External Power Problem with the USB-6215

[evsawefgeedasa]

Hey everybody! I have a problem and I really hope, that you can help me with that:)

I want to drive a relay with the USB-6215 which only has a maximum output current of 50 mA (specified, 30 mA measured). This is unfortunately closely not enough for driving a relay consitently:( So I searched the Internet for a solution and came up with hooking an external power supply to the +5 V and digital ground pin but the current still wont increase.

Does anybody have an idea, what i might doing wrong? I dont really want to build an external relay driving circuit:(

Thanks in advance!

[Duffy2007]

Hello evsawefgeedasa,

you have to built an external circuit with an optokoppler or transitor to switch your relay. The DIO pin normaly provides round about 6mA. Connecting an external power supply to the +5V of the usb device can also damage the device connecting two power supply together is not always a good decission.

What are the specifications of your relay you want to switch?

[evsawefgeedasa]

um, ok! thanks:) I've been afraid, that I have to build an external circuit.

I just want to switch a big fan with the relay. Do you think, that I can use the 5 V Output of the device to power the circuit because when I attach the relay to + 5V an D GND it switches effortlessly.

I'm just not very happy with using an additional external power source just to power the relais, you know?

[Duffy2007]

Hello evsawefgeedasa,

you can try this, but the current is internally limited to 50 mA maximum, shared with digital outputs.