Hi everybody.
I'm trying to simulate a capacitor charging circuit which automatically turns off the main power when the capacitor reaches a given voltage threshold. The system is based on a combination of an op amp, which compares two voltages (reference and voltage sampled from a voltage divider), and a relay that begins the charge (initial position closed) and should be opened when the cap reaches the desired threshold. Now, the circuit seems to work along these lines except for the following facts:
1) The cap doesn't retain the voltage reached: when the power turns off the voltage begins to decline and this apparently has nothing to do with the presence of a balancing resistor...
2) As a consequence the voltage sampled by the opamp begins to decline as well.
3) When the inverting voltage becomes lower than the non-inverting one there are periodic current spikes in the relay's coil (BTW the relay's current doesn't reach 0A when the inverting voltage is higher that the non-inverting one). The relay should stay at open position (i.e. main power off) as long as the cap retains enough voltage as to reach the given threshold...
I really can't figure out what's happening with this circuit...some hints?
Thank you.
I'm trying to simulate a capacitor charging circuit which automatically turns off the main power when the capacitor reaches a given voltage threshold. The system is based on a combination of an op amp, which compares two voltages (reference and voltage sampled from a voltage divider), and a relay that begins the charge (initial position closed) and should be opened when the cap reaches the desired threshold. Now, the circuit seems to work along these lines except for the following facts:
1) The cap doesn't retain the voltage reached: when the power turns off the voltage begins to decline and this apparently has nothing to do with the presence of a balancing resistor...
2) As a consequence the voltage sampled by the opamp begins to decline as well.
3) When the inverting voltage becomes lower than the non-inverting one there are periodic current spikes in the relay's coil (BTW the relay's current doesn't reach 0A when the inverting voltage is higher that the non-inverting one). The relay should stay at open position (i.e. main power off) as long as the cap retains enough voltage as to reach the given threshold...
I really can't figure out what's happening with this circuit...some hints?
Thank you.