APPLICATION NOTE
AN-00987-19
HIGH EFFICIENCY HIGH VOLTAGE FLYBACK
By EASII-IC, X-REL Semiconductor
AN-00987-19 rev1A 2019-07-25
1 of 38
PROPRIETARY INFORMATION
www.x-relsemi.com
© 2019 X-REL Semiconductor
TABLE OF CONTENTS
1 Introduction ...................................................................................................................................... 4
2 Main Features................................................................................................................................... 4
3 Flyback diagram............................................................................................................................... 5
4 Design consideration ........................................................................................................................ 6
4.1 Start-up .................................................................................................................................. 6
4.2 After start-up of the xtr30014 ................................................................................................ 6
5 Component and characteristics choice ............................................................................................. 7
5.1 Start-Up Phase ....................................................................................................................... 7
5.2 XTR30014 settings ................................................................................................................ 8
5.2.1 XTR30014 characteristics: ........................................................................................ 8
5.2.2 FB voltage ................................................................................................................. 8
5.2.3 SWT resistor .............................................................................................................. 8
5.2.4 SSTR resistor ............................................................................................................. 8
5.2.5 R sense calculation for over current .......................................................................... 9
5.3 Switching MOSFET: xtr20411 ............................................................................................ 10
5.4 Transformer characteristics ................................................................................................. 11
5.5 JFET..................................................................................................................................... 12
5.6 Snubber Network ................................................................................................................. 13
5.7 D_out and D_aux (D1,D2) size ........................................................................................... 13
5.8 COUT calculation ................................................................................................................ 13
6 Power supply Performances and waveforms ................................................................................. 14
6.1 Introduction ......................................................................................................................... 14
6.2 Start-up waveform ............................................................................................................... 14
6.3 Voltage Regulation Accuracy .............................................................................................. 15
6.4 Power-good flag from the XTR30014 ................................................................................. 15
6.5 Load Transient Response ..................................................................................................... 16
6.6 Input Transient Response .................................................................................................... 17
6.7 Output Protection ................................................................................................................. 18
6.7.1 MAX output load protection: Fold back point ........................................................ 18
6.7.2 Secondary protection: short circuit.......................................................................... 20
6.7.3 Secondary protection: Over Voltage on Vout ......................................................... 20
7 Efficiency measurement................................................................................................................. 21
7.1 Efficiency vs I
LOAD
.............................................................................................................. 21
7.2 Efficiency vs P
OUT
............................................................................................................... 23
7.3 Efficiency vs V
IN
................................................................................................................. 25
8 Vout measurement ......................................................................................................................... 27
8.1 V
OUT
vs I
LOAD
....................................................................................................................... 27
8.2 V
OUT
vs P
OUT
........................................................................................................................ 29
8.3 V
OUT
vs V
IN
.......................................................................................................................... 31
9 Ripple measurement....................................................................................................................... 33
9.1 RIPPLE vs I
LOAD
.................................................................................................................. 33
9.2 RIPPLE vs V
IN
..................................................................................................................... 33
10 Duty cycle measurement ................................................................................................................ 34
HIGH EFFICIENCY HIGH VOLTAGE FLYBACK
AN-00987-19 rev1A 2019-07-25
2 of 38
PROPRIETARY INFORMATION
www.x-relsemi.com
© 2019 X-REL Semiconductor
10.1 DUTY CYCLE vs I
LOAD
...................................................................................................... 34
10.2 DUTY CYCLE vs V
IN
......................................................................................................... 34
11 System design guidelines/Layout recommendation....................................................................... 35
11.1 Design consideration ........................................................................................................... 35
11.2 Typical Flyback Schematic ................................................................................................. 35
11.3 Bill of Material .................................................................................................................... 35
12 Board Photos .................................................................................................................................. 36
12.1 Board drawing ..................................................................................................................... 36
12.2 Thermal photos .................................................................................................................... 36
13 Conclusion ..................................................................................................................................... 37
14 Important Notice & Disclaimer ..................................................................................................... 38
15 Contact Us ...................................................................................................................................... 38