New Isolated Low Power Flyback DC/DC Converters

Optocoupler-less flyback converters provide stable output voltage and allow for small and highly reliable isolated
power supply solutions

ROHM Semiconductor unveils its new BD7F100HFN-LB IC as part of the family of optocoupler-less isolated flyback converters. The use of this IC simplifies the design of an isolated DCDC converter as the required feedback, normally implemented with expensive optocoupler or complex transformer with 3rd wiring is not anymore necessary. As the number of parts and the board space are reduced drastically, the result is a small-sized and high-reliability isolated type power supply solution.

The IC adopts the ROHM's original Adapted-Type ON-Time Control Technology to control the output voltage. The output voltage is adjustable with external resistor and transformer winding ratio. The device doesn't require external phase compensation parts and an high-speed load response is achievable, which facilitates highly efficient isolated power supply applications. The solution helps saving components, mitigates design risks, simplifies component sourcing management and offers more compact and efficient solutions.

The new device features an input voltage scope of 3V to 40V, an integrated 60V MOSFET switch as well as a soft start function and shutdown control. Ripple noise is reduced due to the fixed switching frequency. PFM mode operation allows high-efficiency in case of light loads. A complete range of protection functions such as input low voltage protection (VIN UVLO), over-current protection (OCP), output short circuit protection (SCP) and temperature protection (TSD) guarantees stable operation and high reliability. Condensation issues occurring in conventional designs with optocoupler are eliminated, improving dramatically the reliability and lifetime of the products. Additionally, ROHM guarantees longevity of supply for this converter in order to address the industrial market.


Key Features

  • Guaranteed long time supply and availability for industrial applications
  • No need for an optocoupler or a transformer 3rd winding
  • The output voltage can be set by two external resistors and the transformer turns ratio
  • Uses Original Adapted Type ON-Time Control Technology
  • High-speed load response
  • No phase compensation required
  • Fixed switching frequency and low power output ripple
  • Efficient light load mode (PFM operation)
  • Shutdown Control
  • Built-in N-Channel MOS
  • Soft start function
  • Output load compensation function
  • Complete protection functions:
    • Input low voltage protection (VIN UVLO)
    • Over-current protection (OCP)
    • Output short circuit protection (SCP)
    • Temperature protection (TSD)


Key Specifications

  • Supply Voltage of Operation: 3 V to 40 V
  • SW Terminal Operating Voltage: 50 V (Max)
  • Built-in MOS Current Limit: 1.25 A (Typ)
  • Switching Frequency of 400 kHz (Typ)
  • ±1.5 % of Reference Voltage Accuracy
  • Quiescent Current: 0 μA (Typ)
  • Operating Current: 2 mA (Typ)
  • Operating Ambient Temperature: -40 °C to +85 °C
  • Junction Temperature of Operation: -40 °C to +125 °C



The new optocoupler-less flyback DC/DC converters are ideal for isolated power supplies for industrial equipment, gate driver circuits secondary power supplies, power supplies for optocoupler, digital isolators and isolated interface drivers power supplies.



BD7F100H samples are available starting from July 2015. Evaluation boards are available on demand.