I'm looking for this type of transformer. I hope the winding ratio of pri and sec is 1:100 or more. I searched with the feedback transformer keyword, but I couldn't find a suitable part. I don't know which keyword is appropriate to googling. Could you give me an advise in detail??

 

I'm going to use that transformer in the circuit below.

 

I searched for “high voltage transformer with feedback winding” and got results which I didn’t pursue very far but here’s one I looked at because I know the company, a rather odd one. I think they said they can do custom windings but they may have something off-the-shelf.

 

You’ll find a transformer like that if you search for “flyback transformer”, but as you want some unusual output voltage (you’ll find 5V and 12V off the shelf) you will have to wind it yourself.
There are so many good, cheap drivers ICs these days that the blocking oscillator is well past its sell-by date, and using a bipolar transistor in a switching power supply is distinctly 1990s.

 

On the face of it, that setup will not oscillate.
The feedback winding terminals should be interchanged, or, the phasing of the windings should be properly marked.

 

Post #2 shows a simplified schematic.
Go to the link in post #3 and look at the data sheets. See the schematics! These are more likely to work.

If it is on the internet, it is most likely is not true. (this comment for example)
Schematics on the internet do not work. Schematics in data sheets mostly do work.

 

You’ll find a transformer like that if you search for “flyback transformer”, but as you want some unusual output voltage (you’ll find 5V and 12V off the shelf) you will have to wind it yourself.
There are so many good, cheap drivers ICs these days that the blocking oscillator is well past its sell-by date, and using a bipolar transistor in a switching power supply is distinctly 1990s.

Then, could you recommend a good way to make 1kV to 2kV output with 5V DC input?

 

Then, could you recommend a good way to make 1kV to 2kV output with 5V DC input?

This is not an easy or trivial task. The power levels we are talking about can be lethal. You are talking about constructing a transformer with a turns ratio with each turn of the primary needing 200 turns on the secondary. With a 1mH primary, the secondary will have an inductance of 40 Henries, which I consider to be an impossible requirement. In addition the output current will be a great deal less than the input current. The defining principle here is that the power out must be less than the power in. I think this is a pipe dream unless you can come up with more information about your actual requirements. Even if we get past that hurdle you will be better off buying an HV supply for your needs. Building your own is just not practical.

A more reasonable goal might be 1KV@25 mA = 25 Watts
I don't think a 5V@5A input supply would be a great choice, more like ±12@1.5A = 36 Watts and you can sustain some losses.

These are pricey, but it gives you some idea of what you are up against:
https://www.advancedenergy.com/glob...a-sheets/en-hv-1le-15le-series-data-sheet.pdf

 

In the circuit posted the feedback coil is connected to the base to ensures that the transistor turns off.