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    This simple variable power supply circuit has a low production cost and delivers an output voltage between 1,5 V and 15 V with a maximum current of 500 mA. Its stabilization is better than 2% if the current consumption does not exceed 350 mA. The variation of the power supply voltage can be made with a potentiometer and when overloading occurs a buzzer sounds a alarm.

    T4 compairs the P1 slider voltage with the output voltage. Then the P1 slider voltage is 0,65 V higher than the adjusted voltage, T2 opens, which stops the T3-T5 Darlington base current. The 18V, 1A transformer voltage must be filtered with B1 and C1. When the output current is more than 500 mA, the Bz1 starts the alarm (overloading). Bz1 must be a 24 V type, auto-oscillating.

    2N3055 variable power supply circuit schematic

    2N3055 variable power supply

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    9 Responses to "2N3055 Variable Power Supply"

    1. I will never agree with those new electronic symbols;they looks crazy,I will keep using my own electronics symbols the way I learned when I studied electronic; I don’t care if that is the new standard of the organization that controls the electronics business but I will keep my own old symbols;these new symbols looks stupid;look at the variable resistor symbol,look at the resistor symbol they are a box that is what they looks like;there is nothing like my old symbols.Nothing like my old electronic symbols

      • As a matter of fact, there are two standards: IEEE (zigzag symbol used mainly in the USA) and IEC (European symbol like in the diagram above). Both of them are of the same age. Nothing has been changed lately regarding those symbols.

      • Funny symbols,looks at the variable resitor looks like a box with a axe. Let me keep my old beautiful symbols forever until the end of the world

    2. what component is Bz1?

    3. Jim Keith Jim Keith says: on October 2, 2012 at 12:31 am

      It appears to be a beeper or buzzer that goes off when the current is above about 0.65A.

    4. 500ma is so low!

    5. Brian Gardner says: on July 17, 2014 at 8:38 am

      Wise up guys a symbol is a symbol learn to read them any way they come just like the metric/imperial measuring tape it all means the same.

    6. Brian Gardner says: on July 17, 2014 at 8:41 am

      To be honest a little complicated I have seen more simplified circuits with the same outcome

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