The ULN2003 has open collector outputs so it can sink current from the gate (provide ground) but how do you source the current to the gate to turn it on.
You must have a resistor connected from the output of the ULN2003 , where is it connected?
The 5v pulses are in the gate or do you mean the ULN input?
Does the mosfet get hot?
Alex
Failure: what happens? shorted source -drain? or gate - source etc..
The Rds(on) is rated at a Vgs of 10V. Check Figure 1 in the datasheet. With a Vgs of 5 volts, the Rds is much higher. In other words, with the same Vds, current is about 9x greater with a Vgs of 10V versus 5V.
I have a difficult time understanding exactly how your devices are connected. It sounds like you are turning on the gate through a 3.3K resistor. That would lead to slow switching, which with the high Rds could be the reason for your device failing.
With a Vgs of 5V and any appreciable current, you need a logic-level mosfet.
John
Edit: Also, don't ignore post #3 about the diode.
same coil for either 28V or 12V operation ? does it mostly fail when its 28V ??
if assuming so, then the transistor may be dropping 16V across it.
0.15A (probably much more!) x 16V = 2.4W
same coil for either 28V or 12V operation ? does it mostly fail when its 28V ??
if assuming so, then the transistor may be dropping 16V across it.
0.15A (probably much more!) x 16V = 2.4W
won't that still need some heat dissipation ? maybe like one of those clip-on heatsinks ?
The enclosure could make a difference too....
And i've seen these transistors easily get hot when relying on its Vds breakdown voltage (55V) as a snubber.......
but for a relay, how often is it going to switch ?
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