Here is LM338 Adjustable DC power supply circuit, 1.2V to 30V. It can provide a current maximum to 5A and 10A. If you have used LM317 or LM350. They are similar, so easy to use with a few components. But LM338 have higher a current than LM317. You can look at a datasheet below more spec.

**Table of Contents**Show All

## LM338 Datasheet and Pinout

The LM138/LM238/LM338 are adjustable 3-terminal positive voltage regulators capable of supplying in excess of 5A over a 1.2V to 32V output range.

They are exceptionally easy to use and require only 2 resistors to set the output voltage.

The careful circuit design has resulted in outstanding load and line regulation comparable to many commercial power supplies.

The LM138 family is supplied in a standard 3-lead transistor package.

**LM338 features**

- 7A Maximum output current
- 5A output current
- Adjustable output 1.2V to 37V
- Line regulation typically 0.005% /V
- Line regulation typically 0.1%
- Thermal regulation
- Current limit constant with temperature

**Pinout of LM338K To-03 and LM338T TO-220**

## LM338 Basic circuit Voltage Calculator

Look at a basic circuit. We use only 2 resistors can set the constant output voltage.

Vout = 1.25V x {1+R2/R1} + Iadj x R2

Some said Iadj is very low current(approx 50uA only).

So, we may chop them up. It is shorter and easy to calculate.

Vout = 1.25V x {1+R2/R1}

Which is better?

For example:

You use R1 = 270 ohms and R2= 390 ohms. It causes output is 3.06V

Is it easy? If you have voltages choice with most resistors. In local stores near you.

look at the list:

1.43V : R1 = 470Ω, R2 = 68Ω

1.47V : R1 = 470Ω, R2 = 82Ω

1.47V : R1 = 390Ω, R2 = 68Ω

1.51V : R1 = 330Ω, R2 = 68Ω

1.51V : R1 = 390Ω, R2 = 82Ω

1.52V : R1 = 470Ω, R2 = 100Ω

1.53V : R1 = 390Ω, R2 = 82Ω

1.56V : R1 = 330Ω, R2 = 82Ω

1.57V : R1 = 270Ω, R2 = 68Ω

1.57V : R1 = 470Ω, R2 = 120Ω

1.57V : R1 = 390Ω, R2 = 100Ω

1.59V : R1 = 390Ω, R2 = 100Ω

1.60V : R1 = 240Ω, R2 = 68Ω

1.63V : R1 = 330Ω, R2 = 100Ω

1.63V : R1 = 270Ω, R2 = 82Ω

1.64V : R1 = 390Ω, R2 = 120Ω

1.64V : R1 = 220Ω, R2 = 68Ω

1.65V : R1 = 470Ω, R2 = 150Ω

1.66V : R1 = 390Ω, R2 = 120Ω

1.68V : R1 = 240Ω, R2 = 82Ω

1.71V : R1 = 330Ω, R2 = 120Ω

1.71V : R1 = 270Ω, R2 = 100Ω

1.72V : R1 = 220Ω, R2 = 82Ω

1.72V : R1 = 180Ω, R2 = 68Ω

1.73V : R1 = 470Ω, R2 = 180Ω

1.73V : R1 = 390Ω, R2 = 150Ω

1.76V : R1 = 390Ω, R2 = 150Ω

1.77V : R1 = 240Ω, R2 = 100Ω

1.81V : R1 = 270Ω, R2 = 120Ω

1.82V : R1 = 150Ω, R2 = 68Ω

1.82V : R1 = 330Ω, R2 = 150Ω

1.82V : R1 = 180Ω, R2 = 82Ω

1.83V : R1 = 390Ω, R2 = 180Ω

1.84V : R1 = 470Ω, R2 = 220Ω

1.86V : R1 = 390Ω, R2 = 180Ω

1.88V : R1 = 240Ω, R2 = 120Ω

1.89V : R1 = 470Ω, R2 = 240Ω

1.93V : R1 = 330Ω, R2 = 180Ω

1.93V : R1 = 150Ω, R2 = 82Ω

1.94V : R1 = 270Ω, R2 = 150Ω

1.96V : R1 = 390Ω, R2 = 220Ω

1.97V : R1 = 470Ω, R2 = 270Ω

1.99V : R1 = 390Ω, R2 = 220Ω

2.02V : R1 = 390Ω, R2 = 240Ω

2.03V : R1 = 240Ω, R2 = 150Ω

2.06V : R1 = 390Ω, R2 = 240Ω

2.08V : R1 = 330Ω, R2 = 220Ω

2.10V : R1 = 220Ω, R2 = 150Ω

2.12V : R1 = 390Ω, R2 = 270Ω

2.13V : R1 = 470Ω, R2 = 330Ω

2.16V : R1 = 330Ω, R2 = 240Ω

2.16V : R1 = 390Ω, R2 = 270Ω

2.19V : R1 = 240Ω, R2 = 180Ω

2.23V : R1 = 470Ω, R2 = 390Ω

2.25V : R1 = 150Ω, R2 = 120Ω

2.27V : R1 = 270Ω, R2 = 220Ω

2.27V : R1 = 330Ω, R2 = 270Ω

2.29V : R1 = 470Ω, R2 = 390Ω

2.29V : R1 = 180Ω, R2 = 150Ω

2.31V : R1 = 390Ω, R2 = 330Ω

2.36V : R1 = 270Ω, R2 = 240Ω

2.37V : R1 = 390Ω, R2 = 330Ω

2.40V : R1 = 240Ω, R2 = 220Ω

2.44V : R1 = 390Ω, R2 = 390Ω

2.50V : R1 = 470Ω, R2 = 470Ω

2.57V : R1 = 390Ω, R2 = 390Ω

2.61V : R1 = 220Ω, R2 = 240Ω

2.65V : R1 = 330Ω, R2 = 390Ω

2.66V : R1 = 240Ω, R2 = 270Ω

2.73V : R1 = 330Ω, R2 = 390Ω

2.74V : R1 = 470Ω, R2 = 560Ω

2.75V : R1 = 150Ω, R2 = 180Ω

2.76V : R1 = 390Ω, R2 = 470Ω

2.78V : R1 = 270Ω, R2 = 330Ω

2.78V : R1 = 220Ω, R2 = 270Ω

2.84V : R1 = 390Ω, R2 = 470Ω

2.92V : R1 = 180Ω, R2 = 240Ω

2.96V : R1 = 270Ω, R2 = 390Ω

2.97V : R1 = 240Ω, R2 = 330Ω

3.03V : R1 = 330Ω, R2 = 470Ω

3.05V : R1 = 390Ω, R2 = 560Ω

3.06V : R1 = 270Ω, R2 = 390Ω

3.06V : R1 = 470Ω, R2 = 680Ω

3.08V : R1 = 150Ω, R2 = 220Ω

3.13V : R1 = 220Ω, R2 = 330Ω

3.14V : R1 = 390Ω, R2 = 560Ω

3.18V : R1 = 240Ω, R2 = 390Ω

3.25V : R1 = 150Ω, R2 = 240Ω

3.28V : R1 = 240Ω, R2 = 390Ω

3.35V : R1 = 220Ω, R2 = 390Ω

3.37V : R1 = 330Ω, R2 = 560Ω

3.43V : R1 = 270Ω, R2 = 470Ω

3.43V : R1 = 390Ω, R2 = 680Ω

3.43V : R1 = 470Ω, R2 = 820Ω

3.47V : R1 = 220Ω, R2 = 390Ω

3.50V : R1 = 150Ω, R2 = 270Ω

3.54V : R1 = 180Ω, R2 = 330Ω

3.55V : R1 = 390Ω, R2 = 680Ω

3.70V : R1 = 240Ω, R2 = 470Ω

3.82V : R1 = 180Ω, R2 = 390Ω

3.83V : R1 = 330Ω, R2 = 680Ω

3.84V : R1 = 270Ω, R2 = 560Ω

3.88V : R1 = 390Ω, R2 = 820Ω

3.91V : R1 = 470Ω, R2 = 1K

3.92V : R1 = 220Ω, R2 = 470Ω

3.96V : R1 = 180Ω, R2 = 390Ω

4.00V : R1 = 150Ω, R2 = 330Ω

4.02V : R1 = 390Ω, R2 = 820Ω

4.17V : R1 = 240Ω, R2 = 560Ω

4.33V : R1 = 150Ω, R2 = 390Ω

4.36V : R1 = 330Ω, R2 = 820Ω

4.40V : R1 = 270Ω, R2 = 680Ω

4.43V : R1 = 220Ω, R2 = 560Ω

4.44V : R1 = 470Ω, R2 = 1.2K

4.46V : R1 = 390Ω, R2 = 1K

4.50V : R1 = 150Ω, R2 = 390Ω

4.51V : R1 = 180Ω, R2 = 470Ω

4.63V : R1 = 390Ω, R2 = 1K

4.79V : R1 = 240Ω, R2 = 680

5.04V : R1 = 330Ω, R2 = 1K

5.05V : R1 = 270Ω, R2 = 820Ω

5.10V : R1 = 390Ω, R2 = 1.2K

5.11V : R1 = 220Ω, R2 = 680Ω

5.14V : R1 = 180Ω, R2 = 560Ω

5.17V : R1 = 150Ω, R2 = 470Ω

5.24V : R1 = 470Ω, R2 = 1.5K

5.30V : R1 = 390Ω, R2 = 1.2K

5.52V : R1 = 240Ω, R2 = 820Ω

5.80V : R1 = 330Ω, R2 = 1.2K

5.88V : R1 = 270Ω, R2 = 1K

5.91V : R1 = 220Ω, R2 = 820Ω

5.92V : R1 = 150Ω, R2 = 560Ω

5.97V : R1 = 180Ω, R2 = 680Ω

6.04V : R1 = 470Ω, R2 = 1.8K

6.06V : R1 = 390Ω, R2 = 1.5K

6.32V : R1 = 390Ω, R2 = 1.5K

6.46V : R1 = 240Ω, R2 = 1K

6.81V : R1 = 270Ω, R2 = 1.2K

6.92V : R1 = 150Ω, R2 = 680Ω

6.93V : R1 = 330Ω, R2 = 1.5K

6.94V : R1 = 180Ω, R2 = 820Ω

7.02V : R1 = 390Ω, R2 = 1.8K

7.10V : R1 = 470Ω, R2 = 2.2K

7.33V : R1 = 390Ω, R2 = 1.8K

7.50V : R1 = 240Ω, R2 = 1.2K

8.07V : R1 = 330Ω, R2 = 1.8K

8.08V : R1 = 150Ω, R2 = 820Ω

8.19V : R1 = 270Ω, R2 = 1.5K

8.30V : R1 = 390Ω, R2 = 2.2K

8.43V : R1 = 470Ω, R2 = 2.7K

8.68V : R1 = 390Ω, R2 = 2.2K

9.06V : R1 = 240Ω, R2 = 1.5K

9.58V : R1 = 330Ω, R2 = 2.2K

9.77V : R1 = 220Ω, R2 = 1.5K

9.90V : R1 = 390Ω, R2 = 2.7K

10.03V : R1 = 470Ω, R2 = 3.3K

10.37V : R1 = 390Ω, R2 = 2.7K

10.63V : R1 = 240Ω, R2 = 1.8K

11.25V : R1 = 150Ω, R2 = 1.2K

11.44V : R1 = 270Ω, R2 = 2.2K

11.48V : R1 = 330Ω, R2 = 2.7K

11.67V : R1 = 180Ω, R2 = 1.5K

11.83V : R1 = 390Ω, R2 = 3.3K

12.40V : R1 = 390Ω, R2 = 3.3K

12.71V : R1 = 240Ω, R2 = 2.2K

13.75V : R1 = 330Ω, R2 = 3.3K

15.31V : R1 = 240Ω, R2 = 2.7K

16.25V : R1 = 150Ω, R2 = 1.8K

16.53V : R1 = 270Ω, R2 = 3.3K

16.59V : R1 = 220Ω, R2 = 2.7K

18.44V : R1 = 240Ω, R2 = 3.3K

19.58V : R1 = 150Ω, R2 = 2.2K

20.00V : R1 = 220Ω, R2 = 3.3K

23.75V : R1 = 150Ω, R2 = 2.7K

24.17V : R1 = 180Ω, R2 = 3.3K

28.75V : R1 = 150Ω, R2 = 3.3K

For example, you need 20V 5A power supply. You look at 20.00V : R1 = 220Ω, R2 = 3.3K.

It is easy, right?

## 1.25V to 30V, 5A Variable power supply using LM338

We may have many ways such as: to modify the **LM317 Variable Regulator 0-30V 1A**. By adding the power transistor MJ2955 in a circuit. As following **Adjustable Voltage and current regulator IC power supply** . Or You may build the **Variable dc regulator 0-30V 5A** circuit, as well. But these methods. Rather cumbersome and wasting too more money.

However, we can build this circuit easily and cheap, By using the packages IC No. LM338 only one, Similar to the LM317 IC number, but it can supply up to 5A, like the circuit shown in Fig.

### How this circuit works

The transformer T1 converts the AC 220V to 24 Vac, so be rectified the current by the bridge diode rectifier BD1 – 10A 400V. Until DCV has come out that the filter capacitor C1 is equal to 35 volts.

The IC1 is the heart of the operation of this circuit. By the voltage output value obtained from the IC depends on the voltage value at the Adj pin of IC1, or can be varied by adjusting the VR1.

However, the output voltage will be approximately equal to 1.25+1.25VR1/R1

The output voltage at the output pin of the IC1 is a more powerful filter with the capacitor C3.

**Parts you will need**

IC1: LM338K, LM338P

D1: Bridge Diode 10A

D2, D3: 1N4007, 1000V 1A diode

R1: 220Ω 0.5W resistors 5%

R2: 12K 0.5W Resistors 5%

VR1: 10K Potentiometer

C1,C3: 4700uF 50V Electrolytic

C2: 0.1uF 50V

LED 5mm

T1: Transformer, 24V 5A secondary

**The Building**

You must **solder** all devices in the PCB to completely, for the IC LM338K should install with a large heat sink. and all device has the poles. Caution connected the correct, especially electrolytic capacitor.

**Figure 2 The PCB layout and components layout**

## NOTE:

Because IC number is high price.You may use the LM317 and transistor, to expand the current demand.

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## 1-20V, 10A Adjustable DC Power Supply

**1.2V-20V 10A adjustable dc power supply using LM338**

If you want **Variable Regulate Power Supply high current more** than 10A up. I would recommend this circuit. Because build easy, use LM338 and LM107 again.

The normal LM338 have current about 5A. Then, must use 2 pcs. It causes more current up to 10A. The VR1 adjusts an output voltage of 1.2V to 20V cover usual usability. This idea can protect all error with two LM338.

If you want to see examples of projects. Using LM338 to multiple connections in parallel. To boost the higher current. Click: **High power supply regulater 0-30V 20A using LM338**

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Dear friend before publishing any circuit you should review,still thanks for sending circuit

you can see my circuits 3d sound which have been patented in 3 countries international application no PCT/US2011/000854. by the way how may r2s you are using, and what is the connection with r1 which is powering led with regulation that is all

i will say copy with sense. Thanks

Dear sir

ref- adj power supply using LM338 1.2 to 30 v

I tried this circuit and i could make a variable voltage only with 1k VR1 variable and not the 10 k , with this the voltage is from 1.5 to 24 volts. But the problem is there is no current at all!!. Please help

Using 10k makes voltage from 24 to 27v only.

Ill try this circuit to heat my model airplane engine´s glow plug. However, since I will use 12 VDC battery instead of AC,I imagine don´t need neither big capacitance filter condenser nor the 1N4007.Will experiment, anyway Thanks a lot and will let you know if I could fly or remained grounded.

what does D2 do?

Dear all, if you insist on building that 1.2V-30V / 5A using the same circuit diagram as mentionned above , you would not really get it adjusted up to 30V , instead you will all get it adjusted from 1.2V – about 8V & that’s all you’ll get! If you really want to have it adjusted from 1.2V -30V , you’ll simply have to remove the R2 -12K resistor & replace it by a 10microfarad 50V electrolytic capacitor & place a 100nF ceramic capacitor in parallel with that 10microfarad 50V electrolytic capacitor that’s it.

this circuit works ok as long as you use a good quality lm338 and keep the input/output voltage differance less than 40 volts

dear sir…….

please can any one tell me how can i make 30v 10A adjustable power supply using lm338 , and can it be possible with pwm…………

thank you ………

dear Sir, can anyone put me through on how to construct a 19v 3.5A regulated DC power supply using solar panel as input for the project. thanks

hi friends,

Can anyone please tell me the voltages of the capacitors (filters) and wattage of the resisters given in the above circuit diagram..

I want to develop 12v 5A, 12v 10A with 4,8,16 outputs. Can you please help?

hi,

can any one help me.what is the “value or number” of bridge rectifier in this circuit…

hiiiii

can any one help me how to convert 12v,5A dc 10.5v 5A dc or 10v5A

This is a high quality bench power supply with adjustable output voltage from 0 to 30V and adjustable output current from few miliamperes to 4 amperes. Built-in electronic output current limiter that effectively controls the output current makes this power supply indispensable in the experimenters laboratory as it is possible to limit the current to the typical maximum that a circuit under test may require, and power it up then, without any fear that it may be damaged if something goes wrong. There is also a visual indication that the current limiter is in operation so that you can see… Read more »

I’m Married!,

I see only one adjustable potentiometer in the circuit. Where would you place the second to control the current, as you say, and what other components would be needed to complete a power supply that is capable of the separate regulation of both voltage and current output, such as you described in your comment above? Adding a meter for each, also, would be particularly useful, wouldn’t you agree? ;~)

can you tell me what is the wattage of the resistors used. thanks

hi can any one tell me how to convert 5v to 30v/2A??

hi friends does it really works..

Hi , can you tell me what is tha wattage of the 2 resistor R1 & R2 ?

Hi,

You can use 0.5W resistor for R1, R2.