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Has anyone built the 10W circuit with the xister and gotten it to work? I can't get the xister to fire. The designer says that it does not need the 470 ohm resistor. If not, he is getting 7.3 volts from ground. I would think it needed the resistor, and possibly more resistance to get the emitter to base bias. Any ideas? jim d

 

If you leave the resistor out, do not connect anything to the emitter except the load. Do not short the emitter to ground.

If you can't get it to work, connect your regulator up by itself and make sure you are getting voltage out of it.

If the regulator is working, then take the transistor and check it. Get a digital meter with a diode tester and hook the meter leads both ways from the emitter to the base. You should read a diode junction there. Same thing from the collector to the base. You should get a diode junction there. Then read across the collector and the emitter. You should get no continuity there.

Make sure whatever you have the power transistor mounted too, is not grounded, since the case of the transistor is the collector. If you have both the regulator and the transistor mounted to the same metal heatsink, one of them has to be insulated from the metal, since the case of the regulator is ground, and the case of the transistor is the collector(+ voltage).

P.S. I am going from memory that the reg case is ground. Double check that with a meter, since my memory is not what it used to be.

 

I have already done all of that except leaving the emitter open. The regulator is working properly, the xister is not shorted or open. I will try using the emitter for load without the resistor. Thanks for your help. jim d

 

Keep the resistor in . Do you have that exact trans? Its prob bad. Make sure its an NPN.

Dick

 

it could also be a bad or reversed diode on the base of the transistor check the band on the diode and make sure the band is toward the regulator can you tell me if there i about 7 volts on the base of the transistor? Check both side of the diode for voltage the transistor side of the diode should about .6 volts lower than the regulator side of the diode

I hope this helps
Mountaineer man

 

No, than band on the diode is the cathode, and should be towards the base of the NPN. If it is towards the regulator, it will not supply any base current to turn the NPN on. The transistor circuit is a simple emitter follower, where the emitter voltage is a Vbe below the base voltage....A better solution would be to use a NFET, in the source follower configuration, instead of a NPN transistor. Therefore, you could replace the regulator with a simple resistor voltage divider (or a pot) to set the output voltage. This is because the gate of the FET does not draw any current....

 

PM or e-mail me and I can send you some material explaining how transistors operate.

 

I know how transistors operate, and IC's, and diodes, and resistors, and capacitors, and coils, etc. That wasn't my original question. My question was, has anyone gotten this particular circuit to work. I have been in electronics for over 35 years, not design, but repair. Don't worry with it, I will get it to work when I find the time. jd

 

Ah....the difference between an engineer, and a technician......

 

I don't know what you mean by that, but I have a good idea. Wouldn't it be nice if we could all be as smart as you are?

We had a problem with a new design one time, so two "engineers" from the factory came to show us dumb *** technicians how it was done. When they left, we had two burned up scopes, a couple meters with melted tips, and no repair. After the "engineers" went back to their engineering, a couple of us got together and completed the repair. Because of this, the engineering dept saw that the difference between designing a product and restoring it to useful operation after it fails is night and day. Procedures were changed because of it.

Almost every engineer I have ever met is so wrapped up in him/herself they think they are natures gift to mankind, but most never progress past being an "engineer."

And by the way, Engineer Bob, my job title included the word engineer, so don't be so quick to pass judgement, and just because one carries the engineer designation behind ones name doesn't automatically elevate his status to that of genius. jd

 

The fact that you have to "WORK" on that simple circuit to get it to work doesn't say much for your technical abilities.....You probably have the emitter and base swapped, a common mistake the inexperienced make with the T03 transistor case.....

 

Wrong again, Bob, on all counts, as you usually are. I got your ****ty PM, so I'll just leave it at that. And Bob, please don't try to help me anymore. You're not very good at it. If I want your advice, I will ask. jd