Variable Power Supply | Electronic Project Circuits

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power supply regulator 0-28V 6A/8 Amp By LM317 and 2N3055

This is an easy to make power supply which has stable, clean and regulator 0-28V 6A/8 Amp output voltage. By using two 2N3055 transistors we become more then 2 times the amount of amps then the power supply delivers, making it real though to brake . Although you could use this design to deliver 20 amps ((with almost no modifications and with a proper transfo and a huge heat sink with a fan), I did not needed such much power. Make sure you mount them on a huge heat sink, as the 2N3055 transistors can get very hot at full load.

Although the 7815 power regulator will kick in on shortcircuit, overload and thermal overheating, the fuses in the primary section of the transformer and the fuse F2 at the output will secure your power supply. The rectified voltage of: 30 volt x SQR2 = 30 x 1.41 = 42.30 volt measured on C1. So all capacitors should be rated at 50 volts. Caution: 42 volt is the voltage that could be on the output if one of the transistors should blow.
P1 allows you to ‘regulate’ the output voltage to anything between 0 and 28 volts. The LM317 lowest voltage is 1.2 volt. To have a zero voltage on the output I’ve put 3 diodes D7,D8 and D9 on the output of the LM317 to the base of the 2N3055 transistors. The LM317 maximum output voltage is 30 volts, but using the diodes D7,D8 & D9 the output voltage is approx 30v – (3x 0.6v) = 28.2volt.
Calibrate your build-in voltmeter using P3 and, of course, a good digital voltmeter.
P2 will allow you to set the limit of the maximum available amps at the output +Vcc. When using a 100 Ohm/1watt varistat the current is limited to approx. 3 Amps @ 47 Ohm and +- 1 Amp @ 100 Ohms.
By Guy, de ON6MU
Read More Source:http://users.belgacom.net/hamradio/schemas/6-20amps_regulatable_powersupplies_on6mu.htm

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Categories: High current power supply, Power supply, Variable Regulator Tags: High current power supply, LM317 power supply, variable power supply

L200 Current Limiting Power Supply

This is a 1-amp variable-voltage PSU. It adjusts from about 3v to 24v: and has the added feature that you can limit the maximum output current. This is invaluable when (for example) you power-up a project for the first time or soak-test a piece of equipment.

SW3 is the on/off switch. It also lets you choose between the output with the current limit and the one without. SW2 provides a selection of three different limits. You can increase or decrease this number if you wish. The limits are fixed by R4, R5 & R6. They are set at 10mA, 25mA & 65mA respectively; but you can choose whatever limits you like. If you try to draw a current above the limit you’ve selected, the output voltage will fall. Thus, the voltmeter indicates when the load on the output is excessive.

The housing should be well ventilated. The heatsink is a folded strip of aluminium about 2mm thick, 18cm long and 6cm tall. SW1 allows you to choose between the (3v to 12v) and (3v to 24v) outputs. This reduces the power the heatsink has to dissipate when the output voltage is low.

The drawing of the front panel is intended mainly as a wiring diagram – you can choose your own layout. The pin spacing of the L200C doesn’t suit the stripboard; but with a little persuasion it can be made to fit. Since the limiting resistors may have a relatively low value, a few ohms between the contacts of the wafer-switch will have a significant effect. If (with time) you find that the limits have fallen, use a spray-cleaner on the switch.