Reversed B-E junctions will not support -40V. They break over around -5v to -7v. Therefore, I think this is a simulation artifact.

Yes, simulators do no always model breakdown or other voltage limits.
In doing a simulation, one always needs to look at the simulation voltages to make sure none are in excess of the devices' ratings (especially when inductors or transformers are involved).

 

Reversed B-E junctions will not support -40V. They break over around -5v to -7v. Therefore, I think this is a simulation artifact.

Bordodynov is generally a brilliant designer, but his addition of B-E diodes is contrary to using reverse current to decrease switching time to the "off" condition as described by DickCappels. I didn't say this is good or bad, I just said that's how it's going to work.

Hi,

Not sure what you mean about "not supporting -40v".
What i was suggesting is that because the voltage is being generated it will blow out the transistor. It may not actually get that high because the transistor will blow out, but then who wants that to be what limits the voltage

Right, -5v would be a maximum after that the transistor could be destroyed. Once destroyed the voltage wont be there anymore because the whole circuit stops functioning.

 

Not sure what you mean about "not supporting -40v".

Trying to clarify my use of words:
The reverse breakdown voltage of a bipolar transistor's B-E junction resembles a zener diode. When I say that the reverse biased B-E junction "won't support" 40 volts, it's like saying a 5.1V zener diode won't support 20V or 30V unless you apply extremely more than its acceptable current range, a range of current that will destroy the junction immediately. The non-destructive application of this function was described in post #10 by DickCappels.

Reversed B-E junctions are tested for their zener voltage (in the factory where they are made) with a small current, they are used for white noise generators in reverse breakdown mode. The only thing left to discuss is how much current is not destructive.

 

Sorry, got interrupted by the telephone.

What i was suggesting is that because the voltage is being generated it will blow out the transistor.

The B-E junction does not get destroyed simply because it is used in Zener mode. Refer to post #10 by DickCappels. This has been explored, measured, and the side effects defined.

 

LTspice allows you to simulate the breakdown voltages. In this case, do:
.model npn npn bvbe=7
I did it once I saw this circuit.
Look at the base currents.

 

I took particular transistors. Add another resistor for better closing.See

 

Sorry, got interrupted by the telephone.


The B-E junction does not get destroyed simply because it is used in Zener mode. Refer to post #10 by DickCappels. This has been explored, measured, and the side effects defined.

Hi again,

What you seem to be suggesting is that we can apply any reverse voltage bias we want to apply and nothing too bad is going to happen to the transistor. I think what you should be saying is that under certain restrained conditions the transistor will only undergo small changes that dont matter to any circuit we are dealing with at present.

Now with that in mind, think about what would happen if we took a regular 5v zener diode connected in series with a 1k resistor and connected that to a 12v car battery. The voltage across the zener would be close to 5v and the voltage across the resistor about 7v (or so) so the current through the zener and resistor would be about 7ma (7.1000 of course). No problem.
Now reduce that resistor to ZERO ohms, connect it back up to the 12v car battery with a knife switch but stand back. What happens to the zener diode? Does it:
A. Write a letter to Congress expressing it's concern over high currents, or
B. Burn up due to over powering


Sure, if you limit the current a zener wont blow out, which i believe is common knowledge. But without some form of current limit it's gone never to return again as a zener.

My actual first hand experience with this has been that the gain may change but also the high frequency response may suffer. That tells me though that some sort of internal damage has occurred and that is not something i like to allow.
A typical unintended test of this is when someone accidentally reverses the emitter and collector leads of a transistor when either soldering into a circuit or plugging into a transistor socket (like the To92 size). The higher +Vcc reverse biases the base emitter when the power is turned on. On power up, the transistor obviously does not work, but once the leads are rearranged back to normal the transistor does not work the same again anyway which indicates that something went wrong with the transistor.

If you could find the paper that was suggesting that we could reverse the voltage to a higher level, that would be good as then we could figure out the operating conditions. However, there's no way they are going to tell me that they connected a base emitter to the secondary of a transformer that puts out plus and minus 40 volts and the transistor survived without serious damage.

Are we dealing with a special case here? Well, Electrician reminded us that the coupling will not be exactly a perfect 1.00 so with that in mind if the coupling is very low then perhaps the current can be limited, but you know what that means now too, that the voltage is limited due to the zener action. But if that 'zener' blows out, it's all over.

Make sense to you?

 

What you seem to be suggesting is that we can apply any reverse voltage bias we want to apply and nothing too bad is going to happen to the transistor.

You can only get a zener (or a reverse biased B-E junction) to break-over at its break-over voltage unless you damage it. You can apply any voltage you want to, as long as you limit the current, at which point the zener will support its labeled voltage.

if you limit the current a zener wont blow out, which i believe is common knowledge. But without some form of current limit it's gone never to return again as a zener.

That's exactly what I said. So why are you still discussing it? Do you think you're educating me?

If you could find the paper that was suggesting that we could reverse the voltage to a higher level,

You can't reverse a zener to any voltage except its inherent break-over voltage without damaging it. Why do you think I should search for some intellectual work to contradict that?

 

You can only get a zener (or a reverse biased B-E junction) to break-over at its break-over voltage unless you damage it. You can apply any voltage you want to, as long as you limit the current, at which point the zener will support its labeled voltage.


That's exactly what I said. So why are you still discussing it? Do you think you're educating me?

You can't reverse a zener to any voltage except its inherent break-over voltage without damaging it. Why do you think I should search for some intellectual work to contradict that?

Hello there,

I am just stating some facts that i happen to know, and if you agree that's just fine, and if you dont, we can discuss it more if you like.

Am i wrong in assuming that the context of this whole discussion is the circuit we have been talking about all along? I have stated things that apply to THIS circuit, not any other circuit. What i was suggesting was that you are referring to zeners in general and although what you say is certainly true, it does not apply to this circuit. That actually had me wondering why you even brought this up.
If the circuit we are dealing with has no current limiting in the reverse mode, it doesnt make that much sense to discuss it. If you go back and read my posts again i think you'll see why i said what i did.

I was asking for the paper so that we can investigate what conditions were present when they made such statements. It sounded interesting if not anything else. Apparently though they were limiting the current so no big deal i guess.

So let me restate my position on this:
1. I agree that limiting the zener current will prevent a zener from blowing out (after all, who would not agree with this).
2. I do not see this action being a factor in this circuit, unless we purposely add it, although if we were to modify it then there are certainly other things to think about too. The circuit as is however has no such protection.
3. I appreciate your interest in this and other topics like this.

 

That actually had me wondering why you even brought this up.

I didn't bring it up. Aleph did that in post #4. Go educate her.

I am just stating some facts that i happen to know, and if you agree that's just fine,

If these are just random thoughts, quit quoting me. It looks like you're talking to me when you do that. There is also a blog space provided for you on AAC.

What i was suggesting was that you are referring to zeners in general and although what you say is certainly true, it does not apply to this circuit.

Yes it does. Read the Thread to see how many people worked out that the B-E junctions are being reverse biased and this can be demonstrated in a simulation as revealed by Bordodynov in post #25.

I do not see this action being a factor in this circuit,

Look at the simulations in posts #9 and #26

I appreciate your interest in this and other topics like this.

I would appreciate your interest if you read and understood the Thread first.

 

I didn't bring it up. Aleph did that in post #4. Go educate her.

Apparently your attitude has turned negative therefore i have nothing else to say to you except that you somehow can not just answer a question you have to insinuate a backdrop of some kind. If you cant find your way to discuss things without copping an attitude then goodbye.

 

Aleph! Please carefully read @OBW0549 's reply! -- He's stating that current from V1 (via R2) forward biases the B-E junction of either Q3 or Q4 dependent upon the induced 'electrical state' of L6 --- An analysis with which, BTW, I wholeheartedly agree

I'm not sure what you mean by "provides the ground reference

HP it's all good! @OBW0549 Tnx! I've got it now!

@Aleph(0)

Here's an experiment for you:

Physically connect the circuit as shown in post #1 but with the following changes:

1) Remove R2.
2) Tie the base of Q3 to the V1 rail with a 2.2 kΩ resistor.
3) Tie the base of Q4 to the V1 rail with a 2.2 kΩ resistor.
4) Account for circuit behavior and reconcile same with LtSpice.
5) Repeat 2, 3 and 4 above but with 1kΩ and 470Ω resistors...

HP as far as I can tell, simulation with two resistors is nearly the same as with the equivalent pullup resistance at just a single base. So 1k from each base gives same simulation result as 470Ω (ideally 500Ω) resistor from just one base. I'll try experiment with real circuit this weekend So if simulation is right I say that just means induced negative excursion _over powers_ pullup on negative end?

View attachment 115443 Why rape transistors. You can put the 3 elements.
See:

Bordodynov sry cuz of language barrier cuz I don't understand In North American English you are asking why I am molesting the transistors! So that doesn't make sense but I guess you are actually saying circuit shouldn't electrically abuse transistors? So that was my question too but look on posts of @#12 and @crutschow so junction is self protecting like _avalanche rated_ diode Also plz remember that I tried external b-e diodes and they hurt circuit efficiency. Tnx for reply

Are you saying that you have one actually bread boarded and up and running?

MrAl that's right cuz we'd never trust simulator for new design! Just for studying existing circuits and then only with a grain of salt cuz it doesn't get more real than reality

In the real life unit you can check the efficiency of course, which will tell all.
You can check for one transistor getting hotter than the other.

MrAl That's right! I use two IR thermometers to make sure transistors stay within 2°C on separate heat sinks.

First, if the output is 50kv and the load 100megs the output current is around 500ua and with a turns ratio of around 600 that means about 0.3 amps on the primary. However, with 1N914 (or equivalent) diodes on the output the current is going to be MUCH higher because the diodes will conduct too much in reverse mode as they are only rated for around 75 volts reverse.

MrAl I'm sry for like just assuming everyone on here has followed all our posts So anyhow appropriate semiconductors give totally bogus simulation So HP just humors Ltspice with semis that give faithful results but uses appropriate components in real life circuit. So in the real circuit, diodes in Delon rectifier stage are just 3 series connected 2CLG30kv/20ma rectifiers on each side. FYI here's pic of low power royer circuit which is what circuit of this thread is based on so you can see HP's notes

Reversed B-E junctions will not support -40V. They break over around -5v to -7v. Therefore, I think this is a simulation artifact.

#12 You're right cuz scope agrees!

What you seem to be suggesting is that we can apply any reverse voltage bias we want to apply and nothing too bad is going to happen to the transistor.

MrAl All I can say is circuit ran all night (10 hrs really) and no shift in BJT parameters so current must be ok?

 

I took particular transistors. Add another resistor for better closing.See
View attachment 115487

Bordodynov Tnx! I can breadboard circuit this weekend!

 

you somehow can not just answer a question

I didn't see you asking a question. I saw you pretending I said something which I did not say, being wrong about how the circuit works, and asking me to document a false premise.

goodbye.

Finally!

 

I feel an urge to thank Bordodynov and crutschow for the simulations. Those two guys keep me fascinated!
Yesterday, they were doing a fast, totem pole, mosfet driver. Every bit as interesting as this Royer oscillator.

 

HP as far as I can tell, simulation with two resistors is nearly the same as with the equivalent pullup resistance at just a single base. So 1k from each base gives same simulation result as 470Ω (ideally 500Ω) resistor from just one base.

That's exactly what I'd expect, since your feedback winding L6 is only a couple of turns of AWG 18 wire, with negligible resistance-- a few milliohms, at most. So with respect to DC, the two bases are effectively shorted together and thus no asymmetry in their drive levels.

As for negative voltage coming from L6 to the base of the OFF transistor, I suspect it's leakage inductance that is limiting the current to a safe value and allowing the b-e junction to simply clamp the negative voltage at whatever the junction's Zener voltage is. With tighter coupling between L6 and the L5/L7 primary I suppose there could be a problem with overheating and thus damage, but not in this case. As you said, the circuit works.

(It's been 20-30 years since I last read up on this subject, but my recollection is that the main effect of allowing BJT base-emitter junction breakdown is to cause a reduction in beta at low currents, and to increase the transistor's noise voltage. Obviously not very relevant in this circuit.)

 

In North American English you are asking why I am molesting the transistors! So that doesn't make sense...

@Aleph(0) ...and I would say that depends upon how many drinks you had prior to casting your licentious regard upon those 'macho' TO3s

TTFN
HP

 

Bordodynov sry cuz of language barrier cuz I don't understand In North American English you are asking why I am molesting the transistors!

and I would say that depends upon how many drinks you had

Around here, it is commonplace to, "rape" a car or appliance for parts.
Raping a transistor isn't far fetched compared to what we do for scrap metal.
Our behavior is more like recycling, but the cars and appliances don't feel that way.

http://www.dictionary.com/browse/rape?s=t

3) an act of plunder, violent seizure, or abuse; despoliation; violation:
the rape of the countryside.

6) to plunder (a place); despoil:
The logging operation raped a wide tract of forest without regard for the environmental impact of their harvesting practices.

 

Around here, it is commonplace to, "rape" a car or appliance for parts.
Raping a transistor isn't far fetched compared to what we do for scrap metal.

I'll take your word for it -- Though I daresay such usage risks denouncement as a paraphiliac (an 'OS' for the 'politic' crowd) 'round here!

TTFN
HP

 

Around here, it is commonplace to, "rape" a car

#12 That sounds like dude in this song So I know it takes all kinds to make world but I say falling in lust with a car can lead to embarrassing injuries!