OK, hadn't heard of this before, thanks for the reply. Looks like for=20
the 24 VDC, I need a P6KE33A, and being bidirectional, I don't have a=20
band end to watch for. :)
On 12/11/13 11:26 PM, Bob Axtell wrote:
> On 12/11/2013 2:31 PM, Carl Denk wrote:
>> My house heating zoning system board has a ULN2803A to complete the
>> circuits controlling 4 solenoid valves, each with a 1500 ohm coil @24
>> VDC =3D 16 ma current by completing the ground side of the circuit. To 2
>> of the outputs, I add a relay to each output with a 17 ma coil and a
>> suppression diode. Supposedly the ULN2803A has an allowable current of
>> 500 ma. There has been 2 failures of the chip drivers, one totally open,
>> the other shows 5VDC, when should be open. I'm assuming the 5 VDC
>> control from the CPU. I am thinking of adding say 100ma fast acting
>> fuses to my connections as protection if the vendor complains.
>>
>> Comments??
> a plain 'ole diode is normally not FAST enough for the relay coil's
> spike.  put a PKE6XXX
> across it instead, a bi-directional version. Use a value of the coil's
> voltage plus 5V.
>
> It'll fix it.
>
> --Bob A
>

--=20
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