LDR on-off using Nmos

Adjust the pot to simulate night/day LDR .... Attach the other section on the right for converse pot action at the same time if reqd. This (adjusted yellow LED) load is fully active when the variable resistance (eg LDR or thermister etc) is high. ...one leg of the LDR to earth, and the other leg to Gate and lower part of top resistor N-Channel real Mosfet eg : IRFZ34N or any standard N Mosfet inc. LL types (eg IRLZ34NPbF) EC Settings here to match above real Mosfet: Rds₍ₒₙ₎= 0.05 Ω max Vgs₍ₜₕ₎ = 3V Transconductance full Load example here...196mA (altered LED settings), 12v but any dc Volts supply and current may be used as per Mosfet datasheet....These Mosfets can take 100W or more with no trouble if used properly....ie no needless volt drop across the mosfet whilst it is on....so keep its Source attached immediately to zero v. For this example here you don't need a heatsink. If you don't have a 100KΩ pot, you could try a different value, or adjust what you have available with a series/parallel resistor. Further modification......hysteresis would be useful to avoid excessive on/off switching at dusk....consider an op-amp or 555 at the LDR.

published 9 years ago