I've done some more tests with a longer timebase. In each case the yellow trace shows the power-on reset at Pin 13 and the blue traces show the gate I/Ps and O/Ps:
Pins 8 and 12 (the feedback):
Pin 9 (the comparator O/P; low at startup until enough current flows)):
Pins 10 and 11 (opposite feedback and driver for the LED):
As you can see the signal at Pin 11 (which should remain high to keep the LED off), goes low after about 100 ms. I can't see why the circuit isn't latching at the initial state.
Over-current Protection Circuit
Re: Over-current Protection Circuit
I've sussed it. Penri, the other day I said that the design of this circuit is tried and tested. That was true, but at the time (August last year), I was using a FET as a cheap and cheerful comparator:
As you can see the default state is active low, so the Latch gets a High until the current exceeds the limit. I hadn't noticed that change and designed the new comparator to be active High.
There are a number of ways round this, but the simplest is to change the comparator circuit. I'll look into this tomorrow.
As you can see the default state is active low, so the Latch gets a High until the current exceeds the limit. I hadn't noticed that change and designed the new comparator to be active High.
There are a number of ways round this, but the simplest is to change the comparator circuit. I'll look into this tomorrow.
Terry
Re: Over-current Protection Circuit
You are right, I was going though the circuit and asking myself why the comparator output was low, it should only go low under an over-current condition.
Re: Over-current Protection Circuit
The Over-current Protection Circuit is now tripping reliably at approx 1.5 A. This Topic should therefor be complete, so I will continue this narrative at viewtopic.php?t=314.
Terry