Fan speed regulation circuit based on multi-point temperature measurement

Abstract

The invention discloses a fan speed regulation circuit based on multi-point temperature measurement, and the circuit comprises a hardware starting control circuit which collects a plurality of heat source temperature points; the software starting control circuit outputs a high level when the collected temperature point reaches a set temperature point, otherwise outputs a low level; the output end is connected with the redundancy control circuit; the redundancy control circuit is used for realizing logical operation of multiple paths of level signals in the hardware starting control circuit and the output of the software starting control circuit; when the input is a high level, the current straight-through circuit outputs a direct current to the optocoupler isolation circuit; when the input is low level, current is not output; the current superposition circuit outputs direct current from the high level output by the hardware starting control circuit through a current-limiting resistor; the optocoupler isolation circuit outputs the direct current to the fan control circuit in proportion; the fan control circuit is used for controlling collector current by adjusting triode base current according to the output of the optocoupler isolation circuit so as to adjust the rotating speed of the fan; and when the fan suddenly stops rotating, the back-filling energy is absorbed.

Description

Technical Field

[0001] This invention relates to a fan speed control circuit based on multi-point temperature measurement, belonging to the field of fan control technology. Background Technology

[0002] Fans operate by using electricity to drive a motor that rotates fan blades. This converts mechanical energy into kinetic energy, accelerating airflow to remove heat from radiators or heat-generating components, thus improving heat exchange efficiency. In terrestrial power systems, fans typically operate at maximum speed immediately upon startup, resulting in significant noise and energy waste. As industry moves towards lower power consumption, higher reliability, and smarter operation, two solutions have emerged. One method involves measuring the temperature of heat-generating components and setting the fan's operating time before starting. While this method eliminates noise under no-load or light-load conditions, it results in the fan operating at maximum speed once started, preventing speed regulation. The other method uses pulse width modulation (PWM) to control the fan motor's input voltage duty cycle, thereby adjusting the speed. While this technology is highly feasible and widely applicable, it presents several challenges: 1. The periodic switching action of PWM can cause electromagnetic interference; 2. It requires complex system design, necessitating PWM control programming in software and high-speed switching drive circuitry in hardware; 3. High-frequency pulse width modulation increases losses in switching elements, leading to reduced efficiency.

[0003] The patent [A Fan Speed ​​Control Circuit, Publication No. CN101789751B, Publication Date January 16, 2013, Invention, Authorized] proposes controlling the output voltage of a switching power supply based on the correspondence between temperature and a switch array, thereby regulating the fan speed. Essentially, it designs a buck converter that adjusts the resistance of the output voltage sampling resistor as the temperature rises, regulating the output voltage based on the voltage closed-loop principle. The disadvantages of this invention are: 1. It requires a large number of switches, resulting in complex control logic; 2. It requires pre-storing all the correspondences between temperature and the control switch array in the logic chip, leading to a complex system flow; 3. Because the buck converter is a non-isolated topology, the ground of the output voltage sampling terminal, the fan power supply ground, and the control module ground are all common, resulting in weak anti-interference capability; 4. Since the output voltage of the buck converter must be lower than the input voltage, the DC fan is limited by the input voltage range, and cannot meet the full-speed requirement when the input voltage is low. Furthermore, its output inductor requires a large size at low frequencies, limiting its applicability in miniaturized power supplies. Existing technologies suffer from problems such as weak anti-interference capabilities, complex system design, and limited universality. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a fan speed control circuit based on multi-point temperature measurement, realizing a redundant control design of hardware and software.

[0005] The technical solution of this invention is:

[0006] This invention discloses a fan speed control circuit based on multi-point temperature measurement, comprising:

[0007] The hardware start-up control circuit collects multiple heat source temperature points and outputs them to the software start-up control circuit; based on the multiple heat source temperature points, it outputs multiple level signals to the current superposition circuit and the redundant control circuit.

[0008] The software-controlled circuit outputs a high level to the current-pass circuit when the collected temperature reaches the set temperature, and outputs a low level to the current-pass circuit otherwise; the output terminal is connected to the redundant control circuit.

[0009] The redundant control circuit enables the multiple level signals in the hardware start-up control circuit to perform logical operations with the output of the software start-up control circuit, and outputs a high level or low level to the current direct circuit.

[0010] The current-through circuit outputs DC current to the optocoupler isolation circuit when the input is high; when the input is low, no current is output.

[0011] The current superposition circuit takes the high level output from the hardware start-up control circuit, passes it through the current limiting resistor, and outputs a DC current to the optocoupler isolation circuit.

[0012] An optocoupler isolation circuit isolates the input ground from the output ground; and outputs the DC current to the fan control circuit in a proportional manner.

[0013] The fan control circuit has its input end connected to the optocoupler isolation circuit and its output end connected to the fan. Based on the output of the optocoupler isolation circuit, the fan speed is adjusted by regulating the base current of the transistor and controlling the collector current. The circuit also absorbs backflow energy when the fan suddenly stops.

[0014] Furthermore, in the above circuit, the hardware start-up control circuit includes a first start-up control circuit, a second start-up control circuit, and a third start-up control circuit. The first start-up control circuit, the second start-up control circuit, and the third start-up control circuit are identical and redundant with each other. The first start-up control circuit includes resistors R9, R10, R11, R12, R13, and operational amplifier chip U1.

[0015] One end of resistor R9 is connected to power supply VCC, and the other end of resistor R9 is connected to the inverting input of op-amp chip U1 and one end of resistor R10. The other end of resistor R10 is connected to control ground. One end of resistor R11 is connected to power supply Vref, and the other end of resistor R11 is connected to the non-inverting input of op-amp chip U1. The non-inverting input of op-amp chip U1 is connected to one end of resistor R12, and the other end of resistor R12 is connected to the output of op-amp chip U1. The output of op-amp chip U1 is connected to pull-up resistor R13 to power supply VCC.

[0016] Furthermore, in the above circuit, the current superposition circuit includes diodes D1, D2, and D3, and resistors R1, R2, and R3; wherein, the anode of diode D1 is connected to the output of the first start-up control circuit, and the cathode is connected to the current-limiting resistor R1; the anode of diode D2 is connected to the output of the second start-up control circuit, and the cathode is connected to the current-limiting resistor R2; the anode of diode D3 is connected to the output of the third start-up control circuit, and the cathode is connected to the current-limiting resistor R3; the other ends of resistors R1, R2, and R3 are connected at a common point to the optocoupler isolation circuit.

[0017] Furthermore, in the above circuit, the optocoupler isolation circuit includes an optocoupler U1 and a resistor R7;

[0018] in,

[0019] The input terminal of optocoupler U1 is connected to the output terminal of the current direct circuit and the current superposition circuit;

[0020] The output terminal of optocoupler U1 is connected to one end of resistor R7 and the input terminal of the fan control circuit;

[0021] The other end of resistor R7 is grounded.

[0022] Furthermore, in the above circuit, the current-passing circuit includes resistors R4, R5, R6, an N-type transistor Q1, and a P-type transistor Q2; wherein,

[0023] The input terminal of resistor R4 is connected to the output terminal of the redundant control circuit and the output terminal of the software start-up control circuit;

[0024] The output terminal of resistor R4 is connected to the base of N-type transistor Q1, the emitter of N-type transistor Q1 is grounded, and the collector of N-type transistor Q1 is connected to the base of P-type transistor Q2 through resistor R5. The emitter of P-type transistor Q2 is connected to the power supply VCC, and the collector of P-type transistor Q2 is connected to the input terminal of the optocoupler isolation circuit through resistor R6.

[0025] Furthermore, in the above circuit, the redundant control circuit includes a NAND gate logic circuit. The input of the NAND gate logic circuit is connected to the output terminals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The NAND gate logic circuit performs NAND gate logic operations on the output signals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The output of the NAND gate logic circuit is connected to the output terminal of the software start-up control circuit. The output high level or low level is supplied to the current direct circuit.

[0026] Furthermore, in the above circuit, the software start-up control circuit includes an MCU and a driver amplifier; wherein, the input of the MCU is the three temperature points collected by the hardware start-up control circuit, which is judged and outputs a level signal to the driver amplifier; the driver amplifier amplifies the level signal and outputs a voltage signal to the current direct circuit; the output terminal of the driver amplifier is connected to the redundant control circuit.

[0027] Furthermore, in the above circuit, the logical operation specifically includes:

[0028] Perform a AND-NOT operation on each level signal of the hardware start-up control circuit, and then perform an AND-NOT operation on the result level value and the output signal of the software start-up control circuit. When both the result level value and the output signal of the software start-up control circuit are high, output a high level to the current direct circuit; otherwise, output a low level to the current direct circuit.

[0029] Furthermore, in the above circuit, the fan control circuit includes a resistor R8, an N-type transistor Q3, and a diode D4; wherein, one end of the resistor R8 is connected to the output terminal of the optocoupler isolation circuit, and the other end is connected to the base of the N-type transistor Q3; the emitter of the N-type transistor Q3 is grounded, and the collector of the N-type transistor Q3 is connected to the anode of the diode D4 and the negative terminal of the fan; the cathode of the diode D4 is connected to the power supply VDD and the positive terminal of the fan.

[0030] The advantages of this invention over the prior art are as follows:

[0031] (1) This invention monitors the temperature of multiple heat-generating components by collecting multiple temperature measurement points on the surface of the heat sink, and designs temperature limits based on the heat resistance of the heat-generating components. Based on the increase of the temperature limits, the fan speed is gradually increased to accelerate the heat exchange rate, prevent the heat-generating components from heating up further, and improve the system reliability.

[0032] (2) The present invention uses a hysteresis comparator circuit to compare the temperature limit with the temperature value at multiple points, and uses a comparator, diode and current limiting resistor in series as a current superposition circuit. Based on multiple adjustment circuits in parallel, the current of the primary side of the optocoupler is adjusted by superimposing the current after passing through the current limiting resistor through the output of multiple comparators, thereby adjusting the voltage of the secondary side of the optocoupler.

[0033] (3) The present invention uses the output voltage of the secondary side of the optocoupler to control the base current of the transistor to realize the speed regulation of the fan, isolates the fan inductor from the common ground of the control circuit, and avoids electromagnetic interference affecting the normal operation of the control circuit.

[0034] (4) The present invention uses the output of the multi-channel comparator as the input of the redundant control circuit. After logic operation, it is hard-connected to the output of the driver amplifier controlled by the microcontroller I / O, and together control the current direct circuit. In order to prevent the fan from working at the maximum speed when some hardware circuits fail or a single temperature measurement point is high, the hardware and software redundant control design is realized.

[0035] (5) The present invention achieves the linear speed regulation function of the fan by setting different threshold points through multiple temperature measurement points monitored. The present invention adjusts the branch current based on Ohm's law, without the need for high-frequency chopping action, thus avoiding the electromagnetic interference problem caused by the periodic high-speed switching of PWM used in traditional technology.

[0036] (6) This invention establishes hardware and software start-up control logic through redundant control circuits, and adopts a control strategy with hardware start-up control circuit as the main circuit and software start-up control circuit as the auxiliary circuit. This prevents the failure of hardware start-up control circuit from causing the fan to fail to start or the wind speed to fail to meet the standard, and effectively reduces the risk of system-level thermal runaway.

[0037] (7) This invention uses the principle of parallel current superposition of multiple comparators to adjust the primary current of the linear optocoupler, and then adjusts the secondary current. It also adjusts the fan speed based on the linear operating region of the transistor, instead of using PWM control. This avoids the switching loss problem caused by high-speed switching drive (including switching loss and conduction loss, which increases with frequency). In addition, since the primary and secondary sides of the optocoupler circuit do not share a common ground, it effectively solves the crosstalk problem caused by the unstable power ground level after the control power and power power are grounded together, greatly enhancing the anti-interference capability of the system and having strong robustness and stability.

[0038] (8) The present invention can realize the speed regulation function with only a few common electronic components (operational amplifier, optocoupler, transistor), without using the complex switch array and high-cost high-speed switch drive circuit in the cited patent [A Fan Speed ​​Regulation Circuit]. It has the characteristics of simple circuit, and the redundant control function does not require complex control logic, but only simple programming, which has the advantages of strong adaptability. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the multi-point temperature measurement fan speed control circuit of the present invention;

[0040] Figure 2 This is the schematic diagram of the temperature acquisition + hysteresis comparator circuit of the present invention;

[0041] Figure 3 This is a linear relationship diagram of the primary and secondary sides of the optical coupler of the present invention. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] like Figure 1 As shown, this invention discloses a fan speed control circuit based on multi-point temperature measurement, comprising:

[0044] The hardware start-up control circuit collects multiple heat source temperature points and outputs them to the software start-up control circuit; based on the multiple heat source temperature points, it outputs multiple level signals to the current superposition circuit and the redundant control circuit.

[0045] The software-controlled circuit outputs a high level to the current-pass circuit when the collected temperature reaches the set temperature, and outputs a low level to the current-pass circuit otherwise; the output terminal is connected to the redundant control circuit.

[0046] The redundant control circuit enables the multiple level signals in the hardware start-up control circuit to perform logical operations with the output of the software start-up control circuit, and outputs a high level or low level to the current direct circuit.

[0047] The current-through circuit outputs DC current to the optocoupler isolation circuit when the input is high; when the input is low, no current is output.

[0048] The current superposition circuit takes the high level output from the hardware start-up control circuit, passes it through the current limiting resistor, and outputs a DC current to the optocoupler isolation circuit.

[0049] Optocoupler isolation circuit isolates the input ground from the output ground; proportionally outputs DC current to the fan control circuit.

[0050] The fan control circuit has its input end connected to the optocoupler isolation circuit and its output end connected to the fan. Based on the output of the optocoupler isolation circuit, the fan speed is adjusted by regulating the base current of the transistor and thus controlling the collector current. It also absorbs backflow energy when the fan suddenly stops.

[0051] Preferably, the hardware start-up control circuit includes a first start-up control circuit, a second start-up control circuit, and a third start-up control circuit. The first, second, and third start-up control circuits are identical and redundant. The first start-up control circuit includes resistors R9, R10, R11, R12, and R13, and operational amplifier chip U1.

[0052] One end of resistor R9 is connected to power supply VCC, and the other end of resistor R9 is connected to the inverting input of op-amp chip U1 and one end of resistor R10. The other end of resistor R10 is connected to control ground. One end of resistor R11 is connected to power supply Vref, and the other end of resistor R11 is connected to the non-inverting input of op-amp chip U1. The non-inverting input of op-amp chip U1 is connected to one end of resistor R12, and the other end of resistor R12 is connected to the output of op-amp chip U1. The output of op-amp chip U1 is connected to pull-up resistor R13 to power supply VCC.

[0053] Preferably, the current superposition circuit includes diodes D1, D2, and D3, and resistors R1, R2, and R3; wherein the anode of diode D1 is connected to the output of the first start-up control circuit, and the cathode is connected to the current-limiting resistor R1; the anode of diode D2 is connected to the output of the second start-up control circuit, and the cathode is connected to the current-limiting resistor R2; the anode of diode D3 is connected to the output of the third start-up control circuit, and the cathode is connected to the current-limiting resistor R3; the other ends of resistors R1, R2, and R3 are connected at a common point to the optocoupler isolation circuit.

[0054] Preferably, the optocoupler isolation circuit includes an optocoupler U1 and a resistor R7; wherein,

[0055] The input terminal of optocoupler U1 is connected to the output terminal of the current direct circuit and the current superposition circuit;

[0056] The output terminal of optocoupler U1 is connected to one end of resistor R7 and the input terminal of the fan control circuit;

[0057] The other end of resistor R7 is grounded.

[0058] Preferably, the current-through circuit includes resistors R4, R5, R6, an N-type transistor Q1, and a P-type transistor Q2; wherein,

[0059] The input terminal of resistor R4 is connected to the output terminal of the redundant control circuit and the output terminal of the software start-up control circuit;

[0060] The output terminal of resistor R4 is connected to the base of N-type transistor Q1, the emitter of N-type transistor Q1 is grounded, and the collector of N-type transistor Q1 is connected to the base of P-type transistor Q2 through resistor R5. The emitter of P-type transistor Q2 is connected to the power supply VCC, and the collector of P-type transistor Q2 is connected to the input terminal of the optocoupler isolation circuit through resistor R6.

[0061] Preferably, the redundant control circuit includes a NAND gate logic circuit. The input of the NAND gate logic circuit is connected to the output terminals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The NAND gate logic circuit performs NAND gate logic operations on the output signals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The output of the NAND gate logic circuit is connected to the output terminal of the software start-up control circuit. The output high level or low level is supplied to the current direct circuit.

[0062] Preferably, the software start-up control circuit includes an MCU and a driver amplifier; wherein, the input of the MCU is three temperature points collected by the hardware start-up control circuit, which are judged and output level signals to the driver amplifier; the driver amplifier amplifies the level signals and outputs voltage signals to the current direct circuit; the output terminal of the driver amplifier is connected to the redundant control circuit.

[0063] Preferably, the logical operation is as follows:

[0064] Perform a AND-NOT operation on each level signal of the hardware start-up control circuit, and then perform an AND-NOT operation on the result level value and the output signal of the software start-up control circuit. When both the result level value and the output signal of the software start-up control circuit are high, output a high level to the current direct circuit; otherwise, output a low level to the current direct circuit.

[0065] Preferably, the fan control circuit includes a resistor R8, an N-type transistor Q3, and a diode D4; wherein, one end of the resistor R8 is connected to the output terminal of the optocoupler isolation circuit, and the other end is connected to the base of the N-type transistor Q3; the emitter of the N-type transistor Q3 is grounded, and the collector of the N-type transistor Q3 is connected to the anode of the diode D4 and the negative terminal of the fan; the cathode of the diode D4 is connected to the power supply VDD and the positive terminal of the fan.

[0066] Example

[0067] like Figure 1 The diagram shown is a schematic of a multi-point temperature measurement fan control circuit, which includes: a hardware start-up control circuit, a software start-up control circuit, a current superposition circuit, a current direct-pass circuit, a redundant control circuit, an optocoupler isolation circuit, and a fan control circuit.

[0068] The hardware start-up control circuit is responsible for collecting temperature data from multiple heat sources. Based on this, different reference temperatures (conditions for increasing fan speed) are set. A hysteresis comparator threshold is used to determine the temperature. When the sampled temperature reaches the reference temperature value, a high-level signal is output to the current superposition circuit. As the number of high-level outputs increases, the total current on the primary side of the optocoupler is superimposed. Because the primary and secondary sides of the optocoupler have a linear relationship, the current in the secondary transistor of the optocoupler increases linearly. After power amplification by the fan control circuit, the fan speed is controlled. For example, when the multiple hysteresis comparator outputs a high level, diodes D1-D3 conduct, and current-limiting resistors R1-R3 superimpose the current onto the primary side of the optocoupler. The linear increase in the primary current causes the base current of the secondary transistor to be proportionally amplified, ultimately adjusting the fan speed through transistor Q3.

[0069] The principle behind the current superposition circuit is as follows: the high-level output from the hardware start-up control circuit is followed by a current-limiting resistor, and the output current increases with the number of channels in the hardware start-up control circuit. For example, when the first channel outputs a high level, the output current is I1; when the second channel outputs a high level, the output current is I2, and so on, with the total output current being the sum of the currents of each channel.

[0070] The software start-up control circuit has the same function as the hardware start-up control circuit, but the difference lies in the implementation method. The hardware start-up control circuit implements start-up control through hardware circuits, while the software start-up control circuit includes an MCU (STM32F103) and a driver amplifier, and implements start-up control through software. Its working principle is: when the temperature point collected by the software start-up control circuit reaches the temperature point designed in the software program, it outputs a high level; otherwise, it outputs a low level.

[0071] The redundant control circuit includes a NAND gate logic circuit (74LVC1G10), which performs NAND logic operations between each output of the hardware start-up control circuit. Furthermore, when any one or more outputs of the hardware start-up control circuit fail, the operating conditions of the software start-up control circuit are simultaneously met, triggering software intervention. The high-level output of the NAND gate controls the DC path on the primary side of the optocoupler to conduct.

[0072] The function of the current pass-through circuit is: when the collected temperature value reaches the threshold, the hardware start-up control circuit fails to output a high level normally, and the temperature continues to rise. If the temperature of a certain channel is too high or the temperature of multiple channels has reached the software set temperature point, the software start-up control circuit will take effect, controlling the current pass-through circuit to pass the maximum power supply current through the primary side of the optocoupler to achieve full conduction of the optocoupler.

[0073] The optocoupler isolation circuit has two functions: first, to isolate the control ground from the fan power ground; and second, to enable the transmission of current between the primary and secondary sides.

[0074] The fan control circuit has two functions: first, to control the collector current by adjusting the base current of the transistor, thereby adjusting the fan speed; and second, to absorb backflow energy when the fan suddenly stops.

[0075] Example 1:

[0076] The hardware start-up circuit includes a temperature acquisition circuit and a hysteresis comparator. For example... Figure 2 The diagram shows the schematic of one circuit in the hardware start-up control circuit. As shown, one end of resistor R9 is connected to the power supply VCC, and the other end is connected to the inverting input of operational amplifier chip U1. The other end of resistor R9 is also connected to one end of resistor R10, and the other end of resistor R10 is connected to control ground. One end of resistor R11 is connected to the power supply Vref, and the other end is connected to the non-inverting input of operational amplifier chip U1. The non-inverting input of operational amplifier chip U1 is connected to one end of resistor R12, and the other end of resistor R12 is connected to the output of operational amplifier chip U1. The output of operational amplifier chip U1 is connected to pull-up resistor R13 to the power supply VCC. U1 is an LM393 (selected because of its low cost and common use), and resistor R10 is a PT100 thermistor. Resistor R10 and resistor R9 are connected in series to convert the voltage to a value. By looking up the relationship between temperature and resistance (positive temperature coefficient, e.g., 0℃ corresponds to 100R, 50℃ corresponds to 120R), the relationship between temperature and voltage can be obtained. The threshold is set using the LM393 op-amp, and the calculation formula is as follows:

[0077]

[0078] The voltage across the thermistor is compared with two thresholds, where the first threshold (Vth1) is greater than the second threshold (Vth2). When the voltage is greater than the first threshold, a high level is output, and when the voltage is less than the second threshold, a low level is output.

[0079] like Figure 1 As shown, the current superposition circuit consists of three channels, including diodes D1, D2, and D3, and resistors R1, R2, and R3. The anode of diode D1 is connected to the output of hysteresis comparator 1, and its cathode is connected to current-limiting resistor R1. The anode of diode D2 is connected to the output of hysteresis comparator 2, and its cathode is connected to current-limiting resistor R2. The anode of diode D3 is connected to the output of hysteresis comparator 3, and its cathode is connected to current-limiting resistor R3. The other ends of resistors R1, R2, and R3 are connected at a common point. When the first hysteresis comparator outputs a high level, I1 = (VCC - Vd) / R1; when the second output is high, the current is calculated as I2 = (VCC - Vd) / R2; and when the third output is high, the current is calculated as I3 = (VCC - Vd) / R3. The total current is calculated as I1 + I2 + I3. (Vd is the diode voltage drop).

[0080] like Figure 3 The diagram shows the primary and secondary side relationship of the optocoupler isolation chip PC817 (selected because of its isolation withstand voltage ≥5000V and proportional adjustment of primary and secondary currents). Based on this diagram and actual testing, we know that: when IF = 1mA, IC = 1.2mA; when IF = 2mA, IC = 2.4mA; when IF = 3mA, IC = 3.6mA. Therefore, when the comparator power supply is 5V, according to Ohm's law, when the primary current of each channel is about 1mA, the resistance of the current limiting resistor is R1 = R2 = R3 = 4.3kΩ (the diode voltage drop is 0.7V).

[0081] like Figure 1 As shown, the current flowing through the secondary transistor of the optocoupler can be divided into two paths: one is the branch with resistor R7, and the other is the branch with resistor R8. For simplicity of calculation, let R7 = R8. (The formula for calculating R8 is R8 = (VDD - 0.7V) / (Ic / h)). FE Ic is the maximum operating current of the fan, h FE (where Ic is the transistor's amplification factor). Since these two branches are connected in parallel, when the secondary transistor of the optocoupler receives 3.6mA, each branch receives approximately 1.8mA. At this point, transistor Q3 is operating in a critical saturation state (according to Ic = β * Ib, assuming an amplification factor of 100, Ic = 180mA can be calculated), and the fan reaches its maximum operating speed.

[0082] Table 1 Truth Table of Redundancy Control Circuit

[0083]

[0084]

[0085] As shown in Table 1, the dynamic logic of the redundant control circuit is as follows: each input NAND gate logic circuit in the hardware start-up control circuit is controlled by the software start-up control circuit 1.

[0086] Note: Logic 1 is high level (VCC), and logic 0 is low level (0).

[0087] Under normal circumstances:

[0088] When the hardware start-up control circuit outputs 000, it outputs 1 after AND-NOT logic operation. When the software start-up control circuit outputs 0, the redundant control circuit outputs 0.

[0089] When the hardware start-up control circuit outputs 100 / 010 / 001 / 110 / 101 / 011, the AND-NOT logic operation outputs 1. When the software start-up control circuit outputs 0, the redundant control circuit outputs 0.

[0090] When the hardware start-up control circuit outputs 111, the AND-NOT logic operation outputs 0. When the software start-up control circuit outputs 0, the redundant control circuit outputs 0.

[0091] In abnormal situations: (Comparator malfunction, software-controlled circuit starts)

[0092] Since the temperature measurement points collected by the software start-up control circuit are the same as those of the hardware start-up control circuit, the software start-up control circuit will only take effect when a certain temperature is too high (exceeding the hardware temperature setting value, for example, the hardware temperature is 50 degrees and the software temperature is set to 70 degrees) or when multiple temperatures (the software temperatures all exceed the hardware temperature setting values) have reached the software-set temperature points. The software start-up control circuit will then set a threshold, outputting a low level by default, and outputting a high level when the set threshold is reached.

[0093] When the hardware start-up control circuit outputs 000, the AND-NOT logic operation outputs 1; when the software start-up control circuit outputs 1, the redundancy control circuit outputs 1.

[0094] When the redundant control circuit outputs a high level, transistor Q1 is turned on through resistor R4. After the emitter of Q1 is connected to control ground, transistor Q2 is turned on through resistor R5. The power supply VCC is turned on by the primary side of optocoupler PC817 through current limiting resistor R6.

[0095] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention...

[0096] The scope shall be defined by the appended claims.

[0097] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A fan speed control circuit based on multi-point temperature measurement, characterized in that, include: The hardware start-up control circuit collects multiple heat source temperature points and outputs them to the software start-up control circuit; based on the multiple heat source temperature points, it outputs multiple level signals to the current superposition circuit and the redundant control circuit. The software-controlled circuit outputs a high level to the current-pass circuit when the collected temperature reaches the set temperature, and outputs a low level to the current-pass circuit otherwise; the output terminal is connected to the redundant control circuit. The redundant control circuit enables the multiple level signals in the hardware start-up control circuit to perform logical operations with the output of the software start-up control circuit, and outputs a high level or low level to the current direct circuit. The current-through circuit outputs DC current to the optocoupler isolation circuit when the input is high; when the input is low, no current is output. The current superposition circuit takes the high level output from the hardware start-up control circuit, passes it through the current limiting resistor, and outputs a DC current to the optocoupler isolation circuit. An optocoupler isolation circuit isolates the input ground from the output ground; and outputs the DC current to the fan control circuit in a proportional manner. The fan control circuit has its input terminal connected to the optocoupler isolation circuit and its output terminal connected to the fan. Based on the output of the optocoupler isolation circuit, the collector current is controlled by adjusting the base current of the transistor, thereby adjusting the fan speed; and the reverse energy is absorbed when the fan suddenly stops.

2. The fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The hardware start-up control circuit includes a first start-up control circuit, a second start-up control circuit, and a third start-up control circuit. The first, second, and third start-up control circuits are identical and redundant. The first start-up control circuit includes resistors R9, R10, R11, R12, and R13, and an operational amplifier chip U1. One end of resistor R9 is connected to power supply VCC, and the other end of resistor R9 is connected to the inverting input of op-amp chip U1 and one end of resistor R10. The other end of resistor R10 is connected to control ground. One end of resistor R11 is connected to power supply Vref, and the other end of resistor R11 is connected to the non-inverting input of op-amp chip U1. The non-inverting input of op-amp chip U1 is connected to one end of resistor R12, and the other end of resistor R12 is connected to the output of op-amp chip U1. The output of op-amp chip U1 is connected to pull-up resistor R13 to power supply VCC.

3. The fan speed control circuit based on multi-point temperature measurement according to claim 2, characterized in that, The current superposition circuit includes diodes D1, D2, and D3, and resistors R1, R2, and R3. The anode of diode D1 is connected to the output of the first control circuit, and its cathode is connected to the current-limiting resistor R1. The anode of diode D2 is connected to the output of the second control circuit, and its cathode is connected to the current-limiting resistor R2. The anode of diode D3 is connected to the output of the third control circuit, and its cathode is connected to the current-limiting resistor R3. The other ends of resistors R1, R2, and R3 are connected at a common point to an optocoupler isolation circuit.

4. The fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The optocoupler isolation circuit includes an optocoupler U1 and a resistor R7; wherein, The input terminal of optocoupler U1 is connected to the output terminal of the current direct circuit and the current superposition circuit; The output terminal of optocoupler U1 is connected to one end of resistor R7 and the input terminal of the fan control circuit; The other end of resistor R7 is grounded.

5. A fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The current-pass circuit includes resistors R4, R5, R6, an N-type transistor Q1, and a P-type transistor Q2; wherein, The input terminal of resistor R4 is connected to the output terminal of the redundant control circuit and the output terminal of the software start-up control circuit; The output terminal of resistor R4 is connected to the base of N-type transistor Q1, the emitter of N-type transistor Q1 is grounded, and the collector of N-type transistor Q1 is connected to the base of P-type transistor Q2 through resistor R5. The emitter of P-type transistor Q2 is connected to the power supply VCC, and the collector of P-type transistor Q2 is connected to the input terminal of the optocoupler isolation circuit through resistor R6.

6. A fan speed control circuit based on multi-point temperature measurement according to claim 2, characterized in that, The redundant control circuit includes a NAND gate logic circuit. The input of the NAND gate logic circuit is connected to the output terminals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The NAND gate logic circuit performs NAND gate logic operations on the output signals of the first start-up control circuit, the second start-up control circuit, and the third start-up control circuit. The output of the NAND gate logic circuit is connected to the output terminal of the software start-up control circuit. The output high level or low level is supplied to the current direct circuit.

7. A fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The software start-up control circuit includes an MCU and a driver amplifier. The MCU receives three temperature points from the hardware start-up control circuit, makes a judgment, outputs a level signal, and sends it to the driver amplifier. The driver amplifier amplifies the level signal and outputs a voltage signal to the current direct circuit. The output of the driver amplifier is connected to the redundant control circuit.

8. A fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The logical operation is specifically as follows: Perform a AND-NOT operation on each level signal of the hardware start-up control circuit, and then perform an AND-NOT operation on the result level value and the output signal of the software start-up control circuit. When both the result level value and the output signal of the software start-up control circuit are high, output a high level to the current direct circuit; otherwise, output a low level to the current direct circuit.

9. A fan speed control circuit based on multi-point temperature measurement according to claim 1, characterized in that, The fan control circuit includes a resistor R8, an N-type transistor Q3, and a diode D4. One end of the resistor R8 is connected to the output of the optocoupler isolation circuit, and the other end is connected to the base of the N-type transistor Q3. The emitter of the N-type transistor Q3 is grounded, and the collector of the N-type transistor Q3 is connected to the anode of the diode D4 and the negative terminal of the fan. The cathode of the diode D4 is connected to the power supply VDD and the positive terminal of the fan.

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