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DV2004ES1 power circuit operation

Filipe Carneiro
Prodigy 70 points

Hi,

We are trying to understand the operation of the power circuit switching in DV2004ES1 (components Q4, R12, Q3, D6, D9, Q2, R10 and R11 in page 5) without success.

What is the porpouse of D6 in this circuit? It seems to us that Q3 will never go to active region, as Ie current would necessarily go through D6 (considering that current going in the Q4 gate is negligible), meaning that Vb = Ve - ~0,5V. Is it right?

This understanding is necessary for us to being able to make some small changes in the circuit (replacing the BJTs for FETs, for example).

Thanks in advance for your support!

  • 0
    TI__Mastermind 31120 points

    Q4 is the switching FET.

    R12, Q3 and D6 is the quick turn off curcuit....When the MOD pin goes low and Q2 turns off, Q3 base is driven high by R12 turning on Q3 which drives current into the BASE of Q4 turning it off quickly.  D6 is reversed biased at this time.  When the MOD pin goes high and turns on Q2, D6 becomves forward biased driving off Q3 and protecting Q3be from being OV'ed, and Q4 is turned on.

    D9 is a zener to drop some of the drive voltage to Q4 to prevent punch through if the input voltage is greater than the VSGmax voltage.

     

    R10 can be used to slow the turn on of Q2 and R11 to keep Q2 off during any high impedance output of the MOD pin.

  • 0 in reply to Charles Mauney
    Prodigy 70 points

    Perfectly clear, thanks a lot!

    I just want to be sure about one point: when you say "R12 reverse biases D6 and turns of Q3" it'd be actually "R12 reverse biases D6 and turns on Q3", right?

  • 0 in reply to Filipe Carneiro
    TI__Mastermind 31120 points

    Thanks....the english was not so clear so I rewrote the response....please read above....Yes Q3 and Q4 are out of phase and are not on or off at the same time.