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Photocoupler-Free Isolated Flyback DC-DC ConverterDevelopment Predicated on Uses in Industrial Equipment


-From here, I would like to ask about the functions and features of the DB7F series of ICs.

We have been discussing the details of operation for awhile now, so let’s again return to basic concepts. The DB7F series of ICs are used to construct isolated flyback converters. Regulation control is performed on the primary side, and so there is no need for a photocoupler or transformer tertiary windings for feedback path isolation. And a MOSFET is incorporated, with the further advantages that miniaturization and improved reliability become possible.

Let’s look at the functions as a power supply IC, taking the BD7F100HFN-LB and the BD7F100EFJ-LB of the series as examples. These two products differ only in the packages used; their basic functions are the same.


  • No need for a photocoupler or transformer tertiary windings.
    • -The output can be set by two external resistors
      and transformer turns ratio.
  • Uses unique adaptive on-time control technology.
    • -High-speed load response is realized and
      external phase compensation parts
      are unnecessary.
  • Fixed switching frequency and
    low output ripple
  • Highly efficient light load mode available (PFM operation)
  • Shutdown/enable control
  • Built-in N-channel MOSFET
  • Soft start function
  • Output load compensation function
  • Protection functions:
    • -Vin under-voltage lock-out protection (Vin UVLO)

    -Over-current protection(OCP)
    -Thermal shutdown protection (TSD)

【Key Specifications】

  • Operating supply voltage: 3 V to 40 V
  • Operating voltage of SW terminal: 60 V (Max)
  • Over-current limit: 1.25 A (Typ)
  • Switching frequency: 400 kHz (Typ)
  • Reference voltage accuracy: ±1.5 %
  • Supply current at shutdown: 0 μA (Typ)
  • Operating supply current: 2 mA (Typ)
  • Operating junction temperature: -40°C to +125°C

【Packages】 W (Typ) × D (Typ) × H (Max)

  • HFN: HSON8 2.90 mm×3.00 mm×0.60 mm
  • EFJ: HTSOP-J8 4.90 mm×6.00 mm×1.00 mm

【Special Notes】

  • Guaranteed long time supply availability to meet the requirements for industrial equipment


-Considering that the operating voltage is 40 V and that the operating temperature range Tj is from -40°C to 125°C, it appears that these products were developed with industrial equipment in mind.

That’s right. Of course they are designed for general-purpose use, but they were developed assuming they would be used in isolated power supplies for industrial equipment. The 40V operating voltage fully supports 24 V as well as 12 V equipment, and from these voltages, general-use 5 V and ±15 V voltages to drive gates can also be generated. And, they operate starting from 3 V, and so are compatible with 5 V input applications as well.

-So this series is also part of ROHM’s efforts to ensure long-term supply of “-LB” specification products for industrial equipment.

Where products intended for industry are concerned, we are moving toward guaranteed long time supply availability. This has been received favourably by our industrial equipment customers.

-Please describe the series lineup.

The DB7F series currently consists of four models, which are the BD7F100HFN-LB, HD7F100EFJ-LB, BD7F200HFN-LB, and BD7F200EFJ-LB. Two device types are each supplied in two different packages. The table below should be easy to understand. Customers can choose products according to the output power and space requirements. The BD7F200xxx-LB products have a minimum input voltage of 8 V, and so do not support 5 V input.

Part No. Package Output Power Max.Input Voltage Input Voltage Range Over Current Limit Switching Frequency Operating Temperature Functions
BD7F100HFN-LB HSON8 1W (Vin=5V)
5W (Vin=24V)
45V 3.0~40V 1.25A 400kHz
-40℃~+125℃ Enable
Soft start
Highly efficient light load mode
Over-current protection
Thermal protection
BD7F200HFN-LB HSON8 10W (Vin=24V) 8.0~40V 2.75A

-The features explained at the beginning–shutdown/enable, soft start, various protection features–have I think become standard functions in the power supply ICs of recent years. But two other features, “adaptive on-time control” and “output load compensation”, are unique functions, aren’t they.

Yes. They are both ROHM-specific features.

-Could you please explain each of these?

( Continued to Part 4 )

Information on Downloading Technical Documents

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

Download Technical Documents

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

Ask Direct to Engineers