Using a Charging Switch pfet for Solar Garden Light

[nickelflippr]

Everyone is probably wore out about this subject, but here goes. Does using a pfet like a Si5855CDC make sense as a high side switch for a solar garden light? May have overlooked something here, so just asking before stocking up.

It includes a handy integrated schottky diode. It has a very low Vgs saturation voltage (1V max), which makes using the solar cell as the light sensor seem feasible. The Rdson of this pfet is < 0.2Ω, much lower than a small signal fet which can be from 1-10Ω. And, the cost is about $0.20.

Looking at other solutions, in low quantities, seems to put them in a $0.50-0.60 range.
1)Ldr, pfet, schottky diode
2)Photodiode, comparator, pfet, schottky diode
3)Pic10f204, schottky diode

 

[audioguru]

The Vgs must be at least 1.8V for it to have a max resistance of 0.222 ohms.
A graph shows a "typical" Mosfet conducting about 250mA but you cannot buy a "typical" one.
With a Vgs of only 1V (its max threshold voltage) then some of these Mosfets conduct only 0.25mA.