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DC Fan Speed Control PWM Signal Introduction

Wayne_ChenADDA RD Chief Engineer

Wayne@adda.com.tw886-8-755-0579 ext:326

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Topical:

1. Speed Control Fan Configuration (old version)

2. What is PWM Signal ?

3. PWM Control Methods Introduction

4. PWM Fan Specification

5. PWM Fan Sample

6. Q & A

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1. Speed Control Fan Structure (old version)

Vcc

Fan

1-1. Use ON/OFF control by Transistor1-1. Use ON/OFF control by Transistor

AdvantageAdvantage：：

I.I. Easy design and control method Easy design and control method

II.II. Price cheaper.Price cheaper.

Disadvantage :Disadvantage :

I.I. Power Dissipation is a design Power Dissipation is a design issue. issue.

II.II. Not use friendly. Not use friendly.

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2. What is PWM Signal ?• PWM(Pulse Width Modulation): It’s a fixed frequency

and pulse modulated for fan speed control. • Whenever change the duty cycle, the fan speed will be

changed by system requirement.

Figure : PWM Control Signal

Duty Cycle 20%Lowest Speed

Duty Cycle 50%Middle Speed

Duty Cycle 80%High Speed

Cycle

Duty Cycle

Duty Cycle = DT / T (%)

(DT)

The Purpose are :The Purpose are :

1. The power dissipation will be saving.1. The power dissipation will be saving.

2. And the working time will be increasing if the battery 2. And the working time will be increasing if the battery could not be charged outside. (especially NB system)could not be charged outside. (especially NB system)

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3. PWM control Methods introduction 3-1Speed Control Fan Structure (old version)

Fan

+Vcc

DisadvantageDisadvantage：：

I.I. Poor Reliability ( Transistor are Poor Reliability ( Transistor are On/OFF continuously)On/OFF continuously)

II.II. Error judgment of tachometer Error judgment of tachometer signal.signal.

AdvantageAdvantage：：

I.I. Easy design and control method Easy design and control method

II.II. Price cheaper.Price cheaper.

Use ON/OFF control by TransistorUse ON/OFF control by Transistor

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Actual Tachometer Signal Waveform

PWM input signal

Error judgment Error judgment of tachometer of tachometer signalsignal

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AdvantageAdvantage：：

I.I. The better The better Reliability Reliability

II.II. RPM StableRPM Stable

III.III. Power efficiency Power efficiency saving.saving.

DisadvantageDisadvantage：：

I.I. Cost expensive. Cost expensive.

II.II. Control Circuit Control Circuit ComplexComplex

OPAIntegrationCircuit

PWMSignalInput

Vcc

Fan

3-2. Regulator Control Fan Configuration3-2. Regulator Control Fan Configuration

(Current version For Notebook <Three Wires>)(Current version For Notebook <Three Wires>)

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PWM input signal

tachometer tachometer signalsignal ( normality)

Actual Tachometer Signal WaveformActual Tachometer Signal Waveform

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3-3. Control PWM Fan Configuration<Four Wires>

PWM Fan

Vcc

Tachometer Output Signal

Low Speed

High SpeedPWM

Signal Input

System Motherboard

Low Speed

High Speed

Vcc

OscillatorComparator

IntegrationCircuit

PWMSignalInput

Driver DCMotorBlock

ControllerBlock

ReferenceVoltage

PWM control Configuration

System Fan

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3-4. Next Generation Version PWM Control Fan: Type A

Type AType A

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3-5. PWM Control Fan: Type B

Type B

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4-1. PWM Input Signal Specification (from system)

• PWM Operating Frequency : 25kHz ± 5kHz

• Maximum Input Low Voltage (VIL-MAX) = 0.8V

• Minimum Input High Voltage (VIH-MIN) = 2.0V

• High Input Impedance (10K ohms at least )

(Consider Fan-In Issue， Driver Capability)

VIL-MAX=0.8V

VIH-MIN=2.0V

Frequency = 25kHz

InputImpedance

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4-2. PWM Fan Specification• Operation Voltage : 5V or 12V ± 10% • Function: Locked Protection and Auto-restart• Apply the Open Collector or Open Drain

Tachometer Output Signal• Low Speed setting with 0~17% (or 20%) on Same

PRM level (Type B)

Open Collector Configuration

FG

Open Drain Configuration

FG

Vcc

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5. PWM Fan sample5-1. Type A( For NB fan suggestion)

PWM Fan Duty Cycle v.s Speed6000rpm Model

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Duty Cycle

Spee

d

Fan Stop Duty Cycle

Fan Start_up Duty Cycle

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5. PWM Fan sample5-2. Type A( All kind of fan could be used.)5-2. Type A( All kind of fan could be used.)

PWM Fan Duty Cycle v.s SpeedAD8025 Model

0

500

1000

1500

2000

2500

3000

3500

4000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Duty Cycle

Sp

ee

d

Fan Stop Duty Cycle

Fan Start_up Duty Cycle

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5. PWM Fan sample

PWM Fan Duty Cycle v.s SpeedAD8025 Model

0

500

1000

1500

2000

2500

3000

3500

4000

0% 10% 17% 20% 30% 40% 50% 60% 70% 80% 90% Full

Duty Cycle

Spee

d5-3. Type B(For Desktops fan suggestion)5-3. Type B(For Desktops fan suggestion)

It’s same duty cycle curve for fan start_up and stop.

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6. Question & Answer (The End)