Soviet power supply design.

Discussion in 'Homework Help' started by kristapsdreija, Jan 22, 2015.

  1. kristapsdreija

    Thread Starter New Member

    Apr 15, 2014
    18
    0
    Hi, folks!
    Could you please help me understand this soviet-time 12V power supply circuit?
    As I understand, it is a constant 12V power supply with adjustable current control via the R120 variable resistor. The DA2 is a dual-supply op-amp similar to the 741.
    What I do not understand is how the NMOS transistor VT25 works in this circuit as well as the transistor pair VT26 and VT27.
    Could you please help me understand how this design works?
    Thank you for your help![​IMG]
     
    Last edited: Jan 22, 2015
  2. bertus

    Administrator

    Apr 5, 2008
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  3. kristapsdreija

    Thread Starter New Member

    Apr 15, 2014
    18
    0
    Oh, I forgot to mention, the VD45 zener is a 9V zener with temp. compensation!
    So the resistors R119, R120 and R121 are meant to adjust the current to the load?
    So that means that the voltage at the non-inverting input of the opamp stays at 12-9 = 3V, and the voltage at the inverting input of the op-amp is varied by the variable resistor R120 and is 3.37V-3.54V depending on the value of R120.
    So, a current flows through the zener and then through the VT25 as a current source fot=r the load at the output?
    What about the transistors VT26 and VT27? What do they do?
    The op-amp is in the differential amplifier mode?
    Thanks bertus!
    edited: Thank you all, I now understand.
    TL
     
    Last edited: Jan 22, 2015
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