High Current 12V-13.8V at 30A,25A,20A,15A Power Supply

Here is a high current 13.8v power supply circuit. What for? Those who want to use a car radio transmitter in the house. You should use a 12V/13.8V Ham Radio power supply.

It is a better way if be a High power out of 5A to 30A according to the size of the transmitter.

And I highly recommend this high-current power supply circuit. Because of Good performance, the output voltage of 13V to 14V depending on the load.

Also, you can change/add components to set the output current of 5A, 10A, 15A, 20A, 25A, 30A. According to real usage. So, help to save and easier to build.

High Current 12V-13.8V at 30A,25A,20A,15A Power Supply

Why this circuit interesting

Of course, you can buy a power supply that simple and effective with a variety of sizes. But if you build them with your own or your friends. It will be a great time while creating this project. And when completed, runs in its function. It will very proud.

Besides, this power supply circuit is also useful as a wide variety. Such as A large DC motor, car audio system, and others. Which you may apply by changing the voltage and current as needed. This circuit is very flexible.

high current 13.8v 30a 25a 20a 15a power supply

The high current 13.8V power supply circuit

Concept of circuit picking

We want the circuit that uses normal parts. So easy to buy in locals stores near us, and cheaper.

Sometimes you may have these components in your house.

Imagine, you have a lot of power transistors, 2N3055. Because it is popular in the transistor power amplifier.

A linear power supply circuit is a better choice. Because it is so easy circuit.

We often use the three-terminal regulator IC likes 78xx, 7812, or 7815.

But It is a big size with large components.

For example, the transformer if you want 30A output current. So you need the least of 30A transformer. It is so big.

By the way.

Its size is not a problem for you. Suppose that you get a big transformer from your grandfather.

Yes, you can try it.

I love the linear circuit.

Note: If you are beginner this circuit may is not suitable for you. You may use circuits below.

How high current 13.8V power supply circuit works

It must have quality Checklists!

We need these.

  • Good protection circuit—When the output short circuit or overload.
  • You can also choose to build a circuit size with output currents as you need. You can increase the current in a step by step, each step of 5A. Start with a minimum currents rate of 5A. And next step 10A, 15A, 20A, 25A and a maximum to 30A.

What is more? See parts of circuit.

Unregulated power supply

This circuit requires a high current DC voltage. See in the circuit below is 21V 30A unregulated power supply circuit.

It is flexible. You can choose a variety of devices as you want, follow these steps.

1. The C1 and F1 using this table.

Output CurrentC1F1
5 A10,000μF2A
10 A15,000μF4A
15 A22,000μF6A
20 A33,000μF8A
25 A47,000μF10A
30 A68,000μF12A

Suppose You want to build 15A output current. With the output voltage of 13.8V.

You should choose C1-22,000 uF 25V.

Equivalent capacitors

But it may do not for sale. We may use five of 4,700uF 25V capacitors to connect together in parallel. So, we have a total capacity of 4,700 μF x 5 is 23,500μF. It is enough to use.

In 30A output, if you cannot buy a 68,000uF 25V electrolytic capacitor. You may use 10,000uF 25V x 6 connect together in parallel. It saves money and easy.

Buy at amazon.com 10,000uF 25V

For example you want 20,000uF you can use 2x 10,000uF.

Use the size of 5A fuse is a slow, or Slow blow fuse.

Constant voltage regulator

This 13.8V power supply circuit uses a regulator IC, LM340T-15. It keeps the level of constant voltage of 15V. Inside this IC has short circuit protection and prevents overheating.

CR: LM340-15 at mouser.com

As a result, this circuit can keep the level output voltage as well. And, If there are overload or short circuit. It will do not damage too.

Now We should use LM7815 because it is popular than that one.

How is current higher

In normal 7812 can power only 1A. We need helping from power transistors, 2N3055.

First, see this circuit. It is a Zener diode and transistor regulator that we are familiar with well.

Zener diode and transistor regulator

Imagine if we use 7815 instead of the Zener diode.
And use a power transistor to increase the output current more.

Learn: Fixed voltage regulator working principle

You may like to see these too.

14.4V DC regulator circuit using 7815 and transistor

The output voltage is 14.4V. Because 0.6V voltage drop across BE of transistor.

Next look at the full circuit diagram again. At output pin of IC1 will be connected to the Darlington emitter follower with the transistor-Q1. Then, Q1 drives six transistors Q2-Q7 in parallel.

Why connects transistor in parallel

To increase the current up. When to connect these 7 transistors Q1-Q7 to complete. It makes can boost up to 30A.

By parallel with the transistor Q2, from the Q3 onwards. Each transistor can increase the current of 5A.

The resistor 0.15Ω at the emitter of each transistor has two act as are:

Connects transistor in parallel boost current upto 30A
  1. Check the current flowing through the transistor. Because there is the voltage drop across them as a ratio of the current flowing through each transistor.
  2. Set the current through the transistor to equally.

Read more: Current limiting resistor

Note: Q1-Q7 is 2N3055 NPN power transistor. Also, you may use TIP35 High-Power Transistors in TO-247. But it is more expensive than a 2N3055.

Better protection

LM340-15 or LM7815 has a wonderful protection system.

  • Short circuit or over current,
    This power supply is not broken. IC1 can prevent overload very well. Even being a long-short circuit throughout the day. It is still in good condition.
  • Hot does not work.
    When the temperature its highly unusual. The high-temperature protection system will order it to temporarily stops responding. Until the temperature drops. It is started as usual.

With the advantages of this IC. It should be installed on a heat sink near the transistor.

When IC1 has been heating up over defined transistor. It stops! Of course, there is no current to the transistor. So, It gradually reduces heat down. IC1 will return to run again.

Keep Reading: Electronic Circuit symbols

SCR Overcurrent protection

In the short-circuit conditions. Or Overload, Or Using too many currents. The Q2 is pulled by the current of 5A. Until the voltage of 0.75V drop across R5 – 0.15 ohms. (emitter pin of Q2). Then, this voltage to gate lead of SCR1. Next, it is enough to trigger SCR1 works immediately.

IC1 is temporarily stopped responding. Because it is overloaded. By earlier, the current of 1A flow through the IC1 and the SCR1 into loaded directly. Not through all transistors.

The SCR1 is working to hold. Until the power supply is cut off. Which automatically resets itself in this manner is called an Electronic circuit breaker.

How much output voltage

The output voltage of the high current 13.8V power circuit is equal to the voltage output of IC1 (15V) minus the voltage drop across the base (B)- emitter (E) of transistor driver (Q1) and the transistor through (Q2) and the voltage drop across R5 emitter of Q2.

Vout = vIC – vbeQ1 – vbeQ2
= 15V – 0.6V – 0.6V
= 13.8V

However, since the voltage drop across R5 may be changed by the current flowing through it.

So, making the voltage output of this circuit is slightly changed the switch from 14V (under no load) It may be of 13V in fully loaded conditions (regulation).

At this level, it will be maintained voltage is better than on the electric of a car. Its output voltage can be changed from 11V to 16V.

And the transmitter is normally used in the car with 12V battery is designed to be compatible with existing 13-14V voltage.

How it builds

Because the components used in this 13.8V power supply circuit there is not much. And most of them are large. Which must be installed on a heat sink.

The operation of this project, so no need to use a PCB. May use point connect the power cord, tighten the nut onto the heat sink. Then, Connect the wires to the other parts onto the heat sink.

Credit: Photo by amazon.com

Choose parts as you want

2. Choose a bridge diode rectifier And the transformer T1 according to usage.

Because LM7815 requires a low input voltage to 17V.  So, the input DC voltage to unregulated to output drop across C1 should be between 18V to 20V.

If less than 17V may not be enough to use the circuit. And, If more than 20V over 20%.

It may have more energy a loss in transistors and ICs. Making must use a larger heat sink. It is too consumes more energy than necessary.

You may choose the size of the transformer 15A. My friends go to the core steel EI at an antique store, then go hire made a new transformer. This is durable and inexpensive.

The power transistor—You can use 2N3055 which easier to buy. Or use TIP3055 is the same as 2N3055. But easy to hold on the heat sink with TO-3P. The Best, TIP35 is more high-power current more than 25A of collector current.

You can select any number SCR1 is 200V 5A such as 2N4441, C122, C106, etc.

You can add LED display to show power on by this how.


If you not like this circuit you can look others circuit more below.

  1. 0-30V 20A High current adjustable voltage regulator circuit
  2. Power Supply for Audio Amplifier, multiple output 12V, 15V, 35V
  3. Boosting the Regulator Currents for IC-78xx
  4. LM338 | Datasheet | Adjustable Power Supply 5A and 10A

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I always try to make Electronics Learning Easy.

Apichet Garaipoom

I love the electronic circuits. I will collect a lot of circuit electronics to teach my son and are useful for everyone.
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