I'm using the TI UC1825AL PWM Control IC in a MIL/Hi-REL DC-DC Converter design. I'm an expert power electronics engineer, but never used the UC1825A before. The only documentation is the datasheet and an app note from the Unitrode days. My customer requires a remote shutdown, referenced to the primary-side (UC1825 side) return. I've attached my schematic in pdf form (2-pages, see page-2). I'm trying to do this by using a small pnp to switch the UC1825A's +5V VRef to the ILimit pin to get it above the 1.2V overcurrent limit to initiate a shutdown. What I don't know is whether this will work for more than 1 clock cycle or not. The app note has a more detailed internal schematic of the ILimit section and it seems like my inhibit goes to the set of an RS flip-flop that also is logically the same as the UVLO. So I would think it should work, but there's not enough detail to tell for sure. I also need to be sure that my simple switching ckt won't mess-up the normal ILimit function as this is a current-mode converter, even over -55C to +85C baseplate.
If my inhibit won't work for some reason the way it is, is there any way other than switching the UC1825A's Vin pin to my +16VDC primary bias voltage?
Thanks and I appreciate any replies.
Regards, Kamran Kazem, V.P., CTO, Magnetic Design Labs, Inc.