ZXBM200X 查看數據表（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

Figure 5

showing resistive divider used with <100k⍀ thermistors

One problem with using an external potential

divider (R1 & R2 in Figure 5) is that the motor

becomes susceptible to supply voltage

changes. Say the supply voltage falls,

normally the speed would drop due to less

voltage across the windings, however as the

potential divider is across the supply, as the

voltage falls so the voltage at the SPD pin will

fall. As a lower SPD voltage represents a

higher speed so a lowering of the supply

therefore causes the fan to speed up. To

overcome this it is probably best to use a

Zener regulated supply to the ZXBM200x.

The following Table 1 gives an indication of

the values required for R1 and R2 against

different thermistor values. It should be

noted that these are only for guidance as the

final value will depend upon the thermistor

and motor characteristics and so will need

fine adjustment by experimentation. If the

ZXBM200x device is to be run from a Zener

regulated supply to control the speed verses

supply voltage variation so R1 and R2 will

need allowances made for the voltage value

of Zener chosen.

As the Bipolar drivers have a slower turn-off

characteristics when driven from the

ZXCB200x series slightly different values of

R2 are required over those for MOSFETs.

When driving the SPD pin from a signal or

thermistor remote from the fan or controller

there may be a need to provide noise

protection at the SPD pin. In order to maintain

a smooth speed control characteristic this

will take the form of a capacitor of between

100nF and 1␮F connected between the SPD

and Gnd pins somewhere close to the device.

This should suffice for most purposes and

can be determined for each particular

application.

A capacitor on this pin also has an effect on

the start-up characteristic of the motor as the

charging of the capacitor will lag behind the

rise of the supply voltage. As a low voltage on

the SPD pin represents a higher speed the

effect at start-up, if the SPD value is not set for

full speed, will be for the motor speed to

increase past its allotted point before settling

back to that required. Whilst for the capacitor

values stated above this effect may not be

noticeable, for values greater than 1␮F it can

be used to advantage. In situations where the

motor will be regularly started at a speed

lower than its practical start value it can help

to get motors started, in effect giving the

motor a ‘kick’ to start it.

Table 1

Thermistor Supply MOSFET

Value Voltage R1 R2

Bipolar

R1 R2

5V 3.3k⍀ 2.2k⍀ 3.3k⍀ 1.5k⍀

4.7k⍀

12V 6.8k⍀ 1.2k⍀ 6.8k⍀ 1.0k⍀

24V 15k⍀ 1.3k⍀ 15k⍀ 1.0k⍀

5V 5.6k⍀ 3.3k⍀ 5.6k⍀ 2.4k⍀

10k⍀

12V 13k⍀ 2.2k⍀ 13k⍀ 1.8k⍀

24V 36k⍀ 3.3k⍀ 33k⍀ 2.2k⍀

5V 24k⍀ 12k⍀ 22k⍀ 8.6k⍀

47k⍀

12V 56k⍀ 9.1k⍀ 56k⍀ 7.5k⍀

24V 130k⍀ 10k⍀ 130k⍀ 8.6k⍀

5V

*

*

**

100k⍀

12V

*

*

*

*

24V

*

*

*

*

* Note: Not normally required - dependent upon

thermistor and speed range needed.

AN 36 - 5

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