Help with Spice Model vs Real Life

Started by Unlikekurt, February 14, 2017, 11:26:14 AM

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Unlikekurt

Hello all,

This is basically a common emitter booster (a la LPB-1) but I wanted a fixed gain of much less for the stage I am working on so R1 is 1.5K and then in order to get the collector set at half supply I changed R3 and R4. 
I wanted to add an emitter follower to be able to drive the next stage.

I made a model in spice and i get the results I expected.  However, when i build the unit in real life the results differ greatly.
I still get the VAC output from Q1 that is expected, but the output from the emitter follower is wonky unless i increase the value of the emitter resistor substantially, say to around 33K. And even then the waveform doesn't seem quite sinusoidal.  it is worth noting that in spice I can even have RE as low as say 600R and it models fine.
Any advice or comment would be appreciated.
Thanks



PRR

#1
Re-re-check pinouts.

What is the difference between DC Voltages modeled and built?
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Gus

To add to what PRR posted try 2N2222 and the 2N5089 spice models in your sim, compare the sim voltages and real voltages
Is this built on a breadboard? if so check you wiring
Emitter followers can have stability issues
A link to something from 2012 that might be useful http://www.diystompboxes.com/smfforum/index.php?topic=99139.msg868712#msg868712


antonis

Sometimes, simulators may give some "unexceptable" results...

i.e. if you have a signal of, say, 500mV and a gain of 100 you may have on output a 50V measurement, despite of the +9V power supply..  :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

bool

Check your transistor pinouts and wiring for errors first.

If your transistor models have different betas than your real-life transistors, the biasing like the one you used can yield predictably unpredictable real-life results.

Once you sort out the "do's" and "donts" with simulations, you can get amazingly accurate results with LTspice. Takes a bit of a learning curve first.