Continuing my work on a half bridge driver . I faced problem of slow Turn on/off of the mosfet due to the "relatively" low output current of the IR21844 mosfet driver (1.4A source and 1.8A sink).

Using the equation I=Q/ton . I found that for the total gate charge of 2500nC (5 mosfets in parallel) switched at 20khz , with the desired Ton 0.5us . I would need 5A.

Searching for a solution lead me to IR application note 978 containing this circuit complementary mosfet current booster

I was thinking if it can be simplified ( 4 transistors per output is too much space for me ) maybe something like 1 STS01DTP06 Or TC4420 on each output (HO and LO) although this is not the purpose of this IC. I am also open for other methods or suggestions that doesnot involve changing the main gate driver.

thanks in advance !


1 Answer 1


In your Previous Question, you show a schematic with your existing gate drive circut with a 30 ohm resistor in series with the gate driver output.

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Using 15 volt gate drive and 30 ohms, your gate drive turn off current is limited to 15v/30 = 0.5 amps (initially).

You can speed up the turn off by adding a diode D2. Whether this will give you the turn off you desire, could be tested before you consider other circuitry. The additional diode does not effect the turn on (reverse biased during turn on). The diode bypasses the 30 ohm gate resistor during turnoff. This is a common practice for achieving higher turn off current.

Reducing your 30 ohm to 10 ohms would also improve turn on current.


The TC4420 driver chip you ask about could be used to increase drive output (and sink). You will likely need more bypass (storage) capacitor to accommodate the increased peak current. You should still use the diode to improve turn off current.


  • \$\begingroup\$ thank you for your input , i indeed decreased the resistance to 10 ohm (during testing but after posting the schematic) to acheive the maximum turn on speed , the turn off will be limited to 1.8A of the chip even if the reverse baised schottkey is added. Thats why i am considering the use of discrete current buffer , i will see if the TC4420 driver is available in local shop and will test to see , mainly because you confirm it can be used for this purpose , by the way in the datasheet show it contains zener on the logic input pwm, but i think i will add external zener just in case \$\endgroup\$
    – ElectronS
    Commented Feb 20, 2016 at 16:25
  • \$\begingroup\$ You originally mentioned the TC4420. And the TC4422 is also a good candidate to increase current driving capability. The TC4422 spec is 9A. Be certain to add energy storage capacitor (bypass capacitor) that is NOT electrolytic. The ceramic capacitor provides the instantaneous current, and electrolytic is much slower in providing instantaneous current. \$\endgroup\$
    – Marla
    Commented Feb 20, 2016 at 16:34

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