The output, VO, provides 5V at 75W maximum and is electrically isolated from the input. Because the UCC3808 is a peak current mode controller, the 2N2222A emitter following amplifier (buffers the CT waveform) provides slope compensation which is necessary for duty ratios greater than 50%. Capacitor decoupling is very important with a single ground IC controller, and a 1μF is suggested for placement as close to the IC as possible. The controller supply is a series RC for start-up, paralleled with a bias winding on the output inductor used in steady-state operation.

Isolation is provided by an optocoupler with regulation done on the secondary side using the UC3965 Precision Reference with Low Offset Error Amplifier. Small signal compensation with tight voltage regulation is achieved using the UC3965 device part on the secondary side. Many choices exist for the output inductor depending on cost, volume, and mechanical strength. Several design options are iron powder, molypermalloy (MPP), or a ferrite core with an air gap as shown in Figure 7-1. The main power transformer is a low profile design, EFD size 25, using Magnetics® Inc. P material which is a good choice at the frequency and temperature in Design Parameters. The input voltage ranges from 36V DC to 72V DC.