Electronic switch when the load is disconnected

Overcurrent relay cut out circuit. To dodge asking for more detail and to cover all bases in functionality, my suggestions is: MPU + current sensing R + relay D from BC

You're basically talking about an electronic circuit breaker. Load gets too heavy, it trips off. I suppose you could do it with a sense resistor and an op amp or comparator, or even just stringing the b/e junction of a transistor across the sense resistor might be good enough for you. You didn't say much about your application.

After it turns off, are you going to turn it back on manually, or do you want the circuit to turn back on by itself? What kind of load are you running?

Nice one. Use a relay and some parts. A more specific reply could be given, if a more specific question was asked.

Ed

Hello,

thanks a lot for your ideas. Further to your emails, I came up with a similar idea using a sensing resistor and a comparator (Trigger Smith) with a reference voltage. The load resistor will be in series with the sensing resistor. So, as you illustrated to me, when the current is interrupted when the load current is too high. It seems a typical circuit breaker (thanks for the tip!).

Unfortunately, for my application, (a test device used for characterising transducers) I must also employ another very low power supply (i.e. battery) for controlling the circuit breaker completely independent from the power supply for the load resistor.

The circuit can be interrupted because high current even for days, hence I must devise a circuit extremely low energy for controlling the circuit breaker. If I put the sensing resistor in series with the load, it will absorb too much current. How can I use the sensing resistor in this case? Any idea? Thanks in advance. Nick

Current sense resistors can be so low in resistance that a piece of "special" wire can be used. Very low loss. Unfortunately, the tiny V across the resistor has to be amplified and an amplifier and control logic will need power from somewhere..

Depending on requirements, an active circuit breaker can be powered up from:

1) Battery 2) Off the load being broken 3) Off the supply driving the load 4) dedicated power supply 5) a transformer winding D from BC

I'm just a hobbyist, so take all this with a grain of salt. You can minimize the power used by the circuit. Take a very low value sense resistor (~hundredths of an ohm) and scale the voltage up using a low power cmos op amp. For a voltage reference you can use the LM385, I hear they run on microamps. If you get a dual op amp, and you can use the other as comparator (with a little hysteresis). You mentioned a relay in your original post. For minimizing power consumption, you might consider using a mosfet, or a latching or alternating relay.