12/10/2023 0 Comments 2n3055 pass transistor schematic![]() ![]() In older, pre-transistorized regulation schemes for high current, light bulb ballasts and a swinging choke often were employed to give some degree of regulation. I don't get how they can consider the first two positions regulated. The 6V and 12V high current output from what I can see is wild from the bridge to a 10Kuf cap with only the fuse and current shunt in line. From the schematic, only the 2A position appears to be regulated in the 15V & 30V ranges with the current limiting ranges. The variable 2A high filtered, regulated position on the third position. ![]() It shows as Walt indicates that there is a 12/10A and 6V/20A position, but says "regulated supply and charger". Here's what that section of the circuit looks like.I took a look at some Fleabay pictures of these supplies. Just make sure you include a small 0.1-ohm resistor in series with the emitter leads and a separate base resistor (100 ohms) for each 2N3055 when paralleling them the collectors can be tied directly together. To increase the output current, you have to parallel the top pass transistor. For example, a 1-amp load limit calculates out to be 0.65 ohms. If you want to lower the output current limit, increase the value of Rsc. (If the input voltage is 28 volts, the output voltage is 13.8 volts, and the load current is 8 amps, then the 2N3055 has to dissipate 113.6 watts of heat - which is pushing the power envelope.) The formula is By limited, I mean I've selected the value of the Rsc resistor, that's across the current limit (pin 2) and current sense (pin 3) pins, so that the power supply output voltage drops to zero when the 8-amp limit is exceeded. The 2N3055 is rated at 115 watts, 15 amps, so I've limited this design to 8 amps. The power supply is powered by a line transformer with a rectified output of about 28 volts DC (anything between 25VDC and 30VDC will work but the higher the input voltage, the hotter the 2N3055 transistors will run). The following circuit is an 8-amp, 13.8-volt power supply using the parts you have on hand. By itself, the LM723 can only provide 150 mA of output current, but external transistors can be added to provide load currents as high as 10 amps and more. This is an easy order, thanks to the venerable LM723 regulator chip. ![]() Short circuit protection would be nice, but not necessary. If you will, I need a circuit that I can use to put these supplies back in use - just a simple regulator circuit to hold at 13.8 volts would do nicely. So now I have two good power transformers and rectifiers that put out about 25 to 30 volts unregulated plus four 2N3055 power transistors on each chassis. The Pyramid was stripped by the previous owner and the Astron burned up the control board. One is a Pyramid 30 amp and the other is an Astron 20 amp. I have two regulated power supplies which are not working. With TJ Byers POPS (Plain Old Power Supply) Question:
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