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From: Hammy on 25 Oct 2007 16:17
I'm using the MC3423 for OVP and the remote activation pin for current
limiting. I've been seeing some pretty weird behaviour. For instances
the MC3423 will activate and apply a gate pulse to the SCR when it
senses an OV the BJT Q1 saturates and pulls the gate to ground as it
should the weird thing is there is still 4.23V on the output ,the
mosfet source. When I apply directly 5V to R9 the SCR fires Q1
Saturates the gate discharges to ground the mosfet is blocking and 0V
is on the output. This will also energise my relay driver (not shown)
turning the main power relay open. The relay takes 25ms to change
state which is to slow.In other words everything works fine until I
use the MC3423 to generate the gate pulse.

The SCR isn't pulsing on/off its on Q1 is definitely saturated all
measured. I've tried all three MC3423 I have and get the same results.
Has anybody used this chip and experienced anything similar?

Schmatic is here

http://i21.tinypic.com/wb5fdv.png
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