Hi all
I would very much welcome some suggestions on how to go about designing a "fallback" power circuit.
I have a load (microprocessor & some logic) which requires +5v at around 160mA. There are two power supply DC voltages available to the circuit, these are +12v and +5v. A common ground is shared by both.
At the moment, the +5v for the load is derived from a linear fixed voltage regulator powered from the +12v line. However, I would like the option of automatically powering the load from either the +5v or +12v supply, in the event that either the +12v or +5v supply voltages fail. Ideally, the +5v to the load would also not be interrupted in the event that one of the supply voltages fails.
I've tried connecting a power diode between the +5v supply and the load so that the load takes power direct from the +5v if the +12v switches off, however the 0.6 volt drop across the diode takes the +5v below an acceptable level. Also, I wondered if the regulator might get damaged by doing this?
So I wondered if there is a better way of adding this automatic fallback without suffering the volt drop using a diode and without risking damage to the voltage regulator. I thought perhaps this could be done using MOSFETs?
Thanks for any suggestions. I'm new to electronics so please be gentle!
I would very much welcome some suggestions on how to go about designing a "fallback" power circuit.
I have a load (microprocessor & some logic) which requires +5v at around 160mA. There are two power supply DC voltages available to the circuit, these are +12v and +5v. A common ground is shared by both.
At the moment, the +5v for the load is derived from a linear fixed voltage regulator powered from the +12v line. However, I would like the option of automatically powering the load from either the +5v or +12v supply, in the event that either the +12v or +5v supply voltages fail. Ideally, the +5v to the load would also not be interrupted in the event that one of the supply voltages fails.
I've tried connecting a power diode between the +5v supply and the load so that the load takes power direct from the +5v if the +12v switches off, however the 0.6 volt drop across the diode takes the +5v below an acceptable level. Also, I wondered if the regulator might get damaged by doing this?
So I wondered if there is a better way of adding this automatic fallback without suffering the volt drop using a diode and without risking damage to the voltage regulator. I thought perhaps this could be done using MOSFETs?
Thanks for any suggestions. I'm new to electronics so please be gentle!