Hi,
I want to use a ERICSSON T10s board (from disassambled phone with LCD) in one of my projects. How can I powering up the board? I couldn't do it by powering up through connector on the board without its battery.
Sincerely, Rustam Bogubaev
You won't be able to use the phone without a battery, the power supply can't handle the current.
-- Steve Sousa
Are you saying that the phone relies on the series resistance of the battery for current limiting? If so, could he fake it with a series resistor? Or is it hopeless?
Just wondering.
--Mac
The power supply has sufficient average current to charge the battery with the phone operating. It does not (generally) have enough power to supply pulses of power needed when transmitting. Dismantling a battery (carefully) and replacing the lithium cell with a large capacitor (10mF?) may work.
How much current does it need.. ?
A good model for the supply is 30ma continuous plus 2A bursts of 577us, 1:8 duty cycle.
see:
pages 11->
page 34 for the transmit waveform if not clear.
I don't think you can meet the "less than 200mV drop on transmit burts" spec (page 10)without a battery, the amount of low esr capacitance needed and the size of the caps will easily exceed the size of the battery.
Other comments: i don't know the chemistry used on the T10, so measure the maximum voltage of a charged battery before designing your supply (I have no idea if the values on page 10 are valid for the T10), cellphones are very very very and i repeat very! sensitive to overvoltage at the battery terminals and will blow the RF amplifiers causing high stand-by consumption.
Besides, the battery is probably used as a "capacitor" for the charging circuit, and the phone simply will not work without it, the protection kicks in.
Just leave the battery connected, and feed the charging circuit, it will draw a very small current and be ready to go at all times, why do you want to remove it?
Best Regards
-- Steve Sousa
A battery will eventually wear out. Proberbly much earlier than a capacitor. And in a stationary setup size won't matter that much. Any ideas on suitable sized capacitor ?
It depends a lot on your power supply and the lenght of you leads. You should place the capacitors as close to the phone as you can, and measure the voltage drop *at the battery terminals on the phone* using an osciloscope, try a couple of 1000uF 6.3V caps from an old motherboard, or at least 3 to 5 330~470 tantalums.
For my tests i made a circuit with a 555 and a mosfet to replicate the circuit on the pdf i pointed you to. I couln't meet the less than 200mV spec only with capacitors without them getting hot, but neither did son*-**iccson themselves on the gt47 modem they sell. I posted a pic at abse of the signal on their modem, if you can get something similar or better you should be ok.
Best Regards
-- Steve Sousa
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