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How can/does a mobile phone provide power to pen drive?

How can/does a mobile phone provide power to pen drive?

  • Mobile phones with USB OTG are not uncommon today. I am wondering that how can a battery operated device like mobile phone power a pen drive? From what I know, the power consumption of pen drive on 5V VBUS is around 100mA. The 5V can be derived from the battery voltage using boost converters, but are these converters so efficient and offer such a high current? This question came to my mind when I came across a topic "connecting a pen drive to my android phone" when browsing for USB OTG. Any thoughts? Thank you.

  • Answer:

    That 100ma rating is a maximum, not the normal rating. The pen drive is mostly idle, and should only need to peak occasionally. USB power can support at least 150ma, generally more. http://en.wikipedia.org/wiki/USB#Power Connecting a device that draws more power is most likely to flatten batteries sooner, but if it is within the USB power specifications, the phone should support it. That said - I am not familiar with the specific limitations of OTG.

LoveEnigma at Electrical Engineering Visit the source

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USB OTG is only possible on Micro or Mini USB connectors. The ID pin is shorted to ground on the host side in the host mode adapter cable. It is unconnected on the side of the pen drive (usually because a desktop USB connection is there with only 4 pins.) Internally on the host device, 5V is produced with a boost converter from the power chips "common" bus. This is sometimes used for internal things, like driving the speaker amp to get the highest power when needed. Yes, boost converters can go from the typical Lithium cell of 3.7-4.2V up to 5V with very high current if needed. Efficiencies vary, but often close to 90%. There is no requirement to use a micro-A or micro-AB connector for host mode, although the USB standard is that if it is a permanent host mode port, the micro-A connector should be used to distinguish it. The only thing required electrically to activate a host mode port is shorting ID pin to ground (if the device supports it).

Joe Sacher

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