USB-6009 Digital Output Current

[sevincom]

Hi, I'm trying to increase the voltage of the digital outputs of USB-6009 device. I read a couple topics about using a relay but I could not manage it.

I was thinking to use 5V supply on the card since it has 200mA current on it, but when I use it with open-collector output, it can not switch the relay. When I measure the current between

5V and ground: 200mA,

5V and output, I read a value around 30-40 mA.

Why can't I use that 200mA with an output? This is the relay I'm using.

If this is not possible, can I use an external 5V supply (with more current) and a digital output to switch the relay without damage the 6009?

[johnsold · Accepted solution]

The digital outputs of the USB-6009 are limited to 8.5 mA. Your relay coli requires much more than that. Even though the power source can provide enough current for the relay, the digital output cannot switch it.

The fix is to use an extermal buffer. The ULN2003 can switch currents up to 500 mA and voltages up to 50 V while being controlled from the digital output.

Lynn

[sevincom]

Lynn, I'm not familiar with these type of components. What I need to do is sending 24V signals to inputs of PLC. On the datasheets I found on Internet, it says ULN2003 can give ground connections to outputs when 5V is applied to the inputs. Is there a model of this product which can give 24V on its' outputs? If there is a model like that, I can remove relays and use only this product.

[johnsold]

You can just use a resistor from the output of the ULN2003 to 24 V. The value of the resistor will depend on the PLC input current requirements.  Note that the ULN2003 inverts the signal. A 5 V input will produce ~ 0 V output while a 0 V input will produce 24 V output.

Lynn

[sevincom]

Thanks Lynn. There is one more thing that I want to ask. As far as I understand, I need to wire the ground terminal of USB-6009 and negative terminal of external 24V source to the Ground terminal of ULN2003. Is wiring this two terminal damage the USB-6009? Do I need to pay attention on anything or can I just wire these two together to the ground of ULN2003?

[johnsold]

You need to have all those grounds connected together - USB-6009 Digital Ground, ULN2003 GND, and the power supply ground. In this case it will not matter how they are connected.  If they are not connected, then one of the devices could be damaged.

Lynn