ZXBM200X データシートの表示（PDF） - Diodes Incorporated.

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ZXBM200X

ZXBM200x SERIES OF VARIABLE SPEED 2-PHASE FAN MOTOR CONTROLLER

Diodes Incorporated. 

Applications Note AN36

Issue1 - JULY 2002

The buffered type of Hall sensor should be of

the latching or bipolar type. These have an

internal amplifier and thus provide a large

amplitude square wave output. This signal is

single ended and is applied into Pin 3, H+, as

shown in Figure 2. On some buffered Hall

sensors the output is of the Open Collector

type and will therefore require a pull-up

resistor (R1 in Figure 2) to attain the full signal

amplitude. The H- pin will require to be held at

a voltage approximately half the Hall output

swing. The potential divider R2 and R3 in

Figure 2 is provided for this.

Speed Control

Applied power, motor efficiency and

mechanical loading determine maximum

motor speed, the controller allows full speed

adjustment by modifying the applied power

only.

Speed control is attained through an integral

Pulse Width Modulation (PWM) circuit within

the ZXBM200x series. The PWM signal

controls the speed by switching the

respective active Phase output at a much

higher frequency, typically 25kHz, compared

with the commutation1 frequency. The PWM

is used to control the percentage of time the

output driver is turned on for. This PWM

circuit is controlled through two pins, Pin 6,

the CPWM pin, and Pin 4, the SPD input. The

CPWM pin has a capacitor attached of 150pF to

produce a 1V p-p 25kHz triangular waveform.

The circuit has also been used quite

successfully with 100pF to produce a PWM

frequency of 34kHz. The motor speed is

determined by the voltage at the SPD pin.

There are two methods for controlling the

ZXBM200x using the SPD pin. The first is the

direct control of the SPD pin by a voltage from

an external voltage source or system

controller. The second method is to use a

thermistor as a temperature sensor so as the

ZXBM200x is in a feedback loop to control the

fan speed against the temperature

conditions. A third method of control is

available by applying a PWM signal from an

external source. All these will be discussed in

more detail in the following sections.

Voltage control of the SPD pin

Voltage control is achieved by applying a

voltage of between 1 volt and 2 volts to the

SPD pin. A voltage of 1 volt on this pin will

ensure the drivers are switched on for 100%

of the PWM duty cycle i.e. the motor will run

at full speed.

Progressively increasing the SPD voltage to 2

volts will reduce the percentage of PWM duty

cycle drive to the Phase windings to reduce

the motor speed. With a SPD voltage of 2

volts the outputs will be switched off all the

time i.e. no drive will be present.

In reality a 2-phase DC brushless motor will

have a minimum practical rotational speed

below which the motor will not run. This is

very much dependant upon the power, size

and mechanics of the motor concerned but

could well mean that anything less than 40%

PWM drive, represented by a SPD voltage of

1.6V, is impractical.

The ability of starting the motor under such

low speed conditions also has to be

considered as in most cases a motor will

rotate at a far lower power input than is

needed to start it. Further discussion will be

given on this subject later.

Note:

1 Commutation is the process of alternate (phase)

switching at the speed of rotation.

AN 36 - 3

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