JP3189459B2 - Phase control circuit of electric water heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase control circuit for an electric water heater.

[0002]

2. Description of the Related Art The structure of an electric water heater is shown in FIG. In the figure, a heater 4 and a thermistor 5 are provided in a tank 3 provided between a water supply port 1 and a shower head 2. Then, while detecting the hot water temperature with the thermistor 5,
The amount of electricity supplied to the heater 4 is controlled in phase by the controller 7 so that the temperature becomes the temperature set by the volume 6, and the running water is heated, and the hot water is discharged from the shower head 2. Next, a conventional phase control circuit for controlling the electric water heater will be described with reference to FIGS.

A power supply circuit 11 generates a DC voltage Vcc from an AC power supply 10 and supplies it to each circuit. Pulse generation circuit 12
Generates a zero-cross pulse synchronized with the AC power supply 10 to drive the discharge unit 14 of the CR charge / discharge circuit 13. During periods other than the zero-cross pulse generation period, since the transistor 15 of the discharging unit 14 is off, the capacitor 17 of the charging unit 16 is charged and the non-inverting input terminal (+) of the comparator 18 which is the output Vs of the CR charging / discharging circuit 13 Potential Vs rises. Then, during the zero-cross pulse generation period, the transistor 15 is turned on, the charge of the capacitor 17 is rapidly discharged, and the potential Vs of the non-inverting input terminal (+) of the comparator 18 becomes almost the emitter potential of the transistor 15. Therefore, the voltage Vs of the non-inverting input terminal (+) of the comparator 18 has a saw-like waveform as shown in FIG.

On the other hand, a DC voltage Vt obtained by amplifying a potential difference between a temperature detecting circuit 19 and a temperature setting circuit 20 by an amplifier circuit 21 is input to an inverting input terminal (−) of the comparator 18. The voltage Vt of the inverting input terminal (-) of the comparator 18 becomes lower as the temperature rises. For example, when the resistance value of the potentiometer 22 is reduced and set to the high temperature side, the voltage Vt of the inverting input terminal (-) of the comparator 18 decreases and approaches 100% conduction. The comparator 18 outputs the output Vs of the CR charge / discharge circuit 13 and the amplifier circuit 2
The output Vt is compared with the output Vt, and when the potential relationship of Vs> Vt is established, Hi is output, the trigger circuit 23 is driven, the triac 24 is turned on, the heater 25 is energized, and the flowing water is heated.
Then, the thermistor 26 of the temperature detection circuit 19 detects a change in the hot water temperature due to a change in the incoming water temperature or the flow rate, and controls the ON phase of the triac 24 to determine the amount of power to the heater 25.
The temperature is controlled to the temperature set by the temperature setting circuit 20.

[0005]

However, in the above configuration, the minimum voltage of the output voltage Vt of the amplifier circuit 21 does not drop to the negative DC voltage Vcc, and the remaining voltage is determined by the output characteristics of the operational amplifier 27. In general, the output characteristics of the operational amplifier 27 are as shown in FIG. 6, and when the output sink current I flows by 0.5 mA, about 0.8 V of the output voltage V remains. For this reason, the phase Ta at which the output Vs of the CR charge / discharge circuit 13 and the output Vt of the amplifier circuit 21 intersect on the 100% energized side is far away from 0 V of the AC power supply 10, and a 100% energized state is required. Despite this, it was not possible to obtain the desired hot water temperature.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a phase control circuit of an electric water heater capable of surely obtaining a 100% energized state and supplying a sufficient hot water temperature.

[0007]

In order to solve the above-mentioned problems, a phase control circuit of an electric water heater according to the present invention connects a charging section of a CR charging / discharging circuit to a GND side of a power supply circuit by connecting a resistor to a GND side of the power supply circuit. The capacitor and the diode in the charging direction were connected in series to the negative DC voltage side, and also connected in series to the resistor connected to the GND side of the power supply circuit, and the discharge unit of the CR charge / discharge circuit was connected to the GND side of the power supply circuit. Resistance and
Connect the collector of the transistor to the connection point between the capacitor connected to the negative DC voltage side of the power supply circuit or the diode in the charging direction, connect the emitter of the transistor to the negative DC voltage side of the power supply circuit, and connect the base of the transistor. Is connected to a pulse generating circuit, and a diode in a discharging direction is connected in parallel with a diode in a charging direction in a phase control circuit.

[0008]

According to the present invention, when the charging section of the CR charging / discharging circuit is started to charge during a period other than the zero cross pulse generation period, the output voltage of the CR charging / discharging circuit is controlled by the diode in the charging direction. The forward DC voltage is higher than the negative DC voltage by the forward voltage.
The charge of the capacitor of the charging section of the R charging / discharging circuit remains by the forward voltage, and this voltage is further added. When the charging section starts charging, the voltage at the time of starting the charging of the diode from the negative DC voltage of the power supply circuit is reduced. The voltage rises by two voltages, and the output of the CR charge / discharge circuit and the lowest output of the amplifier circuit cross (Vs
> Vt) becomes the falling phase of the zero-cross pulse, and a 100% energized state of the heater is obtained.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a phase control circuit diagram of an electric water heater.
Is an AC power supply, 31 is a power supply circuit, rectified by a diode 32,
The voltage is reduced by the resistor 33, stabilized by the Zener diode 34, smoothed by the capacitor 35, and outputs a negative DC voltage Vcc having the connection point between the one end A of the AC power supply 30 and the Zener diode 34 as GND. 36 is a pulse generating circuit for the AC power source 3
A zero-cross pulse Vz synchronized with 0 is generated. Reference numeral 37 denotes a CR charge / discharge circuit which is driven by a pulse
8, the charging section 41 with the charging direction diode 39 and the capacitor 40, and the discharging direction diode 42 and the transistor 4.
3, the discharging unit 44 is configured to output a saw-tooth waveform voltage Vs. A temperature detection circuit 45 detects the temperature of the hot water with a thermistor 46 and outputs a divided voltage with the resistor 47. Reference numeral 48 denotes a temperature setting circuit which sets a hot water temperature by a volume 49 and outputs a divided voltage with the resistor 50. Reference numeral 51 denotes an operational amplifier 52 for impedance conversion by an amplifier circuit, an operational amplifier 53 for amplification, a resistor 54, a resistor 55, and a resistor 56, and the temperature detection circuit 4
5 and the output voltage difference between the temperature setting circuit 48 and the DC voltage Vt. Reference numeral 57 denotes a comparator which compares the output Vs of the CR charge / discharge circuit 37 with the output Vt of the amplifier circuit 51 and Vs> V
If t, Hi is output. 58 is a trigger circuit for the comparator 5
The trigger pulse is output at the phase where the output of the signal No. 7 becomes Hi. A triac 59 is driven by a trigger pulse of the trigger circuit 58. Reference numeral 60 denotes a heater. When the triac 59 is turned on, the AC power supply 30 is supplied to heat the flowing water.

The above configuration will be described with reference to the operation explanatory diagram of FIG. The output Vz of the pulse generation circuit 36 that generates a zero-cross pulse synchronized with the AC power supply 30 is
It becomes Hi at 0 V of 0, and drives the discharge unit 44 of the CR charge / discharge circuit 37. The output V of this pulse generation circuit 36
During the period when z is Lo, the capacitor 40 of the charging unit 41 of the CR charge / discharge circuit 37 is charged via the diode 39 in the charging direction by a time constant determined by the resistor 38.
When the output Vz of the pulse generation circuit 36 is Hi, the transistor 43 is turned on to rapidly discharge the charge of the capacitor 40 through the diode 42 in the discharging direction, and to reduce the voltage of the output Vs to the negative voltage of the power supply circuit 31. The output Vs of the sawtooth wave is output as the DC power supply Vcc potential. The potential at the start of charging of the sawtooth output Vs becomes higher than the negative DC voltage Vcc of the power supply circuit 31 due to the forward voltage of the diode 39 in the charging direction. The diode 4
2 causes the charge of the capacitor 40 to remain by the forward voltage, and this remaining voltage is applied to the diode 39 in the charging direction.
The forward voltage is further increased by two forward voltages (about 1.2 V).

The amplification circuit 51 amplifies the difference between the output voltages of the temperature detection circuit 45 and the temperature setting circuit 48 and outputs a DC voltage Vt. The DC voltage Vt decreases as the resistance value of the volume 49 decreases, The value is higher than the negative DC voltage Vcc of the power supply circuit 31 by 0.8 V because the output voltage V remains about 0.8 V when the output sink current I flows 0.5 mA from the output characteristics of the operational amplifier 53 (FIG. 6). Potential. Also, the flow rate increases with a constant volume 49 resistance value,
Alternatively, even if the incoming water temperature decreases and the resistance value of the thermistor 45 increases, the DC voltage Vt becomes low, and the lowest value is similarly 0.8 V higher than the negative DC voltage Vcc of the power supply circuit 31.

The comparator 57 outputs the output Vs and the output Vt.
Are compared, and when Vs> Vt, the comparator 57 sets Hi
To drive the trigger circuit 58 to output a trigger pulse, and turn on the triac 59 to energize the heater 60. The time point at which the comparator 57 outputs Hi, that is, the phase advances as the output Vt of the amplifier circuit 51 decreases, and the energization amount of the heater 60 increases to the 100% side. As the amount of electricity supplied to the heater 60 increases, the ability to heat the flowing water increases, and the temperature of the hot water that flows out increases. The maximum energization amount of the heater 60 is determined by the minimum value of the output Vt of the amplifier circuit 51.
Even if the potential becomes 0.8 V higher than the negative DC voltage Vcc of
Diode 39 in charge direction and diode 42 in discharge direction
As a result, the potential at the time when the charging unit 41 of the CR charging / discharging circuit 37 starts charging becomes higher than the negative DC voltage Vcc of the power supply circuit 31 by two forward voltages (about 1.2 V).
The phase at which s and the output Vt intersect is the falling phase of the zero-cross pulse Vz of the AC power supply 30, and 100% power can be supplied to the heater 60.

[0013]

As described above, according to the present invention, the charging section of the CR charge / discharge circuit is connected to the resistor on the GND side of the power supply circuit, and the capacitor and the diode in the charging direction are connected on the negative DC voltage Vcc side of the power supply circuit. It is connected in series with the resistor connected to the GND side of the power supply circuit, and the discharge unit of the CR charge / discharge circuit is connected to the resistor connected to the GND side of the power supply circuit and the negative DC voltage Vcc side of the power supply circuit. The collector of the transistor is connected to the connection point of the connected capacitor or the diode in the charging direction, the emitter of the transistor is connected to the negative DC voltage Vcc side of the power supply circuit, and the base of the transistor is connected to the pulse generation circuit. By connecting the diode in the discharging direction in parallel with the diode in the charging direction, the potential at which the charging unit of the CR charging / discharging circuit starts charging is set to the power supply. And the forward voltage of the diode in the charging direction and the forward voltage of the diode in the discharging direction (approximately 1.2 V) higher than the negative DC voltage Vcc of the path. Even if the voltage becomes higher than the power supply Vcc by a voltage (approximately 0.8 V) determined by the output characteristics of the operational amplifier of the amplifier circuit, the phase at which the output Vs of the CR charge / discharge circuit and the output Vt of the amplifier circuit intersect is the rising edge of the zero cross pulse Vz As the phase falls, the maximum duty ratio of the heater can be set to 100%, and a sufficient hot water temperature can be obtained.

[Brief description of the drawings]

FIG. 1 is a phase control circuit diagram of an electric water heater according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the circuit.

FIG. 3 is a configuration diagram of an electric water heater.

FIG. 4 is a phase control circuit diagram of a conventional electric water heater.

FIG. 5 is an explanatory diagram of the operation of the circuit.

FIG. 6 is an output characteristic diagram of an operational amplifier.

[Explanation of symbols]

 Reference Signs List 30 AC power supply 31 Power supply circuit 36 Pulse generation circuit 37 CR charging / discharging circuit 39 Diode in charging direction 41 Charger 42 Diode in discharging direction 44 Discharger 45 Temperature detection circuit 48 Temperature setting circuit 51 Amplification circuit 57 Comparator 58 Trigger circuit 59 Triac 60 heater

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 3/00 F24H 1/20 G05D 23/00

Claims (1)

(57) [Claims] 1. A heater for heating water, a triac for supplying AC power to the heater, a power supply circuit for generating a negative DC voltage from the AC power supply, and a pulse for generating a zero-cross pulse synchronized with the AC power supply. A CR charging / discharging circuit for outputting a sawtooth wave, comprising a generating circuit, a charging unit for charging a capacitor when the zero-cross pulse is not generated, and a discharging unit for discharging charge to the capacitor when the zero-cross pulse is generated. A temperature detection circuit for detecting the temperature of the water heated by the heater, a temperature setting circuit for setting the temperature of the water to be heated by the heater, and amplifying a voltage difference between the temperature detection circuit and the temperature setting circuit. Amplifier, a comparator for comparing the output of the CR charge / discharge circuit with the output of the amplifier, and a triac driven by an output from the comparator. A trigger circuit for outputting a trigger signal, wherein the discharging unit of the CR charging / discharging circuit connects a resistor to the GND side of the power supply circuit, and connects a capacitor and a diode in a charging direction to a negative DC voltage side of the power supply circuit. Connected in series with the resistor in series, the discharging unit of the CR charging / discharging circuit connects a collector of a transistor to a connection point between the resistor and the capacitor or the diode in the charging direction, and connects the emitter of the transistor to the emitter. A phase control circuit for an electric water heater connected to a negative DC voltage side of a power supply circuit, a base of the transistor is connected to the pulse generating circuit, and a diode in a discharging direction is connected in parallel to a diode in a charging direction in a direction opposite to the diode in a charging direction.