I am looking for an electronic component that normally conducts higher amperage (maybe up to 6 A) at lower voltage (normally up to 14.5 V), but when a signal is applied, current will stop flowing. The semiconductor will be between the source and the load (P?). I see something like this before, but I cannot find it now. I could have sworn it was an opto isolator, but as I stated, I cannot find it again. Your help is greatly appreciated.

Edit:
I cannot use a normally closed relay. The switching is too frequent to guarantee longevity of the contacts.

 

I feel sure this is not what you want, but the only switchable, normally on device I can think of is a jfet. Add that to a Triplington Trio (Trademark Registered), add a transistor to switch it all off, and it meets the requirements.

 

thank you. I have looked about and found that what I really need is a P-Channel Depletion-mode MOSFET. While theoretically possible, it appears to difficult to manufacture with any true success. So, I will have to trudge on to find something that will satisfy my needs.

 

Thanks. I simply did not think of depletion mode mosfets. Must have been a senior moment.

 

Not a problem. We cannot be everything to everyone. I'm slowly realizing that.

 

What is the supply voltage that powers your circuit? Why cant you just wire a resistor from gate of an enhancement NFET or PFET to the "opposite rail". That will bias it on so that it is normally On. Shorting the gate to the source will turn the device off.