I'm working on a small device to control a video projector (turn it on and off, etc.) via the RS232 serial port.
It uses <1mA at +5V. I want to try to power it off the receive data (Rx) line, which supplies -12V DC [the projector doesn't send any data, so the line is always in a marking state].
The problem is that I need to drive the transmit data (Tx) line to a positive voltage. I can't just use a linear voltage regulator, because that would make the Tx ground reference -5V with respect to the RS232 ground pin.
I've thought about using an inverting buck or buck-boost converter, but I can't find any commercially-available regulator IC's that have a negative input voltage and positive output. Any ideas for getting +5V from a -12V supply?
It uses <1mA at +5V. I want to try to power it off the receive data (Rx) line, which supplies -12V DC [the projector doesn't send any data, so the line is always in a marking state].
The problem is that I need to drive the transmit data (Tx) line to a positive voltage. I can't just use a linear voltage regulator, because that would make the Tx ground reference -5V with respect to the RS232 ground pin.
I've thought about using an inverting buck or buck-boost converter, but I can't find any commercially-available regulator IC's that have a negative input voltage and positive output. Any ideas for getting +5V from a -12V supply?