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Voltage regulators for (line level?) audio: The GeminiPS

Posted 22nd April 2014 at 01:40 AM by rjm
Updated 23rd April 2014 at 11:40 PM by rjm

Part of a series.

The GeminiPS is another discrete series voltage regulator, with a Zener reference and bipolar pass transistor. It's an old circuit, published in Practical Electronics in 1970-71, and written by D.S. Gibbs and I.M. Shaw. I happen to have a reprint, but there's a nice overview here.

For reference it might be worth checking back to the two transistor regulator. The GeminiPS circuit is related in the sense that it is a more sophisticated take on the same basic principle. With just a handful of components we have a stabilized, 30 W output with soft turn on and short circuit protection. The circuit can be scaled up and down relatively easily, and the complimentary (negative output) version is an easy modification.

The pass transistor (TR2/3, Q2/3) is between the circuit common and the rectifier anodes. This may seem odd, but it was relatively common back in the day when high voltage transistors were both expensive and rare. The idea is to put as much of the delicate circuitry on the low voltage side as possible. It's not foolproof, but it's better than the (now) conventional position on the high voltage side.

The output voltage is adjusted by VR1 in the circuit, or the ratio R1,R2 in the LTSpice sim. R5 controls the maximum output current before the clamping effect turns on. The soft-start rise time is controlled by R3,C2. You can see in the LTSpice simulation shown below, turn on and turn off sequences are free from peaks and oscillation and complete in about 1 second.
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Total Comments 2


  1. Old Comment
    jan.didden's Avatar
    Deleted - was nonsense
    Posted 22nd April 2014 at 11:18 AM by jan.didden jan.didden is offline
    Updated 22nd April 2014 at 11:21 AM by jan.didden
  2. Old Comment
    Preamp's Avatar
    Replace the Zener with a series string of a 8.2V Zener and a red LED for 2x better temperature drift. Using two 4.7V Zeners and a 1N4004 in series is even 7x better; that is only 0.2V output drift from 30C to 100C (simulated).
    Posted 23rd April 2014 at 11:14 AM by Preamp Preamp is offline

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