HP E3610A "DRIVER" Questions

[ZeTeX]

Hey!

I'm looking at the old HP3610 PSU, and I have a few quastions about this part:

This is the driver for the pass mosfets, But my questions are:
1. Why do they need L1 ferrite bead? I guess it is to filter some EMI from the traces but I'm not exacly sure if this is really gonna help something..
2. What does R3+R5 combination does? Without it the driver wouldnt work, But what is the propose of those 2 resistors?
3. R44+C23 or R45+ C22 combination, I guess it is for stability but what exacly those it do? Why do you need it?

Thanks for your time.

[Cerebus]

L1 is probably there to stop Q2 turning into an oscillator - those general purpose small signal transistors have more bandwidth than is helpful sometimes (The 2N2222A, which I think that is, has an Ft of 300MHz).

The resistors are probably providing a bit of isolation from the MOSFET's input capacitance - so as you suspect, a stability thing.

The capacitors are probably providing a bit of AC feed-forward to speed up charging the MOSFET gate capacitance on rapid changes.

I'd have to spend a fair bit longer looking at the full schematic to remove all the "probably"s from the above.

[eevblogfan]

Hello
I remember i have re-drawn this schematic to be specific to the E3610A circuit ,i have paid close attention to the service manual and the E3610A i have had in my hand, there are few components that are not populated in that specific model. try and figure it out and simulate it on LT-spice .

Next week i'll search my notebook and upload picture for you .