inverter driver

Discussion in 'General Electronics Chat' started by green90, Mar 27, 2016.

  1. green90

    Thread Starter New Member

    Sep 3, 2015
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    1-is this good driver for inverter ??
    2-why use diode and capacitor ??
    3-how determine or know correct resistor sizes ??
    qariya-a0eebcf90e.jpg
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    1- It won't work well because there're no emitter resistors to balance the current among the transistors.
    MOSFETs would balance the current automatically.
    Also MOSFETs generally have better efficiency since they don't require base current to turn ON.
    2- The diode-capacitor circuit won't do anything since there is no way to discharge the capacitor, once it's charged through the diode.
    3- The resistors are selected so that the BJT base current is about 1/10th of the collector current.
     
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  3. green90

    Thread Starter New Member

    Sep 3, 2015
    23
    0
    thank you for good explanation ... but resistor are common for all transistor because there emitters shorted together ..which model of mosfet is good for inverter ?
    the BJT base current is about 1/10th or 1/100 of the collector current? and u mean to get saturate and act like switch ?
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    Shorting the emitters together will lead to an imbalance in currents since BJTs have a negative coefficient of on-resistance versus temperature. MOSFETs have a positive coefficient so will automatically balance.

    Pick a MOSFET that has a low ON-resistance so minimize the conduction losses (try to keep the I²R losses below a watt per transistor) with a low gate capacitance to minimize drive requirements.
    If the gate drive voltage is less than 10V, it will also need to be a logic-level type that can be fully on with a lower gate voltage (look at the Vgs used to measure the ON resistance in the data sheet).

    You need the base current to be at least 1/10th of collector current for good saturation as a switch.
     
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