Motors are found almost everywhere in our daily life. If you take a look inside a common home appliance, like a refrigerator, you’ll find some fancy applications of stepper and BLDC motors, the damper and the BLDC fan. These play very important roles to keep the refrigerator working efficiently.Damper
The damper is a small flap that controls the flow of air from the freezer to the refrigerator. It is usually found in the top of the fridge or on the back panel near the top. The damper is controlled by a thermostat, triggering it to open and close depending on the temperature of the air in the refrigerator. Inside the damper there is a permanent magnet (PM) stepper motor and the gear box. Let’s tear down (That is my favorite part of being an engineer!) a damper for a close look at the inside.
As you see, the small PM stepper drives the gear box and makes the flap open or close. This stepper motor is driven by 12 volts and usually doesn’t need current regulation. So how can you tell whether a stepper is voltage driven or current driven? Just measure the DC resistance of the motor phase. If the resistance is about 30ohm to several hundreds of ohms, it should be voltage driven. If the resistance is below 20 ohm, mostly below 10 ohm, it is most likely a current-driven motor. Generally, voltage-driven motors are usually seen on small power PM steppers and unipolar steppers that have very small driven current so that the resistance loss of I2 x R does not get too big. The current-driven type can be found in most mid- or high-power hybrid steppers.
Ok, let’s get back to the topic of the damper. The one I opened has a PM voltage-driven stepper inside with about a 400 ohm phase resistor. Let’s find a perfect driver for it. The DRV8848 is the very one. The 4V to 18V driving voltage range, dual H-Bridge integration, PWM control interface, up to 2A operation, and full protection, makes it perfect to do the damper-driving job. If you want to know more about the driving logic details, check out the reference design for a complete solution with all hardware and software open.
As you can see in the picture below, the refrigerator fan modules keep the cold air cycling and distribution inside the refrigerator uniform without frosting, greatly enhancing the performance of the refrigerator.
This fan module includes a single- or three-phase brushless motor. Now, we see more fans with three-phase BLDC because of its ability to provide compact size with more quiet and efficient long term operation. Both Hall-sensored or sensorless control can be found in this application. Thanks to TI’s three-phase sensorless sinusoidal motor driver, the DRV10983, we can achieve cutting-edge 180° sensorless BLDC control without any struggling on the control algorithm.
We included the DRV10983 as the fan driver for high efficiency and supper quiet operation in the reference design. Since most refrigerator manufacturers are now using PWM supply to power up the fan module and change the speed, we applied a closed-loop speed control utilizing FG feedback and PWM power regulation with minimum hardware change to the existing solutions. With closed-loop speed control, we can keep the desired speed value regardless of the motor parameter variations, power supply changes, mechanical wearing or life time. Learn how the speed control benefits the operation in this video.
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