high current adjustable power supply 4-20 volts 20 amps by LM338
This is High current and Adjustable Volt 0 to 30V 20A.
It easy circuit and nice circuit, Because use IC LM338 and IC 741.
Volt Output adj by VR1-1K. IC LM338 to hold heat-sink. Transformer is 20A up.
I find this circuit, for an electronic friend, according demands of those who want the the power supply, good quality, excellent performance. Can supply the voltage from 4-20 volt and currents up to 20 amperes. or 400 watt
For use in electronic telecommunication. Transmission – radio …. more diverse, if you want Quality is important.
This project is a few piece of equipment, because main equipment used is IC-LM338K, so this power supplies, it is incredibly cheap.
Try to build then you will like it!
How it works
The LM338K that we bring to use be DC regulator circuit on Floating type, The simple applications style of this IC As shown in Figure 1
Figure 1 circuit, in normal conditions, voltage between pin Adj and pin output is equal to 1.25V stable that flow pass R1, R2 will have constant as well.
The output voltage be equal to voltage at pin Adj + 1.25 volt or Calculated as follows
Vo = 1.25 (R1 + R2) / R1
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 be 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.
Therefore, we need to control external circuits. To control the voltage at pin adj, as shown in Figure 3.
From circuit will see that at pin negative of IC be have a half voltage of output voltage and at pin positive have equal to Referenced voltage. Which 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 output voltage that. Until have the same voltage at pin input. So the voltage at pin base of transistor- Q1 is equal to the voltage at pin negative of IC.
The voltage these, to make changes in resistance of transistor, causing voltage in referenced point change.
The resistance of 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.
– 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 transformer that can supply at least 30 amperes, and voltage secondary coil, should not be less than 18 volt.
To optimize the circuits for the capacitor-C2 should better use of 20000MF.
D1_____________Bridge diode 35A
D2_____________1N4148_____ 75V 150mA Diodes
R1_____________150 ohm Resistor 1/2W
R2_____________100 ohm Resistor 1/2W
R3,R4__________4.7K Resistors 1/2W
R5-R8__________0.3 ohm Resistors 5W
C1_____________0.01uF 200V____ Polyester Capacitor
C2,C5__________4,700uF 50V____Electrolytic Capacitors
C3_____________0.1uF 63V_____ Polyester Capacitor
C4_____________10uF 25V tan
C6_____________47uF 35V ____ Electrolytic Capacitors
How to build.
-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.