Flyback_transformer

Hi,

While calculating the Ipeak (peak primary-current) we use
Ipeak(pri)=(Vin(min)*Ton)/Lpri

If the voltage is say 100VDC minimum and 300VDC maximum , then Why are they calculating peak current from the minimum voltage . OTOH when the applied voltage ramps to 300VDC this peak current is substantial?

Thanks
-Adi

Perhaps a better question would be: why is a DC supply swinging from a hundred to three-hundred volts?

flybacks don't have constant on times. the control fet will be shut off when the current hits the peak. the on time will be much less for a 300V input than for a 100V input.

and who are "they"?

Flyback transformers are used exclusively in old tube-type television sets.

The term refers to the horizontal "flyback" period of a video signal when the electron beam returns to the left side of the screen. This served a dual-purpose in the old days to also drive the high voltage transformer.

It's not because the voltage "flys back" or something (though I have listened to many a tedious exposition explaining it as such), it's simply from the video signal.

In CRT TVs the flyback converter was part of the horizontal deflection circuit. The horizontal drive circuit doubled as the HV power supply generating about 25Kv for the CRT.

Flyback transformers are also used in many present day DC-DC converters. They provide a relatively simple way to get transformer isolation between the input and output with a single power transistor driver. They operate much like a buck-boost switching regulator, except that the inductor is split with two (or more) windings to form a transformer. A standard spark ignition system also uses a flyback converter to generate the high voltage.

In a regulated flyback converter the duty cycle of the power transistor is determined by the output voltage feedback.

Thanks , but the question still remains there , Why V(max) isnt taken into account to get the peak current:

Ipeak(pri)=(Vin(min)*Ton)/Lpri


Regards

PS: I am talking with respect to AC/DC converters , DC/DC converters . AND more specifically about DCM mode.

Because for a given power output of a regulated switching power supply the maximum input current occurs at the minimum input voltage since power equals voltage times current.

crutschow said:

Because for a given power output of a regulated switching power supply the maximum input current occurs at the minimum input voltage since power equals voltage times current.

Click to expand...

I get it . I want to know how the ( I primary rms) and (I peak secondary) is derived .

Regards
-Adi