Re: What is TP's voltage?
 

I learned something new today! That is actually some pretty good info

Re: What is TP's voltage?
 

Nope, the device isn't going to be drawing any more than 1A current at any given time. The TP's built-in charging circuit output (to its battery) is smart enough to regulate exactly how much charge is delivered instantaneously (current) and in total (charge capacity). Effectively, all that charging circuit does is regulate how much current flows from its input (whatever is plugged into the mini-USB jack) to its output (the TP's battery). The way to look at is: the charging circuitry in the TP is in control of everything. It is smart, and it will only draw as much current as it wants, no more (provided the charger can maintain a solid 5V). If you really want to understand why, look up ohms law. The battery in the DIY charger is the voltage source, V, and the TP is effectively the resistor, R. The TP will vary this apparent 'R' to its liking, and current, I, will be determined by I=V/R.

What I think is confusing some here is that a battery's 'capacity rating' is not a reflection of how much 'current' HAS to be flowing out of it at all times. That capacity rating is telling you how much charge volume the battery is storing... like a bucket holding 2.5 gallons (g) of water. 'Current' is 'flow' and 'charge capacity' is 'volume.' If you were to draw 2.5 gallons per hour (gph) out of that bucket, you'd have enough supply for 1 hour. One could then easily imagine that drawing 1gph from that same bucket would be a 2.5 hour supply... and so on. Electricity works in basically the same way (except the units are kinda reversed): a battery with 2.5Ah (or 2500mAh, same thing) of capacity drained at 2.5A would last for 1 hour, or a constant 1A drain would give you 2.5 hours of life from that same battery. The capacity is just that, capacity. Just divide the 'capacity' by the average 'current' to figure out how much time, in hours, it will take to drain the battery (t = Ah/A or mAh/mA ). Hope that helps!

Re: What is TP's voltage?
 

Thanks everyone, this is great info. Just to be sure (and I apologize, I don't have the OEM wall charger with me at the moment), but a generic mini-USB wall charger with an output of 5V and 900mA should be fine without endangering the TP, right? thanks in advance

Re: What is TP's voltage?
 

yes, it should be fine

Re: What is TP's voltage?
 

lol. So much mis-information in this thread. It mostly got all sorted out at the end though. I just wanted to add my engineering facts in case people are taking votes to deside who to believe...

1) There is a min/max voltage input. Voltage should be constant. It is safe to assume that it will charge with any voltage between 4.8V-5.1V. Too little voltage will not hurt it, it just won't charge. Too much voltage will hurt it (but you can probably get close to 5.5V or higher before it actually would).

2) There is no min/max current input. If you can only supply 200mA, it will still charge the battery, just slowly (as long as you are not running video or something else that would make the phone consume more that 200mA power on average). If you can supply 10A, it will still only draw what it needs (~1A max when empty, 0A when charged). During charging the current draw will fluctuate and be (on-average) a lot less on an 90% full battery than on a 10% full battery. In any case, you don't need to worry about it, just supply what you can and know that adding more past 1.5A will have no effect on charging speed. Once fully charged, it will not take any current until the battery drops to 98% or so, and then it will start to charge again. When you leave your phone plugged in, it constantly charges to 100%, then discharges to 98%, then charges again.

3) mAh is rating. It means at a full charge it can supply x mA for y hours. It is a very inacurate measurement and in testing you would find much variation depending on the actual variation of current consumption over time, the condition/age of the battery, the tempature of the room, etc. However, assuming a battery rated at 1000mAh was connected to a device with an average current draw of 100mA, it should last ~10 hours. "mA" multiplied by "h" = "mAh"

Re: What is TP's voltage?
 

Get yourself one of these LM2940 5V LDO Regulators -

http://search.digikey.com/scripts/Dk...M2940CT-5.0-ND

read the datasheet, make sure you get the proper input and output capacitors. they're all available from digikey.

Any load (in this case the TP's internal charging circuit) will pull what current it wants. The 1A spec you see on the wall charger is the MAXIMUM current it can provide.

I would use 4 1.5V AA batteries. They will make 6V in Series. This regulator will drop the 6V to a constant 5V. When using a regulator you will need to have a higher voltage input then the output 5V. The LM2940 is a "Low-Drop Out" or LDO regulator meaning it has the lowest input-output differential requirement - so you can get away with as little as 5.5V as an input to regulate to 5V while pulling up to 1A (theres a chart in the datasheet pg 7 top left). Standard non-LDO regualtors may need as high as 7V input.

Remember this is a linear voltage regulator meaning its not as efficient as say a Switch-Mode regulator (aka DC-DC converter), but it is the easiest to implement. You will be losing P = ((Vin - Vout) * Iout) . - So with (6V in - 5V out) * Ioutmax(1A) - your maximum power dissipation in the regualtor will be 1W assuming the maximum current is being pulled by the TP. Depending on the ambient temperature you may need to get a heatsink - look at the figure on pg 11 top left on the datasheet. TO-220 (the package the regulator comes in) is a standard component package and you can find a heatsink on digikey as well. you could also get the battery holder on digikey too as well...