High Current Regulated Supply By LM317

The high current regulator below uses an additional winding or a separate transformer to supply power for the LM317 regulator so that the pass transistors can operate closer to saturation and improve efficiency. For good efficiency the voltage at the collectors of the two parallel 2N3055 pass transistors should be close to the output voltage. The LM317 requires a couple extra volts on the input side, plus the emitter/base drop of the 3055s, plus whatever is lost across the (0.1 ohm) equalizing resistors (1volt at 10 amps), so a separate transformer and rectifier/filter circuit is used that is a few volts higher than the output voltage.

The LM317 will provide over 1 amp of current to drive the bases of the pass transistors and assuming a gain of 10 the combination should deliver 15 amps or more. The LM317 always operates with a voltage difference of 1.2 between the output terminal and adjustment terminal and requires a minimum load of 10mA, so a 75 ohm resistor was chosen which will draw (1.2/75 = 16mA). This same current flows through the emitter resistor of the 2N3904 which produces about a 1 volt drop across the 62 ohm resistor and 1.7 volts at the base. The output voltage is set with the voltage divider (1K/560) so that 1.7 volts is applied to the 3904 base when the output is 5 volts. For 13 volt operation, the 1K resistor could be adjusted to around 3.6K. The regulator has no output short circuit protection so the output probably should be fused.

High Current Power Supply

Since my page was first posted, I have received a number of emails asking about a high current power supply. I looked around, but couldn't find one that was suitable. So, I designed this. It is a linear supply, which might have a few of you rolling your eyes, but it takes very few parts, is simple to build and can supply huge currents.

Schematic
This is the schematic of the High Current Power Supply

Parts
R1 680 Ohm 1/4 Watt Resistor
C1 20,000 - 50,000uF 20-40 Volt Capacitor
C2, C3 100uF 50 Volt Capacitor
C4 0.1uF 50 Volt Capacitor
C5 0.01uF 50 Volt Capacitor
D1 Zener Diode (See Notes)

Q1 2N3055 Or Other (See Notes)
T1 Transformer (See Notes)
BR1 Bridge Rectifier (See Notes)
S1 SPST 250 VAC 10 A Switch
MISC Case, Line Cord, Heatsink For Q1, Binding Posts For Output


Notes

1. D1 should be rated at about one volt higher than then desired output of the supply. A half watt diode will do.

2. Q1 can be a transistor similar to the 2N3055. I chose the 2N3055 for it's availability and power handling (150 watts).

3. T1 should be about 5 volts higher than the desired output of the supply, and rated for about one amp more of current. The voltage overhead is required by the regulator section. The extra current is to keep the transformer from over heating.

4. The choice of BR1 will depend on the voltage and current of your transformer. The rectifier should be rated for 50 volts more than the transformer, and 5 amps more than the transformer.

5. The value of R1 will be smaller when supplying high currents. Expiriment until you get what you need.

6. Heatsink and fans are absolutely necessary!