Steve,

Thanks...

I'm using the National switcher LM2576HVS-5.0 (-40C to +85C). Its capable of converting 7 to 60Vdc into 5Vdc at up to 3Amps (we specs +12 to +48Vdc input). Its cookbook except for two tantalums I added for better -40C operation. This telemetry device operates at very altitudes (ie COLD temperatures) and regulates its internal temperature.

The filter stage in front of that comes from Tim William's (IEE) book. The PLUS terminal immediately enters a polyfuse and on to a node that bridges back to ground through a 48Vdc transorb (SMBJ48A). The node continues to a limiting resistor, then to a rectifying diode and then to the switcher's input reservoir caps. When the customers abide by our specification, this works fine.

But our primary customer does some very strange things. I just heard of a situation where they charge up some other module in flight with some high voltage AC pulses that *could* get into my voltage inputs. I designed an AC tolerant stage for them but my best analog subcontractor is out of town on someone else's job right now.

As you can see, I have it bad when it comes to customer hookups. So while I'm waiting for my subcontractor to return, I thought I'd see what advice I could get in the Forum.

-Jay C. Box