Hello,

I'm trying to build a discrete driver to switch a power transistor (Qg=12nC, Vg=0->6V). I want to push the limits to see what is possible with discrete components (so no driver IC) so I'd like it to have a rise/fall time close to 20ns. This comes down to Ig=12nC/20ns = 0.6A of drive current, assuming constant gate current during the switching. I thought of using a typical BJT push-pull circuit but I'm struggling to find the parts. Am I using wrong specifications? Is using BJTs a bad idea and would MOSFETs (maybe multiple stages) be the better choice here?

The specifications I looked for:
Considering I need at least 0.6A of gate current, but I'd prefer more: Ic>=1A
Vg=0->6V: Vce,br>10V
tr/tf gate <20ns: tprop+tr+tf+tstor BJT < 20ns
The main problem is the BJT time specifications. Some BJTs don't have these spec'ed, and the best BJTs I find have rise/fall times of 30 ns. Not even mentioning storage times (but I know these can be lowered by using baker clamps and speedup caps)... However I know BJT push-pull is often used in commercial drivers. Are these specs just not possible for discrete components or am I looking in the wrong places?

Thanks in advance!

 

See

 

This is a problem I am beating nearest monthes. I have to play with 30 000 pF at 60 MHz where frontier ought be better than 2 nanosec. So, I defined a goal the 2 ns and 300 Amp p-p.
As it comes out the optocoupler in my case (ISO721M) then I am loading the only driver with nanosec capability what has price written with one digit - ISL55110. But I applied three of that brute force parallel to boost the output up to 3000-5000 pF. Separate such 3 feeds high-side booster cascade and 3 the lower side booster cascade. As I am steering the half-bridge, identical system stays as in high side as in low side of output chain.
For making the D regulable I cannot use any 555 or better cheep-end solutions, as they are not stable over 0,5 MHz (may work up to 1,1 MHz but unstable, and I need much more). So I choose the current mirror on 3 bjts of C733 what fills the 330 pF capacitor and when comparator AD96687 sees the voltage on it is higher than 2,50V it shortens capacitor by BF199 and when it is beyond the 1,00V it close the shortener. So I have a beautiful saw-teeth ultralineary oscillator, with accuracy of ca 2.5 nsec.
Then another comparator ADCMP533B measures the voltage on this cap and to other reference voltage source, where I can set the freq, D, tau(dead) and other significant parameters. The result is divided by two for absolute uniformity aim, by SN74LVC2G74 (1 nanosec) and dechifrated by 74AS02D (1 nsec), and laid to optos ISO721M (1 nsec).
Circuit is bit complicated but not so tragic, SMD solves it on 50x60mm PCB, but there is one hard problem I have`nt solved yet - What damn transistors to use for main gate driver booster cascade. Initially I thought about IPD25N06S4L30 but seems they has 8 weeks lead-in time.... damn!. Why else I can find for 25A average (at least), for 1220 pF or less and for 1...maximum 2 nanosec??
I one know a good candidate what cost no more than two-digit price, please tell me.