LM350 adjustable voltage Regulator

The lm350 voltage regulator is 3A DC adjustable power supply IC – LM350 that high-performance. It can apply voltage output 1.25V to 35V. so have a few components. If you add two diode series with the output to reduce voltage start with 0-volts.

This circuit looks like in My first Variable DC Power Supply, but this high current higher than 3-Amp. Therefore they cause you can supply more any load circuit. Which we can buy this IC at many stores but expensive than LM317.

How LM350 variable power supply works

In Figure 1 you will see that the circuit form same the My first Variable DC Power Supply.

1.2V-25V at 3Amp Adjustable Regulators using LM350T

Figure 1

When we apply AC220V or AC110V(for the USA) with pressing S1 to turn on this power supply. ACV will flow F1 for protection when the overload or too much voltage input.

Then the ACV will flow into a transformer that has the ability to transform voltage and current to lower levels of AC-18V and next to BD1-bridge diode to convert AC to DC.

Next, they will through C1-4700uF electrolytic capacitor smooth (filter) the pulsating voltage from a transformer into a steady direct current (DC).

Now we have voltage at this point is 22V to 25V

And then, the current will flow to the input lead of IC1-LM350 power supply.
Which it is an adjustable regulator IC that designed to many supplies for 3Amp output and adjustable over 1.2V to 33-volts, and with current limiting, thermal shutdown, full protection.

See LM350 datasheet

This circuit form I see in the LM350 datasheet, which there is a simple detail to do this:
– In normal operation, the LM350 have nominal 1.25V reference voltage (Vref) between the output lead and Adjustable lead (ADJ). This voltage will across R1+R2 (120 ohms+120 ohms = 240 ohms datasheet) and,
– since the voltage is constant, a constant current then flows through the output set resistor VR1. To adjust voltage output.
-C1, C4-0.1uF is input bypass capacitor, it needs if devices (IC1) more than 6 inches from filter capacitors.

-C3-47uF is bypass capacitor prevents 86dB ripple rejection.
-C5- 100uF is used to improves transient response. Output capacitor in the range of 1uF to 1000uF of tantalum electrolytic is commonly used to provide improved output impedance and rejection of transients.

Protection Diodes
When external capacitors are used with any IC regulators, sometimes necessary to add protection diode to prevent the capacitors from discharging through low current point into the regulator.

Although the surge is short, there is enough energy to damage parts of the IC.

When negative voltage or 20A spikes flow backward the output it will be absorbed voltage with D3-diode.

And Then D2 to protect Out and Adj lead.
And D1 is protected voltage spikes to Input and output lead.

Components list
IC1____LM350T___3 terminal positive voltage regulator 3Amp_____= 1 pcs.
C1_____4700uF 35V Electrolytic capacitors______________________ = 1 pcs.
C3_____47uF 35V_________”_________”___________________________ = 1 pcs.
C5____100uF 50V_________”_________”___________________________ = 1 pcs.
C2,C4___0.1uF 50V_ ceramic capacitors__________________________ = 2 pcs.
BD1_____4A 200V brigde diode__________________________________ = 1 pcs.
D1-D3____1N4007___1A 1000V Diode_______________________________ = 3 pcs.
R1,R2____120 ohms 0.5W resistors______________________________ = 2 pcs.
VR1______Variable Resistors___ 5K(B)___________________________ = 1 pcs.
S1______On-Off or SPST switch__________________________________ = 1 pcs.
F1______0.5A Fuse______________________________________________ = 1 set.
T1______3A 18V to 21V transformer_____________________________ = 1 pcs.
Heatsink, PCB, wires, and others

Make LM350 power supply

The circuit has a few parts you can assemble devices on perforated Board and wiring as Figure 2
The IC1-LM350 power supply must be mounted to big size heatsink because at work times it is very hot.

we assemble and wiring parts on perforated board
Figure 2 we assemble and wiring parts on perforated board.


Before check circuit and wiring for error. Then adjust VR1 to a minimum. Next, we test this project with apply voltage output is 1.2V You can watch the video below. Then adjust the voltage to 12V.

And next, I try to use 12Volts 50watt lamp as the load. The voltage will must not lower than 12V and I measure the current of the lamp of 3.5A.
This project is good as we need to. We are happy. Thank for watching.


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