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Using ULN2003A Relay Driver with mbed

Topic last updated 02 Sep 2011, by Gert van der Knokke. 2 replies
Gerry McMahon
01 Sep 2011

Is it possible to drive ULN2003A reliably with inputs directly connected to mbed digital output lines?

I want to drive reed relays with a max individual coil current of 15mA and a 5V or 12V relay supply voltage.

thanks

Gerry

Christian Lerche
02 Sep 2011

Yes, it's possible. I've done it, but I don't know if it's good for the 'bed or not. But it's definitely works. :-)

Gert van der Knokke
02 Sep 2011

From the datasheet:

The ULN2003 has a 2.7kΩ series base resistor for each darlington pair This is no problem for the mbed to drive, you can use 'pulldown' as output configuration to make sure the mbed drives the high signal 'active'.

For the ULN2003 to sink 200 mA through the output transistors it needs at least 2.4 Volts input.