Fan rotating speed control circuit and switching power supply

Abstract

The invention discloses a fan rotating speed control circuit and a switching power supply, and the fan rotating speed control circuit comprises a controllable duty ratio generation circuit which is used for collecting the working temperature and generating a square wave signal with the duty ratio changing along with the working temperature; and the fan interface control circuit is used for outputting a fan rotating speed control signal according to the square wave signal, and the input end of the fan interface control circuit is connected with the output end of the controllable duty ratio generation circuit. According to the fan rotating speed control circuit, temperature control over the rotating speed of the fan can be achieved through a pure analog circuit, the control precision is high, meanwhile, the circuit is simple, reliability is high, and cost is low.

Description

Technical Field

[0001] The invention relates to power conversion technology, and in particular to a fan speed control circuit and a switching power supply. Background Art

[0002] Using fans to force cooling of the system is a common cooling method for switching power supplies. This cooling method can greatly improve the power density of switching power supply products and reduce product costs. The industry's research on fan control technology has also gradually matured. It can be divided into analog control methods and digital control methods according to the control type. The analog control method refers to building a pure analog circuit to control the fan, and the digital control method refers to using a microprocessor with peripheral circuits to control the fan. The analog control method is mostly used in situations where there are cost requirements and no need for precise control of the fan, while the digital control method is mostly used in situations where fan control has higher precision and flexibility. The existing technology has the following characteristics:

[0003] The digital fan control method can control the fan by software programming according to the actual use conditions due to the existence of a microprocessor. For example, the fan speed can change with the temperature. When the working temperature rises, the speed is increased to meet the heat dissipation requirements. When the working temperature drops, the fan speed is reduced. While meeting the heat dissipation requirements, the fan power consumption and noise during operation are reduced. The digital control method has high control accuracy and strong flexibility, but the fan control must be performed by a microprocessor in conjunction with peripheral circuits, so the cost is high.

[0004] The existing fan simulation control method has a simple circuit, but a single function and poor flexibility. It can only control the fan to run at the maximum speed or stop, and generates unnecessary loss and noise when the operating temperature of the switching power supply is not high. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a fan speed control circuit and a switching power supply, which can effectively control the speed of the fan, and at the same time have a simple circuit and low cost.

[0006] In a first aspect, the present invention provides a fan speed control circuit, comprising:

[0007] A controllable duty cycle generating circuit, used for collecting the operating temperature and generating a square wave signal whose duty cycle varies with the operating temperature;

[0008] The fan interface control circuit is used to output a fan speed control signal according to the square wave signal, and the input end of the fan interface control circuit is connected to the output end of the controllable duty cycle generating circuit.

[0009] Optionally, the controllable duty cycle generating circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a thermistor and a first operational amplifier; the first end of the first resistor is connected to the power supply, the second end of the first resistor is respectively connected to the in-phase input of the first operational amplifier, the first end of the second resistor and the first end of the third resistor, the second end of the second resistor is connected to the reference ground, the second end of the third resistor is respectively connected to the output of the first operational amplifier and the first end of the fourth resistor, the second end of the fourth resistor is respectively connected to the inverting input of the first operational amplifier, the first end of the first capacitor and the first end of the thermistor, the second end of the first capacitor and the second end of the thermistor are both connected to the reference ground, and the output of the first operational amplifier is connected to the input of the fan interface control circuit.

[0010] Optionally, the fan interface control circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor and a first transistor, the first end of the fifth resistor is connected to the power supply, the second end of the fifth resistor is respectively connected to the output end of the controllable duty cycle generating circuit, the sixth resistor and the first end of the seventh resistor, the second end of the sixth resistor is respectively connected to the reference ground and the emitter of the first transistor, the second end of the seventh resistor is connected to the base of the first transistor, the first end of the eighth resistor is connected to the power supply, and the second end of the eighth resistor is connected to the collector of the first transistor.

[0011] In a second aspect, the present invention further provides a fan speed control circuit, comprising:

[0012] A controllable duty cycle generating circuit, the controllable duty cycle generating circuit comprising a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a thermistor and a first operational amplifier; a first end of the first resistor is connected to a power supply, a second end of the first resistor is respectively connected to a non-inverting input end of the first operational amplifier, a first end of the second resistor and a first end of the third resistor, a second end of the second resistor is connected to a reference ground, a second end of the third resistor is respectively connected to an output end of the first operational amplifier and a first end of the fourth resistor, a second end of the fourth resistor is respectively connected to an inverting input end of the first operational amplifier, a first end of the first capacitor and a first end of the thermistor, a second end of the first capacitor and a second end of the thermistor are both connected to the reference ground, and an output end of the first operational amplifier is connected to an input end of the fan interface control circuit;

[0013] The fan interface control circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor and a first transistor, the first end of the fifth resistor is connected to the power supply, the second end of the fifth resistor is respectively connected to the output end of the operational amplifier, the sixth resistor and the first end of the seventh resistor, the second end of the sixth resistor is respectively connected to the reference ground and the emitter of the first transistor, the second end of the seventh resistor is connected to the base of the first transistor, the first end of the eighth resistor is connected to the power supply, and the second end of the eighth resistor is connected to the collector of the first transistor.

[0014] In a third aspect, the present invention further provides a switching power supply, wherein the switching power supply comprises the fan speed control circuit described in the first aspect or the second aspect.

[0015] The working principle of the present invention will be analyzed in conjunction with specific embodiments. Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The fan speed control circuit of the embodiment of the present invention can realize temperature control of the fan speed through a pure analog circuit, with high control accuracy, simple circuit, high reliability and low cost;

[0017] 2. The switching power supply of the embodiment of the present invention uses the fan speed control circuit of the embodiment of the present invention, so the fan speed of the switching power supply can be controlled without microprocessor control, thereby enhancing the compatibility of the switching power supply under different application conditions and having low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a principle block diagram of a fan speed control circuit of the present invention;

[0019] Figure 2 The present invention is a circuit schematic diagram of a fan speed control circuit. DETAILED DESCRIPTION

[0020] In order to make the technical solution of the present invention clearer, the following is a clear and complete description of the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are partial embodiments of the present invention, and ordinary technicians in this field can make other various forms of modifications, replacements or changes to the present invention without creative work, which still fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "including" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, the inclusion of a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings clearly listed, but may include components, unit circuits or control timings that are not clearly listed or inherent to these circuits.

[0022] In addition, the embodiments and features of the embodiments in this application may be combined with each other if there is no conflict.

[0023] It should be understood that, in the specification and the claims, when an element is described as being “connected” to another element, the element may be “directly connected” to the other element, or be “connected” to the other element through a third element; when a step is described as being continued to another step, the step may be directly continued to the other step, or be continued to the other step through a third step.

[0024] First embodiment

[0025] This embodiment provides a fan speed control circuit for controlling the fan speed. Figure 1 FIG. 1 is a schematic diagram of a fan speed control circuit according to a first embodiment of the present invention; see Figure 1 , wherein the fan speed control circuit includes:

[0026] A controllable duty cycle generating circuit comprises an input end and an output end, wherein the input end of the controllable duty cycle generating circuit is used to collect the working temperature of the system, and the output end is used as the input end of the fan interface control circuit, and can generate a square wave signal whose duty cycle changes with the working temperature;

[0027] A fan interface control circuit, comprising an input end and an output end, wherein the input end of the fan interface control circuit is connected to the output end of the controllable duty cycle generating circuit, and the output end of the fan interface control circuit is used to output a fan speed control signal according to a square wave signal;

[0028] When the fan speed control circuit is in operation:

[0029] When the operating temperature of the switching power supply remains unchanged, the operating temperature information collected by the input end of the controllable duty cycle generating circuit remains unchanged, and its output end will generate a square wave signal with a constant duty cycle, which is used as the input signal of the fan interface control circuit, so that the signal PWM control signal at the output end of the fan interface control circuit is also a square wave signal with a constant duty cycle, and the fan speed is controlled to remain unchanged (taking a conventional four-wire fan as an example, the smaller the duty cycle of the PWM control signal, the higher the fan speed, the larger the duty cycle, the lower the fan speed, and the fan speed remains unchanged when the duty cycle remains unchanged);

[0030] When the operating temperature of the switching power supply changes, the operating temperature information collected by the input end of the controllable duty cycle generating circuit changes, and its output end will generate a square wave signal with a smaller (or larger) duty cycle. This signal serves as the input signal of the fan interface control circuit, so that the signal PWM control signal at the output end of the fan interface control circuit is a square wave signal with an increased (or decreased) duty cycle, thereby controlling the fan speed to change (taking a conventional four-wire fan as an example, the smaller the duty cycle of the PWM control signal, the higher the fan speed, the larger the duty cycle, the lower the fan speed, and the fan speed remains unchanged if the duty cycle remains unchanged).

[0031] Figure 1 The fan speed control circuit outputs a square wave signal whose duty cycle changes with temperature when receiving the operating temperature signal through the controllable duty cycle generating circuit. The fan interface control circuit receives this signal as an input signal and outputs a fan speed control signal. The circuit is simple, reliable and low-cost.

[0032] Figure 2 A specific circuit diagram of the fan speed control circuit of the first embodiment of the present invention is shown in FIG. Figure 2 :

[0033] Wherein, the controllable duty cycle generating circuit includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first capacitor C1, a thermistor RT1 and a first operational amplifier; the first end of the first resistor R1 is connected to the power supply VDD, the second end of the first resistor R1 is simultaneously connected to the in-phase input end of the first operational amplifier U1 and the first ends of the second resistors R2 and R3, the second end of the second resistor R2 is connected to the reference ground, the second end of the third resistor R3 is simultaneously connected to the output end of the first operational amplifier U1 and the first end of the fourth resistor R4; the second end of the fourth resistor R4 is simultaneously connected to the inverting input end of the first operational amplifier U1 and the first ends of the first capacitor C1 and the thermistor RT1; the second end of the first capacitor C1 is connected to the reference ground; the second end of the thermistor RT1 is connected to the reference ground.

[0034] The working principle of the controllable duty cycle generating circuit is as follows:

[0035] In the controllable duty cycle generating circuit, the input end is used to collect the working temperature of the system, and the output end is connected to the fan interface control circuit as its input signal.

[0036] When the operating temperature is stable, the resistance of thermistor RT1 remains unchanged, and the controllable duty cycle generating circuit will output a periodic square wave signal. A starting point can be selected to analyze the principle in detail. When the voltage U aGreater than its inverting input voltage U b When the first operational amplifier U1 will output a high level V DD , the voltage at the common-mode input terminal of the first operational amplifier U1 can be calculated At the same time, the high level V output by the first operational amplifier U1 DD The first capacitor C1 is charged through R4, and the voltage across the first capacitor C1 continues to increase. Since the voltage U b = equal to the voltage across the first capacitor C1, and the voltage U b Also continues to increase, when the voltage at the inverting input terminal of the first operational amplifier U1 When the voltage at the inverting input terminal of the first operational amplifier U1 is greater than the voltage at the non-inverting input terminal, the first operational amplifier U1 will output a low level. At this time, the voltage at the non-inverting input terminal of the first operational amplifier U1 is calculated. At the same time, the first capacitor C1 discharges through the parallel resistor, and the voltage across the first capacitor C1 continues to drop, that is, the voltage U1 at the inverting input terminal of the first operational amplifier U1 b Also continues to decrease, when the voltage at the inverting input terminal of the first operational amplifier U1 , that is, the voltage at the non-inverting input terminal of the first operational amplifier U1 is greater than the voltage at the inverting input terminal, and the first operational amplifier U1 outputs a high level V again. DD , back to the entry point, and enter a periodic cycle. The voltage waveform across the first capacitor C1 is a periodic charging and discharging waveform, and the minimum voltage of the first capacitor C1 is The maximum value is When the first operational amplifier U1 outputs a high level, the first capacitor C1 is charged and its voltage will Rise to The time is T1, then the first operational amplifier U1 flips and outputs a low level, the first capacitor C1 discharges, and its voltage will be Down to The time is T2, and the cycle continues like this. Then the output signal of the controllable duty cycle generating circuit is When the operating temperature is stable, the resistance of thermistor RT1 remains unchanged, the charge / discharge time T1 / T2 of the first capacitor C1 remains unchanged, and the controllable duty cycle generating circuit outputs a square wave signal with a constant duty cycle;

[0037] When the operating temperature changes, the resistance of thermistor RT1 will change with the temperature. The change in the resistance of thermistor RT1 directly affects the charging and discharging time of the first capacitor C1, that is, the voltage across C1 changes from Rise to Time T1 and from Down to The time T2 will change, which will affect the duty cycle of the output signal of the controllable duty cycle generating circuit. Taking NTC (negative temperature coefficient thermistor) as an example, when the operating temperature rises, the resistance of the thermistor RT1 decreases, and the voltage across C1 changes from Rise to The time T1 will increase, the voltage from Down to The time T2 decreases, then the duty cycle of the output signal of the controllable duty cycle generating circuit will increase; when the operating temperature decreases, the resistance of thermistor RT1 increases, and the voltage across C1 changes from Rise to The time T1 will decrease, the voltage from Down to As the time T2 increases, the duty cycle of the output signal of the controllable duty cycle generating circuit increases. Will decrease.

[0038] The working principle of the fan interface control circuit is as follows:

[0039] The output signal of the controllable duty cycle generating circuit is used as the input signal of the fan interface control circuit. The output of the fan interface control circuit is connected to the fan pin (taking a conventional four-wire fan as an example, the smaller the duty cycle of the PWM control signal, the higher the fan speed; the larger the duty cycle, the lower the fan speed; the fan speed remains unchanged if the duty cycle remains unchanged).

[0040] The output duty cycle of the controllable duty cycle generating circuit is The square wave signal is used as the input signal of the fan interface control circuit. When the input signal of the fan interface control circuit is high, the first transistor Q1 is turned on, and the output signal PWM control signal of the fan interface circuit is low. When the input signal of the fan interface control circuit is low, the first transistor Q1 is turned off, and the output signal PWM control signal of the fan interface control circuit is high. Then the duty cycle of the output signal of the fan interface control circuit is When the operating temperature remains unchanged, the duty cycle of the output signal of the fan interface control circuit remains unchanged, and the fan speed remains unchanged; when the operating temperature rises, the duty cycle of the output signal of the fan interface control circuit When the operating temperature decreases, the fan interface control circuit output signal duty cycle Increase, control the fan to reduce speed.

[0041] Second embodiment

[0042] This embodiment provides a switching power supply, including any fan speed control circuit in the first embodiment.

[0043] The switching power supply of this embodiment applies the fan speed control circuit of the first embodiment, so that the fan speed of the switching power supply can be temperature controlled. When the operating temperature remains unchanged, the fan speed is controlled to remain unchanged. When the operating temperature increases, the fan speed is increased. When the operating temperature decreases, the fan speed is reduced. The circuit is simple, the reliability is high, and the cost is low.

[0044] The above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention is described in detail according to the embodiments, ordinary technicians in the field can modify or replace the specific implementation methods of the present invention. Any modifications or replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention.

Claims

1. A fan speed control circuit, characterized in that: The fan speed control circuit comprises: A controllable duty cycle generating circuit, used for collecting the operating temperature and generating a square wave signal whose duty cycle varies with the operating temperature; The fan interface control circuit is used to output a fan speed control signal according to the square wave signal, and the input end of the fan interface control circuit is connected to the output end of the controllable duty cycle generating circuit.

2. The fan speed control circuit according to claim 1, characterized in that: The controllable duty cycle generating circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a thermistor and a first operational amplifier; the first end of the first resistor is connected to a power supply, the second end of the first resistor is respectively connected to a non-inverting input of the first operational amplifier, a first end of the second resistor and a first end of the third resistor, the second end of the second resistor is connected to a reference ground, the second end of the third resistor is respectively connected to an output of the first operational amplifier and a first end of the fourth resistor, the second end of the fourth resistor is respectively connected to an inverting input of the first operational amplifier, a first end of the first capacitor and a first end of the thermistor, the second end of the first capacitor and the second end of the thermistor are both connected to the reference ground, and the output of the first operational amplifier is connected to an input of the fan interface control circuit.

3. The fan speed control circuit according to claim 1, characterized in that: The fan interface control circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor and a first transistor, the first end of the fifth resistor is connected to the power supply, the second end of the fifth resistor is respectively connected to the output end of the controllable duty cycle generating circuit, the sixth resistor and the first end of the seventh resistor, the second end of the sixth resistor is respectively connected to the reference ground and the emitter of the first transistor, the second end of the seventh resistor is connected to the base of the first transistor, the first end of the eighth resistor is connected to the power supply, and the second end of the eighth resistor is connected to the collector of the first transistor.

4. A fan speed control circuit, characterized in that: The fan speed control circuit comprises: A controllable duty cycle generating circuit, the controllable duty cycle generating circuit comprising a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a thermistor and a first operational amplifier; a first end of the first resistor is connected to a power supply, a second end of the first resistor is respectively connected to a non-inverting input end of the first operational amplifier, a first end of the second resistor and a first end of the third resistor, a second end of the second resistor is connected to a reference ground, a second end of the third resistor is respectively connected to an output end of the first operational amplifier and a first end of the fourth resistor, a second end of the fourth resistor is respectively connected to an inverting input end of the first operational amplifier, a first end of the first capacitor and a first end of the thermistor, a second end of the first capacitor and a second end of the thermistor are both connected to the reference ground, and an output end of the first operational amplifier is connected to an input end of the fan interface control circuit; The fan interface control circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor and a first transistor, the first end of the fifth resistor is connected to the power supply, the second end of the fifth resistor is respectively connected to the output end of the first operational amplifier, the sixth resistor and the first end of the seventh resistor, the second end of the sixth resistor is respectively connected to the reference ground and the emitter of the first transistor, the second end of the seventh resistor is connected to the base of the first transistor, the first end of the eighth resistor is connected to the power supply, and the second end of the eighth resistor is connected to the collector of the first transistor.

5. A switching power supply, characterized in that: The switching power supply comprises the fan speed control circuit according to any one of claims 1 to 4.

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