Rohm BD7682FJ-EVK-301 User manual

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© 2017 ROHM Co., Ltd.
No. 60AP001E Rev.001
2017.4
User Guide
© 2018 ROHM Co., Ltd.
No. 60UG064E Rev.001
19 Feb 2018
BD7682FJ-EVK-301 EV BOARD USER GUIDE
High voltage input aux power supply ev. Board
Figure 1 –Top and Bottom views
The AUX board is able to operate with both AC and DC input voltages. It is therefore possible to derive the power directly
from the grid or from the system DC link, e.g. after the PFC stage. In case of AC input, the accepted input voltage range
goes from 210 VAC to 480 VAC. In case of DC input, the input range goes from 300 VDC to 900 VDC. This board version “301”
mounts screw connections to facilitate the cabling to 3phase input or Vdc input. It is possible to remove the connectors
and use vertical mounting connectors as an example of module board for Aux power supply in a power system.
The simplified schematic of the AUX board is shown in Figure 2.
Figure 2 –Simplified schematic of the AUX board.
1 –1700V SiC MOSFET SCT2H12NZ
2 –Quasi-resonant controller BD7F682FJ-LB
Board dimensions 80mm x 80mm
1
2
Dsec VOUT
AC Filter Diode
Bridge
Lprim Lsec
Laux
Brown
Out
Gate
VCC
VCC
Gate
Isense
ZT
Feedback
Isense
Feedback
BD7682FJ
Q1
Daux
COSS
+
-
Optocoupler
VDC
+
-
ZT
Mask
Param.
Description
Value
VIN
Input
voltage
210…480 VAC
300…to 900 VDC
VOUT
Output
voltage
12 VDC ± 3%
POUT
Output
power
30 W @ VIN.MIN
40 W @ VIN.MAX
fsw
Switching
frequency
90..120 kHz
Table 1- main electrical parameters.

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
Contents
1Board information....................................................................................................................................... 3
1.1 Schematics........................................................................................................................................ 3
1.2 Flyback Transformer........................................................................................................................... 3
2Board usage............................................................................................................................................... 4
2.1 General information before cabling and powering the board:................................................................... 4
2.2 Cabling ............................................................................................................................................. 5
2.2.1 3 Phase AC connections:............................................................................................................... 5
2.2.2 DC connections:........................................................................................................................... 5
2.3 Test points ........................................................................................................................................ 6
3Implementation and practical tests with AUX Board ........................................................................................ 7
3.1 Operation at no load........................................................................................................................... 7
3.2 Normal operation............................................................................................................................... 8
3.3 Efficiency and temperature measurements............................................................................................ 8
4Summary ................................................................................................................................................ 10
5References............................................................................................................................................... 10
Appendix A. Transformer datasheet and pictures................................................................................... 11
Appendix B. Bill of Materials ............................................................................................................... 12
Appendix C. AUX Board layout ............................................................................................................ 14
Appendix D. Alternative Start-up Circuitry ............................................................................................ 15
This evaluation board is intended for research and development and for expert use in the research and
development facility only. This board is not intended for use for volume production.

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
1 Board information
1.1 Schematics
Please refer to Appendix B for BOM, Appendix C for Layout and Appendix D for alternative startup circuit to improve
efficiency.
1.2 Flyback Transformer
A customized transformer manufactured by Würth Elektronik (www.we-online.com), has been designed.
It is possible to order and get all the information by contacting the producer referring code n. 750316318.
The datasheet of the transformer can be found in Appendix A.
The primary side is composed by two windings in series, while the secondary side has been implemented with two
windings in parallel. The half-windings are interposed, in order to reduce the leakage inductance around 1% of Lpri. This
will impact the switching behavior of the MOSFET. In addition, the windings have been implemented with Litz wire to
reduce the losses due to skin effect.
Parameter
Calculated
Transformer (E25)
Primary inductance
1.07 mH
0.95 mH ±10%
Leakage inductance
--
1% (9 µH)
Maximum primary current
0.86 A
1.5 A *
Turn-ratio primary to secondary
10
10 ± 1%
Turn-ratio secondary to auxiliary
1.92
2 ± 1%
Table 2 - Calculated parameters and characteristics of the used transformer.
Figure 3 - Full schematic of the AUX board
* Core saturation current

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
2 Board usage
2.1 General information before cabling and powering the board:
-Check carefully that the input voltages are within the maximum input range in table 1.
-Double check the cabling before powering the board.
-This board is protected against overload and short circuit.
-Avoid any imperfect connection that can create sparks
-Check the isolation class and section of the cables.
-Apply all appropriate checks and precautions for use of a high voltage board.
-Refer to the notice at the end of this document for proper usage of this board.
-Only use in a technical environment by professionals trained to safely manage high voltage boards.
-This board is only for evaluation purposes and it’s not guaranteed for prolonged usage or usage
in any final product

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
2.2 Cabling
2.2.1 3 Phase AC connections:
The board can be connected directly to 3 Phase mains as for the below connection guide.
Figure 4 - 3Phase AC connection
2.2.2 DC connections:
If the board is connected to an DC source please follow the below connection guide
Figure 5 –DC Voltage input connection
Please note that the board mounts diodes for the possibility to be supplied by AC. Due to high voltage input compatibility
are used 2 diodes in series. To avoid the drop of diodes effect on functionalities (i.e. efficiency measurements) connect
directly to the positive of Capacitor C6 and negative of capacitor C8
Phase 1
Phase 2
Phase 3
Neutral
12Vdc To Load +
Volt Ref To Load -
400Vac to
480Vac 3 Phase
Input DC Voltage+
Input DC Voltage -
12Vdc To Load +
Volt Ref To Load -

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
2.3 Test points
The AUX board contains several testing points, from which it is possible to observe the board operation. The test points
and the related signals are given in the following table.
Test Point
Signal***
TP1
Controller ZT pin
TP2
Controller FB pin
TP5
Controller OUT pin
TP7
Controller VCC pin
TP8
Controller Brown-out pin
TP10
Board VOUT
TP11
Trafo sec. terminal
TP13
Controller GND pin
TP16
Input voltage V IN
TP18
Controller CS pin
Table 3 –Testing points in AUX board.

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
3 Implementation and practical tests with AUX Board
The AUX board has been implemented in a printed circuit board (PCB), whose dimensions are 8 cm x 8 cm –see Figure
6. All surface mount devices (SMD) components have been assembled on the bottom side. On the top side were soldered
the thru hole devices (THD) and connectors. The layout of both sides is given in Appendix C. In the following sections,
experimental results at different input voltages and output power are presented and discussed.
Figure 6 –Top side (left) and bottom side (right) of the AUX board.
3.1 Operation at no load
At no load operation, the controller goes in burst mode –see Figure 16 –and the switching frequency is reduced to some
kHz. The dynamic losses of the Flyback components are consequently reduced. Measured stand-by losses are given in the
table on the right side of Figure 7. They are expected to come mainly from the resistive dividers present on the circuit:
input capacitor balance, start-up and input voltage sense.
DC voltage
Stand-by losses
300 V
0.372 W
900 V
1.7 W
Figure 7 –Waveforms from Flyback switch during burst mode, for VDC = 800 V.
T1
Q1
D20
U1
VGS
VDS
VDC=800V

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
3.2 Normal operation
Figure 8 presents the waveforms from SCT2H12NZ during normal operation of the Flyback circuit, for VDC = 800 V and
different values of output power. Time periods ton, tdecay and tdelay are indicated, according to the description in Error!
eference source not found..
For light power –left side –the controller waits several valleys to switch the MOSFET on. Therefore, the switching
frequency is quite low, eventually below the defined frequency range.
As the output power increases, the number of oscillations is reduced. As consequence, tdelay is reduced, and the switching
frequency increases. At nominal power, the turn-on occurs already in the first valley.
Pout= 5W
Pout= 20W
Pout= 40W
Figure 8 –Waveforms from Flyback switch during different output power conditions, VDC = 800 V.
3.3 Efficiency and temperature measurements
The efficiency of the AUX board has been measured for three different input voltage values. The efficiency curves are
shown in Figure 9. As a DC power source was used, it was connected directly to the input capacitors. This way, the
rectifying bridge is by-passed, saving the losses that would otherwise come from the bridge diodes.
Efficiency is increasing with the output power, and it is higher for lower levels of input voltage. For VDC = 300 V, the
measured peak efficiency η=88% at POUT=33W –above that the overload protection was activated.
The temperature of the main components of AUX board has been measured, namely the SiC MOSFET (Q1), the Flyback
transformer and the secondary diode (D20). The measurements were performed using an infrared camera. The thermal
images are presented in Figure 10. They were taken at room temperature, VDC=800 V and POUT=40W. The case
temperature of the SiC MOSFET (Sp1) is around 84°C, even without the use of an external heatsink and without forced
ventilation. The temperature of the Flyback transformer (Sp2), registered on the winding corner, is slightly above 70°C.
The measured temperature of the output diode (Sp3) was around 95°C.
VGS
VDS
tdelay
tdecay
ton
fsw=45.7 kHz
VDC=800 V
VGS
VDS
fsw=105.0 kHz
VDC=800 V
VGS
VDS
VDC=800 V
fsw=109.0 kHz

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
Figure 9 –Efficiency curve of the AUX board for several DC input voltage values.
Figure 10 –Temperature measurements from main components of the AUX board.
Sp1
Sp2
Sp3

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User Guide
BD7682FJ-EVK-301 EV BOARD
© 2018 ROHM Co., Ltd.
No. 60TRxxxJ Rev.001
No. 60UG064E Rev.001
19 Feb 2018
4 Summary
This document presented the design procedure of an auxiliary power supply, based on Flyback topology, focused on
industrial applications as auxiliary power supply. Main devices of this design are the SiC MOSFET SCT2H12NZ, with very
low on resistance, and the quasi resonant controller BDF768xFJ-LB. They enable a simple electrical and thermal design,
reducing the amount of devices, and avoiding the use of heat-sink for the Flyback switch.
Experimental tests in the AUX board proved the operation principle of the quasi resonant controller. Thermal and efficient
measurements showed also the reduced amount of losses in the SiC MOSFET, proving it is the right choice for auxiliary
supplies in 3-phase industrial systems.
5 References
[1] Datasheet of SCT2H12NZ http://www.rohm.com/web/global/datasheet/SCT2H12NZ/sct2h12nz-e
[2] Datasheet of BDF768xFJ-LB controller family, available at:
http://www.rohm.de/web/de/products/-/product/BD7682FJ-LB
[3] Application Note “BD768xFJ-LB series Quasi-Resonant converter Technical Design”, available at:
http://rohmfs.rohm.com/en/products/databook/applinote/ic/power/acdc_converter/bd768xfj-lb_appli-e.pdf