Flyback duty cycle

One more thing Do a search on any such discussion forum for all questions relating to any part you want to use. For example, look under 3478 (or its family), under discussion here. You are likely to find the maximum number of queries for this particular part on the forum. Why so Remember, this is a Flyback controller with a 100% duty cycle. But don t expect the company to spell that out to you ... 

The peak input current of the discontinuous flyback converter, with a fixed duty cycle and fixed frequency, is defined by... 

Another product is a fairly popular off-line switcher IC family meant for Flyback applications. In an off-line case, the value of Dmax has several more implications. Here we must recall that the earlier generation of this switcher family had a maximum duty cycle of about 67%. When the next generation was conceived, the one-man product-definition team heuristically assigned a Dmax of 78%. His idea was that by allowing a wider input current pulse, we would automatically get a lower current pedestal, and this would enhance the power capability of his device (since this figure was being based purely on current limit, not on dissipation). 

The forward converter (Fig. 10.82) is a variation of the buck converter. It is usually operated in the CCM to reduce the peak currents and does not have the stabihty problem of the flyback converter. The HF transformer transfers energy directly to the output with very small stored energy. The output capacitor size and peak current rating are smaller than they are for the flyback. A reset windingis required to remove the stored energy in the transformer. The maximum duty cycle is about 0.45, which limits the control range. This topology is used for power levels up to about 1 kW. 

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