Abnormal-voltage protection apparatus and method of operating the same

An abnormal-voltage protection apparatus includes a switch unit, a voltage detection unit, and a delay time control unit. The switch unit is coupled to a power supplying path formed between an AC power source and a load. The voltage detection unit detects the AC power source and provides a detection signal. The delay time control unit is coupled to the voltage detection unit and the switch unit, and receives the detection signal and provides a control signal to the switch unit according to the detection signal. When the voltage detection unit detects that the AC power source changes from an abnormal voltage to a normal voltage, the delay time control unit turns on the switch unit by the control signal after a delay time so that the AC power source supplies power to the load through the power supplying path.

BACKGROUND

Technical Field

The present disclosure relates to an abnormal-voltage protection apparatus and a method of operating the same, and more particularly to an abnormal-voltage protection apparatus with delay time function and a method of operating the same.

Description of Related Art

In the countries or regions where the mains supplies are unstable, the abnormal high voltage or low voltage causes electrical appliances to malfunction or even damage in slight conditions, or causes fire hazard accidents in home appliances or even damage to personal safety and property in serious conditions.

At present, the existing protection apparatus with abnormal-voltage detection usually comprises a voltage detection circuit and a relay switch. Please refer toFIG. 1, which shows a block circuit diagram of a protection apparatus with abnormal-voltage detection of the related art. The protection apparatus with abnormal-voltage detection comprises a voltage detection circuit20A and a relay switch10A coupled between an AC power source VACand a load90A.

When the voltage detection circuit20A detects that the AC power source VACis in an abnormal high voltage or an abnormal low voltage, the voltage detection circuit20A provides a control signal SAto turn off the relay switch10A, thereby avoiding the abnormal AC power source VACsupplying power to the load90A. On the contrary, when the voltage detection circuit20A detects that the AC power source VACreturns to be normal from the abnormal voltage, the voltage detection circuit20A provides the control signal SAto turn on the relay switch10A so that the normal AC power source VACsupplies power to the load90A again.

However, in the initial stage of returning to be normal from the abnormal voltage, the AC power source VACis likely to be in the abnormal voltage again since the AC power source VACis still in an unstable condition. At this condition, the relay switch10A would be frequently activated when the AC power source VACis not completely stable and the relay switch10A is immediately turned on, thereby reducing life span of the relay switch10A, and even failing to provide efficient and safe power supply to the load90or rear-end circuits.

SUMMARY

An objective of the present disclosure is to provide an abnormal-voltage protection apparatus to solve problems of reducing life span of the relay switch, and even failing to provide efficient and safe power supply to the load or rear-end circuits when the relay switch is damaged due to its frequent activation.

In order to achieve the above-mentioned objective, the abnormal-voltage protection apparatus comprises a switch unit, a voltage detection unit, and a delay time control unit. The switch unit is coupled to a power supplying path formed between an AC power source and a load. The voltage detection unit detects the AC power source and provides a detection signal according to a voltage value of the AC power source. The delay time control unit is coupled to the voltage detection unit and the switch unit, and receives the detection signal and provides a control signal to the switch unit according to the detection signal. When the voltage detection unit detects that the AC power source changes from an abnormal voltage to a normal voltage, the delay time control unit turns on the switch unit by the control signal after a delay time so that the AC power source supplies power to the load through the power supplying path.

Accordingly, the abnormal-voltage protection apparatus is provided to provide efficient and safe power supply to the load or rear-end circuits and extend life span of the relay switch or switch unit.

Another objective of the present disclosure is to provide a method of operating an abnormal-voltage protection apparatus to solve problems of reducing life span of the relay switch, and even failing to provide efficient and safe power supply to the load or rear-end circuits when the relay switch is damaged due to its frequent activation.

In order to achieve the above-mentioned objective, the abnormal-voltage protection apparatus comprises a switch unit coupled between an AC power source and a load, a voltage detection unit, and a delay time control unit. The method comprises steps of: (a) detecting, by the voltage detection unit, a voltage value of the AC power source; (b) performing, by the delay time control unit, a delay time procedure when the AC power source changes from an abnormal voltage to a normal voltage; and (c) turning on, by the delay time control unit, the switch unit to make the AC power source supply power to the load through the switch unit after a delay time provided during the delay time procedure and the AC power source maintains in the normal voltage.

Accordingly, the method of operating the abnormal-voltage protection apparatus is provided to provide efficient and safe power supply to the load or rear-end circuits and extend life span of the relay switch or switch unit.

DETAILED DESCRIPTION

Reference will now be made to the drawing figures to describe the present disclosure in detail. It will be understood that the drawing figures and exemplified embodiments of present disclosure are not limited to the details thereof.

Please refer toFIG. 2, which shows a block circuit diagram of an abnormal-voltage protection apparatus according to the present disclosure. The abnormal-voltage protection apparatus100is coupled between an AC power source VACand a load90. A rated voltage of the AC power source VACmay be, for example but not limited to, 230 volts AC. Further, the load90may be, for example but not limited to, household appliances supplied with AC power, such as air conditioners, refrigerators, or so on.

The abnormal-voltage protection apparatus100comprises a voltage detection unit10, a delay time control unit20, and a switch unit30. The switch unit30is coupled to a power supplying path PSformed between the AC power source VACand the load90. In one embodiment, the switch unit30is, for example but not limited to, a relay switch. In other embodiments, any of the switch elements, which can disconnect and connect the power supplying path PS, may be used as the switch unit30.

The voltage detection unit10is coupled to the AC power source VAC, and receives the AC power source VACand provides a detection signal SDaccording to a voltage value of the AC power source VAC. The detection signal SDprovided by the voltage detection unit10is corresponding to the voltage value of the AC power source VAC. Also, the electrical information, such as voltage, current, frequency, and so on of the AC power source VACcan be acquired according to the detection signal SD.

The delay time control unit20is coupled to the voltage detection unit10and the switch unit30. The delay time control unit20receives the detection signal SDand provides a control signal SCaccording to the detection signal SD, i.e., the electrical information of the AC power source VAC. Further, the control signal SCis provided to control turning on or turning off the switch unit30so as to connect or disconnect the power supplying path PS, thus controlling the AC power source VACto supply or interrupt power to the load90, detailed description later.

The abnormal-voltage protection apparatus100further comprises a fuse unit40, and the fuse unit40is coupled in series to the power supplying path PSformed between the AC power source VACand the load90. When a current flowing through the power supplying path PSis excessive, the fuse unit40is disconnected to interrupt the current flowing to the load90, thereby providing an overcurrent protection for the load90.

Please refer toFIG. 3, which shows a schematic waveform of a delay control mechanism according to the present disclosure. From top to bottom,FIG. 3presents the AC power source VAC, the detection signal SD, and the control signal SC.FIG. 3further presents level transitions of the detection signal SDand the control signal SCcorresponding to the AC power source VACbe in the abnormal high/low voltage and the normal voltage, detailed description as follows.

For convenience, take the AC power source VACrated at 230 volts for example. Therefore, an upper threshold voltage value VUmay be predetermined to be a specific value, such as 276 volts or to be a percentage increment value, such as 253 volts, i.e., an increment by 10% of the AC power source VACrated at 230 volts. Accordingly, the upper threshold voltage value VUis used to determine whether the AC power source VACis in the abnormal high voltage. In other words, when a voltage value of the AC power source VACis greater than the upper threshold voltage value VU, such as 276 volts, the voltage detection unit10detects that the AC power source VACis in the abnormal high voltage.

Moreover, a lower threshold voltage value VLmay be predetermined to be a specific value, such as 184 volts or to be a percentage decrement value, such as 207 volts, i.e., a decrement by 10% of the AC power source VACrated at 230 volts. Accordingly, the lower threshold voltage value VLis used to determine whether the AC power source VACis in the abnormal low voltage. In other words, when the voltage value of the AC power source VACis less than the lower threshold voltage value VL, such as 184 volts, the voltage detection unit10detects that the AC power source VACis in the abnormal low voltage.

Incidentally, the foregoing “greater than” or “less than” is only a relationship indicating the magnitude of the voltage. Similarly, “greater than or equal to” or “less than or equal to” is also used to indicate whether the AC power source VACis in the abnormal high/low voltage. In one embodiment, a peak voltage of the AC power source VACis compared with the upper threshold voltage value VUand/or the lower threshold voltage value VLto determine whether the AC power source VACis in the abnormal high/low voltage.

It is assumed that the switch unit30is initially turned on, and therefore the AC power source VACnormally supplies power to the load90through the power supplying path PS. At a time point t0, the voltage detection unit10detects that a peak voltage of the AC power source VACis greater than the lower threshold voltage value VLand lower than the upper threshold voltage value VU. In other words, the voltage detection unit10detects that the AC power source VACis normal, and therefore the detection signal SDcan be maintained at a high-level state. At this condition, the delay time control unit20receives the high-level detection signal SDand continuously provides the control signal SCwith a high-level state to continuously turn on the switch unit30.

At a time point t1, the voltage detection unit10detects that the peak voltage of the AC power source VACis greater than the upper threshold voltage value VU, i.e., the voltage detection unit10detects that the AC power source VACis in an abnormal high voltage, and therefore the detection signal SDprovided from the voltage detection unit10is transited, for example but not limited to, from a high-level state to a low-level state. At this time, the delay time control unit20receives the low-level detection signal SDto provide the control signal SC, such as a low-level signal at a time point t1′ to turn off the switch unit30, thereby interrupting the abnormal high-voltage AC power source VACsupplying power to the load90and preventing the load90being affected by the abnormal high-voltage AC power source VAC.

After the time point t1, the voltage detection unit10continuously detects that the AC power source VACis in the abnormal high voltage, and therefore the detection signal SDis still maintained at the low-level state. Also, the control signal SCis still maintained at the low-level state to continuously turn off the switch unit30.

Until a time point t2, the detection signal SDprovided from the voltage detection unit10is transited from the low-level state to the high-level state since the voltage detection unit10detects that the peak voltage of the AC power source VACis greater than the lower threshold voltage value VLand less than the upper threshold voltage value VU, i.e., the voltage detection unit10detects that the AC power source VACreturns to be normal. At this time, the delay time control unit20activates a delay control mechanism as explained below.

When the voltage detection unit10detects that the AC power source VACreturns to be normal and the switch unit30is immediately turned on by the control signal SCprovided by the delay time control unit20to supply power to the load90, there would be following problems in the actual operation. When the AC power source VACreturns to be normal, the AC power source VACis likely to be in the abnormal voltage again since the AC power source VACis still in an unstable condition. At this condition, the voltage detection unit10again detects that the AC power source VACis in the abnormal high voltage. Also, the control signal SCprovided by the delay time control unit20turns off the switch unit30to interrupt the abnormal high-voltage AC power source VACsupplying power to the load90.

The switch unit30would be frequently activated when the AC power source VACis not completely stable and the switch unit30is immediately turned on, thereby reducing life span of the switch unit30. Once the switch unit30is damaged during operation, the switch unit30cannot be controlled by the control signal SC. The slight situation, i.e., a disconnected damage may always disconnect the AC power source VACsupplying power to the load90even though the AC power source VAChas returned to be normal. The serious situation, i.e., a connected damage may always connect the AC power source VACto supply power to the load90even though the AC power source VACis in the abnormal high voltage. Accordingly, it is unable to provide efficient and safe power supply to the load90or rear-end circuits, and therefore the delay control mechanism activated by the delay time control unit20is necessary in order to solve the problem.

At a time point t2, the detection signal SDprovided from the voltage detection unit10is transited, for example but not limited to, from the low-level state to the high-level state since the voltage detection unit10detects that the AC power source VACreturns to be normal. When the delay time control unit20receives the detection signal SDtransited from the low-level state to the high-level state, i.e., the voltage detection unit10detects that the AC power source VACreturns to be normal from the abnormal high voltage, the delay time control unit20turns on the switch unit30by the control signal SCafter a delay time Δtd, i.e., at a time point t3, and therefore the AC power source VACsupplies power to the load90through the power supplying path PS.

As shown inFIG. 3, a length of the delay time Δtd may be the length of one cycle, i.e., a time interval between the time point t2and the time point t3, and two adjacent peak voltages are corresponding to the two time points t2, t3. However, the length of the delay time Δtd may be designed according to requirements or considerations of the actual application, for example, two cycles, three cycles, or one-half cycle. In one embodiment, the delay time control unit20adjusts the delay time Δtd according to a duration time of the abnormal voltage. The duration time represents a time interval from the occurrence of the abnormal voltage to the return of the normal voltage. Therefore, the delay time Δtd can be flexibly set and adjusted according to the duration time. For example, when the abnormal high/low voltage lasts for a longer time, the delay time Δtd is extended. In one embodiment, when the abnormal high/low voltage occurs, the delay time control unit20starts timing, and then ends timing until the AC power source VACreturns to be normal. Also, the time interval is recorded to be as the duration time, and further the delay time Δtd is flexibly adjusted according to the value of the duration time.

In one embodiment, the delay time control unit20adjusts the delay time Δtd according to a magnitude of the abnormal voltage. The delay time Δtd can be flexibly set and adjusted according to the abnormal high degree or abnormal low degree of the AC power source VAC. For example, when the abnormal high/low degree is greater, the delay time Δtd is extended. In one embodiment, the abnormal high degree represents a voltage difference that the magnitude of the abnormal voltage is higher than the upper threshold voltage value VU, and the abnormal low degree represents a voltage difference that the magnitude of the abnormal voltage is lower than the lower threshold voltage value VL. When the voltage difference is greater, the delay time Δtd is extended. Once the AC power source VACis to be in the abnormal voltage again within the delay time Δtd, the control signal SCis continuously low-level to continuously turn off the switch unit30, thereby interrupting the abnormal AC power source VACsupplying power to the load90.

Besides the peak voltage, a valley voltage of the AC power source VACcan be also detected by the voltage detection unit10to determine whether the AC power source VACis in the abnormal high/low voltage. When the voltage detection unit10detects that the valley voltage of the AC power source VACis less than a negative upper threshold voltage value VU, i.e., −VU, the voltage detection unit10detects that the AC power source VACis in the abnormal high voltage. When the voltage detection unit10detects that the valley voltage of the AC power source VACis greater than a negative lower threshold voltage value VL, i.e., −VL, the voltage detection unit10detects that the AC power source VACis in the abnormal low voltage. When the voltage detection unit10detects that the valley voltage of the AC power source VACis greater than the negative the upper threshold voltage value VUand less than the negative lower threshold voltage value VL, the voltage detection unit10detects that the AC power source VACis normal.

The accumulation of the delay time Δtd can be implemented by a hardware manner, such as a delay time circuit or other digital or analog circuits, a firmware manner, or a software manner by the delay time control unit20. The following will be explained by the hardware circuit.

Please refer toFIG. 4AandFIG. 4B, which show circuit diagrams of the delay time control unit according to a first embodiment and a second embodiment of the present disclosure, respectively. The voltage detection unit10comprises a first comparator OP1, a second comparator OP2, a first diode D1, and a second diode D2. As shown inFIG. 4A, two input ends of the first comparator OP1receive the upper threshold voltage value VUand the AC power source VAC, respectively; two input ends of the second comparator OP2receive the lower threshold voltage value VLand the AC power source VAC, respectively. In particular, the voltages VU, VL, VACreceived by the comparators OP1, OP2are actually voltage signals corresponding to the upper threshold voltage value VU, the lower threshold voltage value VL, and the AC power source VACrather than voltages with value of hundreds of volts. An output end of the first comparator OP1is coupled to a cathode end of the first diode D1, an output end of the second comparator OP2is coupled a cathode end of the second diode D2, and an anode end of the first diode D1and an anode end of the second diode D2are coupled to a supply voltage Vcc.

The delay time control unit20comprises a third comparator OP3, a resistor Rt, and a capacitor Ct. As shown inFIG. 4A, a first input end, such as a non-inverting input end of the third comparator OP3is coupled to the resistor Rt, the capacitor Ct, and the supply voltage Vcc, and receives the detection signal SDprovided from the voltage detection unit10. The resistor Rt is coupled between the first input end of the third comparator OP3and a ground end. The capacitor Ct is coupled between the first input end of the third comparator OP3and the ground end. A second input end, such an inverting input end of the third comparator OP3receives a reference voltage Vref. In addition, the reference voltage Vref may be provided by dividing an external voltage by a resistor divider network, which is coupled to the second input end of the third comparator OP3. The first input end of the third comparator OP3receives the detection signal, the second input end of the third comparator OP3receives a reference voltage, and the output end of the third comparator OP3outputs the control signal SC.

A resistance value R of the resistor Rt and a capacitance value C of the capacitor Ct of the delay time control unit20determine a RC time constant, i.e., τ=RC of charging/discharging operation, and therefore a reset function can be implemented. Specifically, when the peak voltage of the AC power source VACis greater than the upper threshold voltage value VU, i.e., the AC power source VACis in the abnormal high voltage, the first diode D1is forward biased, or when the peak voltage of the AC power source VACis less than the lower threshold voltage value VL, i.e., the AC power source VACis in the abnormal low voltage, the second diode D2is forward biased, the detection signal SDoutputted from the voltage detection unit10is transited from the high-level state to the low-level state through the first diode D1(in the abnormal high voltage at the time point t1shown inFIG. 3) or through the second diode D2(in the abnormal low voltage at the time point t4shown inFIG. 3). At this condition, the capacitor Ct discharges through the resistor Rt. When a capacitor voltage (or referred to as “first voltage”) across two ends of the capacitor Ct is less than the reference voltage Vref, the control signal SCoutputted from the third comparator OP3is transited from the high-level state to the low-level state, thereby turning off the switch unit30and interrupting the abnormal AC power source VACsupplying power to the load90.

On the contrary, when the peak voltage of the AC power source VACis less than the upper threshold voltage value VUand greater than the lower threshold voltage value VL, i.e., the AC power source VACis normal or returns to be normal, both the first diode D1and the second diode D2are reverse biased. At this condition, the capacitor Ct is charged by the supply voltage Vcc. When the capacitor voltage, i.e., the first voltage across two ends of the capacitor Ct is greater than the reference voltage Vref, the control signal SCoutputted from the third comparator OP3is transited from the low-level state to the high-level state, thereby turning on the switch unit30and supplying the normal AC power source VACto the load90. In this embodiment, the duration time from the start of charging the capacitor Ct (for example, from zero volt) to the capacitor voltage being greater than the reference voltage Vref is the delay time Δtd, and therefore the resistance value of the resistor Rt and the capacitance value C of the capacitor Ct can be designed to adjust the length of the delay time Δtd. So, the delay time control unit20is configured to produce a first voltage according to the detection signal SD, and compare the first voltage with a reference voltage Vref to produce the control signal SC. And when the AC power source VACchanges from the abnormal voltage to the normal voltage, the delay time control unit20is further configured to increase the first voltage, and change a level of the control signal SAto turn on the switch unit30until the first voltage is greater than the reference voltage Vref.

Moreover, as the second embodiment shown inFIG. 4B, a diode Dt has a cathode end and an anode end. The cathode end of the diode Dt is coupled to the resistor Rt, and the anode end of the diode Dt is coupled to the capacitor Ct. The diode Dt is coupled between the resistor Rt and the capacitor Ct of the delay time control unit20in comparison with the first embodiment shown inFIG. 4A, and the diode Dt is used to provide an effective current discharging path for the capacitor Ct. Since the voltage detection unit10shown inFIG. 4Bis identical to the voltage detection unit10shown inFIG. 4A, it is only illustrated in a block diagram. The detail description of the voltage detection unit10can refer to description of the correspondingFIG. 4Aand is omitted here for conciseness.

Please refer toFIG. 4CandFIG. 4D, which show circuit diagrams of the delay time control unit according to a third embodiment and a fourth embodiment of the present disclosure, respectively. In comparison with the first embodiment shown inFIG. 4A, a transistor switch Qt (for example, a MOSFET shown inFIG. 4C, and a BJT shown inFIG. 4D) is further coupled between the resistor Rt and the capacitor Ct of the delay time control unit20. Also, the transistor switch Qt is controlled by an external signal to provide an effective current discharging path for the capacitor Ct. The transistor switch Qt is coupled between the first input end of the third comparator OP3and a ground end. The resistor Rt is coupled between the transistor switch Qt and the ground end. The capacitor Ct is coupled to the transistor switch Qt, the first input end of the third comparator OP3, and the ground end.

The detail description of the voltage detection unit10and delay time control unit20can refer to description of the correspondingFIG. 4AandFIG. 4Band is omitted here for conciseness.

Refer toFIG. 3again, at the time point t4, the detection signal SDprovided from the voltage detection unit10is transited from the high-level state to the low-level state since the voltage detection unit10detects that the peak voltage of the AC power source VACis less than the lower threshold voltage value VL, i.e., the voltage detection unit10detects that the AC power source VACis in the abnormal low voltage. At this time, the delay time control unit20receives the low-level detection signal SDto provide the low-level control signal SCat a time point t4′ to turn off the switch unit30, thereby interrupting the abnormal low-voltage AC power source VACsupplying power to the load90and preventing the load90being affected by the abnormal low-voltage AC power source VAC.

Since the difference between the abnormal AC power source VACdetected at the time point t4and the time point t1is only the abnormal low voltage (the former) and the abnormal low voltage (the latter), the detailed operation of the voltage detection unit10and delay time control unit20while occurring the abnormal voltage is omitted here for conciseness.

Until a time point t5, the detection signal SDprovided from the voltage detection unit10is transited from the low-level state to the high-level state since the voltage detection unit10detects that the AC power source VACreturns to be normal. The detailed operation of activating the delay control mechanism by the delay time control unit20is omitted here for conciseness.

Similarly, the length of the delay time Δtd to only one cycle time is not limited, and further the detection of the peak voltage of the AC power source VACto determine whether the AC power source VACis normal or abnormal is not limited. Moreover, once the AC power source is to be in the abnormal voltage again within the delay time Δtd, the control signal SCis continuously low-level to continuously turn off the switch unit30, thereby interrupting the abnormal AC power source VACsupplying power to the load90.

Please refer toFIG. 5, which shows a flowchart of a method of operating the abnormal-voltage protection apparatus according to a first embodiment of the present disclosure. The abnormal-voltage protection apparatus is coupled to an AC power source and a load, and the abnormal-voltage protection apparatus comprises a voltage detection unit, a delay time control unit, and a switch unit. The switch unit is coupled to a power supplying path formed between the AC power source and the load.

The method of operating the abnormal-voltage protection apparatus according to the first embodiment includes steps as follows. First, detecting a voltage value of the AC power source (S11). The voltage detection unit is coupled to the AC power source, and receives the AC power source and provides a detection signal according to the voltage value of the AC power source. The detection signal provided by the voltage detection unit is corresponding to the voltage value of the AC power source. Also, the electrical information, such as voltage, current, frequency, and so on of the AC power source can be acquired according to the detection signal.

Afterward, determining whether the AC power source changes from a normal voltage to an abnormal voltage (S12). The voltage value of the AC power source is compared with a predetermined upper threshold voltage value and a predetermined lower threshold voltage value to determine whether a voltage level of the detection signal is transited so as to determine whether the AC power source changes from the normal voltage to the abnormal voltage. For example, when the detection signal is transited from a high-level state to a low-level state, it means that the AC power source is abnormal. When the AC power source does not change from the normal voltage to the abnormal voltage, it means that the AC power source is continuously normal. At this condition, the delay time control unit receives the high-level detection signal and outputs a high-level control signal to continuously turn on the switch unit so that the AC power source continuously supplies power to the load through the power supplying path. On the contrary, when the AC power source changes from the normal voltage to the abnormal voltage, it means that the AC power source is in an abnormal high voltage or abnormal low voltage. At this condition, the delay time control unit receives the detection signal transited from the high-level state to the low-level state and outputs a low-level control signal to turn off the switch unit (S13) and interrupt the AC power source supplying power to the load through the power supplying path.

Please refer toFIG. 6, which shows a flowchart of the method of operating the abnormal-voltage protection apparatus according to a second embodiment of the present disclosure. The method of operating the abnormal-voltage protection apparatus according to the second embodiment includes steps as follows. First, detecting a voltage value of the AC power source (S21). The voltage detection unit receives the AC power source and provides a detection signal according to the voltage value of the AC power source. The detection signal provided by the voltage detection unit is corresponding to the voltage value of the AC power source. Also, the electrical information, such as voltage, current, frequency, and so on of the AC power source can be acquired according to the detection signal.

Afterward, determining whether the AC power source changes from an abnormal voltage to a normal voltage (S22). The voltage value of the AC power source is compared with a predetermined upper threshold voltage value and a predetermined lower threshold voltage value to determine whether a voltage level of the detection signal is transited so as to determine whether the AC power source changes from the abnormal voltage to the normal voltage. For example, when the detection signal is transited from a low-level state to a high-level state, it means that the AC power source returns to be normal. When the AC power source does not change from the abnormal voltage to the normal voltage, it means that the AC power source is continuously abnormal. At this condition, the delay time control unit receives the low-level detection signal and outputs a low-level control signal to continuously turn off the switch unit so as to interrupt the abnormal AC power source supplying power to the load. On the contrary, when the AC power source changes from the abnormal voltage to the normal voltage, the delay time control unit receives the detection signal transited from the low-level state to the high-level state and activates a delay control mechanism.

The delay control mechanism comprises steps as follows. First, performing a delay time procedure by the delay time control unit (S23). The delay time procedure can be implemented by a hardware manner, such as a delay time circuit (for example but not limited to an R-C charge/discharge circuit), or other digital or analog circuits, a firmware manner, or a software manner to accumulate the delay time. Afterward, determining whether the AC power source maintains in a normal voltage (S24). If the AC power source does not maintain in the normal voltage, i.e., the AC power source again changes from the normal voltage to the abnormal voltage after the delay time procedure (S23), the delay time procedure exits to perform the step (S21) again, i.e., to detect the voltage value of the AC power source. At this condition, the AC power source is likely to be in the abnormal voltage again since the AC power source is still in an unstable condition. In order to avoid reducing life span of the switch unit and damaging the switch unit to fail to provide efficient and safe power supply to the load or rear-end circuits since the switch unit is frequently activated, the delay control mechanism activated by the delay time control unit20is necessary.

In other words, when the AC power source returns to be normal, i.e., the determination in the step (S22) is “Yes”, the switch unit is not immediately turned on but the delay time procedure is performed to provide the delay time, i.e., the step (S23) and determining whether the AC power source is to be in the abnormal voltage again is performed, i.e., the step (S24). Once the AC power source is to be in the abnormal voltage again during the accumulation of the delay time, the delay time procedure exits to perform the step (S21) again. Also, the accumulated delay time is removed (returned to zero), and a new delay time is re-accumulated in the next required delay time procedure. Take the R-C charge/discharge circuit for example, the accumulated delay time is implemented by charging the capacitor, and the removed delay time is implemented by discharging the capacitor.

If the determination in the step (S24) is “Yes”, i.e., the AC power source maintains in the normal voltage, determining whether the delay time has arrived during the delay time procedure (S25). If the determination in the step (S25) is “No”, i.e., the delay time has not arrived, the delay time procedure is continuously performed in the step (S23), and further to determine whether the AC power source is to be in the abnormal voltage again, i.e., the step (S24). If the determination in the step (S25) is “Yes”, i.e., the delay time has arrived and the AC power source maintains in the normal voltage during the delay time procedure, and therefore the delay time control unit provides the control signal to turn on the switch unit (S26) to make the normal AC power source supply power to the load through the power supplying path again.

In summary, the steps (S23)-(S25) are performed to ensure the switch unit is not immediately turned on but the delay time procedure is performed to provide the delay time when the AC power source returns to be normal, thereby avoiding frequently activating the switch unit. Moreover, if the AC power source is to be in the abnormal voltage again during the delay time procedure, the delay time procedure exits and the switch unit is continuously turned off, thereby interrupting the abnormal AC power source supplying power to the load.

In conclusion, the present disclosure has following features and advantages:

1. The delay control mechanism is activated when the AC power source returns to be normal from the abnormal voltage so as to provide efficient and safe power supply to the load or rear-end circuits and extend life span of the switch unit or relay switch.

2. The adjustment of length of the delay time and the provision of effective current discharging path can be implemented by designing different circuits with reset function of the delay time control unit and selecting different values of circuit components.