A novel variable frequency modulation technique for multiphase synchronous rectified VRM

A novel modulation control scheme of switching frequency for multiphase synchronous rectified voltage regulator module (VRM) used in such as motherboards is proposed in this paper. The switching frequency is modulated higher as VRM loads more lightly and vice versa, so that the proposed scheme is also called variable-frequency control method. Zero voltage switching (ZVS) can be achieved to boost VRM efficiency without additional auxiliary switches and any storage elements while frequency is modulated. To protect elements in VRM from damage and cause the output ripple under control and in view of the switching frequency being finite, the switching frequency will be fixed constant when the much more loading is added on VRM wherein the load threshold to fix switching frequency constant is found by experiments. Compared to conventional constant switching frequency techniques with 250kHz and 550kHz, experimental results derived from an eight-phase synchronous rectified VRM show the proposed modulation technique is superior to the conventional one, the efficiency can be increased up to 8% for eight-phase VRM under various load conditions.