AvrDude2012
- Aug 1, 2012
- 6
- Joined
- Aug 1, 2012
- Messages
- 6
Hi, I'm new to mosfets and up until a few weeks ago, I didn't know know that p-channel meant high side switching and n-channel meant low side switching.
What I'm trying to do is build a voltmeter for a micro controller to measure up to 500 volts. I'm using a voltage divider to bring the voltage down to 5v for the ADC. However I need the voltage divider disconnected until I read the voltage. To do this I'm using a p-channel mosfet with an n-channel mosfet for the saturation of the p-channel for high side switching of the voltage divider. I also used another n-channel to disconnect the ground object being measured. I want a complete disconnect when not measuring voltage. I also need the speed of mosfets, relays won't cut it. Here is the circuit I'm using:
The problem is when I measure around 100 volts or more, the p-channel locks always on (assuming I fried it) and I have to replace it. It does not lock on until I read the voltage (turn on the p-channel) when it is above 100v or so. Any help would be appreciated.
Thanks,
avrdude
edit to add: The 180k resistor is actually a 10k resistor. Sorry
What I'm trying to do is build a voltmeter for a micro controller to measure up to 500 volts. I'm using a voltage divider to bring the voltage down to 5v for the ADC. However I need the voltage divider disconnected until I read the voltage. To do this I'm using a p-channel mosfet with an n-channel mosfet for the saturation of the p-channel for high side switching of the voltage divider. I also used another n-channel to disconnect the ground object being measured. I want a complete disconnect when not measuring voltage. I also need the speed of mosfets, relays won't cut it. Here is the circuit I'm using:
The problem is when I measure around 100 volts or more, the p-channel locks always on (assuming I fried it) and I have to replace it. It does not lock on until I read the voltage (turn on the p-channel) when it is above 100v or so. Any help would be appreciated.
Thanks,
avrdude
edit to add: The 180k resistor is actually a 10k resistor. Sorry
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