Hi,
I'm trying to operate MOSFET devices with current mirrors. I want a maximum Vgs, to make sure they have minimum Rds_on. The supply rails on the other hand vary a lot, so I decided to use current sources to develop the required Vgs across a resistor. See
Q7 and Q5 make up the current source, using R12 to switch M2. Logic to switch the current source off has been removed. M2 is switched perfectly using this construct. Q6 uses the current source reference output to generate another current of about 1mA. The other BJT's are current mirrors to copy the same current to R48, to switch M6. The problem is that the current through R37 is way larger than the current through R27. Q12,9 and 8 also do not seem to be able to settle at the correct value. I'm wondering why it doesn't work correctly. Can someone help?
Kind regards,
Remco Poelstra