ULN2003 driving a relay

[mlaymance]

I am trying to drive a low current 5VDC relay with a Darlington driver (ULN2003). When I try to drive it with the driver it chatters.

I have a good solid 5VDC supply, and have connected it as in the Manual3 shows. I do not have a Diode across the coil. Should I have one? I can drive the relay direct with no problem. I am wondering about the darlington. Perhaps it isn't being driven hard enough?

I also tried paralleling multiple channels in the darlington, still no change.

Relay has a 52 ohm coil.

Does anybody have any suggestions?

 

[moxhamj]

You don't need a diode - it is inside the chip.

It sounds like either the power supply can't handle the load, or more likely, the power supply can't hanlde the peak current. Try putting a biggish cap across the 5V supply eg 1000uF or even 4700uF if you have one.

V=IR 5=52*I so I presume the power supply can supply 100mA.

 

[sghioto]

mlaymance,

What do you mean by the statement "I can drive the relay direct with no problem".

Steve G.

 

[BeanieBots]

The ULN2003 is a darlington driver.
Whilst darlingtons offer massive gain, the price is the increased volt-drop which can be as high as 1.2v.
A 1.2v loss on a 5v supply is quite a lot percentage wise.

When the output is on, measure the volts across the relay.
Try using a single transistor driver instead. Or a FET.

 

[mlaymance]

If I connect it direct (I know you are not supposed to), the Pic will supply enough current to operate the relay.

I will pick up a couple of transistors today.

Thanks,
Michael

 

[Dippy]

haha, well if you keep testing things like that then you'd better pickup a couple of new PICAXEs too

 

[mlaymance]

ULN2003 Driving a relay

GUys,

Thanks for the assistance.

I added a 1000mfd cap to the 5v output, but I believe the problem was that the 5VDC supply voltage feed to the ULN2003 was on the wrong pin.

WOrks great now..... Thanks,

Michael