flyback transformer design for output voltage varying from 0-100V

Thread Starter

silvi09

Joined Sep 26, 2021
7
I wanted to design a flyback transformer with input voltage of 12v , power 100W and output voltage of (0-100)V. can anyone suggest how to proceed for this and how can I calculate specifications for transformer for this varying output voltage.
 

Papabravo

Joined Feb 24, 2006
18,130
I wanted to design a flyback transformer with input voltage of 12v , power 100W and output voltage of (0-100)V. can anyone suggest how to proceed for this and how can I calculate specifications for transformer for this varying output voltage.
The transformer cannot perform this feat all by itself. You'll also need to explain how it is possible to output 0 volts @ 100 watts. That just might require a power company sub station for starters. In addition, transformers do no work on DC so there is going to be some circuitry involved in converting 12V to some other voltages. It seems like revising your requirements might be a good thing.
 

ronsimpson

Joined Oct 7, 2019
2,011
You have 12V at 10A and you want to make 0 to 100V. ??
You understand that at 100V you will only get 1A. = 100watts.
Does the 100V need to be isolated from the 12V or can the return wire (ground wires) be the same?
It is very hard to make a supply that goes from 0 to 100V. How about 15V to100V? Can not go below 12V. ??
If it really needs to go to "0V" will this work? 0V, or 15 to 100V. Notice the OR. So there is off=0V and working=15 to100V.

Asking questions and more questions so we understand the goal.
 

Ian0

Joined Aug 7, 2020
4,879
I presume you need 100W at 100V output, therefore an output of 1A.
Do you still need 100W at 10V output? That's 10A.
I'd recommend the SG3525, in a push-pull forward-converter circuit.
 

Papabravo

Joined Feb 24, 2006
18,130
I presume you need 100W at 100V output, therefore an output of 1A.
Do you still need 100W at 10V output? That's 10A.
I'd recommend the SG3525, in a push-pull forward-converter circuit.
Would it be impertinent to point out that the TS requested a FLYBACK transformer, not a forward DC-DC converter. We must try to meet the stated requirements.
 

Ian0

Joined Aug 7, 2020
4,879
Would it be impertinent to point out that the TS requested a FLYBACK transformer, not a forward DC-DC converter. We must try to meet the stated requirements.
Not in the slightest, I shall rephrase my response as "Whilst we are establishing the parameters of your power supply, have you also considered the possibility of using a forward converter based upon the SG3525?"
 

Papabravo

Joined Feb 24, 2006
18,130
Not in the slightest, I shall rephrase my response as "Whilst we are establishing the parameters of your power supply, have you also considered the possibility of using a forward converter based upon the SG3525?"
Bravo sir! Well played.
 

Thread Starter

silvi09

Joined Sep 26, 2021
7
Can we change the duty cycle of switching circuit of flyback transformer circuit from 10% to 90% to get the varying voltage at the output ?
 

Ian0

Joined Aug 7, 2020
4,879
Yes, provided that it is always operating in continuous-current mode. i.e. the magnetic field does not reach zero at any time.
 

Thread Starter

silvi09

Joined Sep 26, 2021
7
Yes, provided that it is always operating in continuous-current mode. i.e. the magnetic field does not reach zero at any time.


So , in place of multiple secondary windings for multiple outputs . I can also get multiple outputs by changing the duty cycle right ? will there be any issue of magnetic flux density saturation ...?
 

Papabravo

Joined Feb 24, 2006
18,130
So , in place of multiple secondary windings for multiple outputs . I can also get multiple outputs by changing the duty cycle right ? will there be any issue of magnetic flux density saturation ...?
This is always a possibility and depends on the current in the inductor(s). Depending on the turns ratio and the configuration this can be larger than the output current. There may also be other practical limits on the range of available duty cycle choices. It is generally a good idea to comb the datasheet carefully for such limitations.
 

LowQCab

Joined Nov 6, 2012
1,931
So , in place of multiple secondary windings for multiple outputs . I can also get multiple outputs by changing the duty cycle right ? will there be any issue of magnetic flux density saturation ...?
Why are You stuck on a "Fly-Back" design ????
A "Push-Pull" design would be far more stable and predictable.
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LapTop Power Suppy FLAT .png
 

ronsimpson

Joined Oct 7, 2019
2,011
A simple boost supply will make voltages above the input voltage.
For this example Vin=12V then vout could be 12 through 100V (with some part changes)
1638228883743.png
 
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