SYSTEMS AND METHODS OF OPERATION FOR POWER CONVERTERS HAVING SERIES-PARALLEL MODE ACTIVE CLAMPS
FIG9 shows an alternate embodiment of the series-parallel mode active clamp circuit of FIG2 using a high side auxiliary winding
Referring now to FIG9, another embodiment of the series-parallel mode active clamp circuit discussed in detail above with respect to FIG2, which uses a high side auxiliary winding is shown. According to the embodiment shown in converter circuit 900 of FIG9, the second snubber capacitor, C3, and diode D4 are removed from the circuit of FIG2. In their place, the diode D2 is instead connected between the primary winding P1 and auxiliary primary winding P2 of the transformer TX1, as well as to power switch Q1 (rather than clamp switch Q2). According to the operation of the circuit 900 shown in FIG9, the energy from the leakage inductance is transferred to the snubber capacitor C1 at the turn off transition through D2. This energy does not transfer back in to the transformer, as the diode D3 is reverse biased due to much higher reflected voltage at its cathode node impressed by auxiliary winding. If the two primary windings P1 and P2 have equal turns, and if the reflected voltage across primary P1 is 80V, then the reflected voltage at the source node of clamp switch Q2 would be 160V with respect to Vin. Thus, the current from the snubber capacitor C1 does not transfer energy through clamp switch Q2. When the transformer energy is discharged and it starts to resonate with the equivalent capacitance at the drain node of power switch Q1, energy transfer starts in a manner similar to that presented with respect to FIG2 above, i.e., through D3 and Q2. The turns ratio of the primary and auxiliary winding may be varied during circuit optimization.
embodiment
33
load.Example
9
example
900
circuit
['1. A method of operating a power conversion circuit (200) comprising a transformer (TX1), first and second capacitors (C1, C3), first and second switches (Q1, Q2), and a controller operating the first and second switches to produce a regulated output voltage (Vout) for delivery to a load in an output system, the method comprising: switching the first switch (Q1) on at a first switching frequency, so as to store energy in a primary winding (P1) of the transformer; charging the first and second capacitors (C1, C3) in series via a first diode coupled between the first and second capacitors (C1, C3) by switching the first switch (Q1) off; switching the second switch (Q2) on when current is flowing through a body diode of the second switch; discharging the first and second capacitors (C1, C3) in parallel via a second diode coupled across the first capacitor (C1) and the first diode and a third diode coupled across the second capacitor (C2) and the first diode after all leakage inductance energy has been transferred from the transformer to the first and second capacitors; switching the second switch (Q2) off at a first amount of time before the next switching on of the first switch (Q1), wherein the first amount of time is determined so as to achieve zero voltage switching of the first switch; wherein at least one of the first switching frequency and the first amount of time is variable as determined by operating conditions.']