How can I make an LED light only if the AC voltage is a certain level, and completely ignore the DC voltage?? I have cap in series with it, but that doesn't seem to do the trick.
- posted
16 years ago
LED light based on AC not DC
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- posted
16 years ago
Dr. Mitch-
An LED is a diode, which will rectify the AC, causing the series capacitor to quickly charge up to a peak value. After that, no further current will flow.
Try connecting a diode (or a second LED) back-to-back with the LED, with a suitable resistor to limit current. Since the second diode will conduct when the LED is reverse-biased, the capacitor will only charge to the steady DC voltage.
This just lights the LED. It doesn't determine whether the AC voltage has reached some particular level. Assuming the AC voltage is high enough to overcome the diodes' forward voltage drops, only the LED brightness would change as AC voltage changed. Perhaps an LED level detector would work in place of a simple LED.
Fred