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

Those who want to take the radio transmitters from a car to use in the house. You should use 12V Ham Radio power supply. Better that way, High current 13.8V power supply with enough power out of 5A to 30A. According to the size of the transmitter. I highly recommend this high-current power supply circuit. Because of Good performance, size of output 13V-14V depending on the load.

And, You can choose to build multiple sizes of 5A, 10A, 15A, 20A, 25A, 30A. According to real usage. So, help to save and easier to build.

Of course, you can buy this 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 Ham Radio Power Supply

The circuit diagram

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

Idea of circuit

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

Sometimes you may have these components in your house.

A linear power supply circuit is a better choice. Because it is so easy circuit. There are a few parts in the circuit.

But It is a big size with large components.
For example, 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 grandfather.

Yes, you can try it.

I love the linear circuit.

It must have quality
Checklists—we need these.

  • The 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.

Constant voltage regulator

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


How is current higher

At output pin of IC1 will be connected the Darlington emitter follower with the transistor-Q1. Then, Q1 drives six transistors Q2-Q7 in parallel.

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.

To increase the current up. From the original current maximum of 1A. When to connect these transistors Q1-Q7 to complete 7 pcs. It Makes can supply up to 30A. By parallel with the transistor Q2, from the Q3 onwards there. Each transistor can be expanded current of 5A.

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

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. The current through the transistor to equally.

Read more: Current limiting resistor

Better protection

LM340-15  has a wonderful protection system.

1. Short circuit or over current power supply is not broken. IC1 can prevent overload very well. Even being long-short circuit throughout the day. It is still in good condition.

2. 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 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 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.

Choose parts as you want

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

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

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

Because LM340T-15 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. High power supply regulater 0-30V 20A by LM338
  2. High Current Variable Voltage Regulator 2-36V 10A
  3. Amplifier power supply using High Current Transformer
  4. 10A DC Supply FIX Regulated by IC 78XX and MJ15004
  5. 1-20V 10A adjustable dc power supply by LM338

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Livio Ortega Morales

Saludos cordiales.
Muy importente esta fuente de poder y de gran utilidad en todo circuito.
Quisiera que incluyan circuitos para disparar IGBT.


I think there is an error in that diagram! in the 30 A section, the collector and base of Q7 is shorted rendering the whole regulator circuit
as useless seeing that all bases are in parallel…
that wold leave someone wanting to know, who let the smoke out?


Dear sam, you are right.

shelly tennyson charles

reg ic 7815 is much over heated when i short the out put supply. kindly let me know what should i do. another thing, in put voltage to ic 7815 is about 24 vdc, is this high voltage is the matter.
thanks and regards.


if one of transistor or LM will bow up or LM will lost it’s ground you’ll get high voltage in output.
Got it twice under developing conditions, I will add overvoltage protection in output side.

Michael Amann

If I were to use 2N3055 transistors for Q2 -Q7, would the values for the base and emitter resistors be the same?

Aamir Abbas

please tell me that is this work or not.


Is This Work Or Not?????


Plz Tell Me .

José Antonio Mogrovejo

Excellent circuit,really formidable,this is very easy to understanding



What diode model you use in the bridge ? bdi 25A 100V , i cant found this diode…?


BD1 I am sure he is referring Bridge Diode number 1 BD1 not bdi which is a full wave bridge rectifier at 25 amps.

Correction with the trace from Q6 base to Q7 collector ommited in the link below.

comment image


Narciso Fumero

The transistor Q7 base and collector are in short.
To fix that,the wire going truth colector must finish Q6 collector?
Thanks for your attention.
I believe is going to be a very good project.
Thanks again.

Narciso Fumero

For the 30 amp. Circuit where go the 12 amp. Fuse.


As I can see from datasheets, I can use 2n3055 transistors instead TIP3055 without any other changes. Am I right?
Thanks for circuit!


is the above correct or the one given by ECStrat correct????
plz help….


is the above circuit diagram correct or the one given by ECStrat correct????
plz help….

Billy Bowling

I am in need of a scumadic for a 110V AC, 13.8V 100A DC power supply. I will now tell you what I have and what has been done so far. I have a 3 stage 110V 13.8, 14.6 and 17.5V output transformer capable of 100A. I am using 2N3002 pass transistors X 12! 2 driving 10. I have 2 100V 1000A Stock Astron bridge rectifiers, a 723 complete board, 63V 180000uf cap etc. I am wiring up the pass transistors 2 driving 10 using the crow bar wiring! 0,1 10W ceramic resistors! I already have the pass transistor mounted… Read more »


please tell me which diode used, the rectifier circuit.


Forget this guy. Here’s one that’s similar and actually works. Crowbar and protection explained.


Dr. RJ Bryan KC7ECO

First off, the schematic diagram is complete unreadable, appears to have errors and is pretty much worthless circuit. I would suggest finding a more detailed power supply somewhere else.

Justice Opoku

Dear Sr

i am really happy to ready all over your project. please sr i wont 5vols out voltage and remain all the current.so how
could i do, or i could change ic1 to (7805). thank you .


i have one faulty 24volt /10 amps SMPS.
If i on the powersupply the output LED flickering and the voltages also varying,i want to rectify the SMPS.Kindly give your valuable tips.


Hello Mom Nice circuit and works wonderfull. Gutted out an old 1400 watt UPS and the transformer filled the bill perfectly for a 25 amp supply, the parts were cheap and the whole project went without a hitch. Took a little time doing the artwork for the PC board. At 18 amps it drops down to 12.6 volts and at idle with a 1.7 amp load it’s 13.9 colts which is acceptable and will try it with a receiver in the morning and hopefully I will have no chirp on the transmitter. Needed a supply for the bench and it… Read more »


pls what value of bridge rectifier can handle up to 30amps?

budi ambong

is it right that basis Q7 connecting to collector? i thing its not common.imho


I’m looking for a manual or circuit of a Sharp CD-C25x(bk) on pdf or doc please help



comment image

He made one small mistake.




Hello, but you can have the pattern of the PCB. thanks

g dindial

hi there man i just build this sweet power supply at first i thought it wasnt working so i rechecked and tested every part of the circuit but i figured its because i powered it up when the transformer was already on so the capacitor must of needed to charge and the scr may have tripped took me 6 hrs from scratch to build i got some old power supplies from computers that were blown out and used the heat sinks i bought all the parts it came up to approx 350 TT dollars i would say around 60 us… Read more »

g dindial

dont know the rating of my transformer per say but the output im using read 20.5 v it may be a 30va not sure but it works!


Momename, it would help immensely if you could get someone to proofread and edit your description of this power supply circuit because it is very difficult at times to fully understand exactly what you are trying to describe.

For example: ” – I chose the C1-22,00uF 25V. But not for sale, have to use five 4,700 25V capacitors to parallel these.”

It’s better written thusly: “Because a 22,000uF 25V capacitor was unavailable at the time, I just paralleled five 4,700 25V capacitors instead, which provides the slightly greater capacitance of 23,500uF.”


There’s a really good 13.8 Volt, 30 Amp power supply circuit diagram in the ARRL handbook with clear instructions on how to build it. The voltage is adjustable and it even has remote voltage sensing which automatically compensates for any voltage drop that occurs between the power supply and the load [transceiver]. It uses a very large capacitor of ~500,000uF which allows each of the five 2N3055 pass transistors to run quite cool because they only have about 2-3 Volts maximum dropped across them. If each 2N3055 [or TIP35] pass transistor drops only 3Volts at 6Amps then it will only… Read more »


Hello, I would like to make this circuit but I need variable power supply. Could I add resistor and pot to lm317 and that way change output voltage?


pls dis circuit is not giving me good output current i use 0.22ohm 5wat and bt151 as the scr but am having a droping current of 1amp any help?


Hello sam, but you can have the pattern of the PCB? and can i use 18vdc transfomer on this circuit..? thanks & regards


Please give more details about all Q1,Q2,Q3,Q4,Q5,Q6 & Q7 like volt, power etc and where I can bought all parts from. I m from Raipur chhattishgarh.
I also want to know that how can I blow 2
12 volts 55 watt lamps in my bike discover 100 cc 4g with magnet coil or battery when I connect these with magnet it burns like candle a and when connect with battery it discharge my battery in 15 minutes please tell can I increase its ampiers upto 10 amp or more by little change please give me proper solution ..

Jose Augusto

Greetings, Friend

You have this already drawn design in Proteus, for I am wanting to set up this project but the biggest problem and draw it if possible if you have the project designed to make the gentiliza send to my email [email protected]

Thank you.


Can I use this circuit to power the car amplifier which require around 25amp constant current…

Virat shinde

My Question is
If i want to amplify it more than 30A if near 100A so then what should be need to do changes in circuit


Sir I have 220v ac 18watt input can i output about 30amp using this circuit ?


What would be appropriate transformer power for the product? I guess 15V 30W transformer is too small?

Bayu Dwi Arifianto

If I just need 10 Ampere, R16 C4 C5 I must use it too?


Who ever writes these electronic articles should read the work before posting it because none of these articles make any sense. ????????????????????


dear sir, i have do it, i note that error on schematic ,becouse last tip 35 , the collector is cc with base.
It is OK! Very power, very good,but i’have a problem when i ON. I’think the scr current is very sensible, and a simple car lamp 12v 3A make protection. If i use 1A and following 10A =11A that is OK. The resistor of 100 OHM will upgrade to 120 or 150 OHM???
Thank for your reply.
Best regards…Mike


or R16 < 470 Ohm????

omed neichi

a nice circuit.
thank u


Good circuit. I have built it, worked ok


Buen día tengo un pequeño problema se protege con mucha facilidad y la resistencia de 470 se quema me ayudas ?? Por favor

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