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J Reidy said:sorry i wasnt clear, i meant an easy way to reduce 5v to ~4v..... the phones i am playing with come with a 5v charging adapter. on a previous model i shorted out the power pins on the phone and put 5v direct to battery pins, i was then able to power up by just adding power to the p suppy. Now on the current phone im using the 5v is too much and the phone isnt working properly
Wow.. how do you know all these?Diver300 said:If you are using a GSM phone, a 300 mA supply is hopelessly small. It will not work.
When GSM phones are transmitting, which they have to do briefly to register on the network, they take up to 1.9A, for 1/8th of the time, 216 times a second. So if your power supply isn't up to supplying 1.9A, the GSM phone won't work at all.
The average current is about 240mA when transmiting
The pulse is 579us long at 1.9A. If you need a capacitor to drop less than 1/2 volt, it needs to be at least 2200 uF, and more if you are running from the mains and there will be gaps of 1/2 cycle of the mains.
GSM phone supplies are hard work to get right, because of the pulsed nature of the load. That is why ordinary mobile phones won't work from their chargers alone. They need a battery fitted to work, while, for example, laptops don't.
J Reidy said:or another idea.....
leave the battery + charger connected to the phone, short the power button contacts again, on the v+ line from battery to phone add a switching circuit that will detect ac? whats the best kind of circuit for this? or will i just leave ye all alone till ive finished uni....
bananasiong said:Wow.. how do you know all these?
J Reidy said:sorry, i wasnt clear, i mean to detect the ac voltage when it is applied to the charger, i want to be able to switch it on when i plug it in.