View attachment PWR-CIR-FET.pdf
The enclosed schematic is that of a 3.7v (LiPo) battery charging circuit that will derive it's power from a 5VDC wall wart (for recharging purposes only). To the far right of the circuit you'll see P-Channel Mosfet (Q1) which I would like to use to switch from battery power to 5VDC when it's available, then back to battery when the wall wart is removed.
I have never used any sort of Mosfet before and while I vaguely understand how it works in the circuit, a lot of the terminology eludes me when choosing one for the job. I believe that since my operating voltage is 3.7-5VDC (and future load will operate at 5V), I will need a logic level Mosfet. I'm also looking for SMT that can be hand soldered so the two I've found are:
http://www.digikey.com/product-detail/en/NX2301P,215/568-10314-1-ND/4162477 and
http://www.digikey.com/product-detail/en/DMP2123L-7/DMP2123LDICT-ND/1964766
Now my very basic understanding of how it works is that the Vgs (1.1v and 1.25v as linked) is the voltage differential that the FET will look for at the gate. Since the battery will power down to around 3.7V but operate up to 4.2v, there are times were the differential will be less than 0.8V, do I need a FET with a Vgs of <0.8V?
The enclosed schematic is that of a 3.7v (LiPo) battery charging circuit that will derive it's power from a 5VDC wall wart (for recharging purposes only). To the far right of the circuit you'll see P-Channel Mosfet (Q1) which I would like to use to switch from battery power to 5VDC when it's available, then back to battery when the wall wart is removed.
I have never used any sort of Mosfet before and while I vaguely understand how it works in the circuit, a lot of the terminology eludes me when choosing one for the job. I believe that since my operating voltage is 3.7-5VDC (and future load will operate at 5V), I will need a logic level Mosfet. I'm also looking for SMT that can be hand soldered so the two I've found are:
http://www.digikey.com/product-detail/en/NX2301P,215/568-10314-1-ND/4162477 and
http://www.digikey.com/product-detail/en/DMP2123L-7/DMP2123LDICT-ND/1964766
Now my very basic understanding of how it works is that the Vgs (1.1v and 1.25v as linked) is the voltage differential that the FET will look for at the gate. Since the battery will power down to around 3.7V but operate up to 4.2v, there are times were the differential will be less than 0.8V, do I need a FET with a Vgs of <0.8V?