A quick question for all of you electronically gifted persons out there.
Are there such a thing as a SPDT transistor (single pole, double throw)? I need to control 10 motorized ball valves with wiring like below
I know I can use SPDT relays, but since these valves only draw very little current (12vdc ~50ma), it seams a bit overkill.
I think I already wrote that 
12vdc and 50ma or more detailed
Working current 45+-10ma
Static current 10+-5ma
The "IS" thingy is the powersupply I guess.
3 wires, black, green and red. Black is common.
Apply power to green and the valve opens (takes 3-7 seconds). Remove power from green and apply power to red to close valve
I think I already wrote that:-) 12vdc
What do you mean by polarity? As described above, the common is not switched. Its the positive, that needs to be changed from one wire to another.
As I wrote in the beginning, I know I can use relays, but there has to be another more simple solution for switching such a small load.
I can use a transistor to switch on the green when I want to open the valve, but afaik the nature of a transistor doesnt allow it to be "on", when its not energized (that would be a reverse transistor?)
Have you considered analog switches?
Have you considered analog switches?
Well no because
Working current 45+-10ma
There are switches that will do that. The MAX4580/4590/4600, 1.25 ohm on resistance good for +/- 200 mA, designed as a reed relay replacement:
"The MAX4580 has two NC (normally closed) switches, the MAX4590 has two NO (normally open) switches, and the MAX4600 has one NC (normally closed) and one NO (normally open) switch.
These switches operate from a +4.5V to +36V single supply or from ±4.5V to ±20V dual supplies. All digital inputs have +0.8V and +2.4V logic thresholds, ensuring TTL/CMOS-logic compatibility when using a +12V single supply or ±15V dual supplies. "
Robert