Why did you recommend a P-channel MOSFET to power the 555 rather than a N-channel MOSFET placed between ground and the load? I'm just curious if there was a practical difference. I'd like to build this with cheap and readily available parts.
Voltage regulator pin Enabled is equal gate of the MOSFET and is working at low voltage.
Using P channel MOSFET it is the same as N channel, just different connection.
No difference in using a p-channel fet high-side or an n-channel fet low side.Assuming this circuit is stand-alone (not connected ot anything else).Leo..
NPN is using current, MOSFET voltage to operate, it has very high resistance. Enable pin it put regulator in sleep mode when current consumption is very low, 1-5 uA
I'm also wondering what's the use case for a MOSFET vs NPN transistor for switching power. Does one work better for this case?
When pin EN is connected to 0V regulator is off = sleep, when is 5V regultor is on
The mosfet that switches the LED uses no gate current from the 555.An NPN transistor there would need ~30mA base current from the 555 for the ~300mA LED current it has to switch.The mosfet power switch draws no gate current from the RC time circuit, so that capacitor can be small.A normal transistor would influence that RC circuit too much.If you decide to use a Cmos 555, then you can try the RC circuit on the reset pin to enable/disable the 555.You would then only need a mosfet for the LED (if you can live with the ~60uA idle draw of the 555).Leo..
Average battery = 1000mAh
Correction to post#45.If you use an n-channel fet power switch low-side, then you can't power the LED/mosfet straight from the battery, as you could do with a p-channel fet that only powers the 555.Leo..
the led is all the time on ?
Correct.All the pins of the 555 are "high" (connected to batt+) when the battery switch is off.So also a "high" on the gate of the LED fet.Leo..