NC transistor?

I want to control a 3.2V 20mA normally closed circuit with a normally open
circuit.When the NO circuit becomes closed I want to open the NC circuit. I
want to do this by using the 3.2V power from the NC circuit. Is there such a
thing as a NC transistor?

 

Look up 'depletion mode MOSFET'

 

There are various ways to do this kind of thing. A JFET works this way,
where it passes current when the gate is near the source in voltage. When
the gate diverges from the source voltage (for an N channel, when it gets
more negative, or for a P channel, when it gets more positive) the
transistor will pinch off the current through it.

If you hook up the base of an PNP transistor to the gnd side of the NO
switch (through a 1k resistor), it'll pass current until the NO switch is
closed. If the potential of the base then goes positive, it'll turn off the
transistor.

View with monospaced font:


VCC
+----------+
| |
| |
| o |
|=|> NO |
| o |
| |
| ___ |<
+-|___|--| PNP
| 10k |\
| |
| |
.-. .-.
| | | |
| |Load1 | | Load2
'-' '-'
| |
| |
+----+-----+
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

When the pushbutton is open, Load2 will be powered. When the pushbutton is
closed, Load1 will be powered, but Load2 will not be.

Regards,
Bob Monsen

 

Thank you. I used the PNP transistor and it works fine.