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AC/DC

Isolated Flyback Converters: Performance Evaluation and Check Points

Overview and important features of a power supply IC used in example performance evaluation

In this section, we explain how to evaluate the performance of a designed isolated flyback converter. To this end, we need to understand what kind of isolated flyback converter is designed based on specific design goals and specifications. Obviously because in actuality the design task is performed first, one might suggest the use of the design information; however, in this section we begin by verifying the underlying power supply specifications.

In this design example also, we build a power supply circuit through the use of a power supply IC. As mentioned previously, newer power supply designs are basically and substantially dependent upon the capabilities and functions of the power supply IC. To implement the required power supply specifications, we start out by looking for a power supply IC that can satisfy those specifications and we undertake the design task in accordance with the design examples that are provided with the IC. That said, we begin by checking out the various aspects of the power supply IC to be employed.

PWM Type AC/DC Converter IC: BM2P014

For an evaluation circuit, we use an AC/DC converter IC BM2P014. The figure below illustrates the connections to external components for the construction of internal IC functional blocks and an isolated flyback converter. In nutshell, the IC comprises the following features:

  • Built-in 650V switching MOSFET
  • PWM frequency : 65kHz
  • Current Mode with Per-cycle Over Current Limit function
  • Burst operation/Frequency Reduction function at light load
  • VCC pin Under Voltage protection/Over Voltage protection
  • SOURCE pin Open protection/ Short protection/ Leading-Edge-Blanking functions
  • Soft start
  • Secondary Over Current Protection Circuit (for Isolated devices)
  • Operating power supply voltage range:
    VCC: 8.9V to 26.0V, DRAIN: up to 650V
  • Operating Current: Normal mode 0.950 mA (typ.), Burst mode 0.400 mA (typ.)
  • Operating temperature: - 40℃ to +105℃
  • Package: DIP7 9.20×6.35×4.30 mm

18A_graf01

Given the above diagram, the following key points emerge from these features and diagram:

- The built-in high voltage MOSFET eliminates from the design process the need to select a MOSFET or
   set up component values.

- From the configuration example, it can be seen that only an extremely small number of external
   components are employed.

- For high efficiency at light-load condition, burst operations are enabled and power consumption is
   reduced at standby.

- The IC provides various required protective features.

- In terms of operating temperature range, the IC is well-suited to industrial applications.

 

In this example, we design an isolated AC/DC flyback converter using the type of IC offering the above features.

Further details on the power supply IC may be found in the BM2P014 Data Sheet.

Key Points:

・Evaluating performance involves a verification as to whether given design goals are successfully attained. In other words, an evaluation is possible only if clearly defined design goals are established.


Power Supply Design Technical Materials Free Download

Power Supply Design Technical Materials Free Download

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