How to light an LED with 10.5 V

216

03:39:36

Question: How to light an LED when voltage rises above 10.5 V.

Answer: This can be done using an op-amp comparator. The reference threshold voltage is set by a voltage divider with a 10.5 V Zener diode. The (built-in in EC) op-amp power supply is 15 V, which requires a 650 Ω resistor to deliver 20 mA to the LED.

published 9 years ago

faceblast

9 years ago

note: if you use an actual comparator, the led needs to sink current through the output, as comparators have open-collector outputs and cannot source current. also, the low power series (LM#39 and LM#93) have an absolute max limit of 20mA so be very careful with your led selection, or drive it with a transistor.

cjdelphi

9 years ago

Also... if you change the 1k resistor for a 10k for the zener diode shunt, it works fine here, but does it in real life?

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