JPH07105263B2 - Floor heating system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a floor heating device laid on a floor of a building for heating.

2. Description of the Related Art Recently, floor heating systems have been required to have multiple functions, and a microcomputer (hereinafter referred to as a microcomputer) has begun to be installed to meet the demand. FIG. 6 shows a general circuit block diagram of a floor heating system in which a floor heating system body is divided into two parts and each part is independently controlled by mounting a microcomputer.

Since a detailed description of the circuit will be given with reference to FIG. 7, its operation will be briefly described here. First, regarding the temperature control of the first part of the main body, the signal from the first temperature setting part 9 of the main body is taken in from the input port P _I3 , the signal from the first temperature detecting part 13 is taken in from P _I1 , and compared and set. If the temperature is higher than the detected temperature, a Hi signal is output to the first energization control unit 61 to energize the first heating element. If the set temperature is lower than the detected temperature, the Lo output will be output and the power will not be turned on. The temperature control of the second part of the main body is similar to the temperature control of the first part. The overtemperature detection voltage setting unit 57 sets a voltage for detecting an abnormal temperature rise of the main body, and each of the output voltage from the first temperature detection unit 13 and the output voltage from the second temperature detection unit 14 is set. If an abnormal temperature rise of the main body is detected, the first thyristor 43 and the second thyristor 53 are turned on to blow the thermal fuse 2. Also P
_O8 outputs Lo when no signal is output to the first energization control unit 61 (Lo output) and outputs a gate trigger signal to the first thyristor, and if the first energization control unit 61 has a short circuit failure. If so, the thermal fuse 2 is blown. Similarly, P _O9 outputs Lo when the signal is not output to the second energization control unit 62, and the second thyristor blows out the thermal fuse 2 at the time of a short circuit failure of the second energization control unit 62. As described above, the abnormal temperature rise detection of the main body and the short-circuit failure detection of the energization control unit are performed separately for the first and second parts of the main body.

Now, the operation will be described in detail with reference to FIG. 7 in which the block diagram of FIG. 6 described above is replaced with an actual circuit.

Reference numeral 1 is an AC power supply voltage, 2 is a temperature fuse, and 3 is a power supply circuit, which creates DC power supply voltages V ₁ and V ₂ . 4 is a microcomputer, 5 is a reset circuit of the microcomputer 4, 6 is a clock generation circuit, 7 is an AC synchronous signal generation circuit, 8 is a display unit, 9 is a temperature setting unit of the first part of the main body, 10 is a temperature setting of the second part Section, 11 is a switch section, 12 is a D / A conversion section, 13 is a first partial temperature detection section of the main body, 1
4 is the second part temperature detection part of the main body, 15 and 16 are resistors, 17 is a comparator (comparator) for detecting the temperature of the first part,
18 is a comparator (comparator) for detecting the temperature of the second part, 19 is a comparator (comparator) for detecting an abnormal temperature rise of the first part, 20 is for detecting an abnormal temperature rise of the second part Comparator, 21,22 are diodes, 23,24 are resistors, 25 are PNP transistors, 26,27
Is a resistor, 28 is a PNP transistor, 29 to 32 are resistors, and 33 and 34 are
NPN transistor, 35 is a first power control element (hereinafter referred to as a relay), 36 is a heating element of the first part, 37 is an abnormal overheat detecting element of the heating element 36 of the first part, 38 is an electrode of the heating element 36 of the first part Wires, 39 and 40 are resistors, 41 and 42 are diodes, 43 is a thyristor, 44 is a resistor, 45 is a second power control element (hereinafter referred to as a relay) 46 is a heating element of the second part of the main body, and 47 is a first Two parts heating element abnormal overheat detection element, 48 heating element electrode wire of the second part, 49, 50 resistance, 51, 52 diode, 53 thyristor, 54 resistance, 55, 56 resistance, 57 temperature Excessive temperature rise detection voltage setting unit, 58 is a relay short-circuit fault, and a relay short-circuit fault that detects an abnormal temperature rise of the main body, overtemperature detection unit, 59 is a buzzer unit, 60 is a switch, 61 is a first energization control unit, Reference numeral 62 is a second energization control unit. To each input / output terminal of the microcomputer 4, connect the voltage V ₂ created by the power supply circuit 3 to the terminal V _DD and the GND
Output of the reset circuit 5 to V _SS (GND), RESET pin,
The output of the clock generation circuit 6 is output to the CLOCK terminal, the output of the AC synchronization signal generation circuit 7 is output to the INT terminal, the display unit 8 is connected to the P ₀₁₀ terminal, the temperature setting unit 9 of the first part is connected to the P _I3 terminal, and the second part Temperature setting part 10 to P _I4 terminal, switch part 11 to P _I5 terminal,
The D / A converter 12 is connected to terminals P _{01 to} P ₀₇ , the output of the comparator 17 to the terminal P _I1 , the output of the comparator 18 to the terminal P _I2 , the cathode of the diode 21 to the terminal P ₀₉ , and the cathode of the diode 22 to To the P ₀₈ terminal, the base of NPN transistor 33 is resistor 31
To the P ₀₁₂ terminal, the base of the NPN transistor 34 to the P ₀₁₃ terminal via the resistor 32, and the buzzer section 59 to the P ₀₁₁ terminal.

Now, the eighth flowchart of the temperature signal processing of the microcomputer 4 is shown.
Shown in the figure. After the initial processing (step S1), the signal from the temperature setting section 9 of the first part is taken in from the input port P _I3 and set as the temperature setting value D _I3 of the first part (step S1).
2). Next, the signal from the temperature setting unit 10 of the second portion is taken in from the input port P _I4 and set as the temperature setting value D _I4 of the second portion (step S3). Next, input the A / D converted value of the temperature signal voltage V _T1 from the temperature detector 13 of the first part from the input port P _I1 and input D
_I1 (step S4). Then the temperature detection part of the second part
Input A / D converted value of temperature signal voltage V _T2 from 14 input port P _I2
And input it as D _I2 (step S5). Next step S6
Then, D _I3 and D _I1 are compared. If D _I3 ≧ D _I1 , Lo output is output to P ₀₁₂ (heating element de-energized), timer 1 is activated (step S7), and the process proceeds to step S9. Timer 1 counts up in 1 second. If D _I3 <D _I1 , output port P ₀₉ , P ₀₁₂ to Hi
A signal is output (step S8), and the process proceeds to S9. Output port
If P ₀₁₂ is Hi, NPN transistor 33 turns ON and relay 35
To heat the heating element 36. D in step S9
_I4 and D _I2 are compared (step S9), and if D _I4 > D _I2, then P ₀₁₃
The Lo output is output to (heating element non-energized), the timer 2 is started (step S10), and the process proceeds to A. Timer 2 also counts up in 1 second. If D _I4 <D _I2 , output port P ₀₈ , P ₀₁₃ is Hi
A signal is output (step S11), and the process proceeds to A (step S12). In A (step S12), it is determined whether or not the timer 1 has started, and if it has started, the process proceeds to step S13. In step S13, it is determined whether or not the timer 1 counts up. If not, the timer counts until it counts up. If it counts up, the process proceeds to step S14, and the Lo output is output to the output port P ₀₉ (step S14), and proceeds to step S15. If the timer 1 is not activated in step S12, the process proceeds to step S15. In step S15, it is determined whether or not the timer 2 has started, and if it has not started, the process proceeds to B. If the timer 2 is running, the process proceeds to step S16 and it is determined whether or not the timer 2 has counted up. If it is not counted up, the timer is counted until it is counted up. If it is counted up, the process proceeds to step S17, outputs the Lo output to the output port P ₀₈ , and goes to B (step 2). As described above, the microcomputer performs temperature signal processing.

In FIG. 7, reference numeral 58 denotes a detection circuit for a relay short-circuit failure and an excessive temperature rise of the main body. _First , the method of detecting overheat is explained. The DC voltage V ₁ generated by the power supply circuit 3 is connected to the resistor 5
Divide by 5 and 56 to make overtemperature detection voltage V _RF . When the temperature signal voltage V _T1 of the first portion becomes lower than the overheat detection voltage V _RF (the temperature is abnormally increased), the output of the comparator 19 becomes Lo. Therefore, the transistor 28 turns on and the thyristor
A signal is output to the gate of 43, the relay 35 is turned on, and when the heating element is in the energized state, a large current flows through the resistor 39, causing the resistor 39 to generate heat and blow the thermal fuse 2. The same applies when the temperature of the second part rises abnormally.
_T2 becomes lower than the overheat detection voltage V _RF and comparator 20
Becomes Lo, the transistor 25 is turned on, the thyristor is turned on, the resistor 49 generates heat, and the thermal fuse 2 is blown.

Next, a contact welding detection method will be described. First, when explaining the relay short circuit failure detection method of the first part, as explained in the signal processing flowchart of the microcomputer, the A / D conversion value D _I1 of the temperature signal voltage V _T1 of the first part is smaller than the temperature setting value D _I3 of the first part. And (main unit temperature is higher than the set temperature), P ₀₁₂ Lo
A signal is output, timer 1 is started at the same time, and timer counting is started. At this time, the transistor 33 is off. The timer 1 counts up in 1 second, outputs Lo output to P ₀₉ , turns on the transistor 28, and outputs a gate signal to the thyristor 43. Since the transistor 33 is off, the relay contact 35 is open and the resistor 39
Does not generate heat because it is not energized, but if a short-circuit failure occurs, the contact 35 of the relay is in a short-circuited state and the resistor 39 heats up to blow the thermal fuse 2. The relay short circuit failure detection method of the second part is the same, and when D _I2 is smaller than D _I4 , the Lo signal is output to P ₀₁₃ , and at the same time, the timer 2 is started,
Start timer counting. At this time, the transistor 34 is off
are doing. Timer 2 counts up in 1 second and goes _low on P ₀₈
o Outputs the output, transistor 25 turns on and thyristor 53
The gate signal is output to. Since the transistor 34 is off, the contact of the relay 45 is open and the resistor 49 does not generate heat in a normal state, but if a short circuit failure occurs, the resistor 49 generates heat and the thermal fuse 2 is blown. The timers 1 and 2 that count up in 1 second are provided to ensure the delay time for the relay contact to shift from the short-circuited state to the open state (P ₀₁₂ and P ₀₉ , P ₀₁₃ and P ₀₈₎ . At the same time can not output signal).

As described above, the short circuit failure and the temperature rise of the main body are detected.

Problems to be Solved by the Invention In such a floor heating system, the failure of the relay short circuit of the first and second parts of the main body and the detection of the excessive temperature are separately performed separately, which increases the cost due to the large number of parts. Signal processing is 2
There is a big problem that the program memory is increased because it is partially required. In overtemperature detection, even if the AC power supply voltage fluctuates and the body temperature fluctuates accordingly, the DC power supply voltage is constant, so the overtemperature voltage value is always constant. At the same time, there is a problem in that an excessive temperature rise cannot be detected accurately.

Means for Solving the Problems In order to solve the above problems, the present invention provides a first heating element that heats a first portion of a main body, a second heating element that heats a second portion, and the first heating element. , The first to detect the temperature of the second part,
A second temperature detection unit, a temperature setting unit that sets the temperatures of the first and second parts, a comparison unit that detects the respective signals, and the first and second heating elements according to the signals of the comparison unit. The first and second energization control units for controlling energization to the first and second power control elements of the energization control unit are connected to the first and second rectifying elements, and the respective outputs are The OR output of the output to the energization control element connected to the thyristor via the low level and operated by the first and second Hi signals of the first and second energization control units is a diode and a gate of the thyristor via a transistor. When a short-circuit failure detection unit connected to and the abnormal temperature rise of the first and second parts of the main body is detected, an AND output of an overtemperature detection output that outputs a Lo signal is output to the thyristor via a diode and the transistor. From the temperature rise detector connected to the gate of Those having a that abnormality detector.

Action First and second of the energization control unit, the OR output of the output to the energization control element operated by the second Hi signal is a diode, short-circuit failure detection unit connected to the gate of the thyristor via a transistor , When the abnormal temperature rise of the first and second parts of the main body is detected, the AND output of the overtemperature detection output that outputs the Lo signal is connected to the gate of the thyristor through the diode and the transistor to detect the overtemperature. Since it has an abnormality detection section consisting of a section and a section, a large cost reduction can be achieved due to a large reduction in the number of parts, and the program memory can be used efficiently. Further, since the correction unit is provided in the overheat detection unit so that the overheat detection voltage value becomes a value according to the fluctuation of the AC power supply voltage, the overheat can always be detected accurately.

Embodiments An embodiment of the present invention will be described below with reference to FIGS. 1, 2, 3, and 4.
This will be described with reference to FIGS. In FIG. 2, the same parts as those in FIG. 7 are designated by the same reference numerals. 1 is a schematic block diagram of the present invention, FIG. 2 is a circuit diagram of the present invention,
FIG. 3 is a block diagram of temperature control of the main body using a microcomputer, FIG. 4 is a flowchart of temperature signal processing of the microcomputer, and FIG. 5 is a top view of the floor heating device main body. FIG. 1 is a schematic block diagram of the present invention. Details of the operation will be described later with reference to FIG. 2 and will be briefly described here.
First, regarding the temperature control of the first portion of the main body, the correction signal obtained by correcting the signal of the first temperature detection unit by the output of the power supply voltage fluctuation detection circuit and the signal of the first temperature setting unit 9 are compared, and the set temperature is If it is higher than the detected temperature (corrected), a Hi signal is output to the first energization control unit 61 to energize the first heating element. If the set temperature is lower than the detected temperature (corrected)
Output Lo signal to 61 and do not energize. The temperature control of the second part of the main body is similar to the temperature control of the first part. The overtemperature detection correction voltage setting unit 64 sets a voltage for detecting an abnormal temperature rise of the main body according to the output of the power supply voltage fluctuation detection circuit 63, and the output voltage from the first temperature detection unit 13 The output voltage from the second temperature detection unit 14 is compared, and the AND output and the thyristor 43 are connected. When either of the first and second parts detects an abnormal temperature rise, a gate signal is output to the thyristor 43 and the thyristor 43 is turned on to blow the thermal fuse 2. P
₀₈ is a signal to the first energization control unit 61 and the second energization control unit 62
OR output with the signal to. That is, when both the outputs to the first and second energization control units are Lo, a gate trigger signal is output to the thyristor 43, and if the first or second energization control unit is short-circuited, the thermal fuse 2 is turned on. To melt down. In the above state, if the Hi signal is output to either the first or second energization control unit (assuming 61) and the other has a short circuit failure (assuming 62), immediate detection is not possible. But,
The output to 61 outputs the Lo signal when the temperature of the main body reaches the set temperature, so it can be detected at that time. It is almost unlikely to fall into an abnormal state because the time it takes for the body temperature to reach an abnormal temperature during a short circuit fault is much longer than the time it takes 61 to change from Hi to Lo.

Should an abnormal temperature be reached, the overheat detection unit will work.
Therefore, there is no problem in detecting the short circuit failure of the energization control unit by the above method.

Then, to the thyristor 43, the OR output from the above-mentioned short circuit failure detection section of each energization control section and the AN output of each overtemperature detection section are described.
It is configured to output the AND output with the D output.

The operation will be described in detail with reference to FIG. 2 in which the block diagram described above is replaced with an actual circuit. In Figure 2
63 is an AC power supply rectified voltage V _A generation circuit, and 64 is an overtemperature detection correction voltage V that outputs a correction output according to AC power supply voltage fluctuations.
_RFC setting section, 65 is an abnormal temperature detection section in the controller of the main body, 66 is a comparator for detecting an abnormal temperature rise,
67 is a comparator for detecting the AC power supply rectified voltage value, 68 to 69 are resistors, 70 is a diode, 71 to 73 are resistors, 74
Is a PNP transistor, 75 and 76 are diodes, 77 is a temperature sensor of the first part, 78 is a temperature sensor of the second part, 79 is a power element short circuit failure, and an overtemperature common detection unit. The other circuit parts are the same as in the conventional example.

The output of the comparator 66 is connected to the input / output terminal of the microcomputer 4.
Connect the output of the comparator 67 to the P _I7 terminal and to the P _I6 terminal to the cathode P ₀₈ terminal of the diode 21. The connection of the other part to the microcomputer input / output terminal is the same as the conventional example.

FIG. 3 is a block diagram of microcomputer control of the temperature of the main body, the A / D conversion value of the AC power supply rectified voltage V _A that is the conversion value converted by the A / D conversion unit connected to the same DC power supply voltage V _2. (D _I6), a / D converted value of the temperature signal voltage V _T1 of the first portion (D _I1), a / D converted value of the temperature signal voltage V _T2 of the second portions (D _I2) input to the correction unit. In the correction section, based on D _I6
Calculates a correction value of the D _I1, D _I2 calculates the correction value D _I2C correction value D _I1C and D _I2 of D _I1. Then, in the first part, the correction value D _I1C of the A / D conversion value of this first part and the temperature setting value D _I3 of the first part
Are compared with each other to control the heating element drive section of the first portion by the output of the comparison signal to control the energization of the first heating element. Similarly, the second portion also compares D _I2C and D _I4 and outputs a comparison signal to control energization of the second heating element. Also, the output of each comparison unit is ORed and output to the output port P _{08 of the} microcomputer. FIG. 4 is a flow chart of the temperature signal processing of the microcomputer, and although there is some overlap with the description in FIGS. 3 and 9, they will be described in order of step. After performing the initial processing (step S1), the signal from the first temperature setting unit 9 is taken in from the input port P _I3 and set as the temperature setting value P _I3 of the first portion (step S18). Next, the signal from the second temperature setting unit 10 is input from the input port P _I4 and the temperature setting value D _I4
(Step S19). Then the AC power supply rectified voltage V _A of the A / D conversion value of V _A generated by the generating circuit 63 is input from input port P _I6 D _I6 (step S20). Next, the A / D converted value of the temperature signal voltage V _T1 of the first portion is input from the input port P _I1 and set as D _I1 (step S21). Then the temperature signal voltage V of the second part
The A / D converted value of _T2 is input from the input port P _I2 and set as D _I2 (step S22). In the next step S23, D corresponding to D _I6
A correction value D _{I1C of I1} is calculated (step S23). In the next step S24, the correction value D _I2C of D _I2 corresponding to D _I6 is calculated (step S24). In the next step S25, D _I3 and D _I1C are compared, and if D _I3 D _I1C , the Lo output is output to P ₀₁₂ (heating element 3
6) De-energized (step S26), and proceed to A (step S28). If D _I3 <D _I1C , the Hi signal is output to P ₀₈ and P ₀₁₂ (step S27), and the process proceeds to A (step 28). If P ₀₁₂ is Hi, the transistor 33 is turned on and the heating element 36 is energized. A
In step S28, D _I4 and D _I2C are compared and D _I4 <D _I2C
If so, a Hi signal is output to P ₀₈ and P ₀₁₃ (step S29), and the process proceeds to step S18. If P ₀₁₃ is Hi, the transistor 34 is turned on to energize the heating element 46. If D _I4 ≥ D _I2C , L to P ₀₁₃
o Output is output (step S30), the timer is started (step 31), and the process proceeds to step S32. In step S32, it is determined whether or not the timer counts up. If not, the timer counts until it counts up, and if it counts up, the process proceeds to step S33. Outputs a Lo output to the step S33 in P _08, go to B (step S18). The timer shall count up in 1 second (1S).

As described above, the microcomputer performs temperature signal processing.

Now, FIG. 79 shows an abnormality detecting section for detecting a power control element (hereinafter referred to as a relay) short-circuit failure and an excessive temperature rise of the main body. This detecting section will be described below.

First of all, I will explain how to detect the temperature rise of the main body,
Reference numeral 64 denotes an overtemperature detection correction voltage V _RFC setting unit that outputs a correction output according to the AC power supply voltage fluctuation, and the temperature signal voltage V _T1 of the first part or the temperature signal voltage V _T2 of the second part is _calculated from V _RFC . When it becomes small (the temperature of the main body is abnormally increased), the common output of the comparators 19 and 20 becomes Lo. (That is, the AND output of the comparators 19 and 20 is output to the cathode of the diode 70). Then, the transistor 28 is turned on and a gate signal is output to the thyristor 43, and if the relay 35 or the relay 45 is turned on and the heating element 36 or the heating element 46 is in the energized state, a large current flows through the resistor 39, so that the resistor 39 is turned on. The heat is generated and the thermal fuse 2 is blown. Resistors 71, 73 and transistor 74 form a negative feedback hysteresis circuit,
At the same time that the common output of 19, 20 becomes Lo, the transistor 74 becomes O
The output of comparators 19 and 20 is stabilized by raising V _RFC voltage a little.

Next, a relay short-circuit failure detection method will be described. As explained in the temperature signal processing flowchart of the microcomputer in FIG. 4, the correction value D of the A / D conversion value of the temperature signal voltage V _T1 of the first part
_I1C is equal to or lower than the temperature setting value D _I3 of the first portion, and the correction value D _I2C of the A / D conversion value of the temperature signal voltage V _T2 of the second portion is equal to or lower than the temperature setting value D _I4 of the second portion (first , If the second partial temperature is higher than the set temperature), start the timer and start timer counting. At this time, P ₀₁₂ and P ₀₁₃ are Lo outputs, and the transistors 33 and 34 are both off. The timer counts up in 1 second, outputs Lo output to P ₀₈ , turns on the transistor 28, and outputs a gate signal to the thyristor 43. That is, the OR output of the outputs of P ₀₁₂ and P ₀₁₃ is output to P ₀₈ . (The timer is set to 1 second in order to secure the delay time of the relay as described in the conventional example.) Since the transistors 33 and 34 are off, if the state is normal.
The contacts of relays 35 and 45 are open, but if 35,
If one of the contacts of 45 is short-circuited, the contact of the relay is short-circuited, and the resistor 39 generates heat to blow the thermal fuse 2.

As described above, in the case of relay short circuit failure and over temperature detection, the thyristor is triggered by the AND output of the output signals of the two detection units (when the AND output is Lo output, the thyristor is triggered).
It is configured to do.

When the diode 76 of FIG. 2 energizes only the first part (relay 35 is ON, 45 is OFF), if there is no diode 76, the heat of the second part is generated in the route of relay 35 → diode 75 → heating element 46. This is to prevent erroneous energization that the body also energizes. The diode 75 is also used for the same purpose.

EFFECTS OF THE INVENTION As described above, according to the floor heating apparatus of the present invention, the output signals from the short-circuit detectors of the power control elements of the first and second parts and the over-temperature detectors of the first and second parts. Since the thyristor is also used as the output signal from the thyristor to control the abnormality, the number of parts is greatly reduced, resulting in a significant cost reduction. In addition, the processing method of the program is simplified, and the program memory can be used efficiently. In addition, since the correction unit is provided in the overheat detection unit so that the overheat detection voltage value becomes a value according to the fluctuation of the AC power supply voltage, the overheat of the main body can always be detected accurately.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a floor heating apparatus which is an embodiment of the present invention, FIG. 2 is the same circuit diagram, FIG. 3 is the same temperature control block diagram, and FIG. 4 is the temperature signal processing of the same microcomputer. A flow chart, FIG. 5 is a top view of the same floor heating device main body, FIG. 6 is a circuit block diagram of a floor heating device equipped with a general microcomputer, FIG. 7 is the same circuit diagram, and FIG. 8 is the temperature of the same microcomputer. It is a flow chart of signal processing. 9 …… First temperature setting section, 10 …… Second temperature setting section, 13
...... First temperature detector, 14 ...... Second temperature detector, 17 ...
… First comparison section, 18 …… Second comparison section, 35 …… First power control element, 36 …… First heating element, 45 …… Second power control element, 46 …… Second Heating element, 61 ... first energization control section, 62 ... second energization control section, 77 ... first temperature sensor, 78 ... second temperature sensor, 79 ... abnormality detection section.

Claims (2)

[Claims] 1. A first heating element for heating a first portion of a main body, a second heating element for heating a second portion, and first and second heating elements for detecting temperatures of the first and second portions. A temperature detection unit, a temperature setting unit that sets the temperatures of the first and second portions, a comparison unit that compares the respective signals, and energization to the first and second heating elements by the signal of the comparison unit. First and second energization control units that perform control, and first and second rectifying elements are connected to the respective contacts of the first and second power control elements of the energization control unit, and the output of each is connected to a resistor. Is connected to the thyristor via the first and second energization control sections and is connected to the gate of the thyristor via a diode and a transistor. When the abnormal temperature rise of the short circuit failure detector and the first and second parts of the main body is detected, the Lo signal is output. AN overtemperature detection output to force
A floor heating apparatus having an abnormality detection unit including a D output, a diode, and an overtemperature detection unit connected to the gate of the thyristor via the transistor. 2. The underfloor heating apparatus according to claim 1, wherein the overheat detection unit is configured to make a correction in accordance with fluctuations in the AC power supply voltage.