Son of simple step-up SMPS challenge
Russell McMahon email (remove spam text)
> Ok, I stand corrected. Figure 26 shows a step-up converter with >90%
> efficiency using the MC3... part and a tapped inductor.
The tapped inductor is required for if best possible efficiency is required
due to the dual factors of a NPN high side switch and a Darlington output.
You need to provide a modest high side drive voltage ABOVE Vin effective to
get a saturated switch. The tapped inductor effectively gives you this. If
you don't provide such an arrangement the output switch is not saturated and
at lower input voltages the consequent efficiency loss is significant.
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