DC-DC converter (boost) can't charge cellphone

Jan 22, 2007 5 Replies
W

Hello everyone,



I'm new to electronics design, when building DC-DC converter to charge cellphone, I noticed it did not work. I tried MAX1797, I can get the output voltage: +5.1V, which is good for Moto RAZR, but for some reason, I suspect the output current is not good enough. From the spec, it appears the converter can generate typical Iout = 0.55A.



The link to this IC:

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I did not add any other circuit, just used the circuit from Evaluation kit and adjust R1 and R2 to get Vo=+5.1V.



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I can measure the current to the cellphone, it's around 5mA instead of around several hundreds of mA (i.e. 500mA), the although the voltage is



+5.1 as expected.

I connect the output Vout to cellphone's charging Pin (Vbus of MiniUSB) and also connected GND to cellphone GND. I can hear cellphone is detecting a charger (a beep sound), but it did not charge, if I remove my circuit, got beep again which means "charger" removing detected.



Anyone has idea why it did not work?



Thanks, Gary



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M

Gary, Charing batteries is getting to be more of an art than science these days. I don't know if this is the case with the Razor, but I've seen chargers that want to "communicate" with the battery pack before re-charging. It's not simply a matter of providing voltage anymore.

I think in part, this has to do with so many different battery designs out there. Many, having the same form factor. By communicating with the battery first, the charger can "know" what type of battery chemisty is being used in the device, or for that matter, whether the battery is even a re-chargeable type.

I also think this is a way for manufacturers to force people to by their (and only their) chargers.!? Of course, that could just be the cynic in me...

You can always verify your charger design with a power resistor. If you get the expected rated voltage and current, it's probably OK.

-mpm

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J

Yep. LiIon and NiMH batteries are "smart" and require matching chargers.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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M

go to walmart and buy the $9.74 motorola v3 mobile power cord

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P

The Razr charges through a USB port. Because of this, it needs to negotiate with the supply to determine the available capacity. If it cannot do so (per the USB interface spec) it may refuse to draw sufficient power to charge its batteries. This is what I suspect is going on.

Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ There was a man who entered a local paper\'s pun contest. He sent in ten different puns, in the hope that at least one of them would win. Unfortunately, no pun in ten did.
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