Fan speed pulse filter for a PWM fan

• US 6,262,549 B1
• Filed: 06/29/2000
• Issued: 07/17/2001
• Est. Priority Date: 06/29/2000
• Status: Expired due to Fees

• Current Assignee: Fairchild Corporation (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: Hsueh, Cheng-chi, Yang, Ta-yung, Lin, Jenn-yu G.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US09/607,024
• Time in Patent Office: 383 Days
• Field of Search: 318/461, 318/463, 318/640, 318/464, 388/909, 388/912, 324/160, 324/163, 324/166
• US Class Current: 318/463
• CPC Class Codes: G01P 3/481 of pulse signals
• CPC Class Codes: G01P 3/489 Digital circuits therefor
• CPC Class Codes: Y10S 388/912 Pulse or frequency counter

Abstract

A fan speed pulse filter is used for a PWM fan. The filter comprises a comparator, a latch circuit and a synchronizer. The fan unit, including a tachometer pulse output, is controlled by a PWM signal for determining the fan speed. By comparing the PWM signal with a reference voltage, the comparator generates a reset signal. The latch circuit, coupled to the comparator and the fan unit, receives the reset signal and the tachometer pulse and outputs a filtered tachometer pulse containing no phantom pulses. Furthermore, a synchronizer generates an output signal without interruption when the PWM signal is switched off.

Claims

1. A fan speed pulse filter for a PWM fan, comprising:

a comparator for receiving a PWM signal, wherein the comparator generates a reset signal by comparing the PWM signal with a reference voltage; and

a latch circuit coupled to the comparator and a fan unit, for receiving the reset signal and a tacho-pulse signal generated by the fan unit and outputting a pole signal containing no phantom pulses, wherein when the reset signal is transient from low to high, the pole signal is latched at a low level until the tacho-pulse signal is transient from low to high, and then the pole signal varies in response to the tacho-pulse signal.

2. The fan speed pulse filter for a PWM fan of claim 1, further comprising:

a synchronizer coupled to the latch circuit for generating an output signal without interruption when the PWM signal is off;

an up-counter coupled to the synchronizer;

a Q-buffer coupled to the up-counter and the synchronizer;

a down-counter coupled to the Q-buffer and the synchronizer; and

an oscillator coupled to the synchronizer for providing system clock signals to the synchronizer, the up-counter, the Q-buffer and the down-counter.

3. The fan speed pulse filter for a PWM fan of claim 1, wherein the reference voltage is generated by a voltage divider consisting of a first resistor and a second resistor.

4. A fan speed pulse filter for a PWM fan, comprising:

a comparator for receiving a PWM signal, wherein the comparator generates a reset signal by comparing the PWM signal with a reference voltage;

a latch circuit coupling to the comparator and a fan unit, for receiving the reset signal and a tacho-pulse signal generated by the fan unit and outputting a pole signal containing no phantom pulses, wherein when the reset signal is transient from low to high, the pole signal is latched at a low level until the tacho-pulse signal is transient from low to high, and then the pole signal varies in response to the tacho-pulse signal; and

a synchronizer coupled to the latch circuit for generating an output signal without interruption when the PWM signal is off.