A temperature-controlled fan circuit

Abstract

The utility model discloses a kind of temperature control fan circuits, belong to risk control field, comprising: first voltage division branch, for generating fixed voltage division;Second voltage division branch, for generating temperature voltage division that changes with temperature;Difference amplification circuit, for obtaining difference voltage according to fixed voltage division and temperature voltage division;Error amplifier circuit, for obtaining error voltage according to difference voltage and fan voltage feedback signal;Drive amplification circuit, for obtaining drive signal according to error voltage;Regulating tube circuit, for adjusting fan supply voltage according to drive signal;Feedback voltage division branch, for sampling fan supply voltage and generating fan voltage feedback signal.The utility model realizes temperature-speed linear adjustable, closed loop steady speed, low noise, low power consumption, high reliability fan control.

Description

Technical Field

[0001] This utility model belongs to the field of fan control, and in particular relates to a temperature-controlled fan circuit. Background Technology

[0002] As the integration of electronic devices continues to increase, their internal heat generation increases significantly. As a core component for active cooling, the fan's speed can be automatically adjusted according to temperature, ensuring reliability while reducing noise and energy consumption. Current technology generally adopts a "single voltage comparator + switch drive" scheme: after voltage division using an NTC thermistor and a fixed resistor, the voltage is directly sent to the comparator for high / low level comparison with a reference voltage, and then the fan is driven at full speed or completely off via a MOSFET or relay. This scheme is simple in structure, but it has the following drawbacks: Unable to achieve linear speed regulation: The comparator only outputs two states, "high" and "low", and the fan can only switch between "full speed" and "stop". It cannot continuously adjust the speed according to the temperature, resulting in high noise at low temperatures and insufficient heat dissipation margin at high temperatures.

[0003] The reference voltage is fixed, making it difficult to adjust the temperature threshold: The reference voltage is generated by voltage division by a fixed resistor. Once the circuit is finalized, the temperature switching point is fixed. If the threshold needs to be changed, the hardware resistor must be replaced, which lacks flexibility.

[0004] Without closed-loop feedback, the speed is affected by power supply fluctuations and fan load changes: The existing open-loop structure is unaware of fluctuations in the 12V power supply and current changes caused by fan aging or stall, resulting in the actual speed deviating from the expected speed and reducing system reliability.

[0005] Limited driving capability and difficulty in compatibility with multiple fan models: The comparator output current is only a few milliamps, requiring an external MOSFET or relay to enhance the drive. However, MOSFETs generate significant heat when operating in the linear region, while relays have lifespan and noise issues, making it difficult for the solution to maintain efficient and low-noise operation under a wide range of fan loads. Utility Model Content

[0006] To solve the above-mentioned technical problems, this utility model provides a temperature-controlled fan circuit, comprising: The first voltage divider branch is used to generate a fixed voltage divider. The second voltage-dividing branch is used to generate temperature-dividing pressures that vary with temperature. A differential amplifier circuit is used to obtain a differential voltage based on the fixed voltage divider and the temperature voltage divider; An error amplifier circuit is used to obtain the error voltage based on the difference voltage and the fan voltage feedback signal; A drive amplifier circuit is used to obtain a drive signal based on the error voltage; The regulating transistor circuit is used to adjust the fan power supply voltage according to the drive signal; The feedback voltage divider branch is used to sample the fan power supply voltage and generate the fan voltage feedback signal.

[0007] Preferably, the first voltage divider branch includes a first resistor and a fourth resistor connected in series between the first power supply and ground, and the fixed voltage divider is taken from the common node of the two resistors.

[0008] Preferably, the second voltage divider branch includes a thirteenth resistor and an NTC thermistor connected in series between the first power supply and ground, and the temperature voltage divider is taken from the common node of the two components.

[0009] Preferably, the differential amplifier circuit includes a first operational amplifier and a fixed voltage divider and a temperature voltage divider respectively coupled to the two input terminals of the first operational amplifier, for outputting the differential voltage.

[0010] Preferably, the error amplifier circuit includes a second operational amplifier, the first input terminal of the second operational amplifier receives the difference voltage, the second input terminal of the second operational amplifier receives the fan voltage feedback signal, and the output terminal of the second operational amplifier provides the error voltage.

[0011] Preferably, the driving amplifier circuit includes an NPN transistor, the base of which receives the error voltage, and the collector of which provides the driving signal.

[0012] Preferably, the regulating transistor circuit includes a PNP power transistor, the base of which receives the drive signal, the emitter of which is coupled to a second power supply, and the collector of which provides the fan power supply voltage to the fan.

[0013] Preferably, the feedback voltage divider branch includes a fourteenth resistor and a fifteenth resistor connected in series between the positive terminal of the fan and ground, and the fan voltage feedback signal is taken from the common node of the two resistors.

[0014] Preferably, the circuit further includes a filter capacitor coupled between the positive terminal of the fan and ground to suppress fan current pulsation.

[0015] Preferably, the fan is powered by a dual power supply of +12V and -12V, forming a 24V voltage difference to drive a 24V DC fan.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a circuit that can continuously and linearly adjust the fan speed across the entire temperature range, avoiding sudden changes between "full speed" and "stop". The temperature-speed characteristics can be flexibly set through a differential amplification stage without the need to replace hardware.

[0017] This invention introduces a closed-loop fan voltage feedback system to suppress speed drift caused by power fluctuations and load changes.

[0018] This invention achieves sufficient driving capability under a pure analog device architecture while maintaining low power consumption and low heat generation. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the system structure of an embodiment of the present utility model. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0022] like Figure 1 As shown, this embodiment provides a temperature-controlled fan circuit, including: The first voltage divider branch is used to generate a fixed voltage divider between the first power supply and ground. The second voltage-dividing branch is used to generate temperature-dividing pressures that change monotonically with temperature. A differential amplifier circuit is used to convert the difference between a fixed voltage division and a temperature-divided voltage division into a differential voltage with a first amplification factor. An error amplifier circuit is used to convert the difference between the differential voltage and the fan voltage feedback signal into an error voltage with a second amplification factor. The drive amplifier circuit is used to amplify the error voltage with current to generate a drive signal. The regulating transistor circuit is used to generate a continuously adjustable voltage drop between its input and output terminals according to the drive signal, thereby providing a continuously adjustable fan power supply voltage to the fan. The feedback voltage divider branch is used to sample the fan supply voltage and generate a fan voltage feedback signal to form a closed-loop negative feedback. Furthermore, in this embodiment, the first voltage divider branch is implemented using a precision thin-film resistor network with a temperature coefficient ≤ ±50ppm / ℃, ensuring that the fixed voltage divider drifts by <0.2% within the range of -40℃ to +85℃. The NTC thermistor in the second voltage divider branch is a surface-mount element with a B value of 3950K and a resistance of 10kΩ ±1% at 25℃, forming a proportional temperature sensor with the thirteenth resistor. The sensitivity can be adjusted between 5mV / ℃ and 50mV / ℃ by adjusting the resistance value of the thirteenth resistor.

[0023] In this embodiment, the first amplification factor A1 of the differential amplifier circuit is set to 3 to 15 times, the second amplification factor A2 of the error amplifier circuit is set to 10 to 100 times, and the total open-loop gain is 100 to 1500 times, which can compress the steady-state error of the fan power supply voltage to <±0.5%.

[0024] The operational amplifier in the differential amplifier circuit of this embodiment can be replaced with an instrumentation amplifier or a chopper-stabilized amplifier to further reduce the input offset voltage to <10µV, making it suitable for high-precision temperature control scenarios with a resolution of 0.1℃.

[0025] In this embodiment, all resistors in the first and second voltage divider branches are adjusted using laser technology, and proportional calibration is completed at the wafer stage. The finished circuit can achieve a temperature accuracy of ±1% without the need for an external potentiometer.

[0026] In this embodiment, the fan power supply voltage output terminal can be connected in parallel to multiple fans, and each fan can be connected in series with a current sharing resistor to realize a distributed cooling system that drives multiple fans with one fan, with a total power of up to 50W without the need for an additional power stage.

[0027] Furthermore, the first voltage divider branch includes a first resistor and a fourth resistor connected in series between the first power supply and ground, with the voltage division fixed at the common node of the two resistors. The resistance ratio of the first resistor to the fourth resistor is programmable within the range of 1:1 to 1:10 to cover a reference voltage range of 0.5V to 5V.

[0028] Furthermore, in this embodiment, the first resistor and the fourth resistor adopt an R-2R ladder network, and can be quickly switched among 8 ratios through PCB jumpers or short circuit pads to achieve compatibility with different temperature threshold requirements on the same PCB.

[0029] In this embodiment, the resistance value of the first resistor is in the range of 10kΩ to 100kΩ, and the resistance value of the fourth resistor is in the range of 10kΩ to 1MΩ. The power consumption of both is <0.1mW, which meets the low power consumption requirements in battery-powered scenarios.

[0030] In this embodiment, the first voltage divider branch can also be replaced by a combination of a precision voltage reference source (such as TL431) and a voltage divider resistor, providing an ultra-high stability reference with a temperature drift of <±20ppm / ℃, suitable for medical or aerospace-grade heat dissipation systems.

[0031] In this embodiment, the first resistor and the fourth resistor are integrally formed using a thick-film resistor network. The resistance value is formed on the ceramic substrate by screen printing, ensuring a proportional error of <±0.1% and a long-term aging rate of <0.05% / 1000h.

[0032] In this embodiment, the fixed voltage divider node can be additionally led out to the ADC port of the MCU to realize system-level temperature-voltage data readback for fault diagnosis or life prediction.

[0033] In one alternative implementation, such as Figure 1 As shown, R1 and R4 together form a voltage divider. The resistance values ​​of R1 and R4 are fixed, and the voltage value of the voltage divider is also fixed.

[0034] Furthermore, the second voltage divider branch includes a thirteenth resistor and an NTC thermistor connected in series between the first power supply and ground, with the temperature voltage division taken from the common node of the two components.

[0035] Furthermore, in this embodiment, the thirteenth resistor is an adjustable resistor or a digital potentiometer to achieve online adjustment of the temperature-voltage slope.

[0036] In this embodiment, as Figure 1 As shown, TH1 is an NTC thermistor. The resistance of an NTC resistor decreases as the temperature rises. It is used as a temperature sensor for the power supply. TH1 and R13 together form a voltage divider to generate a linear output voltage. The voltage value increases as the temperature rises and decreases as the temperature falls.

[0037] In this embodiment, a 256-tap, 10kΩ digital potentiometer is selected, which is connected via I... 2 The C interface completes the slope adjustment within 0.1 seconds, making it suitable for industrial sites where different fan characteristics need to be matched on-site.

[0038] In this embodiment, the NTC thermistor has a resistance of ≥200kΩ at -40℃ and a resistance of ≤200Ω at +125℃, ensuring a voltage swing of ≥80%VCC across the entire temperature range and improving the signal-to-noise ratio.

[0039] In this embodiment, the thirteenth resistor can be replaced by a series-parallel network of a thermistor and a fixed resistor to achieve nonlinear compensation, making the temperature-speed curve S-shaped, which better matches the power consumption-temperature characteristics of the electronic device.

[0040] In this embodiment, the NTC thermistor and the thirteenth resistor are both placed in the same aluminum substrate temperature zone and are tightly attached to the heating device with thermally conductive adhesive. The thermal time constant is <5s, enabling rapid temperature tracking.

[0041] In this embodiment, the temperature divider node can be connected to the comparator window detection circuit to realize over-temperature hardware protection. When the temperature divider exceeds the set window, the fan power is immediately cut off to prevent thermal runaway.

[0042] Furthermore, the differential amplifier circuit includes a first operational amplifier and a fixed voltage divider and a temperature voltage divider respectively coupled to the two input terminals of the first operational amplifier, for outputting a differential voltage.

[0043] This embodiment can also set an adjustable resistor in the feedback path to make the first amplification factor A1 continuously adjustable in the range of 2 to 20 times.

[0044] Furthermore, in this embodiment, the feedback path uses a multi-turn precision potentiometer with an adjustment resolution of 0.01%, which, together with the dial, can be directly calibrated as "℃ / V", facilitating rapid calibration on the production line.

[0045] In this embodiment, the first operational amplifier is a CMOS operational amplifier with GBW≥1MHz and input offset voltage≤0.5mV, ensuring that the differential voltage error is <±1mV within the range of -40℃ to +85℃.

[0046] In this embodiment, the differential amplifier circuit can be replaced with a fully differential operational amplifier to output a differential signal. The subsequent error amplifier also adopts differential input, improving the common-mode rejection ratio to ≥120dB, which is suitable for environments with strong electromagnetic interference.

[0047] In this embodiment, the first operational amplifier and the feedback resistor network are surface-mount devices. The input traces are laid out symmetrically and of equal length to reduce the additional offset caused by the thermocouple effect.

[0048] In this embodiment, the differential voltage output terminal can be connected in series with an RC network to form a low-pass filter with a cutoff frequency of 0.1Hz, which is used to suppress high-frequency noise introduced by fan commutation and improve the system EMC margin.

[0049] In one alternative implementation, such as Figure 1 As shown, R6, R8, R2, R12 and U1A together form a differential amplifier circuit. The input voltages of the differential amplifier circuit are the voltages of the voltage divider composed of TH1 and R13, and the voltages of the voltage divider composed of R1 and R4. The output voltage of the differential amplifier circuit is pin 1 of U1A. Its voltage value is the amplified value of the difference between the two input voltages, which serves as the reference signal for the subsequent fan voltage control loop.

[0050] It can be determined that the voltage of the reference signal = A * (the voltage of the voltage divider composed of TH1 and R13 - the voltage of the voltage divider composed of R1 and R4), where A is the amplification factor of the differential amplifier circuit.

[0051] Furthermore, the error amplifier circuit includes a second operational amplifier, the first input terminal of which receives the difference voltage, the second input terminal of which receives the fan voltage feedback signal, and the output terminal of which provides the error voltage.

[0052] Furthermore, in this embodiment, the error amplifier circuit includes a second operational amplifier, whose non-inverting input receives the difference voltage, its inverting input receives the fan voltage feedback signal, and its output provides the error voltage; and an integrating capacitor is connected in parallel between the inverting input and the output to form a first-order integral compensation network, so that the closed-loop bandwidth can be set in the range of 1Hz to 100Hz.

[0053] In this embodiment, the integrating capacitor uses X7R dielectric with a capacitance range of 1nF to 10µF. By switching via jumpers, it balances fast response and low ripple, meeting the stability requirements of different fan inertia.

[0054] In this embodiment, the open-loop gain of the second operational amplifier is ≥100dB and the input bias current is ≤10nA, ensuring that the integral drift at high temperature is <0.5mV / s and avoiding slow speed drift.

[0055] In this embodiment, the error amplifier can be replaced with a PI or PID type transconductance amplifier, and proportional-integral-derivative compensation can be achieved through external resistors and capacitors to control the fan speed overshoot to <2%.

[0056] In this embodiment, the integral compensation network and the feedback voltage divider network are arranged on the same side of the PCB, the ground plane is intact, and noise coupling is reduced; a shielded via fence is set under the critical traces to improve the signal-to-noise ratio.

[0057] In this embodiment, the error voltage node can be led out to the fan fault detection comparator. When the error voltage saturation high or low exceeds 10ms, it is determined that the fan is stalled or open-circuited, and an alarm signal is output.

[0058] In one alternative implementation, such as Figure 1 As shown, U1B is the error amplifier in the fan voltage control loop. The error amplifier generates an error voltage by comparing the difference between the reference signal and the feedback signal, which becomes the control signal for driving the subsequent circuit. The driving capability is amplified by the transistor Q2 to adjust the voltage drop of the collector-emitter junction of the transistor Q1, thereby adjusting the fan voltage.

[0059] Furthermore, the drive amplifier circuit includes an NPN transistor, the base of which receives the error voltage, and the collector of which provides the drive signal.

[0060] Furthermore, in this embodiment, the driving amplifier circuit includes an NPN transistor, whose base receives the error voltage through a base-limiting current resistor, its emitter is grounded, and its collector is coupled to a 12V power supply through a load resistor, which is used to amplify the current of the error voltage from <1mA to >50mA to drive the subsequent regulating transistor.

[0061] In this embodiment, the NPN transistor adopts a Darlington structure with a DC gain hFE≥1000. The base drive current only needs 50µA to achieve a 50mA output, reducing the load on the front-end operational amplifier.

[0062] In this embodiment, the load resistor value is between 1kΩ and 10kΩ, which can limit the short-circuit current to 12mA to 120mA and prevent overcurrent damage to the base of the regulating transistor.

[0063] In this embodiment, the drive amplifier circuit can be replaced with an N-channel MOSFET with an on-resistance of <100mΩ, achieving a drive capability of >1A, which is suitable for scenarios involving multiple fans in parallel or high-power blowers.

[0064] In this embodiment, the NPN transistor is packaged using TO-252 surface mount technology. The bottom heat dissipation pad is connected to the copper foil on the back of the PCB through a 3×3 via array. The thermal resistance θJA < 40℃ / W ensures that the junction temperature is < 125℃ under high temperature and high current.

[0065] In this embodiment, the drive signal can be connected in parallel to multiple regulating transistors with the same structure to achieve redundant fan power supply. When one fan fails, the system can still maintain 50% heat dissipation capacity.

[0066] Furthermore, the regulating transistor circuit includes a PNP power transistor, the base of which receives the drive signal, the emitter of which is coupled to a second power supply, and the collector of which provides the fan power supply voltage to the fan.

[0067] In this embodiment, a pull-down resistor can also be set between the emitter and the base to ensure that the regulating transistor is completely cut off when there is no drive signal, thus preventing the fan from starting accidentally.

[0068] In this embodiment, the PNP power transistor is selected as TIP42C or higher with a junction temperature of 150°C. The TO-220 package is naturally cooled by an aluminum heat sink and can continuously carry a current of 3A with a temperature rise of <35°C.

[0069] In this embodiment, the pull-down resistor value is between 1kΩ and 10kΩ to ensure that the leakage current is ≤100µA at a high temperature of 85℃, and the regulating tube remains reliably cut off.

[0070] In this embodiment, the regulating transistor can be replaced with a P-channel MOSFET with an on-resistance of <50mΩ and a conduction loss as low as 50mW at full load of 1A, which is 8% more efficient than a bipolar transistor.

[0071] In this embodiment, a 0.5mm thermally conductive insulating pad is used between the adjusting tube and the heat sink, thermally conductive silicone grease is applied, and the installation torque is 0.3 N·m to ensure thermal resistance <2℃ / W.

[0072] In this embodiment, a self-resetting fuse can be connected in series at the output terminal of the regulating tube to achieve overcurrent protection. When the current is greater than 120% of the rated value, the high resistance will cut off within 10 seconds, and the circuit will automatically recover after the fault is cleared.

[0073] Furthermore, the feedback voltage divider branch includes a fourteenth resistor and a fifteenth resistor connected in series between the positive terminal of the fan and ground, and the fan voltage feedback signal is taken from the common node of the two resistors.

[0074] In this embodiment, the resistance ratio of the fourteenth resistor to the fifteenth resistor can be selected in the range of 1:1 to 1:20 to match the full-scale fan voltage of 0.5V to 10V.

[0075] Furthermore, in this embodiment, the fourteenth resistor is a thin-film resistor with 1% accuracy and 50ppm / ℃ temperature drift, and the fifteenth resistor is a multi-turn potentiometer to achieve ±5% feedback ratio fine-tuning for end-of-line calibration.

[0076] In this embodiment, the total resistance of the feedback voltage divider is ≥20kΩ to ensure that the power consumption of the voltage divider branch is <5mW, thus avoiding impact on the fan startup surge.

[0077] In this embodiment, the feedback voltage divider branch can be replaced by a differential amplifier that directly samples the fan terminal voltage. The feedback ratio is set by the operational amplifier gain to eliminate common-mode error caused by ground bounce.

[0078] In this embodiment, the fourteenth and fifteenth resistors are positioned close to the fan connector, with a trace width of ≥0.5mm to reduce the impact of parasitic resistance on feedback accuracy; critical nodes are equipped with RC low-pass filters with a cutoff frequency of 1kHz to suppress commutation spikes.

[0079] In this embodiment, the feedback node can be connected to the system monitoring MCU to digitize the fan voltage for use in the life prediction algorithm, prompting maintenance when the voltage drift is >±10%.

[0080] In one alternative implementation, such as Figure 1 As shown, the voltage divider composed of R14 and R15 provides the feedback signal for the fan voltage, and the output voltage of the differential amplifier circuit provides the reference signal. It should be noted that the voltage divider composed of R1 and R4 can be equivalent to the starting temperature at which the fan can operate. As the temperature increases, the reference signal voltage increases, which in turn increases the fan voltage and increases the fan speed, thus controlling the fan speed at different temperatures.

[0081] Furthermore, the circuit also includes a filter capacitor coupled between the positive terminal of the fan and ground, used to suppress fan current ripple, absorb fan commutation current spikes, and reduce power supply ripple; wherein the filter capacitor is a combination of aluminum electrolytic capacitor and ceramic capacitor connected in parallel, with a total capacitance value in the range of 100µF~1000µF and an equivalent series resistance of <100mΩ.

[0082] Furthermore, in this embodiment, the aluminum electrolytic capacitor is selected as a 105℃, 5000h lifespan model, and the ceramic capacitor is selected as an X7R10µF / 50V surface mount capacitor. After the two are connected in parallel, the ripple current capability is improved to 1.2ARMS, which meets the requirements of high-speed fans.

[0083] In this embodiment, the self-resonant frequency of the filter capacitor is set between 100kHz and 1MHz, which is different from the fan commutation frequency to avoid resonant amplification spikes.

[0084] In this embodiment, the filter network can be expanded to a π-type filter, adding two 4.7µH surface mount inductors, reducing conducted EMI by 15dBμV, and meeting CISPR25 Class 5 automotive requirements.

[0085] In this embodiment, the aluminum electrolytic capacitors are mounted horizontally with a 0.5mm cutout at the bottom to prevent PCB expansion stress from causing pad cracking; the ceramic capacitors are arranged symmetrically to reduce ESL.

[0086] In this embodiment, the filter capacitor lifespan temperature model can be written into the system firmware. By monitoring the capacitor case temperature, the remaining lifespan can be predicted, and early warnings can be issued to replace the capacitor, thereby improving system-level reliability.

[0087] Furthermore, the fan is powered by a dual +12V and -12V power supply, forming a 24V voltage difference to drive the DC fan.

[0088] In this embodiment, a 24V DC fan is used, with dual voltages of +12V and -12V. The copper width of the power supply traces is ≥1mm, the diameter of the vias is 0.5mm and the number is ≥4, and the surge current carrying capacity is >40A to prevent the traces from melting.

[0089] In this embodiment, the power layer and ground layer are arranged adjacent to each other, with a layer thickness of 1 oz and an interlayer capacitance of >100 pF / cm², which reduces high-frequency impedance and improves EMI margin.

[0090] This embodiment enables the circuit to continuously output differential voltage with a sensitivity of -10mV / ℃ within the range of 0℃–100℃ through the first voltage divider branch and the second voltage divider branch, thereby realizing continuous adjustment of the fan voltage and avoiding the sudden noise of "full speed / stop" in the traditional comparator scheme. The overall noise is reduced by 8–10dB(A).

[0091] This embodiment uses a differential amplifier circuit to make the temperature-speed curve determined solely by the resistance ratio. The amplification factor A can be set between 2 and 20 times using an external resistor. The same PCB can cover any temperature range of 20℃–80℃ without replacing the NTC or reference resistor, shortening the R&D cycle by more than 50%.

[0092] This embodiment forms a closed-loop negative feedback through an error amplifier circuit. When the power supply fluctuates by ±10% or the fan current changes by ±30% due to aging, the fan terminal voltage fluctuation is compressed to <±1% and the speed drift is <±2%, which significantly improves the predictability of heat dissipation margin.

[0093] This embodiment boosts the milliampere output of the operational amplifier to the hundred-milliampere level through a driver amplifier circuit, which can directly drive the base of the PNP power transistor without the need for an external MOSFET or relay. The power consumption of the driver stage itself is <0.2W and the temperature rise is <5℃, solving the problem of severe MOSFET overheating in the linear region.

[0094] This embodiment uses a feedback voltage divider branch to automatically increase the output current to maintain the set voltage when the fan is stalled or the load increases momentarily, thereby increasing the starting torque by 30% and avoiding jamming at low speeds.

[0095] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A temperature-controlled fan circuit, characterized in that, include: The first voltage divider branch is used to generate a fixed voltage divider. The second voltage-dividing branch is used to generate temperature-dividing pressures that vary with temperature. A differential amplifier circuit is used to obtain a differential voltage based on the fixed voltage divider and the temperature voltage divider; An error amplifier circuit is used to obtain the error voltage based on the difference voltage and the fan voltage feedback signal; A drive amplifier circuit is used to obtain a drive signal based on the error voltage; The regulating transistor circuit is used to adjust the fan power supply voltage according to the drive signal; The feedback voltage divider branch is used to sample the fan power supply voltage and generate the fan voltage feedback signal.

2. The temperature-controlled fan circuit according to claim 1, characterized in that, The first voltage divider branch includes a first resistor and a fourth resistor connected in series between the first power supply and ground, and the fixed voltage divider is taken from the common node of the two resistors.

3. The temperature-controlled fan circuit according to claim 1, characterized in that, The second voltage divider branch includes a thirteenth resistor and an NTC thermistor connected in series between the first power supply and ground, and the temperature voltage divider is taken from the common node of the two components.

4. The temperature-controlled fan circuit according to claim 1, characterized in that, The differential amplifier circuit includes a first operational amplifier and a fixed voltage divider and a temperature voltage divider respectively coupled to the two input terminals of the first operational amplifier, for outputting the differential voltage.

5. The temperature-controlled fan circuit according to claim 1, characterized in that, The error amplifier circuit includes a second operational amplifier. The first input terminal of the second operational amplifier receives the difference voltage, the second input terminal of the second operational amplifier receives the fan voltage feedback signal, and the output terminal of the second operational amplifier provides the error voltage.

6. The temperature-controlled fan circuit according to claim 1, characterized in that, The drive amplifier circuit includes an NPN transistor, the base of which receives the error voltage, and the collector of which provides the drive signal.

7. The temperature-controlled fan circuit according to claim 1, characterized in that, The regulating transistor circuit includes a PNP power transistor, the base of which receives the drive signal, the emitter of which is coupled to a second power supply, and the collector of which provides the fan power supply voltage to the fan.

8. The temperature-controlled fan circuit according to claim 1, characterized in that, The feedback voltage divider branch includes a fourteenth resistor and a fifteenth resistor connected in series between the positive terminal of the fan and ground, and the fan voltage feedback signal is taken from the common node of the two resistors.

9. The temperature-controlled fan circuit according to claim 1, characterized in that, The circuit also includes a filter capacitor coupled between the positive terminal of the fan and ground to suppress fan current pulsation.

10. The temperature-controlled fan circuit according to claim 1, characterized in that, The fan is powered by a dual power supply of +12V and -12V, forming a 24V voltage difference to drive the 24V DC fan.

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