Patent ID: 6541947
Filing Date: 2003-04-01
Classification: H02M,Y02B

Abstract:
A step-down constant-current transformer for converting an input d.c. voltage into a lower output d.c. voltage, comprising:a first controllable switch, including a first MOSFET transistor, connected in series between a first input terminal and a choke; a capacitor connected in parallel to the first input terminal and a second input terminal; a second controllable switch, including a second MOSFET transistor, connected in parallel, upstream from the choke, forming a synchronous rectifier; a control unit driving the first and second MOSFET transistors, the control unit blocking the second MOSFET transistor upon the occurrence of a reverse current condition to prevent a reverse current; a comparator for detecting voltage having an output, the comparator receiving an electric potential at a drain terminal of the second MOSFET transistor at an inverting terminal and receiving an electric potential at a source terminal of the second MOSFET transistor at a non-inverting terminal and comparing the potentials received at the respective inverting and non-inverting terminals, and emitting from the output a controlling output signal indicating a reverse current condition when the electric potential at the drain terminal is higher than the electric potential at the source terminal.