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Soft starting power supply

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Author Topic: Soft starting power supply  (Read 13007 times)
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« on: June 09, 2005, 08:07:44 PM »

I want to share with you a power supply design that has advantages of both solid state and vacuum tube power supplies, but don't need vacuum tube rectifiers to buy and replace.
A first, it starts softly, raising a voltage up slowly, waiting for tubes to warm up and to start consuming a current. As the result of a current, due to a positive feedback it more quickly increases output voltage up to a regulated value, after that a positive feedback stops working, but a negative feedback starts to dominate, stabilizing output voltage on a given level, and decreasing a ripple level, without a costly and heavy chokes, without vacuum tubes to regulate output voltage.

Please be advised that no one polarity of a rectifier and filter cap must be grounded!
Also, it produces a negative bias voltage that may be used for good, otherwise leave it as is (it is a positive feedback loop for soft starting).

Vout=12V*(R5/(R6+R7)) so you may vary output voltage.
Minimum input voltage should be no less than 5V + ripple + Vout + 12V.

« Reply #1 on: November 28, 2007, 06:39:06 PM »

I am still getting lots of questions about the power supply.
A first, why such transistors?
Because I had them in a bin.
You may use something that keeps up with currents, voltages, powers...
Also, why not Op Amp to compare output voltage VS reference one?
Because better regulation is not needed for a tube gear, otherwise it would be a poorly designed gear that depends on a voltage so much.
And third, R4 may be moved to the left (between source and Zener) and calculated such a way so the PS will limit output current when accidentally shorted out. The value of the resistor should be selected something like for a voltage drop of 8V on the maximal current.

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