Frequency detection circuit

Abstract

The utility model relates to the technical field of frequency detection, and discloses a frequency detection circuit, which comprises a voltage division circuit, a hysteresis comparison circuit and a frequency calculation unit, and is characterized in that a first end of the voltage division circuit is connected with a positive end of a reference power supply, and a second end of the voltage division circuit is connected with a first input end of the hysteresis comparison circuit; the third end of the comparator circuit is connected with the output end of the hysteresis comparison circuit; the second input end of the hysteresis comparison circuit is connected with a first power supply, the first power supply end of the hysteresis comparison circuit is connected with the positive end of an external power supply, the second power supply end of the hysteresis comparison circuit is grounded, and the output end of the hysteresis comparison circuit is connected with the input end of the frequency calculation unit; the frequency calculation unit calculates an output frequency of the first power supply based on a first level signal and a second level signal. According to the utility model, when the first power supply voltage is in zero-crossing oscillation in a hysteresis range, a level signal which is not overturned is output, so that the accuracy and the stability of a frequency detection result are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of frequency detection, in particular to a frequency detection circuit. Background Art

[0002] Inverters usually use op amps / comparators to perform zero-crossing detection, detect the zero-crossing point of the mains, and calculate the mains frequency. The general zero-crossing detection circuit compares the input signal mains with the reference voltage. When the input voltage is higher than the reference voltage, the output is high; when the input voltage is lower than the reference voltage, the output flips to a low level. If the input mains signal has a slight interference near the reference voltage, the output voltage will flip multiple times at the zero crossing, resulting in abnormal calculation of the grid voltage frequency. Utility Model Content

[0003] Therefore, the technical problem to be solved by the present invention is to solve the problem in the prior art that when the input voltage of the comparison circuit fluctuates, the output signal is flipped, resulting in inaccurate calculation of the input voltage frequency, thereby providing a frequency detection circuit.

[0004] In order to achieve the above object, the utility model provides the following technical solutions:

[0005] The utility model provides a frequency detection circuit, comprising: a voltage divider circuit, a hysteresis comparison circuit and a frequency calculation unit, wherein the voltage divider circuit has a first end connected to the positive end of a reference power supply, a second end connected to the first input end of a hysteresis comparison circuit, and a third end connected to the output end of the hysteresis comparison circuit; the hysteresis comparison circuit has a second input end connected to the first power supply, a first power supply end connected to the positive end of an external power supply, a second power supply end grounded, and an output end connected to the input end of the frequency calculation unit; the reference power supply provides a reference voltage to the first input end of the hysteresis comparison circuit through the voltage divider circuit; when the voltage of the first power supply gradually increases to a first preset voltage, the second output end of the hysteresis comparison circuit is connected to the positive end of an external power supply, the second power supply end is grounded, and the output end is connected to the input end of the frequency calculation unit. The voltage at the first input terminal of the hysteresis comparison circuit is greater than the voltage at the first input terminal of the hysteresis comparison circuit, and the comparison signal output by the hysteresis comparison circuit is flipped from the first level signal to the second level signal; when the voltage of the first power supply gradually decreases to the second preset voltage, the voltage at the first input terminal of the hysteresis comparison circuit is greater than the voltage at the second input terminal of the hysteresis comparison circuit, and the comparison signal output by the hysteresis comparison circuit is flipped from the second level signal to the first level signal; the second preset voltage is less than the first preset voltage; when the voltage of the first power supply is less than the first preset voltage and greater than the second preset voltage, the hysteresis comparison circuit maintains the current output state; the frequency calculation unit calculates the output frequency of the first power supply based on the first level signal and the second level signal.

[0006] The frequency detection circuit provided by the utility model can flexibly set the hysteresis value of the hysteresis comparison circuit, that is, the first preset voltage and the second preset voltage, according to the amplitude of the first power supply; when the first power supply voltage gradually increases and is greater than the first preset voltage, the output signal of the hysteresis comparison circuit is flipped from the first level signal to the second level signal; when the first power supply voltage gradually decreases and is less than the second preset voltage, the output signal of the hysteresis comparison circuit is flipped from the second level signal to the first level signal; when the first power supply voltage fluctuates within the first preset voltage and the second preset voltage interval, that is, when the first power supply voltage fluctuates through zero within the hysteresis range, the hysteresis comparison circuit maintains the level of the current output signal without flipping, thereby ensuring that when the first power supply voltage fluctuates within the hysteresis range, the level signal input to the frequency calculation unit will not repeatedly flip and jump, and the accuracy and stability of the frequency detection result are improved.

[0007] In an optional embodiment, the voltage divider circuit includes: a first resistor and a second resistor, wherein the first resistor has a first end connected to the positive end of the reference power supply, and a second end connected to the first end of the second resistor and the first input end of the hysteresis comparison circuit; the second resistor has a second end connected to the output end of the hysteresis comparison circuit.

[0008] The frequency detection circuit provided by the utility model can divide the voltage of the reference power supply to different degrees by adjusting the resistance values ​​of the first resistor and the second resistor, thereby adjusting the magnitude of the voltage at the first input terminal of the hysteresis comparison circuit to adjust the flipping condition of the output signal of the hysteresis comparison circuit, thereby improving the flexibility of the circuit.

[0009] In an optional embodiment, the frequency detection circuit also includes: a first filtering circuit, whose first end is connected to the first power supply, whose second end is connected to the second input end of the hysteresis comparator circuit, and whose third end is grounded, and is used to filter out interference signals at the second input end of the hysteresis comparator circuit.

[0010] In the frequency detection circuit provided by the utility model, the first filter circuit can filter out interference signals in the first power supply, thereby preventing the interference signals from affecting the judgment process of the hysteresis comparison circuit, and further improving the accuracy of the output signal of the hysteresis comparison circuit.

[0011] In an optional embodiment, the first filtering circuit includes: a third resistor and a first capacitor, wherein the first end of the third resistor is connected to the first power supply, and the second end of the third resistor is connected to the first end of the first capacitor and the second input end of the hysteresis comparator circuit; the second end of the first capacitor is grounded.

[0012] In an optional implementation, the frequency detection circuit further includes: a second filtering circuit connected in parallel with the reference power supply and configured to filter out interference signals of the reference power supply.

[0013] The frequency detection circuit provided by the utility model and the second filter circuit can filter out interference signals in the reference power supply, thereby preventing the interference signals from affecting the judgment process of the hysteresis comparison circuit and further improving the accuracy of the output signal of the hysteresis comparison circuit.

[0014] In an optional implementation, the second filtering circuit includes: a second capacitor connected in parallel with the reference power supply.

[0015] In an optional embodiment, the frequency detection circuit also includes: a third filtering circuit, a first end of which is connected to the output end of the hysteresis comparison circuit and the positive end of the external power supply, a second end of which is connected to the input end of the frequency calculation unit, and a third end of which is grounded, and is used to filter out interference signals at the output end of the hysteresis comparison circuit.

[0016] The frequency detection circuit provided by the utility model, the third filter circuit can filter out the interference signal in the output signal of the hysteresis comparison circuit, improve the accuracy of the signal input to the frequency calculation unit, and thus improve the calculation result of the frequency calculation unit.

[0017] In an optional embodiment, the third filtering circuit includes: a fourth resistor and a third capacitor, wherein the first end of the fourth resistor is connected to the output end of the hysteresis comparison circuit and the positive end of the external power supply, and the second end of the fourth resistor is connected to the first end of the third capacitor and the input end of the frequency calculation unit; the second end of the third capacitor is grounded.

[0018] In an optional embodiment, the frequency detection circuit also includes: a fourth filtering circuit, a first end of which is connected to the first power supply end of the hysteresis comparison circuit, a second end of which is connected to the positive end of the external power supply, a third end of which is connected to the negative end of the external power supply and then grounded, and a fourth end of which is connected to the output end of the hysteresis comparison circuit, and is used to filter out interference signals from the external power supply.

[0019] In an optional embodiment, the fourth filtering circuit includes: a fifth resistor, a sixth resistor and a fourth capacitor, wherein the first end of the fifth resistor is connected to the first power supply end of the hysteresis comparison circuit and the first end of the fourth capacitor, and the second end of the fifth resistor is connected to the first end of the sixth resistor and the positive end of the external power supply; the second end of the sixth resistor is connected to the output end of the hysteresis comparison circuit; the second end of the fourth capacitor is connected to the negative end of the external power supply and then grounded. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A composition diagram of a specific example of a frequency detection circuit according to an embodiment of the present utility model;

[0022] Figure 2 It is a schematic diagram of a hysteresis comparison circuit according to an embodiment of the utility model;

[0023] Figure 3 The figure is a structural diagram of a specific circuit of the frequency detection circuit of the embodiment of the utility model. DETAILED DESCRIPTION

[0024] The technical solution of the utility model will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0025] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present utility model, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0027] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This embodiment provides a frequency detection circuit, such as Figure 1As shown, it includes: a voltage divider circuit 1, a hysteresis comparison circuit 2 and a frequency calculation unit 3, wherein the voltage divider circuit 1 has a first end connected to the positive end of a reference power supply VREF, a second end connected to a first input end of the hysteresis comparison circuit 2, and a third end connected to an output end of the hysteresis comparison circuit 2; the hysteresis comparison circuit 2 has a second input end connected to a first power supply, a first power supply end connected to a positive end of an external power supply VCC, a second power supply end grounded, and an output end connected to an input end of the frequency calculation unit 3; the reference power supply VREF provides a reference voltage Uref to the first input end of the hysteresis comparison circuit 2 through the voltage divider circuit 1.

[0029] Figure 1 In the embodiment, when the voltage of the first power supply gradually increases to the first preset voltage U1, the voltage at the second input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the comparison signal output by the hysteresis comparator circuit 2 is flipped from the first level signal to the second level signal; when the voltage of the first power supply gradually decreases to the second preset voltage U2, the voltage at the first input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the second input terminal of the hysteresis comparator circuit 2, and the comparison signal output by the hysteresis comparator circuit 2 is flipped from the second level signal to the first level signal.

[0030] Figure 2 In the embodiment, the second preset voltage U2 is less than the first preset voltage U1; when the voltage of the first power supply is less than the first preset voltage U1 and greater than the second preset voltage U2, the hysteresis comparison circuit 2 maintains the current output state; the frequency calculation unit 3 calculates the output frequency of the first power supply based on the first level signal and the second level signal.

[0031] In this embodiment, the first power source takes the mains as an example, and the frequency calculation unit 3 is used to detect the voltage frequency of the mains according to the level signal output by the hysteresis comparison circuit 2 .

[0032] Specifically, Figure 1 In the embodiment, after the voltage divider circuit 1 divides the reference power supply VREF, the reference voltage Uref is output to the first input terminal of the hysteresis comparison circuit 2, and the first power supply voltage is input to the second input terminal of the hysteresis comparison circuit 2. Since the hysteresis comparison circuit 2 will output a high level signal and a low level signal respectively according to the comparison results of the voltages at the two input terminals, the first preset voltage U1 and the second preset voltage U2 are respectively set according to the high level signal and the low level signal output by the hysteresis comparison circuit 2 and the size of the reference voltage Uref, that is, the high threshold voltage and the low threshold voltage of the hysteresis comparison circuit 2 are set by adjusting the size of the reference power supply VREF, and the hysteresis range of the hysteresis comparison circuit 2 is formed between the first preset voltage U1 and the second preset voltage U2.

[0033] Specifically, refer to Figure 1 and Figure 2, the output states of the hysteresis comparison circuit 2 include the following situations:

[0034] (1) When the voltage of the first power supply is in a gradually increasing state and is less than the high threshold voltage of the hysteresis comparator circuit 2, that is, less than the first preset voltage U1, the voltage at the second input terminal of the hysteresis comparator circuit 2 is less than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the hysteresis comparator circuit 2 continues to output the first level signal.

[0035] (2) When the voltage of the first power supply gradually increases to the high threshold voltage of the hysteresis comparator circuit 2, that is, equal to the first preset voltage U1, the voltage at the second input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the comparison signal output by the hysteresis comparator circuit 2 is flipped from the first level signal to the second level signal.

[0036] (3) When the voltage of the first power supply is gradually increasing and is greater than the high threshold voltage of the hysteresis comparator circuit 2, that is, greater than the first preset voltage U1, the voltage at the second input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the hysteresis comparator circuit 2 continues to output the second level signal.

[0037] (4) When the voltage of the first power supply is in a gradually decreasing state and is greater than the low threshold voltage of the hysteresis comparator circuit 2, that is, greater than the second preset voltage U2, the voltage at the second input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the hysteresis comparator circuit 2 continues to output the second level signal.

[0038] (5) When the voltage of the first power supply gradually decreases to the low threshold voltage of the hysteresis comparator circuit 2, that is, equal to the second preset voltage U2, the voltage at the first input terminal of the hysteresis comparator circuit 2 is greater than the voltage at the second input terminal of the hysteresis comparator circuit 2, and the comparison signal output by the hysteresis comparator circuit 2 is flipped from the second level signal to the first level signal.

[0039] (6) When the voltage of the first power supply is gradually decreasing and is less than the low threshold voltage of the hysteresis comparator circuit 2, that is, less than the second preset voltage U2, the voltage at the second input terminal of the hysteresis comparator circuit 2 is less than the voltage at the first input terminal of the hysteresis comparator circuit 2, and the hysteresis comparator circuit 2 continues to output the first level signal.

[0040] Specifically, based on the above analysis and combined with Figure 1 and Figure 2It can be seen that when the voltage of the first power supply is greater than the second preset voltage U2 and less than the first preset voltage U1, the voltage of the first power supply is within the hysteresis range of the hysteresis comparison circuit 2, and the hysteresis comparison circuit 2 will maintain the current output state without jumping. Therefore, when the voltage of the first power supply fluctuates within the hysteresis range, the output state of the hysteresis comparison circuit 2 will not flip continuously, thereby improving the stability of the signal input to the frequency calculation unit 3, thereby improving the accuracy of the frequency calculation unit 3's detection result of the first power supply frequency.

[0041] It should be noted that when the first power supply is AC power, it is necessary to consider setting the first preset voltage and the second preset voltage according to the requirements of the AC power voltage detection range to ensure the hysteresis capability of the hysteresis comparison circuit; and the hysteresis range cannot be set too small to avoid the AC power voltage zero fluctuation amplitude exceeding the hysteresis range and affecting the frequency calculation.

[0042] The frequency detection circuit provided in this embodiment can flexibly set the hysteresis value of the hysteresis comparison circuit, that is, the first preset voltage and the second preset voltage, according to the amplitude of the first power supply; when the first power supply voltage gradually increases and is greater than the first preset voltage, the output signal of the hysteresis comparison circuit is flipped from the first level signal to the second level signal; when the first power supply voltage gradually decreases and is less than the second preset voltage, the output signal of the hysteresis comparison circuit is flipped from the second level signal to the first level signal; when the first power supply voltage fluctuates within the first preset voltage and the second preset voltage interval, that is, when the first power supply voltage fluctuates through zero within the hysteresis range, the hysteresis comparison circuit maintains the level of the current output signal without flipping, thereby ensuring that when the first power supply voltage fluctuates within the hysteresis range, the level signal input to the frequency calculation unit will not repeatedly flip and jump, thereby improving the accuracy and stability of the frequency detection result.

[0043] In some optional embodiments, such as Figure 3 As shown, the voltage divider circuit includes: a first resistor R1 and a second resistor R2, wherein the first resistor R1 has a first end connected to the positive end of the reference power supply VREF, and a second end connected to the first end of the second resistor R2 and the first input end of the hysteresis comparator circuit 2; the second resistor R2 has a second end connected to the output end of the hysteresis comparator circuit 2.

[0044] For example, Figure 2 In the embodiment, the hysteresis comparison circuit 2 is an operational amplifier. By adjusting the resistance values ​​of the first resistor R1 and the second resistor R2, the input voltage U input to the in-phase terminal of the operational amplifier can be adjusted. + When the voltage of the reference power supply VREF is 1.5V, according to the virtual short and virtual disconnect characteristics of the operational amplifier:

[0045]

[0046] Among them, UO is the output voltage of the operational amplifier, then the operational amplifier non-inverting input voltage U + And the inverting input voltage U - for:

[0047]

[0048] Since the output of the operational amplifier is high or low level (i.e., the first level signal U OH And the second level signal U OL ), so the high threshold voltage and the low threshold voltage (i.e. the first preset voltage U1 and the second preset voltage U2) of the hysteresis comparison of the operational amplifier are respectively:

[0049]

[0050]

[0051] Among them, U1 is greater than U2, and the output state of the operational amplifier includes the following situations:

[0052] (1) When the voltage U of the first power supply i When the voltage U1 of the inverting terminal input of the operational amplifier is in a gradually increasing state and is less than the high threshold voltage of the operational amplifier, that is, less than the first preset voltage U1, the inverting terminal input voltage U - Lower than the input voltage U + , the operational amplifier continuously outputs the first level signal U OH .

[0053] (2) When the voltage U of the first power supply i When the voltage U1 of the inverting terminal input of the operational amplifier gradually increases to the high threshold voltage of the operational amplifier, that is, equal to the first preset voltage U1, the inverting terminal input voltage U - Higher than the common-phase input voltage U + The comparison signal output by the operational amplifier is composed of the first level signal U OH Flip to the second level signal U OL .

[0054] (3) When the voltage U of the first power supply i When the voltage U1 of the inverting terminal input of the operational amplifier is gradually increased and is greater than the high threshold voltage of the operational amplifier, that is, greater than the first preset voltage U1, the inverting terminal input voltage U - Higher than the common-phase input voltage U + , the operational amplifier continuously outputs the second level signal U OL .

[0055] (4) When the voltage U of the first power supply iWhen the inverting input voltage U of the operational amplifier is in a gradually decreasing state and is greater than the low threshold voltage of the operational amplifier, that is, greater than the second preset voltage U2, the inverting input voltage U - Higher than the common-phase input voltage U + , the operational amplifier continuously outputs the second level signal U OL .

[0056] (5) When the voltage U of the first power supply i When the operational amplifier's non-inverting input voltage U + Higher than the inverting input voltage U - The comparison signal output by the operational amplifier is composed of the second level signal U OL Flip to the first level signal U OH .

[0057] (6) When the voltage U of the first power supply i When the voltage U1 of the inverting terminal input of the operational amplifier is gradually reduced and is less than the low threshold voltage of the operational amplifier, that is, less than the second preset voltage U2, the inverting terminal input voltage U - Lower than the input voltage U + , the operational amplifier continuously outputs the first level signal U OH .

[0058] Exemplarily, when the first power supply is the mains, the actual value of the grid voltage corresponding to U1 is U AC1 , the actual value of the grid voltage corresponding to U2 is U AC2 When the grid voltage rises to U AC1 When the grid voltage drops to U AC2 When the output signal of the operational amplifier is reversed again. The frequency calculation unit 3 calculates the frequency of the mains power grid according to the changes of the high and low level signals. Since the operational amplifier has a hysteresis function, there is a certain oscillation when the grid voltage passes through zero, and the oscillation value is within U AC2 ~U AC1 When the frequency is between 0 and 1, the output signal of the operational amplifier will not flip, thereby ensuring the stability of the frequency detection of the frequency calculation unit 3.

[0059] In some optional embodiments, such as Figure 3 As shown, the frequency detection circuit also includes: a first filter circuit 4, a second filter circuit 5, a third filter circuit 6 and a fourth filter circuit 7, wherein the first filter circuit 4 has a first end connected to the first power supply, a second end connected to the second input end of the hysteresis comparator circuit 2, and a third end grounded, and is used to filter out interference signals at the second input end of the hysteresis comparator circuit 2.

[0060] like Figure 3As shown, the second filtering circuit 5 is connected in parallel with the reference power supply VREF and is used to filter out the interference signal of the reference power supply VREF.

[0061] like Figure 3 As shown, the third filtering circuit 6 has a first end connected to the output end of the hysteresis comparison circuit 2 and the positive end of the external power supply VCC, a second end connected to the input end of the frequency calculation unit 3, and a third end grounded, and is used to filter out the interference signal at the output end of the hysteresis comparison circuit 2.

[0062] like Figure 3 As shown, the fourth filtering circuit 7 has a first end connected to the first power supply end of the hysteresis comparator circuit 2, a second end connected to the positive end of the external power supply VCC, a third end connected to the negative end of the external power supply VCC and then grounded, and a fourth end connected to the output end of the hysteresis comparator circuit 2, and is used to filter out the interference signal of the external power supply VCC.

[0063] For example, Figure 3 As shown, the first filter circuit 4 includes: a third resistor R3 and a first capacitor C1, wherein the third resistor R3 has a first end connected to the first power supply, and a second end connected to the first end of the first capacitor C1 and the second input end of the hysteresis comparison circuit 2; the first capacitor C1 has a second end connected to the ground. The second filter circuit 5 includes: a second capacitor C2, which is connected in parallel with the reference power supply VREF.

[0064] For example, Figure 3 As shown, the third filtering circuit 6 includes: a fourth resistor R4 and a third capacitor C3, wherein the fourth resistor R4 has a first end connected to the output end of the hysteresis comparator circuit 2 and the positive end of the external power supply VCC, and a second end connected to the first end of the third capacitor C3 and the input end of the frequency calculation unit 3; the third capacitor C3 has a second end connected to ground.

[0065] For example, Figure 3 As shown, the fourth filtering circuit 7 includes: a fifth resistor R5, a sixth resistor R6 and a fourth capacitor C4, wherein the fifth resistor R5 has a first end connected to the first power supply end of the hysteresis comparator circuit 2 and the first end of the fourth capacitor C4, and a second end connected to the first end of the sixth resistor R6 and the positive end of the external power supply VCC; the sixth resistor R6 has a second end connected to the output end of the hysteresis comparator circuit 2; and the fourth capacitor C4 has a second end connected to the negative end of the external power supply VCC and then grounded.

[0066] It should be noted that those skilled in the art can set the type and quantity of the filter circuits as needed, and the specific circuit structures of the first filter circuit, the second filter circuit, the third filter circuit and the fourth filter circuit are not limited here.

[0067] Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A frequency detection circuit, characterized in that: include: Voltage divider circuit, hysteresis comparison circuit and frequency calculation unit, wherein: A voltage divider circuit, a first end of which is connected to the positive end of a reference power supply, a second end of which is connected to the first input end of the hysteresis comparison circuit, and a third end of which is connected to the output end of the hysteresis comparison circuit; A hysteresis comparison circuit, wherein the second input terminal thereof is connected to the first power supply, the first power supply terminal thereof is connected to the positive terminal of the external power supply, the second power supply terminal thereof is grounded, and the output terminal thereof is connected to the input terminal of the frequency calculation unit; The reference power supply provides a reference voltage to the first input terminal of the hysteresis comparison circuit through the voltage divider circuit; When the voltage of the first power supply gradually increases to a first preset voltage, the voltage at the second input terminal of the hysteresis comparison circuit is greater than the voltage at the first input terminal of the hysteresis comparison circuit, and the comparison signal output by the hysteresis comparison circuit is flipped from a first level signal to a second level signal; When the voltage of the first power supply gradually decreases to a second preset voltage, the voltage at the first input terminal of the hysteresis comparison circuit is greater than the voltage at the second input terminal of the hysteresis comparison circuit, and the comparison signal output by the hysteresis comparison circuit is flipped from the second level signal to the first level signal; The second preset voltage is less than the first preset voltage; When the voltage of the first power supply is less than the first preset voltage and greater than the second preset voltage, the hysteresis comparison circuit maintains the current output state; The frequency calculation unit calculates an output frequency of the first power source based on a first level signal and a second level signal.

2. The frequency detection circuit according to claim 1, characterized in that: The voltage divider circuit includes: a first resistor and a second resistor, wherein: a first resistor, a first end of which is connected to the positive end of the reference power supply, and a second end of which is connected to the first end of the second resistor and the first input end of the hysteresis comparator circuit; A second resistor has a second end connected to the output end of the hysteresis comparison circuit.

3. The frequency detection circuit according to claim 1, characterized in that: Also includes: The first filter circuit has a first end connected to the first power supply, a second end connected to the second input end of the hysteresis comparator circuit, and a third end connected to ground, and is used to filter out interference signals at the second input end of the hysteresis comparator circuit.

4. The frequency detection circuit according to claim 3, characterized in that: The first filtering circuit includes: a third resistor and a first capacitor, wherein: a third resistor, a first end of which is connected to the first power supply, and a second end of which is connected to the first end of the first capacitor and the second input end of the hysteresis comparator circuit; The first capacitor has a second terminal connected to the ground.

5. The frequency detection circuit according to claim 1, characterized in that: Also includes: The second filtering circuit is connected in parallel with the reference power supply and is used to filter out interference signals of the reference power supply.

6. The frequency detection circuit according to claim 5, characterized in that: The second filtering circuit comprises: A second capacitor is connected in parallel with the reference power supply.

7. The frequency detection circuit according to claim 1, characterized in that: Also includes: A third filtering circuit, having a first end connected to the output end of the hysteresis comparison circuit and the positive end of the external power supply, a second end connected to the input end of the frequency calculation unit, and a third end grounded, is used to filter out interference signals at the output end of the hysteresis comparison circuit.

8. The frequency detection circuit according to claim 7, characterized in that: The third filtering circuit includes: a fourth resistor and a third capacitor, wherein: a fourth resistor, a first end of which is connected to the output end of the hysteresis comparison circuit and the positive end of the external power supply, and a second end of which is connected to the first end of the third capacitor and the input end of the frequency calculation unit; The third capacitor has a second terminal connected to the ground.

9. The frequency detection circuit according to claim 1, characterized in that: Also includes: A fourth filtering circuit, having a first end connected to the first power supply end of the hysteresis comparator circuit, a second end connected to the positive end of the external power supply, a third end connected to the negative end of the external power supply and then grounded, and a fourth end connected to the output end of the hysteresis comparator circuit, is used to filter out interference signals from the external power supply.

10. The frequency detection circuit according to claim 9, characterized in that: The fourth filtering circuit includes: a fifth resistor, a sixth resistor and a fourth capacitor, wherein: a fifth resistor, a first end of which is connected to the first power supply end of the hysteresis comparison circuit and the first end of the fourth capacitor, and a second end of which is connected to the first end of the sixth resistor and the positive end of the external power supply; a sixth resistor, a second end of which is connected to the output end of the hysteresis comparison circuit; A fourth capacitor has a second end connected to the negative end of the external power source and then grounded.

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