JPH08221139A - Power supply unit - Google Patents

Abstract

PURPOSE: To provide a power supply unit which can perform precise power control over a heater and is started up fast and small in power consumption. CONSTITUTION: In power source operation, a load current detecting circuit 17 detects the secondary-side load current of an AC transformer 13 and when a CPU 18 supplies a dummy current so that the load current becomes constant, the distortion of the secondary-side waveform of the AC transformer 13 becomes constant. For the purpose, the generation timing of electricity feeding timing pulses for starting feeding an AC voltage to the heater is corrected so that the phase difference between the real zero-crossing of the AC input voltage and zero-cross detection timing is canceled during the CPU 18 power source operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply unit applied to an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art A conventional power supply device will be described with reference to FIGS. 10 is a schematic connection diagram of a conventional power supply device, FIG. 11 is a waveform diagram of each part in the device, and FIG. 12 is an input voltage characteristic diagram of the delay time .DELTA.t shown in FIG.
Note that FIG. 12 is a characteristic diagram when the power consumption of the heater 4 is 1100 W, the resistance value is 7.6Ω, and the frequency of the AC input voltage is 50 Hz.

In FIG. 10, 1 is an AC input terminal, 2 is a diode bridge, 3 and 9 are transformers, 4 is a heater in a fixing heater unit incorporated in a copying machine or the like, 5
Is a triac, 6 is a phototriac, 7 is a CPU for power supply control, 8 is a primary / secondary insulation element, 10 is a three-terminal regulator, 11 is a thermistor for detecting the temperature of the heater 4, and 12 is an AC input voltage detection circuit. is there.

Next, the operation of each section of the above-mentioned conventional apparatus will be described.

An AC voltage waveform is input to the AC input terminal 1 (a in FIG. 11), and the AC voltage is supplied to the primary side of the transformer 3 via the diode bridge 2 and the capacitor 201. Here, the switching element 101 such as a transistor is turned on and off by a control signal from the CPU 7 via the insulating element 8, and LC resonance between the inductance L of the transformer 3 and the capacitance C of the capacitor 202 causes the secondary side of the transformer 3. An alternating current waveform is generated and converted into a direct current by the diode 301 and the capacitor 203. A voltage corresponding to this DC-converted voltage is taken into the + 24V monitor port P ₁ of the CPU 7, and the ON width or OFF width of the signal supplied to the switching element 101 is controlled so that this voltage becomes the voltage corresponding to 24V. . This control signal is output from the + 24V control port P ₂ of the CPU 7. The 24V generated here is supplied to each unit in the apparatus. AC input terminal 1 to transformer 9
The signal output via the above is input to the AC input voltage detection circuit 12, and the detection signal corresponding to the AC input voltage is taken into the AC monitor in port P ₅ of the CPU 7.

Furthermore, the signal output from the transformer 9 is input to the base of the transistor 102, and a detection signal that rises or falls at the timing when the AC voltage from the AC input terminal 1 crosses the zero point is sent to the CPU 7 as a zero cross i.
Take in n port P ₆ .

Similarly, the signal output from the transformer 9 is
Converted to direct current by the diode 302 and the capacitor 204,
A voltage of + 5V is output via the three-terminal regulator 10 and is supplied to a logic system unit such as the CPU 7 which operates with a + 5V power source. Further, the signal (voltage) obtained by converting the output of the transformer 9 into a direct current may be used as a power source for another unit in the power source circuit.

Heater control port P of CPU 7
_The ON / OFF signals output from ₄ are supplied to the photo triac 6, and the AC voltage from the AC input terminal 1 is applied to the heater 4 via the triac 5.

Further, the thermistor 11 sends a detection signal corresponding to the temperature of the heater 4 to the temperature detection port P _{3 of the} CPU 7.
Supply to.

Next, the overall operation of the conventional device will be described.

First, the AC input voltage detection circuit 12 detects what voltage the AC voltage at the current AC input terminal 1 is, and inputs the detection signal to the CPU 7.

In order to supply a desired electric power to the heater 4, the CPU 7 refers to a table calculated or pre-calculated based on the characteristic diagram of FIG. 12 and the detected input voltage to delay time Δ. Determine t.

Thereafter, at the timing when Δt calculated by the CPU 7 is added to the timing (b in FIG. 11) input to the zero-cross in-port P ₆ , the heater control port P ₄ causes the triac 5 to have a desired ON holding time or more. Is output (c in FIG. 11), and a voltage is applied to the heater 4 (d in FIG. 11). By repeating this operation, it is possible to apply a substantially constant power to the heater 4 regardless of the magnitude of the AC input voltage and obtain a desired temperature rise.

After the heater 4 reaches the target temperature, the thermistor 11 detects the temperature of the heater 4 and performs feedback control for finely adjusting the delay time Δt so as to match the set temperature.

[0015]

Generally, an OA device such as an electric appliance or a copying machine clearly indicates what current of a maximum amount is consumed from an outlet according to its product specifications and safety standards. Need to comply. For example, 100V,
In the 15A copier, the fixing heater unit is 11
If the current consumption of 4A is consumed by the units A and other units, it will be within the standard.

However, although the fixing heater unit is controlled in synchronization with the zero cross of the AC input voltage, the AC transformer 9 is not only used for the zero cross detection but also as a voltage source for supplying a voltage to other circuits. It's being used. Therefore, when each circuit operates and a load is drawn, the + side of the waveform on the secondary side of the AC transformer 9 is cut by the output impedance (the shaded portion in FIG. 11) and the waveform is distorted (FIG. 11). E), the phase difference ΔT between the zero cross point 1a of the AC input voltage waveform and the output signal of the zero cross detection circuit (transistor 102) that detects the zero cross point based on the waveform on the secondary side of the AC transformer 9 fluctuates. It will be. Therefore, the timing of energizing the heater 4 also shifts due to load fluctuations (see FIG.
1 f), the current consumed by the fixing heater unit is 1
There is a possibility that it will exceed 1A.

Further, at that time, since the electric power supplied to the heater 4 varies, a thermal overshoot occurs when the temperature of the heater 4 is raised, and the protection circuit is opened due to excessive temperature rise of the fixing heater unit. It is also possible that the heater 4 operates or the heater 4 breaks.

Therefore, conventionally, the delay time Δ shown in FIG.
By considering t to be large in advance, a margin was provided so that the maximum current consumption of the fixing heater unit does not exceed 11 A, but as a result, the time until the heater 4 reaches the set temperature becomes longer, and copying is performed. This led to an increase in the warm-up time of the machine.

Therefore, the present invention has been made in view of the above circumstances, and it is possible to accurately control the electric power of the heater, and to provide a power supply device that starts up quickly and consumes less electric power. It is intended.

[0020]

According to a first aspect of the present invention, there is provided a power supply device comprising: an AC input voltage detecting means for detecting the magnitude of an AC input voltage; and a primary winding connected to the AC input voltage side to form a secondary winding. An AC transformer having one end of the wire as a ground potential and a zero-cross detecting means for detecting a zero-cross timing at which the potential of the other end of the secondary winding of the AC transformer intersects the ground potential are provided. In the power supply device for controlling the amount of energization time to the target load by outputting an energization timing pulse for starting energization of the AC voltage to the target load after a predetermined time has passed from the zero-cross detection timing,
Load current detection means for detecting the load current on the secondary side of the transformer, a load connected to the latter stage of the load current detection means, a switching element for changing the current flowing to the load by controlling the input pulse width, and the load Based on the detection value of the load current control means for controlling the input pulse width to the switching element so that the load current detected by the current detection means has a preset current value, and the detection value of the AC input voltage detection means, The present invention is characterized by further comprising a correction means for correcting the generation timing of the energization timing pulse so as to cancel the phase difference between the true zero cross of the AC input voltage and the zero cross detection timing.

According to another aspect of the power supply device of the present invention, the AC input voltage detecting means for detecting the magnitude of the AC input voltage, the primary winding is connected to the AC input voltage side, and one end of the secondary winding is grounded. And a zero-cross detecting means for detecting the timing of the zero-cross when the potential of the other end of the secondary winding of the AC transformer crosses the ground potential, and a predetermined time from the zero-cross detecting timing of the zero-cross detecting means. In a power supply device that outputs an energization timing pulse for starting energization of an AC voltage to a target load after a lapse of time to control the amount of energization time to the target load, a load current that detects a load current on the secondary side of the AC transformer. The AC input voltage detection is performed by switching the detection table and the correction table relating to the generation timing of the energization timing pulse according to the detection value of the load current detection circuit. Correction means for correcting the generation timing of the energization timing pulse so as to cancel the phase difference between the true zero-cross of the AC input voltage and the zero-cross detection timing based on the detection value of the means. To do.

According to another aspect of the power supply device of the present invention, the AC input voltage detecting means for detecting the magnitude of the AC input voltage, the primary winding is connected to the AC input voltage side, and one end of the secondary winding is grounded. And a zero-cross detecting means for detecting the timing of the zero-cross when the potential of the other end of the secondary winding of the AC transformer crosses the ground potential, and a predetermined time from the zero-cross detecting timing of the zero-cross detecting means. Timing at which the load current on the secondary side of the AC transformer largely changes in a power supply device that outputs an energization timing pulse for starting energization of an AC voltage to a target load after a lapse of time to control the amount of energization time to the target load. Then, the correction table for the generation timing of the energization timing pulse is switched, and the AC input voltage is detected based on the detection value of the AC input voltage detection means. The to cancel the phase difference between the true zero crossing and the zero-cross detection timing, and is characterized in that it comprises a correcting means for correcting the generation timing of the energizing timing pulses.

[0023]

According to the power supply device of the present invention, when the load current of the AC transformer is detected during the operation of the power supply and a dummy current is supplied so that the current becomes constant, the waveform of the waveform on the secondary side of the AC transformer is detected. The distortion becomes constant. Therefore, during power supply operation, AC
The generation timing of the energization timing pulse is corrected so as to cancel the phase difference between the true zero cross of the input voltage and the zero cross detection timing.

According to another aspect of the power supply device of the present invention, the correction means switches the correction table according to the amount of load current of the AC transformer to determine the phase difference between the true zero cross of the AC input voltage and the zero cross detection timing. The generation timing of the energization timing pulse is corrected so as to turn it off.

According to another aspect of the power supply device of the present invention, the correction means switches the correction table at the timing when the load current on the secondary side of the AC transformer fluctuates greatly to detect the true zero-cross and zero-cross detection timing of the AC input voltage. The generation timing of the energization timing pulse is corrected so as to cancel the phase difference between and.

[0026]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the power supply device of the present invention.

As shown in FIG. 1, the power supply device of the present embodiment has an AC input terminal 1 to which an AC voltage waveform is input and a primary winding 13a connected to the AC input terminal 1 to connect a secondary winding. One end of
3b is used as a ground potential, an AC transformer 13 is used as a voltage source, a diode 14 and an electrolytic capacitor 15 for converting the output of the AC transformer 13 into a direct current, and a voltage converted into a direct current by the diode 14 and the electrolytic capacitor 15 is used as a voltage source. A three-terminal regulator 16 that outputs a voltage of + 5V for supplying to a logic system unit that operates with a + 5V power source, such as a CPU 18 described later, and an AC transformer 1.
Load current detection circuit 17 for detecting the load current on the secondary side of
A CPU 18 for reading the current value detected by the load current detection circuit 17; a dummy resistor (dummy load) 19 connected to the subsequent stage of the load current detection circuit 17; A switching element 20 that controls the current flowing through 19, an AC input voltage detection circuit 21 that detects the magnitude of the AC input voltage from the AC input terminal 1, and a transistor 22a that receives the signal output from the AC transformer 13 as a base. A zero-cross signal detection circuit 22 that detects a zero-cross signal and a DC / DC converter 23 that generates a power supply voltage to be supplied to the + 24V system unit from the output of the AC transformer 13 are connected as shown in FIG. In the figure, reference numeral 24 is a power switch for controlling the switching element 25.
Although omitted in the figure, a heater (target load) 4, a triac 5, and a phototriac 6 are connected between the AC input terminal 1 and the CPU 18, as in the conventional example shown in FIG. , The CPU 18 has the thermistor 11
Is connected.

The load current detection circuit 17 detects the load current on the secondary side of the AC transformer 13, that is, the amount of current flowing through the load 26 such as the three-terminal regulator 16, the temperature control circuit of the heater and other power supply control circuits. To do.

The AC input voltage detection circuit 21 inputs a signal output from the AC input terminal 1 via the AC transformer 13 and outputs a detection signal corresponding to the AC input voltage to the CPU 18.
Is what you enter. In addition, the AC input voltage detection circuit 2
The value of the AC input voltage detected by 1 may be an effective value, a peak value, or a quasi-peak value.

The zero-cross detection circuit 22 outputs to the CPU 18 a detection signal that rises or falls at the timing when the potential of the other end 13c of the secondary winding of the AC transformer 13 crosses the ground potential.

The CPU 18 includes a load current detection circuit 17
The current value detected by is controlled so as to be a preset current value (total current value of each load). That is, when the load is small, a pulse having a long ON width is output to the switching element 20 as shown in FIG. 2, and when the load is large, a pulse having a short ON width is output to the switching element 20 to perform switching. By controlling the on / off of the element 20, the value of the current flowing through the dummy resistor 19 is controlled so that the load current is always constant. By doing this, A
The distortion of the waveform on the secondary side of the C transformer 13 becomes constant, and the true zero-cross and zero-cross detection circuit 2 due to load fluctuations.
It is possible to minimize the fluctuation of the phase difference ΔT from the detection signal of No. 2.

Further, in the CPU 18, the fluctuation of the phase difference ΔT between the true zero-cross and the detection signal of the zero-cross detection circuit 22 due to the fluctuation of the input voltage is shown in FIG.
As shown in FIG. 5 (when the voltage falls), it occurs, so this is corrected. That is, regarding the variation of ΔT due to the variation of the input voltage, a correction table as shown in FIG. 6 is provided in the CPU 18, and the phase difference ΔT corresponding to the current input voltage value detected by the AC input voltage detection circuit 19 is calculated. To do. Then, the CPU 18 delays the above-mentioned phase difference ΔT after fetching the signal from the zero-crossing detection circuit 22 (the phase difference ΔT may have both “+” and “−” signs), and further the desired power to the heater 4. After delaying by a delay time Δt for applying, the heater 4 is started by outputting a start pulse for energizing the heater 4.

By performing such control, the phase difference ΔT between the true zero-cross and the detection signal of the zero-cross detection circuit 22 due to the variation of the load current and the input voltage is controlled as if it were not, and the heater is accurately controlled. It is possible to control the consumption current and the applied voltage of No. 4 described above.

Next, the operation of the first embodiment will be described.

The AC input voltage detection circuit 21 inputs the signal output from the AC input terminal 1 via the AC transformer 13 and inputs the detection signal corresponding to the AC input voltage to the CPU 18. Further, the load current detection circuit 17 detects the load current on the secondary side of the AC transformer 13 and outputs the detection result as CP.
Input in U18. Further, the zero-cross detection circuit 22 is
A detection signal that rises or falls at the timing when the potential of the other end 13c of the secondary winding of the AC transformer 13 crosses the ground potential is output to the CPU 18.

The CPU 18 controls the on / off of the switching element 20 to control the value of the current flowing in the dummy resistor 19 so that the current value detected by the load current detection circuit 17 becomes a preset current value. Control.

Further, the CPU 18 calculates the phase difference ΔT corresponding to the current input voltage value by referring to the correction table based on the detection signal from the AC input voltage detection circuit 21.

Next, the CPU 18 waits for ΔT (phase difference) ± Δt (delay time) with respect to the detection signal from the zero-cross detection circuit 22, and then outputs a start pulse for energizing the heater 4 to energize the heater. To start.

FIG. 7 is a circuit diagram showing a second embodiment of the power supply device of the present invention. This embodiment differs from the first embodiment shown in FIG. 1 in that the dummy resistor 19 and the switching element 20 are omitted, and the CPU 18 is provided with a correction table as shown in FIGS. The correction table (or calculation formula) is switched according to the load current amount detected by 17, and the energization timing pulse generation timing is set so as to cancel the phase difference ΔT between the true zero cross of the AC input voltage and the zero cross detection timing. Is to be corrected.

Next, a third embodiment of the power supply device of the present invention will be described. This embodiment differs from the second embodiment shown in FIG. 7 in that the load current detection circuit 17 is omitted and the CPU 18
If a correction table as shown in FIGS. 8 and 9 is provided inside the image forming apparatus such as a copying machine or a printer, and the load current is significantly changed during the operation sequence (for example, the power control circuit of the heater 4). When the current flows in and out of), the correction table is switched at that timing to correct the generation timing of the energization timing pulse so as to cancel the phase difference ΔT between the true zero cross and the zero cross detection timing. It was done. In the case of such a configuration, the present invention can be applied only by providing a correction table even with the conventional circuit configuration.

[0042]

According to the present invention described in detail above, the following effects can be obtained.

According to the invention described in claim 1, the distortion of the waveform on the secondary side of the AC transformer becomes constant, and the phase difference between the true zero-cross of the AC input voltage waveform and the output signal of the zero-cross detecting means is corrected. Since it is possible to accurately determine the timing of energizing the heater, it is possible to accurately control the electric power of the heater, and it is possible to provide a power supply device that starts up quickly and consumes less power. it can.

According to the second aspect of the present invention, since the correction table is switched according to the load current amount on the secondary side of the AC transformer, it becomes possible to control the electric power of the heater with high accuracy, and the rise of the heater is prevented. It is possible to provide a power supply device that is fast and uses little power.

According to the third aspect of the invention, the correction table is switched at the timing when the load current on the secondary side of the AC transformer fluctuates greatly. It is possible to perform power control with high accuracy, and it is possible to provide a power supply device that starts up quickly and consumes less power.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a current control pulse according to the first embodiment.

FIG. 3 is a diagram showing a current control pulse according to the first embodiment.

FIG. 4 is a diagram showing a relationship between a true zero cross and an output signal of a zero cross detection circuit at the time of rising of a voltage in the first embodiment.

FIG. 5 is a diagram showing a relationship between a true zero-cross and an output signal of a zero-cross detection circuit at the time of a voltage fall of the first embodiment.

FIG. 6 is a relationship diagram between an input voltage and a phase difference ΔT according to the first embodiment.

FIG. 7 is a circuit diagram of a second embodiment of the present invention.

FIG. 8 is a diagram showing an example of a correction table in the second embodiment.

FIG. 9 is a diagram showing an example of a correction table in the second embodiment.

FIG. 10 is a circuit diagram of a conventional power supply device.

FIG. 11 is a waveform chart of each part in the conventional power supply device.

FIG. 12 is an input voltage characteristic diagram of delay time Δt in the conventional power supply device.

[Explanation of symbols]

 4 Heater (Target Load) 17 Load Current Detection Circuit 18 CPU 19 Dummy Resistor (Dummy Load) 20 Switching Element 21 AC Input Voltage Detection Circuit 22 Zero Cross Detection Circuit

Claims (3)

[Claims] 1. An AC input voltage detecting means for detecting a magnitude of an AC input voltage, an AC transformer in which a primary winding is connected to an AC input voltage side, and one end of a secondary winding is set to a ground potential.
Zero cross detection means for detecting the timing of the zero cross at which the potential of the other end of the secondary winding of the AC transformer crosses the ground potential, and a zero cross detection means for detecting a zero cross timing from the zero cross detection timing to the target load AC
In a power supply device that outputs an energization timing pulse for starting energization of a voltage to control an amount of energization time to a target load, a load current detection unit that detects a load current on the secondary side of the AC transformer, and the load current. A load connected to the latter stage of the detection means, a switching element that changes the current flowing through the load by controlling the input pulse width, and a load current detected by the load current detection means so that the load current has a preset current value. A load current control means for controlling an input pulse width to the switching element and a phase difference between a true zero cross of the AC input voltage and the zero cross detection timing are canceled based on a detection value of the AC input voltage detection means. And a correction unit that corrects the generation timing of the energization timing pulse. 2. An AC input voltage detecting means for detecting the magnitude of an AC input voltage, an AC transformer in which a primary winding is connected to an AC input voltage side, and one end of the secondary winding is at a ground potential.
Zero cross detection means for detecting the timing of the zero cross at which the potential of the other end of the secondary winding of the AC transformer crosses the ground potential, and a zero cross detection means for detecting a zero cross timing from the zero cross detection timing to the target load AC
In a power supply device that outputs an energization timing pulse for starting energization of a voltage to control an amount of energization time to a target load, a load current detection unit that detects a load current on the secondary side of the AC transformer, and the load current. The correction table regarding the generation timing of the energization timing pulse is switched according to the detection value of the detection means, and the position of the true zero-cross of the AC input voltage and the zero-cross detection timing is determined based on the detection value of the AC input voltage detection means. To cancel the phase difference,
A power supply device comprising: a correction unit that corrects the generation timing of the energization timing pulse. 3. An AC input voltage detecting means for detecting the magnitude of the AC input voltage, an AC transformer in which the primary winding is connected to the AC input voltage side, and one end of the secondary winding is at the ground potential.
Zero cross detection means for detecting the timing of the zero cross at which the potential of the other end of the secondary winding of the AC transformer crosses the ground potential, and a zero cross detection means for detecting a zero cross timing from the zero cross detection timing to the target load AC
In a power supply device that outputs an energization timing pulse for starting energization of a voltage to control the amount of energization time to a target load, the energization timing pulse is generated at a timing when the load current on the secondary side of the AC transformer largely changes. The generation timing of the energization timing pulse is switched so as to cancel the phase difference between the true zero-cross of the AC input voltage and the zero-cross detection timing based on the detection value of the AC input voltage detection means by switching the correction table regarding the timing. A power supply device comprising: a correction unit that corrects