FLYBACK_CONVERTER calculations help

Hi,

I guess: yes. But without details...

You need to provide some electrical specifications.
And you need to show what you have done so far. Don´t expetc others do your job.

Did you do an internet search, a forum search .. see the links in the box "similar threads" below.

Klaus

Siddharth_saxena said:

can anyone help me out with my fly back converter calculation ?

Click to expand...

just tell us what you have done yourself. Next you tell where you have got stuck. I guess it is an assignment and you are expected to do it yourself, right?

Are you talking about the common DCR snubber across the primary winding? Then it resembles the behavior of a buck-boost converter:

1) The primary produces a current kick at Turn-off.
2) Diode steers current surge so it charges capacitor.
3) Resistor discharges capacitor during second half of the cycle.

The goal is to select RC values so that their snubbing action generates minimum heat and minimum stress on components.

I'd say, you have more problems to select a meaningful resistor value...

What are the transformer parameters in your simulation? Without transformer leakage inductance, you don't need a snubber at all. Capacitor value depends on energy stored in leakage inductance and acceptable overvoltage. Resistor must be able to discharge the capacitor til next pulse.

FvM said:

I'd say, you have more problems to select a meaningful resistor value...

What are the transformer parameters in your simulation? Without transformer leakage inductance, you don't need a snubber at all. Capacitor value depends on energy stored in leakage inductance and acceptable overvoltage. Resistor must be able to discharge the capacitor til next pulse.

Click to expand...

i took leakage inductance as 2uH, turns ratio is 1:1.

c_mitra said:

just tell us what you have done yourself. Next you tell where you have got stuck. I guess it is an assignment and you are expected to do it yourself, right?

Click to expand...

not really

Siddharth_saxena said:

i took leakage inductance as 2uH, turns ratio is 1:1.

Click to expand...

Related to which main inductance?

Is my waveform is correct ?
oscilloscope1 :across switch
oscilloscope2 :across channel A -R3
across channel B- R4
oscillloscope3 :across R6

FvM said:

Related to which main inductance?

Click to expand...

Sir transformer leakage reactance

R6 (looks like 20 ohms) drains the capacitor very quickly after Turn-off. I believe you can select a higher ohm value so that discharge lasts the remainder of the cycle. Maybe 100 ohms.

I'm sorry, I see now R6 is 20k. Then it may be more effective if you increase the capacitor value. A reasonable volt level to charge it is 1.5 or 2 times the supply voltage. Remember a higher volt rating puts more stress on the cap, as well as costs more money. And higher voltage causes your resistor to need a higher Watt rating, also more money

I'm looking again... What polarity is applied to the transformer primary? Your schematic makes it appear that positive goes to the lower end.

it's 20k.

swap the mosfet and the DC source - it's drawn wrong