Prevent Transistor Leakage

[fatman57]

I am amateur and a thought occurred - one reason to use Relays over Transistors (apparently) is when it is in an off position there will be no leakage to the load.

At the expense of an extra component or two is there a way to prevent leakage when using transistors? Would a Zener diode on the output of the transistor prevent all leakage? I am guessing not as the leaking voltage will still be similar to the transistor output voltage (haven't measured yet) but the current will be lower - are there diodes that prevent the flow of current until a breakdown amperage?

Thanks!

 

[(*steve*)]

Everything is relative. At some level even relays have leakage.

A zener diode won't help you.

The issue is whether the leakage is significant.

 

[BobK]

Try measuring the leakage on your switching circuit.

I measured a PN2222 with 30V from C to E and the base grounded through 100K. My meter reads 0.0 uA

It you are getting leakage much higher than that, show us your circuit.

Bob

 

[AnalogKid]

I am amateur and a thought occurred - one reason to use Relays over Transistors (apparently) is when it is in an off position there will be no leakage to the load.

Depends entirely on the load.

At the expense of an extra component or two is there a way to prevent leakage when using transistors?

Yes.

Would a Zener diode on the output of the transistor prevent all leakage?

No.

are there diodes that prevent the flow of current until a breakdown amperage?

Yes. But your initial premise is incorrect in two ways. First, "off" is a relative term, not an absolute. Because if its internal design, a load might quit drawing current when its source voltage is below a certain value, even if that value is several volts. Also, if you are assuming that all solid state devices leak some small current when in an off state, then so would the diodes you are asking about, as they are just simple solid state devices. Also, even relays allow a very small leakage current, especially in AC circuits. OK, veryveryveryvery small, but you didn't say what you consider "off" to be.

ak