So it appears this is not a mains transformer, but a push-pull amplifier driver.
What Wattage?
They are available on Digiky from $8 to $30,

 

That's the weirdest inverter circuit.. the BASE of the transistors connected to the transformer and the COLLECTORs cross-coupled with 1k resistors??? WTF?? Surely thats the wrong way round?

Notwithstanding that, and the lack of a CT, I guess this is meant to self-oscillate. Surprisingly it seems, redrawn correctly, it might just work. A 9v battery will last a few minutes, unless it outlives the transistors which are on the edge of their power rating. I've used some typical resistance and inductance values for a 30w power transformer as spec'd in post #1, but the efficiency is rubbish as the oscillation is far too high a frequency (100kHz).

A H-bridge of course wouldn't self-oscillate so is far more complex.

 

You can try this variant of circuit:

 

That's the weirdest inverter circuit.. the BASE of the transistors connected to the transformer and the COLLECTORs cross-coupled with 1k resistors??? WTF?? Surely thats the wrong way round?

I think the transistors circuit should be like this -- Fig. 2 Transistor-transformer oscillator circuit produces 480 volts.

 

I thought the reason you used a center tap was to reverse the direction of the field in the core to prevent it saturating. I don’t see how using two transformers this way does that. Wouldn’t both transformers see a field in only one direction?

Edit to add: A bridged circuit would reverse the field.

Hello there,

That's a good observation. The center tap allows use of just two transistors, but i question the practicality of that anyway.
The reason is that one of the two windings is only being used half of the time, which seems like a waste of copper. Of course the wire thickness can be thinner so maybe that makes up for it. Most of the higher power converters though do not use center taps they use an H bridge.
The other problem with a center tap is that when one transistor is 'on', the other winding end is at 2 times the power buss level. For a power buss of 200 volts that means one end of the other winding is at 400 volts, which means transistors that can support two times the DC buss supply voltage. That in turn places more limitations on the transistors which may be too much to deal with.

 

You can try this variant of circuit:
View attachment 273524

Hi,

One thought comes to mind. DId you check the peak current in the transistor collectors?
I dont know offhand if it is too high but worth a check as transistors turn on faster than they turn off and power supply punch through is always a concern.

 

Hi,

One thought comes to mind. DId you check the peak current in the transistor collectors?
I dont know offhand if it is too high but worth a check as transistors turn on faster than they turn off and power supply punch through is always a concern

Hi,
Yes, I did.
Diagrams below are identical for all 4 transistors, only polarity of pulses for top 2 transistors is reverse.



With choke 48 μH, connected in series with V1, pulses look like:

 

The

That's the weirdest inverter circuit.. the BASE of the transistors connected to the transformer and the COLLECTORs cross-coupled with 1k resistors??? WTF?? Surely thats the wrong way round?

Notwithstanding that, and the lack of a CT, I guess this is meant to self-oscillate. Surprisingly it seems, redrawn correctly, it might just work. A 9v battery will last a few minutes, unless it outlives the transistors which are on the edge of their power rating. I've used some typical resistance and inductance values for a 30w power transformer as spec'd in post #1, but the efficiency is rubbish as the oscillation is far too high a frequency (100kHz).

A H-bridge of course wouldn't self-oscillate so is far more complex.

View attachment 273483

Resistor is 330 ohm

 

Using two identical step down transformers it would look like this.
View attachment 273469

Keep in mind when making inverters like this your output waveform is not a nice clean sine wave. You will get a square wave shape or MSW (Modified Sine Wave). The signal driving the transformer will also be a square wave which your transformer needs to work with much as your load needs to work with. The driver circuit determines the frequency. You mention a 9 volt battery. Depending on load a 9 volt PP3 type alkaline battery will be very short lived. You make no mention of anticipated load current? All of this would go much better with everything well defined.

With a single transformer it simply will not work out and using two they should be identical.

Ron

Thanks

Do you mean identical transformer? I have 2 15v transforms can I use it?

 

T

What is the Voltage Rating of your Transformer Primary, and Secondary Windings ?
Are You using the Transformer "backwards" to create a much higher AC Voltage ?
.
.
.

Transformer input 240v that primary and the output is 15v 2amp secondary

 

Greinacher circuit or Villard circuit.

Any schematic?

 

Can

I thought the reason you used a center tap was to reverse the direction of the field in the core to prevent it saturating. I don’t see how using two transformers this way does that. Wouldn’t both transformers see a field in only one direction?

Edit to add: A bridged circuit would reverse the field.

Can you please support with schematic?

 

Hi,
Yes, I did.
Diagrams below are identical for all 4 transistors, only polarity of pulses for top 2 transistors is reverse.

View attachment 273530
View attachment 273535
With choke 48 μH, connected in series with V1, pulses look like:
View attachment 273539

Hello again,

You may have to zoom in on those current peaks to see the true value of the peak.
If this is a scope output you can check the power supply to see if it drops down at the same time.
If this is a simulation, you can check the current out of the power source or even place a small resistor in series and check for a voltage drop that coincides with the current peaks.

 

Thanks

Do you mean identical transformer? I have 2 15v transforms can I use it?

In a word yes.

Ron

 

Two transformers works, but either the primary or the secondary of one must be phase-reversed to the other - note dots on windings - here primary is reversed, secondary in phase.: (NB base resistors reduced to 330R)

 

One more circuit with 2 transformers:

If this is a simulation, you can check the current out of the power source

Power supply current (circuit in post #23):

 

@Danko - the transformers you've used, are those actual figures from a power transformer datasheet; if not how did you get to them?

 

@Danko - the transformers you've used, are those actual figures from a power transformer datasheet; if not how did you get to them?

Sixty years in electronics field.
Calculating and fabricating circuits and parts.
So now brain somehow automatically finds appropriate values,
which sometimes need small adjustment only.

 

Sixty years in electronics field.
Calculating and fabricating circuits and parts.
So now brain somehow automatically finds appropriate values,
which sometimes need small adjustment only.

Understood... just seemed a little low on inductance for iron-core power transformer... and I note no series resistance which can have a significant effect.

 

@Danko - the transformers you've used, are those actual figures from a power transformer datasheet; if not how did you get to them?

Hi there,

I am not sure how he decided to do it, but normally the primary would depend on the frequency such that the core does not saturate near the end of the longest pulse.
The secondary uses the turns ratio based on inductance rather than actual turns such as Vout/Vin=sqrt(Ls)/sqrt(Lp).