HELP find npn high gain transister 2sd1780 nec

[drunkencat129]

oke i looked everywhere i was wondering is there a way i can make one if thease i realy need a few of them for a prototype temp board im makeing hear is the pdf

its just a high gain transister npn with a zeaner diod at the base to the colecter i was wondering if its posible to make one with a normal transister and zeaner diod hear is the pdf

 

[fechter]

I don't see why not.

I've never seen a setup like that. Why does it need the zener diode? In most applications the zener won't be doing anything.

 

[bigmoose]

I've not seen them in low voltage devices before. But I have used the integral zener in an IGBT that I used for an ignition coil driver. What it protected against was HV breakdown of the coil (windings to ground) if the coil was fired without a load (sparkplug/wire). If you did this, and there was no interwinding capacitance, the secondary voltage would theoretically go to infinity. So the IGBT's I used had a 400 volt zener in it, so using it with a 1/100 turn ignition coil limited the secondary voltage to 40,000 volts.

This device I think had a 60 volt zener, and the part was listed as a coil driver/hammer driver/motor driver. They may be doing the same thing, intrinsic protection. It protect against overvoltaging the Vce by partially turning on the transistor when the zener conducts.

If you are not driving an inductive load, you do not need the zener.

 

[drunkencat129]

i know its a pain i need to find somthing thats either a cross refrence to that part or a way to make it with a normal transistor and a zeaner dioed i just add to the 2 legs i realy badly need the 2sd1780 because its going to have a coil with a triger on it im testing for now but thiss works well i just need a replacement i need about 10 of them if u guys can help me out id be vary grateful thanks

 

[drunkencat129]

I don't see why not.

I've never seen a setup like that. Why does it need the zener diode? In most applications the zener won't be doing anything.

i dont know y it needs one but i know its its in the circut its energised all the time i was fooling with somthing and had an idea just need to get it runing so i can isolate and test how it works and is trigered but to do that i got to replace the part i fryed lol by mistake lol shorted the coil lead plugs lol its a purge control solinoid i wanted to isolate it to work on an air brake jsut fooling with somthing need hand on finding hte part lol

 

[bigmoose]

First, as said, a discreet NPN and a discreet zener will work exactly fine as a functional replacement. As for a substitute, I spent about 20 minutes last night and didn't run across an epi NPN with a 2000 hfe... More detail would help in figuring a functional substitute. For example are you replacing something critical in a factory built ECM... or fabricating your own prototype.

Reason I ask, is what is the inductance you are driving and at what speed? You can snub the coil with a simple diode and use an unprotected NPN or a cheap TIPxxx darlington. The deal is it won't turn off or release fast. Doing the zener snub of the flyback voltage allows for about a 50 to 250 times faster turn off, that is collapse of the magnetic field in the solenoid coil.

 

[bigmoose]

Ok, if you have to replace with two discreets try the following: Use a Fairchild KSD1273 and a separate 60 v zener 1N5264 and you should be fine. Sample/buy from Fairchild; or Mouser stocks them. Mind the pinouts it is not a direct pin out replacement. The KSD1273 is base collector emitter yours is emitter collector base; so mind the pinouts carefully. This should work for you. Perhaps others have suggestions/refinements for you.

Good luck.