Flyback Converter

DickCappels

Joined Aug 21, 2008
10,138
What amount of ripple is acceptable depends entirely on the application.

If your power source is AC and your required output is clean DC this is best done with an adequate Cin.

Your question is quite broad. Do you have a specific example?
 

Papabravo

Joined Feb 24, 2006
21,094
There is no concept of a single "acceptable" value. Every design is based on a set of requirements, which must be EXPLICITLY articulated. If there is no requirement, then presumably you are free to do whatever you like. It is not uncommon for some designers to go way beyond the use of an input capacitor(s) if they do have stringent requirements.
 

Ian0

Joined Aug 7, 2020
9,618
There are flyback LED drivers which operate on unregulated rectified AC, so 325V peak, with 325V of ripple.
 

Thread Starter

shivani14079ee2014@gmail.

Joined Nov 17, 2021
6
What amount of ripple is acceptable depends entirely on the application.

If your power source is AC and your required output is clean DC this is best done with an adequate Cin.

Your question is quite broad. Do you have a specific example?
Sir , My input voltage range is 85-265ac and output is 20watts and 12 volts. So in this case can I ignore Cin?
 

DickCappels

Joined Aug 21, 2008
10,138
Not unless your design can tolerate such a wide range of input voltage without problem (the wide range could result in oscillation) and your application can tolerate the ripple that results on the output.

What is your example -like powering an electormaget, or an audio audio amplifier?
 

Ian0

Joined Aug 7, 2020
9,618
You have to store energy somewhere, and it takes up less room and costs less to store it at a higher voltage. If stored in the output capacitor, the converter has to be able to deliver double the current.
The only problem in storing it at the input side is passing the harmonic current regulations (EN61000-3-2)
 

ronsimpson

Joined Oct 7, 2019
2,954
Cin is there for a reason(s).
-it helps keep switcher noise off the power line
-it supplies power to the IC (brains) at zero crossing time. With out it the IC might have to restart every 1/2 cycle.

I think you should use the capacitor that the application note has.

This is a light bulb project not a normal power supply. Most power supplies you might have 10% ripple. In a PFC (Power Factor Correction power supply) the ripple at the full wave bridge is close to 100%. You want to pull current off the power line in a sine wave. To do that the voltage on the input needs to drop to a very low value at zero crossing.
 
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