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Thermal runaway in class AB amp biasing

  1. May 2, 2015 #1
    I was watching this video


    and I have the question, if using a bjt as a diode what is the difference (thermal characteristics) from a regular diode, I ask this because on-semi makes bjt's with diodes in them specifically for class ab amps, is their any benefit besides less thermal lag?
     
  2. jcsd
  3. May 3, 2015 #2

    Baluncore

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    Sorry, I do not have video bandwidth.

    Can you give a link to the On-Semi BJTs with sensing diodes.
    Diode Vpn is used to compensate for the BJT Vbe of the output stage.

    Do you have thermal runaway in a class AB amp ?
    If so, can you post a circuit diagram of the output stages.
     
  4. May 4, 2015 #3
  5. May 4, 2015 #4

    Baluncore

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    The advantage of the diode on the output transistor die is the excellent thermal tracking. There is no problem using either a diode or a BJT for external compensation.
    The magnitude of the current flowing through the base bias chain with the thermal compensating PN junctions is similar to the current through the output transistor base emitter connections. You need to check your currents in that part of your circuit.
     
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