Hey guys, im using a ic to control a latching relay, it works most of the time then all of sudden it would stop... Its not a code issue, since im bench testing it right now.
Parts List:
1. ne720-1a-z latching relay,http://www.relaymall.co.kr/pdf/NE720.pdf.
2. Couple of darlington npn. http://www.nteinc.com/specs/200to299/pdf/nte261.pdf
Basically the circuit is: each darlington drives the set and reset pin of the relay, and the common is sourcing 12v through a 10ohm 5w resistance since the case of the relay says "7v" and the measure resistence between the pins was 12 ohm, that gives me 416mA rounded it up to 600ma. That gives me ic of 600ma, the hfe of the nte261 is 1000, Ib=0.6/1000=>0.6mA, since im driving a darlington voltage drop is 1.4 from a 5v ic output is 5-1.4=3.6v, base resistor used is a 3.9kohm...3.6/3900 gives me 0.9mA to saturate the transistor. Im asssuming my math is correct, everything works as expected.
Here is the problem all of a sudden the circuit will stop working and one of the npn will switch on without any voltage to the base, i even disconnected the base pin to make sure and the transistor will stay on, at first i thought a bad transistor and replaced the transistor array with new ones and the same thing happened. Than it will work again for no particular reason, i checked the B-E voltage and was getting 1.4v without nothing connected to the base.
Heres a pic of the circuit (i know the npn are not correctly drawn, this was a sketch up).
Parts List:
1. ne720-1a-z latching relay,http://www.relaymall.co.kr/pdf/NE720.pdf.
2. Couple of darlington npn. http://www.nteinc.com/specs/200to299/pdf/nte261.pdf
Basically the circuit is: each darlington drives the set and reset pin of the relay, and the common is sourcing 12v through a 10ohm 5w resistance since the case of the relay says "7v" and the measure resistence between the pins was 12 ohm, that gives me 416mA rounded it up to 600ma. That gives me ic of 600ma, the hfe of the nte261 is 1000, Ib=0.6/1000=>0.6mA, since im driving a darlington voltage drop is 1.4 from a 5v ic output is 5-1.4=3.6v, base resistor used is a 3.9kohm...3.6/3900 gives me 0.9mA to saturate the transistor. Im asssuming my math is correct, everything works as expected.
Here is the problem all of a sudden the circuit will stop working and one of the npn will switch on without any voltage to the base, i even disconnected the base pin to make sure and the transistor will stay on, at first i thought a bad transistor and replaced the transistor array with new ones and the same thing happened. Than it will work again for no particular reason, i checked the B-E voltage and was getting 1.4v without nothing connected to the base.
Heres a pic of the circuit (i know the npn are not correctly drawn, this was a sketch up).