  In this paper, a highly compact, low power (<10W), high frequency (2 MHz)
isolated active clamp forward converter, comprising a coreless Printed Circuit
Board-based transformer is proposed. To decrease the size of converter, high
switching frequency is considered which lead to decrease in inductor, capacitor
and transformer size. Highly switch loss due to hard switching is an important
constraint of forward topology to increase frequency. In this paper, the active
clamp circuit is added to forward topology to achieve zero voltage switching
and decrease switching loss drastically. Due to zero voltage switching, the
proposed converter can operate in high frequency. The principle of active clamp
forward converter is described in this paper. Another constraint to increase
the switching frequency of forward converter is transformer core losses. In
this paper, coreless PCB-based transformer is proposed and implemented to be
utilized in the structure of the active clamp forward converter. Instead of
classic core-based transformer, using a PCB-based transformer as the power
transmitter has increased the efficiency due to elimination of core hysteresis
loss. The equivalent circuit, transfer function and input impedance of
PCB-based coreless transformer are presented in high frequency. Finally, an
experimental prototype of the active clamp forward converter which uses a
coreless transformer is implemented. The experimental results of proposed
converter are presented to evaluate the theoretical analysis and performance.
