Is it OK to have power at the emitter/collector of relay driving BJTs and motor driving MOSFETs if the bases and gates are connected to unpowered logic?
I ask because I keep my 5 V logic unpowered in standby (both Vdd and Vss at ground), except for the standby on/off controller and remote control reciever, but the unregulated 12 V going to the relays and volume motor is not turned off by a relay since I assumed current wouldn't flow through with a lack of signal at the base/gate. This way I don't have to worry about adding another relay to turn off the 12 V. Could something get fried or not work right in such a setup?
I ask because I keep my 5 V logic unpowered in standby (both Vdd and Vss at ground), except for the standby on/off controller and remote control reciever, but the unregulated 12 V going to the relays and volume motor is not turned off by a relay since I assumed current wouldn't flow through with a lack of signal at the base/gate. This way I don't have to worry about adding another relay to turn off the 12 V. Could something get fried or not work right in such a setup?
Everything should be OK. I suggest you add a pull-down resistor (10k or so) between the gate and source of the switching FET to ensure that you don't get the possibility of a floating gate.
Although HCMOS outputs will go to a maximum of a diode drop above ground when no power is applied, other families like 74LCX have outputs that go high-impedance with no power applied.
Although HCMOS outputs will go to a maximum of a diode drop above ground when no power is applied, other families like 74LCX have outputs that go high-impedance with no power applied.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.