a constant voltage to the output.

Other parts working.

• IC1-IC2 do not need to hold the heat sinks because of the very low currents.
• C5, C6 are the filter capacitors to reduce ripple signal.
• C7 cleans the transient voltage to the output.
• LED1 is an indicator of Power ON. And R1 is the current limiter of LED1.
• C1, C2, C3, C4 are the filter capacitors to smooth DC pulse to DC stable voltage.  If you have them a lot. They are good.

Higher current

If you want 12V dual power supply that higher current more than 500mA. This circuit is good for you.

In the circuit, it is similar to the above circuit. But they change some components as follows.

• Change the current size of a transformer of 1A secondary coil.
• Using Full wave rectifier diodes is better. They have 4 diodes, 1N4007.
• So, You can use two filter capacitors. But there is a higher current than above.
• C3, C4, C7 and C4 filter capacitors to clean transient voltage from input.
• Also, C5 and C6 capacitor filtered the ripple voltage to the output.
• LED1 shows power on using a limiting current resistor.

Recommended:

• What is switching Power supply VS Linear, How does it work?
• Power ON delay circuit and Surge Protector without transformer

Parts you will need

• IC1: 7812 positive voltage regulator
• IC2: 7912 negative voltage regulator
• D1-D4: 1N4007, 1000V 1A Diodes
• C1,C2: 2,200uF 35V electrolytic capacitors
• C3, C4: 0.22uF 50V Ceramic capacitors
• C5, C6: 100uF 35V Electrolytic capacitors
• C7, C8: 0.1uF 50V Ceramic capacitors
• LED1 as you like
• R1: 2.7K 0.5W resistor
• T1: 220V or 117V to 15V CT 15V 1A transformer
• S1: ON-OFF power switch
• F1: 0.5A Fuse

Other external circuit ideas:
+/-12V DUAL POWER SUPPLY

How to build

In this project, you can assemble them on the perforated board. It is easy to use, and so cheap.

Cautions
You need to know the pins of all components. You need to do them correctly only. For example, I put the wrong electrolytic capacitor. When entering the power supply, causing it to burst. I was shocked too much. But I do not discontinue this project.

Look at pin connection of 7912, 7812, diode, and an electrolytic capacitor.

You must connect pins of electrolytic capacitors, diode and LED. It does not work and destroy.

We often use a 78xx series. So, you can use 7812 is same.

But…

7912 Pinout

Be careful 7912 pinouts is not the same 7812. It is difference pins input and ground.  I switched it. My 7912 is too hot.  Please look at it again.

Thank you for reading the poor English story.

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