Ok, it's an electronic fuse, see pic.
I've seen this posted in 3 different places, by 3 different people. Assuming they are not all wrong, then I must be making the mistake somewhere.
These are the instructions for what's supposed to happen:
When connected, nothing happens until the start/reset button is pushed. Current continues to flow unless the current drops below a certain level.
The current flowing through SCR T1 sinks below the holding level when the current is rerouted through T2 (2N3055). T2 and RS are built into the electronic fuse circuit for this purpose. If the voltage drop at RS exceeds the base-emitter-diode trigger voltage of T2 (~0.7V), the transistor conducts thereby bypassing the SCR T1. The resistance value of RS must be at least 0.2 Ohms. The resistance of RS must be such that RS multiplied by the fuse current shut-off value equals 0.7 volts. (E=IR)
Once T2 bypasses T1, the current flowing through the SCR sinks below the holding level and T1 shuts off. This in turn causes the voltage drop at resistor RS to sink below the base-emitter trigger voltage of T2 and the transistor shuts off. The end result is the shutting off of the whole circuit. The DC fuse can be reactivated by pressing the start/reset button.
The value of resistor R1 is dependent on the supply voltage. Multiply the supply voltage by 1K Ohms to get the value of R1. Connect the DC electronic fuse circuit to the PLUS line of the load. The voltage drop of the circuit is less than 1 volt.
This is what actually happens:
It does turn on when the button is pushed.
It will not turn off when more current flows than is supposed to or when more voltage is supplied. I've gone up to 3x the shut off current.
It will turn off if the circuit is broken, until reset is pushed again...
I've tried simulating the circuit at www.falstad.com/ but this does not work either. When the voltage drop across RS goes above 0.7V, the fuse does not shut off.
I'm not familiar enough with transistor circuits to spot the error. I can't find a fault in my wiring. My pinouts are correct as are the input and output polarities.
Any explanations why this isn't working as it should?
Thanks
I've seen this posted in 3 different places, by 3 different people. Assuming they are not all wrong, then I must be making the mistake somewhere.
These are the instructions for what's supposed to happen:
When connected, nothing happens until the start/reset button is pushed. Current continues to flow unless the current drops below a certain level.
The current flowing through SCR T1 sinks below the holding level when the current is rerouted through T2 (2N3055). T2 and RS are built into the electronic fuse circuit for this purpose. If the voltage drop at RS exceeds the base-emitter-diode trigger voltage of T2 (~0.7V), the transistor conducts thereby bypassing the SCR T1. The resistance value of RS must be at least 0.2 Ohms. The resistance of RS must be such that RS multiplied by the fuse current shut-off value equals 0.7 volts. (E=IR)
Once T2 bypasses T1, the current flowing through the SCR sinks below the holding level and T1 shuts off. This in turn causes the voltage drop at resistor RS to sink below the base-emitter trigger voltage of T2 and the transistor shuts off. The end result is the shutting off of the whole circuit. The DC fuse can be reactivated by pressing the start/reset button.
The value of resistor R1 is dependent on the supply voltage. Multiply the supply voltage by 1K Ohms to get the value of R1. Connect the DC electronic fuse circuit to the PLUS line of the load. The voltage drop of the circuit is less than 1 volt.
This is what actually happens:
It does turn on when the button is pushed.
It will not turn off when more current flows than is supposed to or when more voltage is supplied. I've gone up to 3x the shut off current.
It will turn off if the circuit is broken, until reset is pushed again...
I've tried simulating the circuit at www.falstad.com/ but this does not work either. When the voltage drop across RS goes above 0.7V, the fuse does not shut off.
I'm not familiar enough with transistor circuits to spot the error. I can't find a fault in my wiring. My pinouts are correct as are the input and output polarities.
Any explanations why this isn't working as it should?
Thanks
Attachments
-
56.1 KB Views: 106