Rohm BD7682FJ-EVK-301 Manual de usuario

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No. 60AP001E Rev.001

2017.4

User Guide

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

Dsec VOUT

AC Filter Diode

Bridge

Lprim Lsec

Laux

Brown

Out

Gate

VCC

Gate

Isense

Feedback

Isense

Feedback

BD7682FJ

Daux

COSS

Optocoupler

VDC

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

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

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 ± 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

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

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

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

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.

D20

VGS

VDS

VDC=800V

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User Guide

BD7682FJ-EVK-301 EV BOARD

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

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

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

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