I bought some made-in-China NE555P timers. With the simple monostable circuit from a Philips datasheet, the circuits work, but what I see on the oscilloscope doesn't make sense. So I've misunderstood something, or perhaps these clones are behaving badly.
Here's my circuit.
Here's my confusing trace of what I see on the capacitor.
My understanding is that the discharge line should be "open"/High impedance, allowing the capacitor to charge. When the flip-flop sets (output goes low), discharge should be pulled low. So I don't understand the "camel-hump" that tops up the capacitor after my output goes low: could the discharge pin (or the threshold pin) be sourcing the current that is topping up my capacitor before it switches to "drain"?
With faster timeouts the camel-hump is less pronounced.
Thanks for any insights, or even the advice that this should definitely not be happening, and I should buy some better quality components instead.
Peter
Here's my circuit.
Here's my confusing trace of what I see on the capacitor.
My understanding is that the discharge line should be "open"/High impedance, allowing the capacitor to charge. When the flip-flop sets (output goes low), discharge should be pulled low. So I don't understand the "camel-hump" that tops up the capacitor after my output goes low: could the discharge pin (or the threshold pin) be sourcing the current that is topping up my capacitor before it switches to "drain"?
With faster timeouts the camel-hump is less pronounced.
Thanks for any insights, or even the advice that this should definitely not be happening, and I should buy some better quality components instead.
Peter