High-efficiency DC-to-DC power supply with synchronous rectification

Claim 1

A synchronous rectifier circuit comprising: (a) a transformer having a primary winding and a secondary winding; (b) first, second and third controlled devices, each having a current path and a control electrode; (c) a power supply device; (d) a load circuit; (e) said primary winding of said transformer being connected in series with said current path of said first controlled device and said power supply device; (f) said secondary winding of said transformer being connected in series with said current path of said second controlled device and said load circuit; (g) said current path of said third controlled device being connected across said load circuit; (h) a drive pulse generator circuit having an output in the form of repetitive pulses of variable duty cycle, said output being coupled to a first control node and said output being inverted and coupled to a second control node; (i) a first means detecting when said first control node is in a condition to activate said control electrodes of said first and second controlled devices, said first means first producing and sensing a turn-off level to said control electrode of said third controlled device then producing a turn-on level to said control electrodes of said first and second controlled devices; (j) and a second means detecting when said second control node is in a condition to activate said control electrode of said third controlled device, said second means first producing and sensing a turn-off level to said control electrodes of said first and second controlled devices then producing a turn-on level to said control electrode of said third controlled device.

Claim 6

A method of controlling the gate voltages of power transistors in a synchronous regulator power supply of the type having at least first, second and third power transistors, where the first and second transistors have current paths in series with the primary and secondary windings, respectively, of a transformer, and the third transistor has a current path connected across a load, comprising the steps of: (a) detecting the voltage across the load and generating repetitive voltage pulses having a pulse width inversely related to said voltage across the load; (b) applying said voltage pulses to the gates of said first and second transistors and applying the inverse of said voltage pulses to the gate of said third transistor; (c) and detecting the voltage on the gates of said first and second transistors and preventing the gate of said third transistor from rising to a value which would turn on said third transistor unless said voltage on the gate of said first and second transistors is substantially zero.

Claim 7

A method of controlling the gate voltages of power transistors in a synchronous regulator power supply of the type having at least first, second and third power transistors, where the first and second transistors have current paths in series with the primary and secondary windings, respectively, of a transformer, and the third transistor has a current path connected across a load, comprising the steps of: (a) detecting the voltage across the load and generating repetitive voltage pulses having a pulse width inversely related to said voltage across the load; (b) applying said voltage pulses to the gates of said first and second transistors and applying the inverse of said voltage pulses to the gate of said third transistor; (c) and detecting the voltage on the gates of said first and second transistors and preventing the gate of said third transistor from rising to a value which would turn on said third transistor unless said voltage on the gate of said first and second transistors is substantially zero.