Hi,
For a home project of mine, I am in need of a simple timed switch. My load is a LED light bank which draws ~1A. My source 7.5V from a solar panel charged battery. THis unit has the option to turn on the light from dusk til dawn, but what i want it for is to turn on for only maybe 5~6hrs, so it shuts off around the time i go to bed, i dont want it on all night. Now this unit is to be placed out of easy reach, so i can't just turn it on/off as i please, So scowering the internet, i've across this 24 hr timer circuit which uses a relay and the 4060 binary counter. ( http://uk.geocities.com/ronj_1217/c4060s.html ) , so something like circuit 2 would definately work. What i'm sort of wondering is why must i use the relay? Can't i just turn on/off the FET directly from the output of the 4060? shouldn't this reduce current usage, # of components, and boardspace of this circuit? I'm thinkin of using the IRF9520 p-channel FET, which can handle up to 6A drain current, has a Vgs(th) of 4V, and Rds(on) of 0.6Ohm. Shouldnt the only difference i should encounter be the voltage drop of (1A*0.6Ohm)=0.6V across this switch? I placed a 1kOhm resistor between the FET and the IC because i think i remember hearing that should be done due to gate capacitance of power FETs being so large, and the switching on/off of the FET can create a large transient gate current, enough to damage the IC?
So just wondering if this would work or are there other issues that would prevent this from working that i am not seeing, or should i stick with the relay circuit?
Thanks,
For a home project of mine, I am in need of a simple timed switch. My load is a LED light bank which draws ~1A. My source 7.5V from a solar panel charged battery. THis unit has the option to turn on the light from dusk til dawn, but what i want it for is to turn on for only maybe 5~6hrs, so it shuts off around the time i go to bed, i dont want it on all night. Now this unit is to be placed out of easy reach, so i can't just turn it on/off as i please, So scowering the internet, i've across this 24 hr timer circuit which uses a relay and the 4060 binary counter. ( http://uk.geocities.com/ronj_1217/c4060s.html ) , so something like circuit 2 would definately work. What i'm sort of wondering is why must i use the relay? Can't i just turn on/off the FET directly from the output of the 4060? shouldn't this reduce current usage, # of components, and boardspace of this circuit? I'm thinkin of using the IRF9520 p-channel FET, which can handle up to 6A drain current, has a Vgs(th) of 4V, and Rds(on) of 0.6Ohm. Shouldnt the only difference i should encounter be the voltage drop of (1A*0.6Ohm)=0.6V across this switch? I placed a 1kOhm resistor between the FET and the IC because i think i remember hearing that should be done due to gate capacitance of power FETs being so large, and the switching on/off of the FET can create a large transient gate current, enough to damage the IC?
So just wondering if this would work or are there other issues that would prevent this from working that i am not seeing, or should i stick with the relay circuit?
Thanks,
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