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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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AN2644 датащи(PDF) 17 Page - STMicroelectronics |
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AN2644 датащи(HTML) 17 Page - STMicroelectronics |
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17 / 64 page  AN2644 The LLC resonant half-bridge converter 17/64 Note, however, that working in the inductive region is not a sufficient condition in order for ZVS to occur. In the above discussion, it has been said that the voltage of the node HB could swing from Vin to zero "provided IR is large enough". Of course the same holds if we consider node HB's swing from zero up to Vin. What actually happens when Q1 turns off with positive IR current is that the associated inductive energy level of the resonant tank circuit is maintained at the expense of the energy contained in the capacitance CHB. If the inductive energy (∝ IR 2) is greater than that owned by CHB (∝ Vin 2) C HB will be completely depleted and the voltage of the node HB will be able to reach -VF, injecting DQ2 and allowing Q2 to turn-on with essentially zero drain-to-source voltage. Similarly, when Q2 turns off with negative current, part or all of the associated inductive energy will be transferred to CHB. If the available inductive energy is greater than that needed to charge CHB up to Vin+VF, the node HB will be allowed to swing all the way up until DQ1 is injected, thus clamping the voltage, and Q1 will be able to turn-on with essentially zero drain-to-source voltage. Seen from a different perspective, the inductive part of the tank circuit resonates with CHB, and this is the origin of the term "resonant transition" used for designating resonant converters having this property. This "parasitic" tank circuit active during transitions is formed by CHB with the series inductance Ls if during the half-bridge transition there is current circulating on the secondary side (so that Lp is shorted out) or with the total inductance Ls + Lp if there is no current conduction on the secondary side. The above mentioned energy balance considerations, however, are not still sufficient to guarantee ZVS under all operating conditions. There is an additional element that needs to be considered, the duration of the deadtime TD. The first obvious consideration is that the duration of the deadtime represents an upper limit to the time the node HB takes to swing from one rail to the other: in order for the mosfet that is about to turn on to achieve ZVS (i.e. to be turned on with zero drain-to-source voltage), the transition has to be completed within TD as depicted in Figure 9. However, the way the Figure 13. Bridge leg transitions in the neighborhood of inductive-capacitive regions boundary a) c) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is hard switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF b) d) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is soft switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current a) c) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is hard switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF a) c) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is hard switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF b) d) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is soft switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF b) d) V HB I R I(Lp) V HB I R I(Lp) IR = 0 IR = 0 Q1’s body diode conduction Q2 is hard switched Q1’s body diode is recovered Q2 is soft switched Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF Q1 ON Q2 OFF Q1 OFF Q2 ON Q1 OFF Q2 OFF V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current V HB = Node HB voltage I R = Tank circuit’s current I(Lp) = Lp (magnetizing) current |
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