Transistor booster design

Remember them? Hell, they are still being made and sold for antique car radio repair & restorations.

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Reply to
Michael A. Terrell
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Here you go, a "real" manufactured IC...

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Note the date ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Yeah, that's practical...

Reply to
Fred Bloggs

It was in most calculators of that era... display power.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

This is the one. He is too busy criticizing me than to look at the circuit.

Reply to
linnix

And manufactured right. I have to check into making small enough transformer. Using 80% 1000uH:10uH mutual inductors, the model is at:

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It takes longer to reach the target voltage, but I guess that's OK. I had to limit the spice run to 20 ms.

Reply to
linnix

I saw it, but it's still lacking.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Unless great care is employed, this circuit is also known as an EMI source. It is unlikely a circuit requiring magnetics is going to be cost competitive with an RC-relaxation oscillator anyway. There is also the interaction with the finite and possibly large battery impedance when the transistor current spikes that may introduce yet another unpleasant surprise unless you hunk it down with a hefty cap incurring even more expense.

Reply to
Fred Bloggs

And then larger inductor/transformer to charge it. Otherwise, it takes a long time to startup. Also, the output has very sharp corners, I guess that's where the EMI come from. See:

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Reply to
linnix

Engineers should always employ great care.

Any efficient flyback converter will generate EMI.

How are you going to make a flyback converter without magnetics?

There is also the

So draw us a boost converter that has no current spikes.

John

Reply to
John Larkin

Looks like the oscillation frequency is very low. Try reducing the base cap.

On reflection, it would probably be best to ground the emitter and put the feedback winding from the R-C to the base, with maybe a bit of series resistance.

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Blocking oscillators are analytically a bit tricky. Very tricky, actually... there's a lot going on.

John

Reply to
John Larkin

I liked your tinylogic circuit - but I think linnix wants to do it just with discrete semis and an inductor. I suppose transistors are

*very* cheap.

I wonder is there a better 2-transistor circuit?

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John Devereux
Reply to
John Devereux

Main problem is building the additional CMOS Schmitt trigger cell. Transistors are cheap, but additional processes are expensive.

Reply to
linnix

Doesn't this have the same problem with driving the base negative?

Reply to
linnix

It's part of a chip? I had not realised that! I don't know anything about chip design, but I would think you need to be even more careful to avoid e.g. latchup. Are your passive parts external?

I'm still wondering...

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John Devereux
Reply to
John Devereux

While the transistor is on, the + end of the feedback winding drives the base, and the - end sucks current out of the timing capacitor, which charges negatively. When the transformer saturates, the base drive dies, the collector kicks up, and the base voltage spikes down, a combination of the negative cap voltage and the reversed drive from the transformer winding. That shouldn't zener the transistor, so the transformer turns ratio needs to be high. But we don't need a lot of base drive, so a high ratio is OK... maybe a volt peak or less would work. The requirement to not zener the transistor could be a constraint at high flyback ratios, 5:1 or so roughly. One could add a series diode to protect the base, but that's cheating.

After a pulse, the base will be negative and it won't fire again until the resistor recharges the cap.

I *said* it was tricky. Its combination of simplicity and complexity is sort of nice.

John

Reply to
John Larkin

booster

It's also very cheap, very reliable, and highly efficient. Not much to not like, except the original design struggle, and the special transformers that sometimes result.

Reply to
Winfield Hill

Maybe something like this?

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Reply to
Tolstoy

It will be regulated and enabled by a micro. If the micro does not see oscillations (rising output), it can toggle the common emitter junction. This by itself should create enough impulses to start it. It only requires 15V for 30 to 60 seconds, then off for a few minutes.

So far, it does not seem to have problem starting by itself. The problem is drawing more than 4mA from the batteries.

Yes, hard to put big L & C inside.

Reply to
linnix

Any ordinary PWM controlled boost converter has no spikes, the current drawn from the supply is triangular, possibly more like sawtooth for high boost ratios. The blocking oscillator is a different animal. When the transformer goes into saturation, the transistor collector current skyrockets as an exponential with positive time constant, and because it was saturated with a good amount of excess base charge, this current can attain very large magnitudes. And all this is occurring while Vce is making a very fast step transition from Vce,sat to Vcc. This is not a good picture, current spikes and dV/dt going into the millimeter wave region. And I don't think you can reliably design one at more than

100KHz. Any old PWM boost is easily taken to 500KHz, that shrinks the V-us requirement on the T1 magnetizing inductance considerably, but not entirely in proportion because of the increased hysteresis losses. You will be using something like a 250V-us part for your blocking oscillator.
Reply to
Fred Bloggs

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