Self-Adjusting Current Injection Technology

Abstract

A method includes providing a transformer with primary and current injection windings, a primary switch connected to the primary winding, a parasitic capacitance reflected across the primary switch, a secondary rectifier means, and a current injection circuit including a current injection switch connected to the current injection winding, and a unidirectional current injection switch connected to the current injection winding. The method includes switching on the current injection switch to start a current injection flowing from a controlled voltage source, through the unidirectional current injection switch and further through the current injection winding. The current injection reflects into the primary winding, thereby discharging the parasitic capacitance reflected across the primary switch. The method includes turning on the primary switch with a delay time after the current injection switch turns on and turning off the current injection switch after the current injection reaches zero amplitude.

What is claimed is: 
     
         1 . A DC-DC converter comprising:
 a primary side having a primary switch and a secondary side;   a transformer having a primary winding at the primary side, a secondary winding at the secondary side, and a current injection winding;   an input voltage source;   a primary switch connected to the primary winding;   a parasitic capacitance reflected across the primary switch;   a current injection circuit comprising:
 a current injection switch connected to a first terminal of the current injection winding, and a unidirectional current injection switch connected to a second terminal of the current injection winding, wherein the second terminal is not connected to the current injection switch; 
 a controlled voltage source connected to the unidirectional current injection switch and to the current injection switch at an end of the current injection switch which is not connected to the current injection winding; and 
 a current injection capacitor connected between the unidirectional current injection switch and the controlled voltage source; 
   wherein, in response to the current injection switch switching on, a current injection begins flowing from the current injection capacitor, discharging the current injection capacitor until a voltage across the current injection capacitor becomes lower than the voltage controlled source, after which the current injection flows through the unidirectional current injection switch and from the voltage controlled source, extracting energy from the voltage controlled source, until the current injection reaches a zero level, referred to as an inflection point, and the current injection reflects into the primary winding with an amplitude proportional to a turn ratio of the current injection winding to the primary winding;   the current injection reflected into the primary winding discharges the parasitic capacitance reflected across the primary switch;   the primary switch turns on with a delay time after the current injection switch turns on; and   after the inflection point, the current injection reflected into the primary winding changes its polarity and flows through the primary winding from the input voltage source and through the turn on primary switch and reflects into the current injection winding proportional to the turn ratio of the primary winding to the current injection winding, thereby charging said current injection capacitor.   
     
     
         2 . The DC-DC converter of  claim 1 , wherein the delay time is sufficient for the primary switch to turn on at a predetermined voltage level. 
     
     
         3 . The DC-DC converter of  claim 2 , wherein the predetermined voltage level is zero. 
     
     
         4 . The DC-DC converter of  claim 1 , wherein the controlled voltage source has a level which is sufficient for the primary switch to turn on at a predetermined voltage level. 
     
     
         5 . The DC-DC converter of  claim 4 , wherein the predetermined voltage level is zero. 
     
     
         6 . The DC-DC converter of  claim 1 , wherein the current injection switch is turned on in a valley of a voltage across the primary switch during ringing, so as to create zero voltage switching conditions for the primary switch with minimum energy consumption. 
     
     
         7 . The DC-DC converter of  claim 1 , wherein the current injection circuit comprises part of one of a flyback topology, a boost topology, and a buck topology.