Flyback BCM

simone frasanni

Hi to all,

In Flyback Boundary conduction mode and PSR regulation, is it possibile to have a duty cycle more than 50% ?

I'm working with this topology and I can get a small power (about 5W) with very wide input voltage range. But, if I have low input voltage, the duty becames about 75%.

Can someone explain me how much is the maximum duty acceptable in flyback BCM ?

thanks in advance

Simone

over 9 years ago

0 Eric Faraci over 9 years ago

TI__Expert 8210 points

A flyback converter can operate anywhere between 0-100% duty cycle if the right control technique and controller are used. The 50% maximum limit typically seen is caused by subharmonic oscillations in the peak current mode control loop. If there is slope compensation on the sensed current the duty cycle can be increased beyond 50%, otherwise there will be stability issues regulating the output.

Our Power Supply Design Seminars, notably Under the Hood of Flyback SMPS Designs go into more depth about this topic.

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