CN117250552A - Power failure/undervoltage detection circuit and method for alternating current power supply - Google Patents

Abstract

The invention provides a power failure/undervoltage detection circuit and method of an alternating current power supply, wherein the detection circuit comprises an alternating current acquisition circuit, a level comparison circuit, a direct current bias circuit and a period judgment circuit, the alternating current acquisition circuit comprises an acquisition resistor and an instrument operational amplifier, and the acquisition resistor is connected with the alternating current power supply and the instrument operational amplifier; the direct current bias circuit comprises an operational amplifier, and the operational amplifier is connected with an alternating current acquisition circuit and direct current bias; the level comparison circuit comprises a comparator, and the comparator is connected with the operational amplifier and a preset threshold voltage; the period judging circuit is connected with the output end of the comparator, the output end outputs an output state indicating signal of the alternating current power supply, and the output state indicating signal comprises a normal signal or a power failure/undervoltage signal. The detection circuit and the method can be used for rapidly detecting alternating current power failure, the circuit is completed by adopting a full-hardware analog circuit, the circuit is reliable and stable in work and high in response speed, interference of noise waves can be effectively eliminated, and the detection circuit and the method have good application effects.

Description

Power failure/undervoltage detection circuit and method for alternating current power supply

Technical Field

The invention relates to an onboard power supply detection design technology, in particular to a power failure/undervoltage detection circuit and method of an alternating current power supply.

Background

The stability of the on-board power supply is very important for the on-board electronic equipment, especially for the on-board computer products, because even if the power supply is under-voltage or interrupted in millisecond level, the product working state is possibly wrong, even unknown faults occur, and the stability and the reliability of the whole on-board system are affected. Meanwhile, the airborne power supply network is a very severe environment, and fluctuation of an airborne generator, on-board/ground power supply, high-power load switching, lightning stroke and the like can directly influence the stability of the airborne power supply, so that the monitoring of the power supply quality by the airborne electronic equipment is very important, and the fluctuation of the power supply is monitored in real time, and the power supply enters an emergency state immediately once abnormal power supply is detected, so that necessary countermeasures and protection measures are taken, such as important data storage, working mode switching, key equipment protection and the like.

The power supply quality monitoring comprises direct current power supply monitoring and alternating current power supply monitoring, wherein the direct current power supply monitoring is relatively simple, and accurate monitoring can be realized through comparing direct current levels, filtering, anti-shake, amplitude limiting, hysteresis and other operations. The monitoring of the alternating current power supply is complex, and the voltage value is continuously changed and the time timing is negative because the alternating current power supply is an alternating signal, so that the accurate monitoring of the alternating current power supply cannot be met through a simple comparison circuit.

At present, the traditional detection mode of the alternating current power supply is as follows: the alternating current power supply signal is converted into a direct current level signal through bridge rectification or a true effective value circuit, and then the direct current level signal is compared with a reference level to obtain a power supply state indication. Although this approach can collect the ac power supply state, it is less time-efficient, and in order to reduce the ripple and ac component of the output dc voltage to improve the collection accuracy, a comparable capacitance is usually used, so that the monitoring circuit has a large τ value (τ=r×c), and thus a period of time is required to respond when the voltage drop/under-voltage occurs or recovers. For example: when power is lost, the response time of the general monitoring circuit is more than 20ms, the airborne alternating current power supply is 400Hz, the power supply frequency of variable-frequency alternating current is even 800Hz at most, the frequency is far higher than the power frequency of 50Hz, the circuit is more difficult to track the change and fluctuation of the voltage value due to the higher frequency, more than 10 periods pass after the monitoring circuit responds, and the use requirement of an airborne computer cannot be met.

Moreover, in order to meet the requirement of rapidly detecting the change of alternating current power supply, part of products predict the subsequent waveform conditions by adopting a mode of tracking the change of waveforms by circuits, but the method needs an ultra-rapid operation core and a large-scale anti-interference circuit, and has the defects of high cost and large volume.

Disclosure of Invention

The invention discloses a power failure/undervoltage detection circuit and method of an alternating current power supply, aiming at solving the technical problems that the response of the power failure/undervoltage detection of the alternating current power supply in the prior art is slow and can not meet the use requirement of an onboard computer, and the technical problems of high cost and large volume caused by the requirement of an ultra-fast operation core and a large-scale anti-interference circuit.

The technical scheme for realizing the aim of the invention is as follows:

in a first aspect, the present invention provides a power down/brown-out detection circuit for an ac power supply, including:

the alternating current acquisition circuit comprises an acquisition resistor and an instrument operational amplifier, wherein the input end of the acquisition resistor is connected with the alternating current power supply, the output end of the acquisition resistor is connected with the instrument operational amplifier, the alternating current acquisition circuit is used for carrying out serial voltage division and equal proportional reduction on an acquired sampling signal of the alternating current power supply, and preferably, an absolute value acquisition circuit can be added to shape sine waves into steamed bread waves;

the direct current bias circuit comprises an operational amplifier, wherein the same-phase end of the operational amplifier is connected with the alternating current acquisition circuit and the direct current bias circuit, and the direct current bias circuit is used for outputting a sine wave voltage signal or a steamed bread wave voltage signal with the direct current bias after the direct current bias is applied to the alternating current power supply sampling signal with equal proportion shrinking;

the level comparison circuit comprises a comparator, wherein the inverting terminal of the comparator is connected with the output terminal of the operational amplifier, the non-inverting terminal of the comparator is connected with a preset threshold voltage, and the level comparison circuit is used for comparing the sine wave voltage signal with direct current bias with the preset threshold voltage and then outputting a rectangular wave signal;

the input end of the period judging circuit is connected with the output end of the comparator, the period judging circuit is used for judging the period of the rectangular waveform signal according to a preset period, the output end of the period judging circuit outputs an output state indicating signal of the alternating current power supply according to a judging result, and the output state indicating signal comprises a normal signal or a power-down/undervoltage signal.

Further, the collection resistor comprises a collection resistor R1, a collection resistor R21 and a collection resistor R2, the resistance values of the collection resistor R1 and the collection resistor R21 are equal, the ratio of the resistance values of the collection resistor R1 and the collection resistor R21 to the resistance value of the collection resistor R2 is greater than 900, and the instrument operational amplifier is used for collecting differential mode voltages at two ends of the collection resistor R2 after the collection resistor R1 and the collection resistor R2 are serially connected and divided with the collection resistor R21.

Further, the ac collection circuit further includes a filter capacitor C1, where the filter capacitor C1 and the collection resistor R2 are connected in parallel between the in-phase end and the anti-phase end of the operational amplifier of the meter.

Further, the power failure/undervoltage detection circuit further comprises an absolute value acquisition circuit, wherein the input end of the absolute value acquisition circuit is connected with the instrument operational amplifier, the output end of the absolute value acquisition circuit is connected with the direct current bias circuit, the absolute value acquisition circuit and the alternating current acquisition circuit are combined to form an alternating current acquisition circuit with absolute value sampling, the absolute value acquisition circuit comprises a resistor, an operational amplifier and a diode, the absolute value acquisition circuit comprises the resistor, the operational amplifier and the diode, and the direct current bias circuit is used for supporting loop test of the self-test circuit BIT on the absolute value acquisition circuit;

further, the direct current bias circuit further comprises a resistor R5 and a resistor R6 which are connected in parallel with the inverting end of the operational amplifier, the other end of the resistor R5 is grounded, and the other end of the resistor R6 is connected to the output end of the operational amplifier. The alternating current acquisition circuit is connected with the same-phase end of the operational amplifier through a resistor R3, and the direct current bias is connected with the same-phase end of the operational amplifier through a resistor R4.

Further, the cycle determination circuit includes any one of a watchdog circuit, a monostable trigger circuit, and an anti-bounce circuit.

Further, the watchdog circuit comprises a watchdog, an input pin WDI of the watchdog is connected with an output end of the comparator, and an output pin WDO outputs the output state indication signal;

the WT pin and the RT pin of the watchdog are connected with the ground through a capacitor, and different watchdog timeout times are set through adjustment of WT/RT parameters.

Further, the monostable trigger circuit comprises a monostable trigger, an input pin TRIG of the monostable trigger is connected with the output end of the comparator, and an output pin OUT outputs the output state indication signal;

the DIS pin and the THRS pin of the monostable trigger are connected with an RC network, the RC network comprises a time setting resistor R9 and a delay capacitor C2, the RC network and the TRIG pin are connected through a triode V3, and the RC network is used for discharging the delay capacitor C2.

Further, the anti-bouncing circuit comprises an anti-bouncing device, an input pin IN of the anti-bouncing device is connected with an output end of the comparator, an output pin OUT outputs the output state indicating signal,

the anti-rebound device is connected with a voltage dividing resistor R10 and a voltage dividing resistor R11 through a VCC pin and a DIV pin, and the SET pin is connected with the ground through a time setting resistor R9.

In a second aspect, the present invention provides a power failure/undervoltage detection method of an ac power supply, including:

the voltage waveform of the alternating current power supply is subjected to partial pressure acquisition, and a first sine wave sampling signal with equal proportion reduction is obtained; or the voltage waveform of the alternating current power supply is subjected to partial pressure acquisition to obtain a second sine wave sampling signal with equal proportion reduction, and an absolute value acquisition circuit is adopted to shape the second sine wave sampling signal into a steamed bread wave sampling signal;

applying a direct current bias to the first sine wave sampling signal or the steamed bread wave sampling signal, and outputting a sine wave voltage signal or a steamed bread wave voltage signal with the direct current bias;

comparing the sine wave voltage signal or the steamed bread wave voltage signal with a preset threshold voltage to output a rectangular wave signal;

judging the period of the rectangular wave signal according to a preset period, and outputting a power-down/undervoltage signal when the falling edge of the rectangular wave signal is not detected in the preset period.

Compared with the prior art, the beneficial effects that above-mentioned at least one technical scheme that this description embodiment adopted can reach include at least:

the power failure/undervoltage detection circuit and the method of the alternating current power supply can rapidly detect alternating current power failure, the circuit is completed by adopting a full hardware analog circuit, the circuit is reliable and stable in work and high in response speed, interference of noise waves can be effectively eliminated, and the circuit has a good application effect. The detection circuit is adopted to detect and verify the power failure condition of 115VAC/400Hz, the power failure/undervoltage detection point is set to be 78VRMS during the test, and an alternating current acquisition circuit with absolute value sampling is used corresponding to the peak voltage 110 Vpk. Through testing, after the power failure condition of the alternating current power supply occurs, the circuit detects the power failure in about 1.3ms, and the power supply change can be effectively detected for the undervoltage lower than 80VRMS, so that the circuit meets the use requirement of a system.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a block diagram of a power down/brown-out detection circuit for an AC power supply according to an embodiment of the present invention;

FIG. 2 is a circuit diagram of an AC acquisition circuit in an embodiment of the invention;

FIG. 3 is a circuit diagram of an AC acquisition circuit with absolute value sampling in an embodiment of the present invention;

FIG. 4 is a circuit diagram of a DC bias circuit according to an embodiment of the invention;

FIG. 5 is a circuit diagram of a level comparison circuit according to an embodiment of the invention;

FIG. 6 is a waveform diagram of the input and output of the level comparison circuit according to an embodiment of the present invention;

FIG. 7 is a circuit diagram of a cycle determination circuit in an embodiment of the invention;

FIG. 8 is a circuit diagram of a watchdog circuit according to an embodiment of the present invention;

FIG. 9 is a circuit diagram of a monostable flip-flop according to an embodiment of the present invention;

FIG. 10 is a circuit diagram of an anti-bounce circuit according to an embodiment of the present invention;

FIG. 11 is a flow chart of power down/brown-out detection of an AC power source in an embodiment of the invention;

100, an alternating current acquisition circuit; 200. a DC bias circuit; 300. a level comparison circuit; 400. a cycle determination circuit; 500. and an absolute value acquisition circuit.

Detailed Description

Embodiments of the present application are described in detail below with reference to the accompanying drawings.

Other advantages and effects of the present application will become apparent to those skilled in the art from the present disclosure, when the following description of the embodiments is taken in conjunction with the accompanying drawings. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. The present application may be embodied or carried out in other specific embodiments, and the details of the present application may be modified or changed from various points of view and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features of the embodiments may be combined with each other without conflict. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

A first embodiment of the present invention provides a power-down/undervoltage detection circuit of an ac power supply, as shown in fig. 1, the power-down/undervoltage detection circuit includes: an ac acquisition circuit 100, a dc bias circuit 200, a level comparison circuit 300, and a cycle determination circuit 400.

The ac collection circuit 100 includes a collection resistor and an instrument operational amplifier, an input end of the collection resistor is connected with the ac power supply, an output end of the collection resistor is connected with the instrument operational amplifier, and the ac collection circuit is used for amplifying an ac power supply signal of the collected ac power supply. Specifically, referring to fig. 2, the collecting resistor includes a collecting resistor R1, a collecting resistor R21 and a collecting resistor R2, the resistance values of the collecting resistor R1 and the collecting resistor R21 are equal, the ratio of the resistance values of the collecting resistor R1 and the collecting resistor R21 to the resistance value of the collecting resistor R2 is greater than 900, and the instrument operational amplifier is used for collecting differential mode voltages at two ends of the collecting resistor R2 after the collecting resistor R1 and the collecting resistor R2 are serially connected and divided with the collecting resistor R21.

In this embodiment, taking an AC acquisition circuit to acquire a 115V AC power supply signal (AC) output by an AC power supply source as an example, the amplitude is reduced by dividing the voltage of an acquisition resistor R1, an acquisition resistor R21 and an acquisition resistor R2 with different resistance values to obtain an AC power supply signal in equal proportion, for example, the sampling amplitude of 0.1% of 115V AC power supply can be obtained by the proportion of 999kΩ to 1kΩ, and the sampling amplitude is proportionally amplified by an instrument operational amplifier i.a, and besides the amplified signal, the characteristics of high input impedance and low output impedance of the instrument operational amplifier are utilized to ensure that the AC power supply signal is not interfered, and the output signal has a certain driving capability, so that the high common mode voltage tolerance characteristic of the instrument operational amplifier is more suitable for the circuit scene.

Further, in order to reduce the disturbance of the noise in the sampling circuit, referring to fig. 2, the ac acquisition circuit 100 further includes a filter capacitor C1, where the filter capacitor C1 and the acquisition resistor R2 are connected in parallel between the in-phase end and the anti-phase end of the operational amplifier of the meter, and the filter capacitor C1 can eliminate high-frequency noise.

In practical application, the ac acquisition circuit 100 may be further provided with a clipping circuit and an interface protection circuit, and the clipping circuit and the interface protection circuit may use existing general-purpose circuits, which will not be described in this embodiment.

In a modified embodiment of the power down/under voltage detection circuit, as shown in fig. 3, the power down/under voltage detection circuit further includes an absolute value acquisition circuit 500, an input end of the absolute value acquisition circuit 500 is connected with the operational amplifier of the meter, an output end of the absolute value acquisition circuit 500 is connected with the dc bias circuit 200, the absolute value acquisition circuit 500 and the ac acquisition circuit 100 are combined to form an ac acquisition circuit with absolute value sampling, the absolute value acquisition circuit includes a resistor, an operational amplifier and a diode, and the dc bias is used for supporting loop test of the absolute value acquisition circuit by the self test circuit BIT. More specifically, referring to fig. 3, the absolute value acquisition circuit 500 includes resistors R10 to R14, 2 operational amplifiers OP, a diode V1, and a diode V2. In order to further improve the response speed, in this embodiment, a full-bridge rectifier circuit (without a capacitor) or a high-precision absolute value sampling circuit based on an operational amplifier is arranged at the rear stage of the existing ac acquisition circuit, so as to obtain an absolute value waveform of ac power supply sampling, shape the original full-period sine waveform into an absolute value waveform of steamed bread wave, and detect the power failure/undervoltage of the power supply in a period not exceeding half a period.

Referring to fig. 4, the dc bias circuit 200 includes an operational amplifier, the in-phase end of the operational amplifier is connected with the ac acquisition circuit 100 and dc bias, the dc bias circuit 200 is configured to apply dc bias to the ac power supply sampling signal with a small equivalent proportion and then output a sine wave voltage signal or a steamed bread wave voltage signal with dc bias, and meanwhile, the dc bias circuit 200 also has a function of performing loop test on the power failure/under-voltage detection circuit.

Further, referring to fig. 4, the dc bias circuit 200 further includes a resistor R5 and a resistor R6 connected in parallel to the inverting terminal of the operational amplifier, and the other end of the resistor R5 is grounded, and the other end of the resistor R6 is connected to the output terminal of the operational amplifier. The alternating current acquisition circuit is connected with the same-phase end of the operational amplifier through a resistor R3, and the direct current bias is connected with the same-phase end of the operational amplifier through a resistor R4.

Specifically, the input signal of the dc bias circuit 200 is the output ac_sense signal of the AC acquisition circuit 100 or the AC acquisition circuit with absolute value sampling, that is, the AC power supply of 115V is sampled or the equal-proportion small signal after absolute value processing, the purpose of the dc bias circuit 200 is 2, firstly, the positive and negative signals of the original voltage are converted into the dc signal with the AC component through dc bias, the interference when approaching zero voltage is avoided, the use of the operational amplifier with single-side power supply is convenient, and the use of the operational amplifier with single-side power supply is supported, the loop test of the product self test circuit (BIT) can be supported, the BIT circuit is implemented by the following V _REF The voltage is adjusted to detect the corresponding working state changes of the AC_sense and the subsequent AC_Fail signals output by the DC bias circuit to detect whether the circuit functions normally or not, thereby realizing loop-back test. Fig. 2 shows a dc bias circuit obtained by a typical adder circuit, and other circuits having the same effect can be used as the dc bias circuit.

In FIG. 4, V _REF Is a DC bias voltage V _REF The method is realized through the reference source, in an actual product, the reference source adopts a scheme of a controlled reference source, the scheme is controlled by an external circuit, a higher bias voltage can be set in an initial power-on state, misoperation caused by initial state jitter is prevented, the reference source voltage does not need to be too high, and the use of a direct current bias voltage of about 2V can be met basically.

The level comparison circuit 300 includes a comparator, an inverting terminal of the comparator is connected to an output terminal of the operational amplifier, an in-phase terminal of the comparator is connected to a preset threshold voltage, and the level comparison circuit is configured to compare the sine wave voltage signal with the dc offset with the preset threshold voltage and output a rectangular waveform signal.

Specifically, referring to fig. 5, the level comparison circuit 300 includes a comparator CMP, a resistor R7, and a resistor R8, wherein the comparator CMP compares the ac_sense signal outputted from the dc bias circuit to convert it into a rectangular wave signal with periodic information, and the principle is to compare the ac_sense signal with a preset threshold voltage V _th Comparing, wherein the comparison result is rectangular wave; above threshold voltage V _th Part of the output of (2) is low, but below V _th Part of the output of (2) is high. The waveforms input and output through the level comparison circuit 300 are shown in fig. 6, and V is shown in fig. 6 by taking an ac acquisition circuit with absolute value sampling as an example _REF Adding DC bias to the AC sampling signal, at V _th Under the comparison of threshold voltage, the comparison result of COMP_OUT is obtained, and the duty ratio of the output rectangular wave of the comparator is continuously increased along with the continuous reduction of the peak value of the alternating current sampling voltage, but as long as the sampling peak value voltage is higher than the threshold voltage V _th A low level occurs for a certain period of time within a half period of time; when the alternating current sampling peak voltage is lower than V _th After this, the comp_out output is high and the periodic rectangular wave no longer appears.

In FIG. 6, the threshold voltage V _th As with the DC bias voltage V in FIG. 4 _REF The reference source is realized by the reference source, in an actual product, the reference source adopts the scheme of a controlled reference source, the voltage of the reference source in the initial state of power-on is lower, and the voltage of the reference source gradually rises after power-on, so that misoperation in the starting process is prevented.

The input end of the period determination circuit 400 is connected to the output end of the comparator, the period determination circuit 400 is configured to determine the period of the rectangular waveform signal according to a preset period, and the output end of the period determination circuit 400 outputs an output state indication signal of the ac power supply according to a determination result, where the output state indication signal includes any one of a normal state and a power failure/undervoltage state. The three circuits of the ac acquisition circuit 100, the dc bias circuit 200, and the level comparison circuit 300 convert the original ac power supply signal into discrete signals that meet the usage conditions, so long as the ac power supply is available (i.e., the peak voltage shown in fig. 8 is higher than the preset threshold), an effective falling edge and a period of low level will necessarily occur within a half period, so that the period determination circuit 400 only sets the active time, the falling edge or the low level is in an effective state, the effective state is not detected within the preset time, the power failure/undervoltage is determined, and if the effective signal is continuously monitored, the power supply voltage is determined to be normal, and thus, rapid monitoring and determination of the ac power supply voltage are realized.

Further, referring to fig. 7, the period determining circuit 400 may be implemented using any one of a watchdog circuit, a monostable trigger circuit, and an anti-bouncing circuit, where any one of the watchdog circuit, the monostable trigger circuit, and the anti-bouncing circuit supports adjustment of the determination period.

Referring to fig. 8, the watchdog circuit includes a watchdog, an input pin WDI of the watchdog is connected to an output end of the comparator, and an output pin WDO outputs the output state indication signal; the WT pin and the RT pin of the watchdog are connected with the ground through a capacitor, and different watchdog timeout times are set through adjustment of WT/RT parameters. Taking a 400Hz power supply system as an example, the minimum operating frequency is 360Hz, the corresponding period is 2.78ms, if the AC acquisition circuit 100 of fig. 2 is used, and a certain margin is set, if no valid WDI dog feeding signal is received within 3ms, the output signal ac_fail of the output status indication signal is low, and at this time, it can be determined that power failure or under-voltage has occurred. If the alternating current acquisition circuit with absolute value sampling in fig. 3 is adopted, the power failure or undervoltage detection can be realized by only setting the feeding interval time of 1.5 ms. In addition, the watchdog circuit further comprises an external control circuit, and the external control circuit can set different watchdog timeout time by adjusting WR/RT parameters so as to meet the requirements of different frequency power supply systems such as 50Hz, 60Hz and the like.

Referring to fig. 9, the monostable trigger circuit includes a monostable trigger, an input pin TRIG of the monostable trigger is connected with an output end of the comparator, and an output pin OUT outputs the output state indication signal; the DIS pin and the THRS pin are connected with an RC network, the RC network comprises a time setting resistor R9 and a delay capacitor C2, the RC network is connected with the TRIG pin through a triode V3, and the RC network is used for discharging the delay capacitor C2. Specifically, referring to fig. 9, the configuration RC network using the pin TRIG as its input signal, the resistor R9 and the delay capacitor C2 as delay times sets a delay time of 2.97ms, and the pin OUT is connected to the output state indication signal ac_fail. Normally, the output signal of the level comparison circuit 300 continuously sends OUT a valid TRIG signal in a delay time, and the output of the monostable trigger pin OUT is high (i.e. no power-off signal is sent OUT); if no valid TRIG signal is received again within the delay time, the output state indication signal AC_Fail of pin OUT goes low, indicating that a power loss or undervoltage has occurred. It should be noted that, because of the characteristic of the monostable flip-flop circuit that prevents continuous input, it is necessary to synchronously control the discharging of the output delay capacitor when the TRIG signal is low, and to discharge the delay capacitor C2 through the transistor V3 to ensure effective delay after the next TRIG signal turns high. Similarly, the output delay time in the monostable trigger circuit can be adjusted through the RC network, and the monostable trigger circuit can adapt to different requirements of different power supply frequencies.

Referring to fig. 10, the anti-bouncing circuit includes an anti-bouncing device, an input pin IN of the anti-bouncing device is connected with an output end of the comparator, an output pin OUT outputs the output state indication signal, a VCC pin and a DIV pin of the anti-bouncing circuit are both connected with a voltage dividing resistor R10 and a voltage dividing resistor R11, and a SET pin of the anti-bouncing circuit is connected with ground through the time setting resistor R9. Specifically, the anti-rebound circuit uses a circuit with a delay response function, a rising edge is configured to be delayed, a falling edge is configured to be normal response, an output signal of the level comparison circuit is used as an input IN signal of the anti-rebound circuit, the OUT output delay time is preset according to the minimum working frequency of a power supply, an inverter is added after the delay circuit, under normal conditions, the output signal of the level comparison circuit continuously sends OUT a valid IN falling edge signal within the delay time, and the output of the delay circuit is very high (does not send OUT an electrical signal); and if the effective falling edge signal is not received again within the delay time, sending out a power-down signal. In an actual circuit, output delay time can be adjusted in an external circuit through related circuit parameters of the SET and the DIV pins, and different requirements of different power supply frequencies can be met.

The second embodiment of the present invention provides a power failure/undervoltage detection method of an ac power supply, as shown in fig. 11, including:

s1, carrying out partial pressure acquisition on a voltage waveform of an alternating current power supply to obtain a first sine wave sampling signal with equal proportion reduction; or the voltage waveform of the alternating current power supply is subjected to partial pressure acquisition to obtain a second sine wave sampling signal with equal proportion reduction, and an absolute value acquisition circuit is adopted to shape the second sine wave sampling signal into a steamed bread wave sampling signal;

s2, applying direct current bias to the first sine wave sampling signal or the steamed bread wave sampling signal, and outputting a sine wave voltage signal or a steamed bread wave voltage signal with the direct current bias;

s3, comparing the sine wave voltage signal or the steamed bread wave voltage signal with a preset threshold voltage, and outputting a rectangular wave signal;

and S4, judging the period of the rectangular wave signal according to a preset period, and outputting a power-down/undervoltage signal when the falling edge of the rectangular wave signal is not detected in the preset period.

The power failure/undervoltage detection circuit and the method of the alternating current power supply can rapidly detect alternating current power failure, the circuit is completed by adopting a full hardware analog circuit, the circuit is reliable and stable in work and high in response speed, interference of noise waves can be effectively eliminated, and the circuit has a good application effect. The detection circuit is adopted to detect and verify the power failure condition of 115VAC/400Hz, the power failure point is set to be 78VRMS during the test, and an alternating current acquisition circuit with absolute value sampling is used corresponding to the peak voltage 110 Vpk. Through testing, after the power failure condition of the alternating current power supply occurs, the circuit detects the power failure in about 1.3ms, and the power supply change can be effectively detected for the undervoltage lower than 80VRMS, so that the circuit can meet the use requirement of a system.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, and various modifications and variations can be made to the embodiments of the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A power down/brown-out detection circuit for an ac power supply, comprising:

the alternating current acquisition circuit comprises an acquisition resistor and an instrument operational amplifier, wherein the input end of the acquisition resistor is connected with the alternating current power supply, and the output end of the acquisition resistor is connected with the instrument operational amplifier;

the direct current bias circuit comprises an operational amplifier, and the same-phase end of the operational amplifier is connected with the alternating current acquisition circuit and the direct current bias;

the level comparison circuit comprises a comparator, wherein the inverting terminal of the comparator is connected with the output terminal of the operational amplifier, and the non-inverting terminal of the comparator is connected with a preset threshold voltage;

and the input end of the period judging circuit is connected with the output end of the comparator, the output end outputs an output state indicating signal of the alternating current power supply, and the output state indicating signal comprises a normal signal or a power failure/undervoltage signal.

2. The power failure/undervoltage detection circuit of an alternating current power supply according to claim 1, wherein the collection resistor comprises a collection resistor R1, a collection resistor R21 and a collection resistor R2, the resistance values of the collection resistor R1 and the collection resistor R21 are equal, the ratio of the resistance values of the collection resistor R1 and the collection resistor R21 to the resistance value of the collection resistor R2 is greater than 900, and the instrument operational amplifier is used for collecting differential mode voltages at two ends of the collection resistor R2 after the collection resistor R1 and the collection resistor R2 are serially connected with the collection resistor R21 for voltage division.

3. The power down/under voltage detection circuit of an ac power supply according to claim 2, wherein the ac acquisition circuit further comprises a filter capacitor C1, the filter capacitor C1 and the acquisition resistor R2 are connected in parallel between the in-phase end and the anti-phase end of the operational amplifier of the meter.

4. A power failure/undervoltage detection circuit of an ac power supply according to any one of claims 1 to 3, further comprising an absolute value acquisition circuit, wherein an input end of the absolute value acquisition circuit is connected with the instrumentation op amp, an output end of the absolute value acquisition circuit is connected with the dc bias circuit, and the absolute value acquisition circuit and the ac acquisition circuit are combined to form an ac acquisition circuit with absolute value sampling;

the absolute value acquisition circuit comprises a resistor, an operational amplifier and a diode, and the direct current bias is used for supporting loop-back test of the self-test circuit BIT on the absolute value acquisition circuit.

5. The power down/under voltage detection circuit of an ac power supply according to claim 1, wherein the dc bias circuit further comprises a resistor R5 and a resistor R6 connected in parallel to an inverting terminal of the operational amplifier, and the other end of the resistor R5 is grounded, and the other end of the resistor R6 is connected to an output terminal of the operational amplifier;

the alternating current acquisition circuit is connected with the same-phase end of the operational amplifier through a resistor R3, and the direct current bias is connected with the same-phase end of the operational amplifier through a resistor R4.

6. The power down/undervoltage detection circuit of an ac power supply according to claim 1, wherein the cycle determination circuit includes any one of a watchdog circuit, a monostable trigger circuit, and an anti-bounce circuit, and any one of the watchdog circuit, the monostable trigger circuit, and the anti-bounce circuit supports adjustment of the determination cycle.

7. The power down/brown-out detection circuit of an ac power supply according to claim 6, wherein said watchdog circuit comprises a watchdog, an input pin WDI of said watchdog is connected to an output of said comparator, an output pin WDO outputs said output status indication signal, and a WT pin and a RT pin of said watchdog are both connected to ground via a capacitor.

8. The power failure/undervoltage detection circuit of an alternating current power supply according to claim 6, wherein the monostable trigger circuit comprises a monostable trigger, an input pin TRIG of the monostable trigger is connected with an output end of the comparator, and an output pin OUT outputs the output state indication signal;

the DIS pin and the THRS pin of the monostable trigger are connected with an RC network, the RC network comprises a time setting resistor R9 and a delay capacitor C2, the RC network and the TRIG pin are connected through a triode V3, and the RC network is used for discharging the delay capacitor C2.

9. The power down/under voltage detection circuit of an ac power supply according to claim 6, wherein the anti-bounce circuit includes an anti-bounce device, an input pin IN of the anti-bounce device is connected with an output terminal of the comparator, and an output pin OUT outputs the output state indication signal;

the VCC pin and the DIV pin of the anti-bouncing circuit are connected with a voltage dividing resistor R10 and a voltage dividing resistor R11, and the SET pin of the anti-bouncing circuit is connected with the ground through the time setting resistor R9.

10. The power failure/undervoltage detection method of the alternating current power supply is characterized by comprising the following steps of:

the voltage waveform of the alternating current power supply is subjected to partial pressure acquisition, and a first sine wave sampling signal with equal proportion reduction is obtained; or the voltage waveform of the alternating current power supply is subjected to partial pressure acquisition to obtain a second sine wave sampling signal with equal proportion reduction, and an absolute value acquisition circuit is adopted to shape the second sine wave sampling signal into a steamed bread wave sampling signal;

applying a direct current bias to the first sine wave sampling signal or the steamed bread wave sampling signal, and outputting a sine wave voltage signal or a steamed bread wave voltage signal with the direct current bias;

comparing the sine wave voltage signal or the steamed bread wave voltage signal with a preset threshold voltage to output a rectangular wave signal;

judging the period of the rectangular wave signal according to a preset period, and outputting a power-down/undervoltage signal when the falling edge of the rectangular wave signal is not detected in the preset period.