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UCC28600: Flyback IC with less standby power loss and less PCB size with 230AC 50 hZ to 5VDC 5A.

venkata syamala
Prodigy 10 points
Part Number: UCC28600
Other Parts Discussed in Thread: TL431, UCC28730, UCC24650, UCC28740

Hi all, 

I need to design isolated flyback convrter (230V AC to 5V DC@ 5A) for one of my project. 

our main requirement  is the design should have very less stand by power,less BOM cost and smaller PCB size. so i have selected UCC28600 IC for my design. This IC is Secondarty side regulation with less stand by current. i done some research i found another IC that UCC28730DR. This IC has primarey side regulation with zero stand by power loss. 

I want to know that what is the difference between primary side regulation and secondary side regulation ICs. 

Could you please suggest any better options rather than these ICs. 

 

Regards 

Venkata

 

  • 0
    TI__Mastermind 40500 points

    Hello Venkata,

    Thank you for your interest in TI flyback controllers.

    The difference between primary-side regulation (PSR) and secondary-side regulation (SSR) controllers is where the voltage sensing and error signal generation takes place.  

    SSR uses a secondary-side regulator, often such as the TL431 shunt regulator, to directly sense the output voltage, compare it to a reference voltage, and send an error signal to the primary side through an opto-coupler.  The primary side does the error-to-PWM conversion.

    PSR senses the output voltage indirectly by reflected voltage from the AUX winding on the primary side.  The reflected voltage is only valid during the flyback demagnetization interval, so the controller samples the AUX winding voltage (scaled down through a resistor divider) during flyback, compares it to an internal reference, generates an internal error signal, and converts to PWM all within the primary-side controller chip.  

    Therefore, PSR is simpler, but less accurate at +/-5% regulation capability, and slower transient response at light loads, because it samples less often at lower light-load switching frequencies.  SSR is more accurate (can be +/-1% or better) regulation and maintains faster transient response, but is more complicated and needs the secondary-side regulator and opto-coupler to accomplish this.  

    The UCC28730 can maintain fast transient response when used with the companion chip UCC24650 to monitor the output at the lowest of frequencies.
    Note: Zero stand-by power loss is not guaranteed.  The UCC28730 can help to achieve it because it is able to switch at extremely low frequency to minimize bias power.  However, many other system level consideration factor into the total stand-by loss, including leakage currents of the semiconductors and bulk capacitors.  
    For a 25W design, <5mW may not be achievable, but <10mW might be achievable with diligent design work.    

    Another controller to consider is UCC28740, which is SSR, but may help to achieve <30mW stand-by loss.

    Regards,
    Ulrich