phantom voltage multiplier

[cloudhopper]

I'm wanting to put higher voltage on a mic diaphragm as well as provide ability to center supply for figure of 8 pattern on dual diaphragm mics. Will this circuit work? What transistors would you suggest? I know the final output side current draw is almost negligible but how do I calculate the losses to determine supply current draw?

[bob91343]

Obviously the base resistors will have 96 V so that gives the loss in the base resistors. The loss in the transistors will be small. The transformer core is really the unknown. I assume, due to the lack of a resonating capacitor, you are relying on saturation of the core to determine frequency. So that is the main unknown.

Incidentally, you offer no protection for the reverse voltage on the bases, so they will break down when that side goes negative. You should do something about that.

[cloudhopper]

Originally Posted by bob91343

Obviously the base resistors will have 96 V so that gives the loss in the base resistors. The loss in the transistors will be small. The transformer core is really the unknown. I assume, due to the lack of a resonating capacitor, you are relying on saturation of the core to determine frequency. So that is the main unknown.

Yes, the transformer saturation would determine the frequency, how would a resonating cap be tied into the circuit?

Originally Posted by bob91343

Incidentally, you offer no protection for the reverse voltage on the bases, so they will break down when that side goes negative. You should do something about that.

Would the diodes solve that? I changed the resistors to 47K because 10K would suck too much current. Also, how do you figure 96V on the resistor with a 48V supply?

[bob91343]

When the left hand transistor conducts and the left side of the winding is thus grounded, the right side, due to transformer action, will soar to double the supply voltage, or 96 V.

The diodes are in the wrong place. They should be in anti parallel with the base-emitter junctions. A resonating capacitor would be across the winding.

Frankly, this is not a circuit for the casual designer. Many years ago I designed many like it and you need a square loop core material to minimize losses and help define the square waveform. So the best would be to wind your own. You may need speedup capacitors across the base resistors. Furthermore, the transistors experience high voltage in the off state and must be capable of withstanding that.

Perhaps you should reconsider and use a Colpitts or Hartley oscillator. Or even a relaxation oscillator (flyback).

[cloudhopper]

Originally Posted by bob91343

Perhaps you should reconsider and use a Colpitts or Hartley oscillator. Or even a relaxation oscillator (flyback).

can you point me to a book or article that discusses this? The high voltage current draw is so tiny but I want the voltage in the 150V or so range. And I don't have much 48V current to start with.

[cloudhopper]

I don't really care what the frequency or waveform looks like so long as it rectifies to clean dc when I'm all done. Also, since the secondary current draw is so tiny, I can live with some inefficiencies.

[bob91343]

Just Google the terms. Or consult any basic electronics textbook. These are classic circuits and have been around since before I was born, and I am old. Originally of course they used tubes but all the rules apply to solid state.

A flyback circuit is often used for photoflash use. And you will find them in modern switching power supplies as well.

I also suggest you operate above the audio range or you may find the noise will get into your system. And will radiate to other circuits, so it should be carefully filtered and shielded. You show no filtering on the primary side, but it's important.

[cloudhopper]

Originally Posted by bob91343

Just Google the terms. Or consult any basic electronics textbook. These are classic circuits and have been around since before I was born, and I am old. Originally of course they used tubes but all the rules apply to solid state.

A flyback circuit is often used for photoflash use. And you will find them in modern switching power supplies as well.

I also suggest you operate above the audio range or you may find the noise will get into your system. And will radiate to other circuits, so it should be carefully filtered and shielded. You show no filtering on the primary side, but it's important.

I'm wanting to put this inside the mic body so it has to be small, you mention flyback but are there flyback transformers small enough and wound for about a 4X increase? How do I use a flyback in a manner that sets the frequency above 30kHz or so to be above audio? and how do I filter and shield this from the rest of the 48V circuit?

Maybe I'm dreaming thinking I can accomplish this feat but I'm sure there are usb mics that do something simliar.

[scott wurcer]

Are there any USB mics with externally polarized capsules? The files section at the Yahoo micbuilders group has several schematics some from commercial mics.

[cloudhopper]

Originally Posted by scott wurcer

Are there any USB mics with externally polarized capsules? The files section at the Yahoo micbuilders group has several schematics some from commercial mics.

Here's several that are usb with externally polarized capsules.

USB Mics | Sweetwater.com