Better transistor test jig for SPICE

Why not bias the emitter with a high resistance to a large negative voltage, like 2400 ohms and -12V? Hold the base at 0VDC, put in a healthy emitter bypass cap, and away you go.

On a sunny day (Mon, 31 Jan 2011 09:02:07 -0800) it happened "Joel Koltner" wrote in :

Nice. Many years ago when it was not busy, boss told me make something to measure transistors. I designed a nice curve tracer, pulsed, so you did not exceed Pmax. I used relays... And a lot of semi-conductors, a x y output for the scope, NPN PNP selector, potmeters, switches. Something like that could be added to this.

All that said: I only used it once or twice. And these days we have data-sheets, unless you are at the edge of what it can do, as J.Larkin sometimes does, there is not a really big need. And if there is, then every circuit is different.

Just feed the emitter with a current source, and maybe also bias the base with a rough 700mV so that the bias point is as close as possible to the real value.

Yep. That's the way to do it.

Bypass to ground goes below L1.

Or use an adjustable current source in the emitter path (below L1, and add some series R to the bypass cap). ...Jim Thompson

Hi Jan,

I have a kit for Tom Gootee's curve tracer

The problem with data sheets is that they can only give you plots of various parameters at a rather finite number of bias points. The next step up, of course, is the SPICE model... but even there, not all SPICE models will include, e.g., proper noise components, so you're sometimes still stuck with having to just measure the thing in the actual circuit.

---Joel

That does gets rid of one power supply:

...and I can see now where I want to go... here's one with just a constant current source:

It might be nice to be able to set the collector current rather than the emitter current in that one, but it's definitely a nice improvement over what I started with. That's probably about as good as it gets for "simple" approaches...

Thanks for the help,

---Joel

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

This is what I ended up with:

What's the series R to the bypass cap (C1) do? (Even in real circuits, I'll have an emitter resistor, but it's generally bypassed by just a single cap to ground.)

What DC bias do you normally keep your emitters at anyway when you're doing a

Thanks,

---Joel

To replicate the real circuit while testing.

I bias everything primarily via mirrors, which you can't economically afford. ...Jim Thompson

Joel Koltner a écrit :

If you really insist on having collector current set, then:

• measure base current (use a 0V or 0.7V voltage source)
• copy that into a voltage using a CCVS (H source)
• heavily filter that 1F/1K RC
• inject that current into the emitter, additionally to the (now) "collector current" current source...

Fred Bartoli a écrit :

... obviously using a VCCS (G source)

Hmm, I see. OK, definitely a bit too messy -- I'll live with setting emitter currents. :-)

I appreciate your knowledge here!

---Joel

Joel Koltner a écrit :

You can also, if you have a reasonable value for your transistor current gain, parametrize your current source:

.parameter beta=77 Ic=10m

Ie n1 n2 DC={Ic*(1+1/beta)}

do,

A similar assignment, but for linear pass element beta grading. T replace an old one that burned operator fingers.

RL

Hi Fred,

Hmm, good idea...

This is the final circuit:

The real thing performs within a dB or so of the simulation, which I'm rather impressed by -- Measured results:

What it looks like in real life:

While the circuit appears to function as designed, I'm all for suggestions as to how to improve its robustness.

---Joel

On a sunny day (Mon, 31 Jan 2011 16:04:18 -0500) it happened legg wrote in :

do,

Nice picture :-)

This might be interesting, bias point is selected with IC and VCE values:

I translated that into SPICE netlist -you need to replace alias with proper values-:

• Y11/YIE AND Y21/YFE CIRCUIT I10 11 10 AC 0.1M VAUX11 0 11 AC 0 V10 20 0 DC VCEVCE ; VCE VAUX10 20 30 DC 0 F10 0 40 VAUX10 1 ICSET10 40 0 DC ICICM ; IC R10 40 0 1MEG G10 0 10 40 0 1 G20 0 50 40 0 1 Q10 20 10 0 MODELNAME QTEST10 30 50 0 MODELNAME
• Y12/YRE AND Y22/YOE CIRCUIT VOUT1 1 2 AC 1 V1 2 0 DC VCEVCE ; VCE VAUX1 2 3 DC 0 QTEST1 1 4 0 MODELNAME Q2 3 5 0 MODELNAME F1 6 0 VAUX1 1 ICSET1 0 6 DC ICICM ; IC R1 6 0 1MEG E1 4 0 6 0 1 E2 5 0 6 0 1 .OP .SAVE ALL .AC DEC POINTS FMINMEG FMAXMEG .PRINT AC (I(VAUX11)/V(10)) (-I(V10)/V(10)) (-I(VOUT1)/V(1,2)) (-I(E1)/V(1,2)) .END

Best Regards, M. Emmanuel