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Re:Transistors discussion

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Wow, the AD149 brings fond memories. It was the 1st TO3 transistor that I have ever seen! Without wading through Google, I have a Philips 1969 transistor databook beside me (Philips was my 1st job), and that PNP germanium transistor's base-emitter junction did not avalanch (but the transistor sure leaked a lot).
Your shaver's inverter probably used un-polarized "colour-striped" caps since it probably ran at a frequency high enough that electrolytics (did you also call them elcos?) were not needed. My Philishaver's universal motor runs on anything, any frequency AC or DC.
The inverter's cap polarity should be obvious.

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In those days, few people except you and me knew much about transistor circuits! Those Philips engineers just didn't know, so uni-polar was chosen.
For the capacitors in this project, most of the time the collector-side of the capacitor is positive:
1) During its charging when the collector is near +24V (center-tapped transformer action) and the other end of the capacitor is at about +1V (forward-biased base of the other transistor). Notice that there is little current-limiting here.
2) During most of its discharging, when the collector is at about +0.5V, and the other end of the capacitor is at about -7V (avalanching base-emitter junction of the other transistor) (again, little current-limiting), then the capacitor continues discharging into its resistor.
3) With the collector still at about +0.5V, the other end of the capacitor rises to about +0.7V when the base of the other transistor becomes forward-biased and that transistor turns-on.
So the capacitor gets only about 0.2V of reverse-polarity, for only a moment.
Any capacitor can withstand a reverse-polarity of only 0.2V for a moment. Few, if any, capacitors can withstand a reverse-polarity of 23V with a very high charge current, nor continuing charge/discharge high currents.

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In those days, few people except you and me knew much about transistor circuits! Those Philips engineers just didn't know

You seem to give yourself quite a lot of credit. I find it hard to believe.
Perhaps you could get a job with Phillips and teach them a few things... ::)

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Credit? Of course I'm proud of myself.
Philips? While they were showing to me their top-secret audio-cassette and LED, I was teaching them about transistors. Been there, done that:

(Philips was my 1st job)

Job? I'm playing with "Freedom 55" now, plus a little consulting on the side.
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Here is a link to an article on transistor history. It is very interesting.


Actually, I think there were quite a few who knew quite a lot about transistors since it's development in the late 1940s.


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Hey! Who started this topic here and put my name on it?
But let's continue without locking nor deletions:

1) The author's web-site's forum has 5 pages of complaints about this project with all-kinds of capacitors (tantalum, elecrolytic, non-polar) blowing-up.
2) One that didn't blow-up complained that its output was only 37W.
3) There was only one who claims to have success with this project:
Re:"Power?" Inverter

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Output Transistors in Square-wave Inverter Circuits:

1) How much current must be drawn from a 12V battery to produce 300W output from a square-wave inverter circuit?

Well, you need to draw at least 300W, plus some more to account for losses such as transistor saturation voltage-loss (which produces heat) and transformer wire resistance. So let's assume that the losses are 10%. But since the 12V battery actually measures 13.2V, which is also 10% higher, then we can ignor the losses since they cancel the extra battery voltage.

Since Power = Voltage X Current, then the current from the 12V battery must be 25A.

2) How much current must the transistors conduct?

Each output transistor must conduct that 25A, alternating back and forth into the center-tapped transformer winding.

3) Can 2N3055 transistors be used?

No, unless they are paralleled (matched, or with emitter resistors to equalize variations of their current gain). The 2N3055 transistor has a maximum collecter current rating of 15A. But it has a guaranteed minimum current gain of only 5 with 10A of collector current, and even less current gain (not specified) at a higher collector current.
If we parallel two 2N3055 transistors and operate them with 10A of collector current each, then the current sum is only 20A, which is still not enough.
But since the current gain could be 5, the bases current will be 4A, which we can add to the transformer winding if we use a darlington configuration for driver transistors. Now the total current will be 24A, which is close to the 25A required.
So the original 2-transistor inverter must have at least 6 transistors. (to be continued)

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