Snap action night light...

[Externet]

What considerations should be taken to build a dusk-to-dawn switch that will turn fully on abruptly at dark instead of gradually ramping on ?
I prefer to use a phototransistor and a mosfet. No LDR, no transistor. Will turn on a tiny 3V motor, no leds.

 

[Harald Kapp]

Use a comparator with a fairly large hysteresis.
The comparator will give you the on/off signal instead of a ramp.
The hysteresis will prevent the circuit at dusk and dawn from repeatedly turning on and off during the transistion from light to dark and vice versa.

 

[Alec_t]

This might suit your complementary MOSFET IC if its FETs are logic-level types with low turn-on threshold voltages :


R1 value depends on the photodiode sensitivity. R3 provides hysteresis feedback. Either could be replaced by a trimmer for set-up.

 

[Harald Kapp]

NIce simple comparator wit power output.
The current from the photodiode may be a bit low to provide the necessary drive on a 200 kΩ load resistance. R1 may need to be increased.