Recent content by blcpro

Thanks for the help everyone. I'm still having trouble finding a datasheet to confirm, but the markings in the picture on ebay do look very similar to the chip. B

Hello all, I recently found myself trying to identify an IC (which I still havn't) and realized I can't find a reliable source for identifying ICs by their markings. In my specific case, it is an 8-pin SOIC, probably an Op-amp of some kind, with the following marking: 1350 PAXM I have also...

Re: mcgyvr, "When creating a pcb library as long as you assign the proper pin (be it a number/name or whatever) to match the schematics icon it should never be an issue. If the schematic is right then the layout will be too..always" That is true if you do assign pin numbers, but not true if...

I'm having a disagreement with another engineer on the convention for numbering the anode and cathode of a diode. We both use ORCAD for schematic designs. I always use diode parts with pins numbered 1 for cathode and 2 for anode. His designs only name the terminal, with no numbering. We were...

I do tend to stare at my circuits too long. Sometimes it helps. Sometimes it don't.

Also, for this MOSFET, the gate threshold voltage seems pretty low (typically -1.9V), so I think thats why I needed such a large value for C126, so that the gate charge builds as slowly as possible in that region.

Thanks, OperaHouse. In my test setup I'm actually using 1Mohm and 2.2uF cap to keep the turn on time very slow. I'm able to measure the inrush current, and it doesn't spike more than about 9 amps. The MOSFET can handle up to 40A (so it claims), and previously, before the adjustments, I saw...

UPDATE: I have been testing some of my ideas and some of the suggestions posted here before I redo the board layout. I have attached an updated schematic with my changes so far. What do you guys think? After some testing, I discovered that I probably did not need as much capacitance as I had...

Thanks for your comments.. I have been experimenting with larger resistor values and different ratios, and I can see some slower turn-on times. Also, I have experimented with some inrush current limitors, and so far the problem has not happened again. I am re-designing the circuit to take...

Thanks for the suggestions, I'll keep them in mind while I re-evaluate the circuit. B

That very well may be the problem... I'll have to do some more testing and see if an ICL (NTC thermistor type) might fix the problem. Thanks very much for bringing this to my attention. B

Oh, but if the inrush current exceeded the S-D junction limit? Would that be the cause of the failure? Or is that exactly what imcjoek meant to say?

This may cause the Source-Gate junction to fail? Yes, I would expect a large in-rush current, but my thermal printhead might demand fairly large currents (as much as 7 amps, in the worst case) for short bursts. Granted, that's really what the large capacitors are for, but I wouldn't want the...

The schematic didn't attach the first time... here it is again: http://files.engineering.com/getfile.aspx?folder=9faae616-a2fb-4c52-8f08-6f1aafd9b877&file=PMOS_Fails.jpg

Hey all, I'm having some trouble with a PMOSFET which I use to supply power to a thermal printhead. The problem is, after several days, or several power cycles, the PMOSFET seems to become a short circuit, and can't be turned off. In the schematic provided, Q1 controls the turn-on and...