allanvv
Advanced Member level 4
I can easily switch a load between 0 and +15V using a mosfet. However, now I need to switch a load between -15V and 15V, at around 250kHz, from a micro out of 3.3V. Now the mosfet gate needs to have a negative voltage to be able to switch.
Currently I'm trying this circuit:
https://i.imgur.com/G8edT.png
When the PNP turns on, current flows through the 1k resistor to Vss which pulls the gate to voltages around Vss, allowing it to switch.
There is a relatively long delay from my logic output to the pnp turning on. In simulation the 2n3906 had 1.5us delay, while the 2n5401/mmbt5401lt1 had only 300ns delay, which is acceptable. I then tested the circuit out in real life, but found the switching delay to be 1.8us.
Should I just try a higher bandwidth transition PNP? I've never figured out how to pick what BJT's to use...
Currently I'm trying this circuit:
https://i.imgur.com/G8edT.png
When the PNP turns on, current flows through the 1k resistor to Vss which pulls the gate to voltages around Vss, allowing it to switch.
There is a relatively long delay from my logic output to the pnp turning on. In simulation the 2n3906 had 1.5us delay, while the 2n5401/mmbt5401lt1 had only 300ns delay, which is acceptable. I then tested the circuit out in real life, but found the switching delay to be 1.8us.
Should I just try a higher bandwidth transition PNP? I've never figured out how to pick what BJT's to use...