Having studied the forums on BJT as a switch, I thought the following would be straightforward: I need a simple (very simple) circuit to flash an LED when the battery pack is no longer being charged. The pack is 48v, 47.5v nominal when off the charger and under normal load, and 54v+/- when charging. So the attached circuit using a 48v zener should have worked. But the LED refuses to behave, flashing above 48v, and on steady with a flicker below. The voltage at the zener-R2 junction varies between 0v and 6.4v, when the circuit is powered from 40v to 56v. The transistor is a BC556 with a tested hFE of 420-450. I've replaced the transistor and the LED to no avail.
Am I missing something fundamental here?
Would a low power MOSFET (I have J182 P-channel devices on hand) be a better choice?
Am I missing something fundamental here?
Would a low power MOSFET (I have J182 P-channel devices on hand) be a better choice?
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