I want to power some hobby servos from a USB 5V supply. I am daisy chaining 2 ports together from a powered hub so that I can draw up to 1A. Should I power the servos directly from this supply, or is there some kind of simple protection circuit that I should add between servos and USB supply to prevent accidental damage to the hub?
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1\$\begingroup\$ Don't be surprised if you can't pull more than 200 mA at best. Also the hub, if it's of reasonable quality, should already have the needed protection, but don't count on it. \$\endgroup\$– AndrejaKoAug 8, 2012 at 7:38
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2 Answers
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USB 2.0 and 3.0 standards have battery charging profile and configurations to support drawing more current than that.
But if USB 1.0 the maximum current you could draw is 500mA.
Either way you need to communicate with the host, so specific chip is required.
-- please note that I'm not working for maxim. :P
answered Aug 8, 2012 at 7:43
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1\$\begingroup\$ Is the battery charging profile mandatory on computers and USB hubs? From all I've seen so far, the answer is no (that is to say: Higher currents are only available form specially marked charging ports), so I'd like to see some sources which support the claim that there are ways to get more than 500 mA form standard USB2.0 port and more than 900 mA from standard USB 3.0 port. \$\endgroup\$ Aug 8, 2012 at 8:25
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The best way to drive your servo is by using a servo driver/motor driver (circuit), it amplifies the electric signal and transfers required current to drive your servos. You just have to give input from your USB to servo driver and output from driver will provide sufficient current. I did a project and it worked for me.
By using motor driver:
1) You can avoid any accidental damage as you mentioned above.
2) 1 port USB supply would be enough as well (not sure).
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1\$\begingroup\$ I'm not quite sure what you mean by "amplifies the electric signal" here, but you can't get more power out than you put in. Could you give an example of the circuit you are talking of? \$\endgroup\$ Aug 8, 2012 at 10:08
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\$\begingroup\$ i meant by amplification of electric current. \$\endgroup\$– NishuAug 8, 2012 at 12:03
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\$\begingroup\$ Okay, so do you mean add another power supply as well as the USB supply? Or convert the voltage/current? (e.g. switching reg) Can you give an example circuit? The thing I'm trying to understand is why you think it would be possible to use just 1 USB port instead of 2 by using this circuit. \$\endgroup\$ Aug 8, 2012 at 12:13
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\$\begingroup\$ Exactly, as you said we cannot get more power than input power. For taking more current, we can get more current by dropping our input voltage or from one another power supply. Earlier i misunderstood your question, there are power signal and control signal wire in servo, power signal carries zero current when servo isn't receiving any control signal, current amplifies with presence of control signal.That's why i did answer "i meant by amplification of electric current". \$\endgroup\$– NishuAug 9, 2012 at 12:10