I am attempting to roughly measure the resistance of a relay coil with a MCU's AtoD input. The circuit is 5V to a pot (or voltage divider) to the relay coil and then to ground with the output of the pot going to the ADC. My problem is when I'm finished reading the relay coil, rectified 120VAC (positive peaks to 170V) or 330VDC may be switched in it's place. The simple solution is to put a relay (not the one being read) between the pot and the relay coil and just disconnecting the high voltage when not doing AtoD's. That works fine but with the complexity of my circuit, I'm already using over 30 of these isolation relays.
I'm considering using a 74HC4066 analog switch in place of the isolation relay but when the switch is turned off, you'd think that the max voltage on either side of the switch would be the devices VCC. But from the last sentence in the following data sheet note, I can't tell whether high voltages are allowed or not.
Notes (nY and nZ are input/output pins)
1. To avoid drawing VCC current out of pin nZ, when switch current flows in pin nY, the voltage drop across the
bidirectional switch must not exceed 0.4 V. If the switch current flows into pin nZ, no VCC current will flow out of
pin nY. In this case there is no limit for the voltage drop across the switch, but the voltages at pins nY and nZ may
not exceed VCC or GND.
Hopefully someone here can tell me if I can have up to 330VDC on one of the two switch pins when the switch is off or direct me to a discrete analog switch circuit that would withstand HV when off.
I'm considering using a 74HC4066 analog switch in place of the isolation relay but when the switch is turned off, you'd think that the max voltage on either side of the switch would be the devices VCC. But from the last sentence in the following data sheet note, I can't tell whether high voltages are allowed or not.
Notes (nY and nZ are input/output pins)
1. To avoid drawing VCC current out of pin nZ, when switch current flows in pin nY, the voltage drop across the
bidirectional switch must not exceed 0.4 V. If the switch current flows into pin nZ, no VCC current will flow out of
pin nY. In this case there is no limit for the voltage drop across the switch, but the voltages at pins nY and nZ may
not exceed VCC or GND.
Hopefully someone here can tell me if I can have up to 330VDC on one of the two switch pins when the switch is off or direct me to a discrete analog switch circuit that would withstand HV when off.