Power MOSFET. LLC resonant. Antonino Gaito. Market & Application Development Section Manager.

Transcription

1 Power MOSFET C resonant Antonino Gaito Market & Application Development Section Manager antonino.gaito@st.com

2 Outline 1. SRC - Series C tank overview 2. PRC - Parallel C tank overview 3. SRC + PRC = SPRC Series Parallel C tank overview 4. C resonant 5. MOSFET body diode recovery (possible root cause) 6. Our product target

3 1. SRC - Series C tank - overview

4 C RESONANT Hal Bridge C C series unctioning R et s talk about one resonant circuit type: the SERIES RESONANT TANK. The maximum gain transer is obtained when input signal requency (i) is equal to the resonant requency (r), that is when the C impedance is null, and so into the voltage divider the all voltage is reported on the R. i r

5 C RESONANT Hal Bridge C C series unctioning R By increasing the R value (null ideally) the actor Q decrase. So at a ixed s the shiting between and increases. o Q R i s

6 C RESONANT Hal Bridge Vbus Q1 C series unctioning C out C out oad This is a real C series circuit. The input signal is ixed by MOSFETs switching sequence, so requency switching s is equal to i. Q2 GND i r

7 C RESONANT Hal Bridge Vbus Q1 C series unctioning C out C out oad The R value now is due to the relected load value (Req). Q2 Req = GND i r

8 C RESONANT Hal Bridge Vbus Q1 C series unctioning C out C out oad In a real C series hal bridge circuit lower load, higher R and so lower Q. Q2 Req = GND NO OAD FU OAD i r

9 C RESONANT Hal Bridge Vbus Q1 C series unctioning C out C out oad The r is a boundary between two operation mode: Zero volage switching (ZVS) and Zero current switching (ZCS) Q2 GND ZVS (s>r) ZVS i r

10 Vbus Q1 C series unctioning C Ir out C out oad The r is a boundary between two operation mode: Zero volage switching (ZVS) and Zero current switching (ZCS) Q2 GND ZVS Z (s>r) Z Ir Ir inductive zone

11 C RESONANT Hal Bridge Vbus Q1 C series unctioning C out C out oad The r is a boundary between two operation mode: Zero volage switching (ZVS) and Zero current switching (ZCS) Q2 GND ZCS (s<r) ZCS i r

12 Vbus Q1 C series unctioning C Ir out C out oad The r is a boundary between two operation mode: Zero volage switching (ZVS) and Zero current switching (ZCS) Q2 GND ZCS Z (s<r) Z Ir Capacitive zone

13 C RESONANT Hal Bridge Vbus Q1 Q2 C out C out oad 1 DRAWBACKS It can be seen rom the operating region that at light load, the switching requency need to increase to very high to keep output voltage regulated. This is a big problem or SRC. GND i r

14 C RESONANT Hal Bridge Vbus Q1 Q2 C out C out oad 1 DRAWBACKS It can be seen rom the operating region that at light load, the switching requency need to increase to very high to keep output voltage regulated. This is a big problem or SRC. GND 2 High turn o current at high input voltage condition. i r

15 2. PRC - Parallel C tank - overview

16 C RESONANT Hal Bridge C parallel unctioning C R et s talk about one resonant circuit type: the PARAE RESONANT TANK. The maximum gain transer is obtained when input signal requency (i) is equal to the resonant requency (r). i r

17 C RESONANT Hal Bridge C parallel unctioning C R By decreasing the R value (ininite ideally) the actor Q decrase. Q o R i s

18 C RESONANT Hal Bridge Vbus Q1 C parallel unctioning out C out oad In a real C parallel hal bridge circuit lower load, higher R and so higher Q. Q2 C Req = GND NO OAD FU OAD i r

19 C RESONANT Hal Bridge Vbus Q1 C parallel unctioning out C out oad The r is a boundary between two operation mode: Zero volage switching (ZVS) and Zero current switching (ZCS) Q2 C GND ZCS (s<r) ZVS (s>r) ZCS ZVS i r

20 C RESONANT Hal Bridge Vbus Q1 Q2 C out C out oad 1 DRAWBACKS Compare with SRC, the operating region is much smaller. At light load, the requency doesn't need to change too much to keep output voltage regulated. So light load regulation problem doesn't exist in PRC. GND i r

21 C RESONANT Hal Bridge Vbus Q1 Q2 C out C out oad 1 DRAWBACKS Compare with SRC, the operating region is much smaller. At light load, the requency doesn't need to change too much to keep output voltage regulated. So light load regulation problem doesn't exist in PRC. GND 2 High turn o current at high input voltage condition (by simulation these values are higher than the SRC ones). i r

22 3. SRC + PRC = SPRC Series Parallel C tank - overview

23 We should overcome the SRC and PRC drawbacks. We want to: 1. Reduce the high turn o current at high input voltage (rom the SRC) 2. Obtain no high requency changes to regulate at no load (rom the PRC) C R C R + = SRC PRC

24 We should overcome the SRC and PRC drawbacks. We want to: 1. Reduce the high turn o current at high input voltage (rom the SRC) 2. Obtain no high requency changes to regulate at no load (rom the PRC) C1 C2 R SPRC

25 The SPRC has two resonant requencies. One low resonant requency determined by series resonant tank and C1. One high resonant requency determined by and equivalent capacitance o C1 and C2 in series; usually working at its highest one is more eicient. C1 C2 R SPRC

26 The SPRC combines the two good characteristics o SRC and PRC, but unortunately the operation between the two resonant requencies is in ZCS working. C1 ZCS C2 R SPRC

27 4. C resonant

28 In order to create a ZVS unctioning between these two requencies we substitute one capacitor with a inductance, by obtaining the C resonant circuit. C1 C 1 C2 R 2 R SPRC (CC) C

29 The beneit o C resonant converter is narrow switching requency range with light load and ZVS capability with even no load. Vbus Q1 C 1 Cr r 2 out C out R oad Q2 GND m C

30 Vbus Q1 C unctioning Q2 Cr r m out C out oad There are two resonant requencies: r1 1 2 r C r GND For s r1 the C works like a SRC tank. This unctioning is present at high load condition, that is when the m is paralleled with a low impedance.

31 Vbus Q1 C unctioning Q2 Cr r m out C out oad There are two resonant requencies: 1 r 2 2 ( r m ) C r GND For s r 2 the C works like a PRC tank. This unctioning is present at low load condition. In this region we do not work because o the ZCS unctioning.

32 Vbus Q1 C unctioning Cr r out C out oad In the requency range r 2 s r1 Q2 m the two unctioning are mixed. GND r 2 r 1

33 Vbus Q1 C unctioning Cr r out C out oad In the requency range r 2 s r1 Q2 m the two unctioning are mixed. GND r 2 r 1

34 Vbus Q1 C unctioning Cr r out C out oad In the requency range r 2 s r1 Q2 m the two unctioning are mixed. GND

35 C unctioning In the requency range r 2 s r1 the two unctioning are mixed.

36 C unctioning In the requency range r 2 s r1 the two unctioning are mixed.

37 C unctioning In the requency range r 2 s r1 the two unctioning are mixed.

38 C unctioning In the requency range r 2 s r1 the two unctioning are mixed.

39 C unctioning Region 2 We plot three operating regions. Region 1 ZVS Region 1 Region 2 Region 3 ZVS ZCS Region 3

40 C Beneits 1. No high switching requency at low load 2. ZVS unctioning guaranteed by m (even with zero load) 3. Turn o current not related to load but only to m 4. Secondary diodes do not recover HIGH EFFICIENCY

41 5. MOSFET body diode recovery (possible root cause)

42 During a low to high load transition the driving circuit should be able to oblige MOSFET to move in ZVS and positive turning o current zone. I this is not guaranteed MOSFET could work in a dangerous zone. ZVS ZCS ZVS

43 At low load steady state condition the system is working near the lower requency resonant. ZVS on and positive turn o drain current is guaranteed. ideal ZVS real ZCS ZVS OW OAD HIGH OAD Ater the load variation (rom low to high) the switching requency should ollow the new resonant requency. I this does not happen (like in the picture), the system state passes across the Region 3 and ZVS on and positive turn o drain current are missed. So when MOSFET is turned o current is lowing also through its body diode; because o the antagonist MOSFET turning on a body diode recovery can occurs.

44 6. Our product target

45 1. ow Coss_eq to help the ZVS transition 2. ow Vsd to reduce the losses during the body diode conduction 3. Improve the dv/dt capability

46