Single Resistor Replaces Optocoupler and/or Aux Winding in Flybacks

Typically, in order to stabilize the output voltage of isolated power supplies methods using limited life components such as optocouplers and/or auxiliary winding are employed. In contrast, ROHM has developed isolated flyback dc-dc converter controllers that eliminate the need for these types of feedback circuits.

Applying feedback at the primary side in order to detect the voltage and current at the secondary side eliminates the need for an optocoupler or auxiliary winding along with other necessary components.

This simplifies design considerably, resulting in improved reliability, greater energy savings, and increased miniaturization. Stable output voltage is achieved using just a single resistor.

ROHM’s proprietary flyback method makes it possible to stabilize the output voltage using only a single resistor, eliminating the need for a photocoupler or auxiliary winding. This greatly simplifies design while contributing to smaller sets. In addition, long-term supply is guaranteed, ensuring worry-free use in industrial applications.

The simple, efficient design is well-suited for industrial power supplies (i.e. FA equipment), power storage systems, solar inverters, servo amps, and high power inverters.

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In addition to samples of the BD7F100xxx-LB and BD7F200xxx-LB, an evaluation board integrating the BD7F100HFN-LB is available for purchase through online distributors.

The BD7F100HFN-EVK-001 evaluation board makes it easy to evaluate and verify operation of Rohm’s isolated flyback dc-dc converter controller (24V input, 5V/800mA output).

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Adaptive ON time control improves load response characteristics

Conventional isolated power supply control ICs are susceptible to large variations in output voltage with instantaneous load current fluctuations.

In response, ROHM developed an adaptive ON time control method based on the market-proven ON time control design utilized for non-isolated power supply control ICs.

This new method significantly improves response characteristics against instantaneous load current fluctuations, reducing output voltage variations by more than 65% – to less than 200mV (at a load current of 1A and rise time of 100µs) – resulting in improved reliability.

Key Features

  • High-speed load response achieved through adaptive on-time control
  • Automatic light load mode enables high efficiency throughout the entire load range
  • Eliminates the need for parts that cross the isolation boundary, improving safety
  • Limited-life components such as optocouplers are not required enabling longer-term operation
  • Supports multi-output configuration for superior cross regulation
  • The lineup includes 2 models offered in 2 different package types.

ROHM Semiconductor
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