# 0-30V 20A High current adjustable voltage regulator circuit

If you are looking for a high current Adjustable voltage regulator circuit. This may be a better choice for you.

It can give the output current 20A or 400watts and can adjust the voltage of 4 to 20V—or apply to 0 to 30V easily. It is good quality, excellent performance and durable with PCB.

For use in electronic telecommunication, High power radio transmitter, etc.

This project uses a few components. Because of use fours of LM338—-5A voltage regulator and IC- 741—popular op-amp—in linear power supply mode.

Try to build then you will like it!

## How it works

The LM338K that we bring to use be DC voltage regulator circuit on the Floating type, The simple applications style of this IC As shown in Figure 1 How to use LM338 IC in basic

Figure 1 circuit, in normal conditions, the voltage between pin Adj and pin output is equal to a 1.25V stable that flow pass R1, R2 will have constant as well.

The output voltage be equal to the voltage at pin Adj + 1.25 volt or Calculated as follows

Vo = 1.25 (R1 + R2) / R1

## High current with parallel LM338

In normal IC-LM338 Can supply up to 5 amps, but to load current maximum 20 amps, we will bring it to parallel.

What to watch out, when we connect many IC with parallel form, is the average current flowing through the circuit. Each equally.

The easiest way is to connect a resistor to the output pin of IC as shown in figure 2.

The value of the resistors-Rs used to it, it will be much less than the R1.

Based on the circuit, we can set.

IoRs = 1.25 – Vo(R1/(R1+R2) )

And from the work of circuits set of down, will be.

IiRs = 1.25 – Vo (R1 /(R1+R2) )

From these two equations, which are all the same, it is that Io = Ii.

Or simply, the current through the LM338 IC both are equal.

In practice, we do not circuits to use it. Since the voltage across drop Rs will change based on the current flowing through the load and Referenced voltage of IC. Also, different from each other.

##  External LM338 controls using uA741

Therefore, we need to control external circuits. To control the voltage at pin adj, as shown in Figure 3.

From the circuit, we will see that at pin negative of IC to have a half voltage of output voltage. And at pin positive to have equal to Referenced voltage.

Which it is caused by a constant current flowing through the transistor to Rs and P1.

From the properties of the op-amp circuit to the regulated level output voltage that. Until having the same voltage at pin input.

So the voltage at pin base of a transistor- Q1 is equal to the voltage at pin negative of IC.

The voltage these, to make changes in resistance of the transistor, causing voltage in referenced point change.

The resistance of the transistor is inversely proportional to the output voltage, to compensate for the voltage loss of Rs. Due to the does not equal flow of these load current. High power DC regulator 4-20 volts 20 amps by LM338

• From all principles above, we have circuits applications, as shown in Figure 4, if you want to add the IC-LM338, enabling them to be higher current.
• For a transformer that can supply at least 30 amperes, and voltage secondary coil, should not be less than 18 volts.

To optimize the circuits for the capacitor-C2 should better use of 20000uF.

Read: How to use LM317 Datasheet and pinout

## How to make a high current adjustment voltage regulator Parts list
IC1: LM741
IC2-IC5: LM338K or LM338P
Q1: BD140
D1: Bridge diode 35A
D2: 1N4148, 75V 150mA Diodes
R1: 150Ω Resistor 0.5W
R2: 100Ω Resistor 0.5W
R3, R4: 4.7K Resistors 1/2W
R5-R8: 0.3Ω Resistors 5W
C1: 0.01uF 200V, Polyester Capacitor
C2,C5: 4,700uF 50V, Electrolytic Capacitors
C3: 0.1uF 63V, Polyester Capacitor
C4: 10uF 25V Tantalum
C6: 47uF 35V, Electrolytic Capacitors

## Build 20A High current adjustable power supply

• All the devices in the circuits. Devices can be soldered onto the PCB as shown in Figure 5. Unless you change the input capacitor-C2 has increased these. I will have to install it on outside of PCB.
• Bridge diode must be attached heat sink neatly. To help extend the life and durability.
• For IC-LM338 that you need to install on a big size heatsink as well. Be careful, the body of the IC to the heat sink Short decisively.
• When all is finished soldering equipment, test input AC power to this project.
• Then adjust VR1 until the output voltage as needed, and test the Load and adjust VR1 until the output voltage is the voltage should be unchanged.

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