help with semiconductor

[rye]

hey folks. hopefully you can help me out. i want a semiconductor that will only switch on at a given voltage. i want to charge a cap and only have it discharge to the load when it has charged to a particular voltage. i've looked into transistors but they seem to start conducting at a much lower voltage than their rated voltage. what product will only switch on at a specific voltage, be it 12v/24v or a 100v? im not a sparky so laymans terminoligy would be great. maybe i need a particular circuit to acheive this? thanks.

 

[BobK]

diac, silicon controlled rectivier (SCR), programmable unijunction transistor (PUT) can all perform this function.

However, you are probably better off with a circuit involving a comparator and a MOSFET. This would be more accurate and flexible.

Bob

 

[rye]

Thanks. I will google those things!