evandude
New Member
anyone know how a 7805/78L05 voltage regulator behaves when there is no voltage applied to its input, but there is a voltage on its output?
I am using an L05 in an RS232 level shifter. it connects to the target circuit via a 4-wire cable (TX,RX, Power, and GND)
the idea is that the level shifter can be powered off the target circuit if the power pin is connected to +5v in the target, and then the +12v supply to a 2-pin header on the level shifter is left unconnected. This means the output of the regulator is connected to the +5v supply but the input is floating. If, however, the target circuit does not have the power line connected for whatever reason (battery power consumption issues, minimizing external connections, etc) then I would simply plug 12v onto the header on the level shifter, which powers it via the voltage regulator.
I am just wondering if I need to put in a jumper or switch to disconnect the regulator output from the 5v line when the regulator input is not connected.
I am using an L05 in an RS232 level shifter. it connects to the target circuit via a 4-wire cable (TX,RX, Power, and GND)
the idea is that the level shifter can be powered off the target circuit if the power pin is connected to +5v in the target, and then the +12v supply to a 2-pin header on the level shifter is left unconnected. This means the output of the regulator is connected to the +5v supply but the input is floating. If, however, the target circuit does not have the power line connected for whatever reason (battery power consumption issues, minimizing external connections, etc) then I would simply plug 12v onto the header on the level shifter, which powers it via the voltage regulator.
I am just wondering if I need to put in a jumper or switch to disconnect the regulator output from the 5v line when the regulator input is not connected.