high voltage generator

Discussion in 'General Electronics Chat' started by ljw, Jun 18, 2015.

  1. ljw

    Thread Starter New Member

    Jun 18, 2015
    8
    0
    hello,
    any expert can help me explain the working principle of below circuit? the circuit will generate a high DC voltage according to input of opamp, but i am don't understand the theory behind the circuit...

    Thanks and regards
    ljw
     
  2. #12

    Expert

    Nov 30, 2010
    16,256
    6,754
    That circuit does not generate voltage, it regulates voltage. It is clearly written that YOU provide +/- 430 volts DC and the circuit only controls how much voltage appears at the output terminal.
     
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  3. ljw

    Thread Starter New Member

    Jun 18, 2015
    8
    0
    yes, you are right, but how does it control how much voltage on the output? what is the purpose of the Q1?
     
  4. #12

    Expert

    Nov 30, 2010
    16,256
    6,754
    Q1 is in common base configuration. That means you can have quite a lot of voltage on the collector, but collector current only flows in proportion to the emitter current. Instinct says, "That's incredible! That would depend on the gain of the transistor, which is not very predictable in a batch of 1000 transistors, and it changes with temperature!"

    The massive amount of delicacy required in controlling Q1 is in the op-amp. ;)
     
  5. mxg2579

    New Member

    Jun 10, 2015
    15
    7
    In this circuit, what is the purpose of D14? It appears like it would be reverse biased, so what does it do? Sorry, you'll have to excuse my seemingly "basic" questions, I'm very new to electronic circuits. I know about diodes and mainly MOSfets, and a little BJT's but putting them all together still is hard for me to grasp.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    Q1 is acting as a non-inverting voltage level shifter. Its gain is set by circuit elements, but varies with temperature as Vbe changes. As noted, it is inside the overall feedback loop so its gain variations are compensated for by the opamp.
    D14 does look reverse biased. That might be a drafting error. Where did this circuit come from?

    ak
     
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