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Topic Why the need for PFC stage for an LLC converter 
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Why do we need PFC stage for a LLC converter?
 
Date 12/26/2015 7:51:08 AM 
Author Venkat 
Pageviews 1223 
      

 

Responses
Response topic PFC stage for an LLC converter?? 
Message
If you only need 50W output power, definitely do-able without a PFC stage, even for a 90-264VAC input range.

The trick is in the magnetics design, for wide input voltage range.

Nice aspect of integrated magnetics LLC deisgn, is the excellent isolation between the input and output stages. This makes it really ideal for a life support product, where DC voltage from the medical apparatus may be in close contact with the patient blood supply (CF ap).

Re magnetics design, use a Mathcad type program, and the analysis becomes less experimental, and more of a straight forward path.

As others have stated if you need Line harmonics compliance for the EU, then you are locked into a PFC stage, if Input Power is greater than 75W to 100W. (Note between 75W and 100W input power, it is possible to meet 230Vac Class A Line Harmonics compliance by adding about 500uH differential mode inductor, and no actual need for Line harmonics control in the USA market.)
 
Author Dave L. 
Date 1/5/2016 11:29:37 AM 
 
Response topic The need for the PFC stage 
Message
In most power supplies the PFC stage is needed for:

- Comply with line current harmonic regulations
- Adequate ride-through and holdup time for AC line disturbances
- Higher overall efficiency due to the higher DC/DC stage input voltage
- For PWM converters a pre-regulated input voltage would allow for a maximization of duty cycle and a resulting better efficiency
- For LLC converters a pre-regulated input voltage would allow an optimized design within a narrower switching frequency range and a resulting better efficiency
 
Author Darius 
Date 12/26/2015 8:23:08 AM 
 

 




 
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