Drawing 10V from 2 USB ports

[martin11ph]

I read somewhere that the USB port can produce an output of 5V and 500mA. Is it possible to send signals out from the port using VB perhaps? This is geared towards producing a 10V 500mA source(I will use the 2 ports in series) that can be triggered at will using a program. Hope someone has an idea or any references that I can read. Thanks!

 

[BobK]

Do not try to put two USB ports in series. They are likely both connected to the same power supply and when you connect the + of one to the - of the other you will be shorting it. You cannot get 10V this way.

Bob

 

[daGenie]

i really dont think u can connect 2 ports in series...........i think all ports are connected in parallel, so that is not really possible............try 2 c whether u can work with the maximum output of the usb port..............also, u shouldn't use the maximum power of the usb port but something a little less...........e.g. 5V, 400mA...............good luck

 

[martin11ph]

I see. Thank you for sharing that. Is there any way I can get around 10V and 500mA from the computer and program it?

I've used parallel and serial ports before but they can't give me that much. I recall serial giving me -12 to 12V at 10mA.

 

[BobK]

What is it your are trying to do?

Bob

 

[daGenie]

i doubt it............just try to manage the 5V; if u can't, create an external power supply that would power the device, then use the usb only for data transmission

 

[martin11ph]

Use the computer to signal a POS register. At the moment, I use several pins from the parallel port to trigger a 6V relay which passes the necessary 12V from the internal computer power supply to the register. I was looking for a better way to accomplish it particularly, without the relay.

 

[Aggie]

There should be another power plug on the inside of your computer (if this is a desktop. If this is a laptop ignore the rest. )

If you test the molex plug output of your internal power supply, you will find one that is +12V at some amperage rating probably larger than you need (check the specs on your power supply). Just build a stable voltage converter down to your 10V. Then just figure out how to drop the amperage if necessary.

Just some thoughts.

 

[martin11ph]

There should be another power plug on the inside of your computer (if this is a desktop. If this is a laptop ignore the rest. )

If you test the molex plug output of your internal power supply, you will find one that is +12V at some amperage rating probably larger than you need (check the specs on your power supply). Just build a stable voltage converter down to your 10V. Then just figure out how to drop the amperage if necessary.

Just some thoughts.

I am currently using this. When the relay is triggered by the parallel port, this 12V power flows to the register. If there was a way to directly control this voltage, I would use it. However, I do not know how.

 

[martin11ph]

Bump. Any other ideas? Thanks for the help.

 

[duke37]

You could make an invertor to step up the 5V to 10V. There will be power loss and will need over twice the 10V load current to be supplied by the 5V supply.
There are capacitor pump chips to do this job.

 

[ArmRules]

Boost Converter

Im not sure a charge pump will provide the current you need. The USB port has a max of 500mA output as stated. The USB spec defines a unit load as 100mA. I believe that to get the max of 500mA that the slave device is supposed to talk to the port and negotiate the 500mA.In my experience though I have not had problems drawing the 500mA from the port.

You could use a boost converter like an LM simple switcher or a TPS61040 to boost the voltage. Your available power is 5Vx.5A so 2.5W this means the max current you can get from your 10V supply is 250mA. slightly less as the converter will not be 100% efficient.

I dont believe there is anyway to disable the port 5V supply from software in the PC. So you are still left with the problem of how to switch the slave circuit on and off.