Re: 5vdc to 4vdc?
iDk wrote:
>hi. i have just tried to read some notes on the manual of the mobile
>phone. the maximum battery voltage is 5.4vdc. my decision on dropping
>the 5vdc usb supply voltage to 4vdc is in order for me in safe limit
>because the normal battery rating of mobile phone like nokia is 3.6vdc.
>and also i saw on the schematic of a dongle which is being powered thru
>USB the positive side they put in series a 1A diode (1N4001 i think?)
>then this will serve as a power supply of the mobile phone. is that safe
>enough for a mobile phone just by putting a 1A diode in series?
I think you have missed something.
You must differ between nominal voltage (or max discharge voltage) and charge voltage.
If you want to charge a Lithium Ion, the max charge voltage is 4.2Vdc and
max nominal is 3.7Vdc (older type 3.6Vdc)
If you want to charge a Ni-MH battery, the max charge voltage is about 1.5Vdc
for a cell (with 3 cells, 4.5Vdc) and max nominal is 1.2Vdc (3.6Vdc/3 cells)
And above that you need some headroom (dropout voltage) for the charger if its a linear type.
So for a Lithium Ion charger you probably need min 4.5Vdc supply and slightly more for a Ni-MH.
If its a switching charger, the supply voltage depends of the type.
I presume also that you are going to supply the charger in the mobile and not try to feed the battery directly.
Because then you must built a charger and that’s is something completely different.
If you want to learn more about battery try to look at different manufactures, for ex. Panasonic
https://www.panasonic.com/industrial/battery/oem/