Transformer for CDI.

[abuhafss]

I am building a DC-CDI.

For 12V-300V DC convertor, I am considering to use ferrite bobbin to make the transformer.

Primary 15 turns of 0.5mm wire
Secondary 400 turns of 0.2mm wire

Is it okay to use it with 555 oscillator + MOSFET (at about 2kHz)?

 

[schmitt trigger]

2 Khz is an order of magnitude lower than the lowest acceptable SMPS frequency. Use at minimum 20 Khz.

Additionally, that core you are holding, with its gigantic distributed air gap, is useful for inductors, but not for transformers. You need fully enclosed cores like EE or PQ cores to wind a transformer.

Lastly, your wire's diameter depends on the actual current that you require. And given that, you must ensure that all the required turns plus isolation fit within the core's window area.

 

[abuhafss]

I have made an EE transformer as per specs given in this link (in the last just before the videos).

**broken link removed**

It is supposed to be used in switch mode boost circuit based on UC3845 to convert 12V to about 350V.

Here is the schematic of the converter

**broken link removed**

Before using the transformer in UC3845 circuit, I tested it with 555 (astable oscillator at about 45kHz) and mosfet. The output is about 1100VAC. Just confused, if it will give 350V with UC3845.

And I should mention, I also made a transformer using ferrite bobbin as mentioned in my first post. That is also giving about 1100VAC with 555+mosfet.

 

[schmitt trigger]

"And I should mention, I also made a transformer using ferrite bobbin as mentioned in my first post. That is also giving about 1100VAC with 555+mosfet."

And how much current were you drawing when you made the measurement?

In a flyback converter, the transformer it is not a transformer per se, but a coupled inductor. With a minimal load, one can generate inordinate amounts of voltage. But under load, the total energy transfer by the inductor is limited by LI^2 and with an open-air core the inductance will be far lower than with a gapped EE core.

And...a 0.5mm wire will not carry several amps of current.

 

[abuhafss]

OBERSERVATIONS:

Input = 12.8V

EE Transformer
Output = 1000V approx.
Current drawn = 60.5mA
Mosfet = normal

Bobbin Transformer
Output > 1000V
Current drawn = 0.55A
Mosfet = Hot

My actual confusion is still there....will the EE transfer give about 350V with UC3845 as per schematic?