The Industry’s First DC/DC Converter Capable of DC Fan Motor Speed Control

ROHM has recently announced the availability of a buck DC/DC converter optimized for DC fan motor power supplies used in applications such as cold air circulation in refrigerators.

In recent years, ‘Smarter’, ‘Smaller’, and ‘Higher Efficiency’ have emerged as the 3 biggest challenges facing the electronics industry, which is experiencing increased market demand. In addition, it is said that close to 50% of the world’s electricity demand is used to drive motors, making it necessary to achieve more intelligent, compact, high efficiency motor drive in order to protect the environment and improve structural designs.

Until now, however, DC fan motor power supply blocks used in refrigerators and other equipment are primarily configured using discrete components, making it difficult to provide high accuracy control or carry out high frequency drive. As a result larger coils and output capacitors are required for the peripheral circuit, increasing mounting area considerably, which can be problematic.

The BD9227F is the industry’s first power supply IC capable of controlling the rotational speed of DC fan motors with high accuracy by linearly varying the output voltage based on the PWM duty signal generated by the MCU. In addition to more accurate control vs conventional discrete configurations, ROHM leverages proprietary IC analog circuit design technology to achieve circuit optimization along with high frequency (1MHz) drive. This supports the use of smaller peripheral components (i.e. coil, output capacitor), reducing footprint by 75% while improving power conversion efficiency by 19% (at 300mA output), contributing to greater accuracy, increased miniaturization, and higher power conversion efficiency in DC fan motor applications.

Key Features

1．Linear output voltage control ensures high accuracy control of motor rotational speed

With conventional discrete configurations there is no output voltage linearity with respect to the pulse duty supplied to the PWM terminal, making it difficult to accurately control the motor rotational speed.

In contrast, the BD922F provides linear control of the output voltage based on the PWM duty signal generated by the MCU, enabling high accuracy control of the rotational speed of DC fan motors.

2．Mounting area reduced by 75%

Discrete solutions do not support higher frequency PWM signal input from the MCU. As a result larger coils and capacitors are required, which can present problems by significantly increasing mounting area.

The BD9227F, on the other hand, features internal frequency control that allows for drive frequencies up to 1MHz, reducing mounting area by approx. 75% over conventional systems by enabling the use of smaller peripheral components, including coils and capacitors.

3．High efficiency across the entire load range

The BD9227F improves efficiency across the entire load range. For example, at a load of 300mA power conversion efficiency is increased by 19%, and the difference becomes even more pronounced at higher loads.

4．Supports 100% duty

Integrating a high-side PMOS makes it possible to generate an output voltage at 100% duty – rare for an IC.

Specifications

Terminology

PWM (Pulse Width Modulation) / Duty

PWM is a method for controlling the output voltage by varying the ON/OFF times in each cycle through repeated switching. Duty refers to the ON-time ratio within each PWM period, with a higher ratio corresponding to higher output voltage.