My house heating zoning system board has a ULN2803A to complete the=20
circuits controlling 4 solenoid valves, each with a 1500 ohm coil @24=20
VDC =3D 16 ma current by completing the ground side of the circuit. To 2=20
of the outputs, I add a relay to each output with a 17 ma coil and a=20
suppression diode. Supposedly the ULN2803A has an allowable current of=20
500 ma. There has been 2 failures of the chip drivers, one totally open,=20
the other shows 5VDC, when should be open. I'm assuming the 5 VDC=20
control from the CPU. I am thinking of adding say 100ma fast acting=20
fuses to my connections as protection if the vendor complains.

Comments??
--=20
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