I have a 0.9V-5V to 5V USB booster but I am only getting 4.92V. The product I'm using to needs 5V to charge.

Is there anyway I can boost to voltage to 5.1V or 5.2V?

  • 5
    \$\begingroup\$ USB is specified down to 4.75V so it is well within spec. If your device takes USB power to charge and won't work down to that, then that one is out of spec. \$\endgroup\$ – PlasmaHH Jul 31 '15 at 10:40
  • \$\begingroup\$ As pointed out by @PlasmaHH if the product you are using is USB compatible it should charge OK. You may be able to change the output voltage by tweaking a component value or two but we would need to know specifically which charger you have. There is no guarantee anybody here will know the circuit well enough to tell you what component you need to change however. \$\endgroup\$ – Warren Hill Jul 31 '15 at 10:48
  • \$\begingroup\$ @WarrenHill its a iphone usb charger \$\endgroup\$ – walter Jul 31 '15 at 10:51
  • \$\begingroup\$ @PlasmaHH I thought a iphone usb couldn't charge under 5v? \$\endgroup\$ – walter Jul 31 '15 at 11:11
  • \$\begingroup\$ @walter: if that is the case, it is another entry in a list of why it is crappy. \$\endgroup\$ – PlasmaHH Jul 31 '15 at 11:17

It's probably nothing to do with the voltage per se. Phones use resistors on the data lines on a charger connection to communicate the information on what the charger is capable of- the iPhones won't attempt to charge with open data lines.

Since this varies from phone-to-phone and as new models are developed, it's best researched on the fly, but for today, the information from LadyAda is as good as any, and more accessible than some of the more official sources (such as chip datasheets). Choose according to the capabilities of your charger.

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  • 1
    \$\begingroup\$ I had this same problem and you're correct. \$\endgroup\$ – DLS3141 Jul 31 '15 at 19:29

4.92V is 1.6% low. It is perfectly normal for a regulator (which is what resides in the booster) to have a 2% (on many occasions more) tolerance.

The product you are charging (if you identify it I can answer more certainly) will very probably accept 5V +/- 5% at least.

  • \$\begingroup\$ its a iphone 4, using the usb charger it come with \$\endgroup\$ – walter Jul 31 '15 at 10:52
  • \$\begingroup\$ iphone 4...That's your problem. Take a look at the answer above, you need some 1% resistors on the data lines. 4.92V should charge the phone if your charger is set up correctly. \$\endgroup\$ – DLS3141 Jul 31 '15 at 19:29

It's likely due to too small a wire gauge inside the cable, resulting in voltage loss in the cable itself. 99+% of charger cables are 28 gauge. After market micro USB cables will pretty much always result in charging at 500 mA, maybe less. Solution? Get a 24 gauge cable -- 24 gauge is ~ 60% larger then 28 gauge.


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