Hi there,
This is a latching circuit that is eventually to be used to activate a relay that is running a 12V, 30A power supply. The idea is that you switch the power on but require a push to make button press to energise the circuit, and if the power is cut it will not work again till the push to make switch is used again.
Right then, i have been struggling with this circuit now for a number of weeks. I am using a 9V battery and instead of a relay as the load, I am using an LED and a 150Ω resistor. Every time I put this onto a breadboard it works as expected. As soon as I transfer it to a bit of strip board and solder it, it no longer works and the light just comes on when the main power supply is switched on.
So now, I have had this circuit on a breadboard for about 24 hours now, and I have been testing it over time, I wanted to know if it would drain the battery if the main switch was left on. This test worked wonderfully and all was going well. So now I come to switch it on after the main switch has been off for 6 hours or so, only for the light to just come on without the trigger being used. I replaced the battery in case it was something to do with voltage supply, but no change. Then I removed the transistors one at a time and tested them with a multimeter on diode setting - ground probe to base and then probe the collector and emitter then swapped probes and tested again. Both transistors came out fine, with equally high or equally low readings. When I replaced the same transistors back to their original positions, suddenly the circuit works again.
My suspicions are that the resistor values may be incorrect, so that the transistors don't reach saturation and so don't switch properly or that there is something wrong with the capacitor.
If anyone could shed some light on this I would be very grateful.
Kind regards
Rob K
This is a latching circuit that is eventually to be used to activate a relay that is running a 12V, 30A power supply. The idea is that you switch the power on but require a push to make button press to energise the circuit, and if the power is cut it will not work again till the push to make switch is used again.
Right then, i have been struggling with this circuit now for a number of weeks. I am using a 9V battery and instead of a relay as the load, I am using an LED and a 150Ω resistor. Every time I put this onto a breadboard it works as expected. As soon as I transfer it to a bit of strip board and solder it, it no longer works and the light just comes on when the main power supply is switched on.
So now, I have had this circuit on a breadboard for about 24 hours now, and I have been testing it over time, I wanted to know if it would drain the battery if the main switch was left on. This test worked wonderfully and all was going well. So now I come to switch it on after the main switch has been off for 6 hours or so, only for the light to just come on without the trigger being used. I replaced the battery in case it was something to do with voltage supply, but no change. Then I removed the transistors one at a time and tested them with a multimeter on diode setting - ground probe to base and then probe the collector and emitter then swapped probes and tested again. Both transistors came out fine, with equally high or equally low readings. When I replaced the same transistors back to their original positions, suddenly the circuit works again.
My suspicions are that the resistor values may be incorrect, so that the transistors don't reach saturation and so don't switch properly or that there is something wrong with the capacitor.
If anyone could shed some light on this I would be very grateful.
Kind regards
Rob K