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I have a IR Line Laser with following Specs

Output Power : 60mw

Wavelength : 780nm

Working Voltage : 5.0VDC

Working Current : <200mA

Laser Shape Line

for details please visit the link http://www.aliexpress.com/item/60mw-780nm-Infrared-Laser-Line-Module-120-degrees/1517656084.html

i would like to power this device using a USB port via a cable. iknow USB has an output voltage 5V but isnt it 500mA ?? Some say Device draws only required current from USB port

My question is can i directly connect laser to USB port by cutting a USB cable? Or should i convert 500mA to 200mA? If so how can i do it ? Can someone specify a solution?

Thanks in Advance

Victor
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  • Should i need to convert 500mA of usb to 200mA ??!!! Some say no problem only thevoltage is the thing tht counts!! – Victor May 29 '14 at 04:53
  • Read the link that passerby posted and it will tell why you are fine. Normally this should be closed as a duplicate, but the issue here is how to pull power from a USB port and tricking the controller to keep power applied, or this even a problem? – placeholder May 29 '14 at 05:33

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Well, if you are looking for a quick fix, you can go ahead and plug it into USB. Although a Fuse (200mA) in series with the diode might help. This is good solution only if you are going to use it for very short duration like few hours (continuous use).

But if you want to use it continuously for a very long time like days, this might affect the motherboard of your PC (as the continuous current might lead to heat). If you are using a laptop, there will be side effects on the battery for sure.

So depending on your application, one might or might not suggest you to use a USB as power source.

Damon
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  • Since all motherboard USB ports must support at least 500 mA, why would heat of continuous operation be a problem for the computer? It's already rated at more than what's being used. – AndrejaKo May 29 '14 at 05:41
  • All USB ports on PC are designed to deliver 500mA current AT MAX and NOT AT LEAST. Some ports first initialize USB using 100mA current limit. After enumeration, they increase it to 500mA on request of USB device. chech this :- http://www.ti.com/lit/an/slyt118/slyt118.pdf – Damon May 29 '14 at 06:03
  • That's not true. Here's a quote from current USB specification:`Root port hubs: Are directly attached to the USB Host Controller. Hub power is derived from the same source as the Host Controller. Systems that obtain operating power externally, either AC or DC, must be capable of supplying at least six unit loads to each port. Such ports are called high-power ports. Battery-powered systems may supply either one or six unit loads. Ports that can supply only one unit load are termed low-power ports.` – AndrejaKo May 29 '14 at 06:18
  • As you can see, the minimum limit for a motherboard USB port today is 6 units. Back in the era of USB 2.0, it was 5 units. In any case, root port must be capable of providing at least 500 mA to a device. The negotiation procedure is there because device doesn't know if it's connected to a self-powered hub, which must provide full power to its each port, or a bus-powered hub, which can provide up to one unit per port using 2.0 specification. Also helpful site: http://www.usb.org/developers/docs/ – AndrejaKo May 29 '14 at 06:21
  • Thanks for the quick response i will using this laser continously for only less than 1 hour(max). if i want tot regulate voltage to 3.3V which regulator can i use? – Victor May 29 '14 at 06:22
  • Thank you @AndrejaKo I will most certainly look into that. – Damon May 29 '14 at 07:08