JP2001145257A - Current-limiting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current-limiting circuit for reducing size and costs with an easy and inexpensive phase control circuit configuration. SOLUTION: A phase control conduction circuit for energizing a load with an AC voltage is composed of a zero-cross opto-isolation conduction element driver 6 for turning on or off the phase control conduction circuit, a resistor 1 for determining phase and a capacitor 11 being connected to the zero-cross opto-isolation conduction element driver 6, a zero-cross opto-isolation conduction element driver 12 being connected in parallel with the capacitor 11, a selection control block 16 for turning on or off the output of the zero-cross opto-isolation conduction element driver 6, a trigger element 10 that is connected to the capacitor 11, and a conduction element 14 for turning on or off the conduction to the load with a trigger signal from the trigger element 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents excessive current generated when a halogen lamp is turned on in an electrophotographic apparatus having a fixing device, and prevents excessive current generated when a load used in another system is energized. And a current limiting circuit.

[0002]

2. Description of the Related Art As an energizing means of an electrophotographic apparatus having a fixing device provided with a halogen lamp, a power thermistor is used to prevent a large current transiently flowing at the start of energization of the lamp. FIG. 4 is a conventional current limiting circuit diagram, and FIGS. 5 and 6 are the same current waveform diagrams. In FIG. 4, 2, 3, 18
Is a resistor, 5 is a zero-cross opto-isolation energizing element driver, 14 is a bidirectional energizing element (triac), 15 is a surge absorber, 16 is a selection control block, 17 is a 5V power supply, 19 is a capacitor, 20, 21
Is a power thermistor, and 22 is a halogen lamp.
In FIG. 4, a triac 14 which is a bidirectional conducting element is shown.
And a zero-cross opto-isolation energizing element driver 5 for outputting a signal for driving the driver, and power thermistors 20 and 21.

[0003]

However, today, there is a demand for a high-speed electrophotographic apparatus having a fixing device equipped with a halogen lamp, and a high-power halogen lamp is required. There is a limit in the power capacity of the power thermistor, and a plurality of power thermistors are connected in series for the measure.

[0004] The power thermistors 20 and 21 shown in FIG. 4 have a resistance of several Ω at the beginning of energization, and the resistance greatly decreases during normal energization. Therefore, at the initial stage of lighting of the halogen lamp, the occurrence of an excessive current can be prevented by the resistance. The current waveform A1 shown in FIG. 5 shows the current-limited waveform.

[0005] The waveform in FIG. 6 is the current value A0 when there is no current limiting means, and shows a higher value than A1. According to this conventional technique, a plurality of expensive power thermistors are required, resulting in an increase in cost. Further, the area of the printed circuit board for realizing it is required to be large, so that the cost and size cannot be reduced.

There has also been proposed a method of using a plurality of low-power halogen lamps instead of the high-power halogen lamps and shifting the lighting timing to prevent an excessive current. However, the mounting area becomes large, the size cannot be reduced, and the cost increases. .

Further, a photocoupler is connected to an AC power supply via a resistor, a start point of a signal output from the photocoupler is monitored by software, and then the count value is counted by a soft timer. A phase control energizing method has been proposed in which a trigger signal is output to a bidirectional energizing element (triac) when time has elapsed, and energization to a load is started. However, this conventional method uses a CPU
And cannot be used for general purposes. In addition, since the weight of control by software is large, phase control energization method does not operate normally due to runaway of software, and there is a danger that excessive inrush current will cause other components to burn out, so a countermeasure circuit for this is necessary. Increases cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current limiting circuit which can be reduced in size and cost with an easy and inexpensive phase control circuit configuration.

[0009]

According to the present invention, a current limiting circuit according to the present invention is provided with 1/1 of one cycle from a zero cross point of an AC voltage waveform.
A phase control energizing circuit for applying an AC voltage to the load at a point greater than 4 and less than 1/2
A zero-cross opto-isolation energizing element driver for N / OFF control, a resistor and a capacitor connected to the zero-cross opto-isolation energizing element driver, a zero-cross opto-isolation energizing element driver connected in parallel to the capacitor, and the opto-isolation energizing element driver A selection control block for controlling ON / OFF of an output of an element driver or a zero-cross opto-isolation energizing element driver, a trigger element connected to the capacitor, and ON / OFF of energization to a load by a trigger signal from the trigger element. Of the current-carrying element.

With this configuration, it is possible to provide a current limiting circuit that can be reduced in size and cost with an easy and inexpensive phase control circuit configuration.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first aspect of the present invention is a phase control energizing circuit for energizing an AC voltage to a load from more than 1/4 to less than 1/2 of one cycle from a zero crossing point of an AC voltage waveform. A zero-cross opto-isolation energizing element driver for ON / OFF control of the phase control energizing circuit, a resistor and a capacitor for phase determination connected thereto, and a zero-cross opto-isolation energizing element driver connected in parallel to the capacitor When,
A selection control block for ON / OFF control of the output of the opto-isolation energizing element driver or the zero-cross opto-isolation energizing element driver;
The trigger element connected to the capacitor and the trigger signal from the trigger element turn on the power supply to the load,
It was composed of an energizing element that was turned off.

According to a second aspect of the present invention, there is provided a timer control section for controlling the operation of the phase control energizing circuit based on the temperature of a predetermined portion and controlling the operation time of the phase control energizing circuit.

With the above configuration, it is possible to provide a current limiting circuit which can be reduced in size and cost with an easy and inexpensive phase control circuit configuration.

(Embodiment 1) FIG. 1 is a diagram showing a current limiting circuit according to Embodiment 1 of the present invention, and FIG. 2 is an explanatory diagram showing the same control timing, voltage and current limiting waveforms. In the following description, the same elements as those of the related art are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, 1, 4, 9, and 13 are resistors,
Reference numerals 5, 6, and 12 denote zero-cross opto-isolation energizing element drivers, 7, 8 denote rectifier diodes, 10 denotes a trigger element, and 11 denotes a capacitor.

In FIG. 1, first, a selection control block 1
When the signal 25 is input to the zero-cross opto-isolation energizing element driver 12 from 6, the output is turned on.
Then, the electric charge of the capacitor 11 is discharged to be 0V. Next, after a predetermined time, when the signal 23 is input from the selection control block 16 to the zero-cross opto-isolation energizing element driver 6, the output turns on and the charging current flows from the resistor 1, but the zero-cross opto-isolation energizing element driver 12 Because the output of is turned on, the condenser 1
1 is not charged. Therefore, the trigger element 10 does not output a trigger signal, and the energizing element 14 does not turn on.

When the signal 25 from the selection control block 16 is turned off after a predetermined time, the output of the zero-cross opto-isolation energizing element driver 12 is turned off, and AC
A charging current flows from the zero cross point T2 of the voltage waveform to the capacitor 11 via the phase determining resistor 1 (FIG. 2). When the charging voltage of the capacitor 11 reaches a predetermined value, the trigger element 10 is turned on with a delay of T5 from T2, a trigger current is supplied to the gate of the energizing element, the energizing element is turned on, and the phase-controlled energizing voltage V1 is supplied to the halogen lamp 22. Is done. As shown in FIG. 2, the energizing voltage V1 is generated in a period that is more than の and less than の of one cycle (T3) of the AC power supply, and thus has a value lower than the peak voltage value V0.

Accordingly, the peak current A2 when the voltage V1 is supplied to the halogen lamp 22 becomes lower than the peak current value A0 (FIG. 6) when the voltage V0 is supplied. A0 shown in FIG. 6 indicates a peak current value at the time of V0. Next, when the AC voltage waveform is reversed, a charging current flows to the phase determining resistor 1 via the capacitor 11. When the charged voltage of the capacitor 11 reaches a predetermined value, the trigger element 10 outputs a trigger signal to the energizing element 14 and the energizing element 14 is turned on, and the current whose phase is opposite to the current waveform is controlled by the halogen lamp 2.
2 is supplied.

As shown in FIG. 2, the peak current value decreases when the energization by the phase control is continued for a predetermined time, because the temperature of the filament of the halogen lamp rises and its impedance rises. Thereafter, the signal 23 from the selection control block 16 is turned off and the signal 24 is turned on.
The output of the zero-cross opto-isolation energizing element driver 5 is turned on, and the AC voltage is supplied to the trigger element 10 via the resistor 2. When a predetermined voltage value is reached, the trigger element 10 supplies a trigger current to the gate of the current-carrying element 14, so that the current-carrying element 14 is turned on. In this way, a normal energizing voltage is supplied to the halogen lamp 22. The diodes 7, 8 and the resistor 9 improve the hysteresis of the operation of the phase control circuit.

(Embodiment 2) FIG. 3 is a circuit diagram of a current limiting circuit according to Embodiment 2 of the present invention. Embodiment 2
Has a function of controlling the operation of the phase control energizing circuit according to the first embodiment based on the temperature of a predetermined portion, and a timer control unit for controlling the operation time of the phase control energizing circuit.

In FIG. 3, reference numeral 26 denotes a timer control unit;
7, a temperature sensor; and 28, a temperature comparison unit. In FIG. 3, the filament temperature of the halogen lamp is indirectly detected by a temperature sensor 27 disposed at a predetermined location, and the value is input to a temperature comparison unit 28. The temperature comparison unit 28 compares a preset value with the output of the temperature sensor 27, and if the detected temperature is low, the signals 25 and 23 from the selection control block 16 via the timer control unit 26 which controls the operation time of the phase control circuit. And the phase control circuit starts operating. The operation of the phase control circuit is the same as that of the first embodiment, and the description is omitted. After the phase control circuit operates for a predetermined time, the signals 25 and 23 from the selection control block 16 are turned off and the operation of the phase control circuit stops. Next, a signal 24 from the selection control block 16 is output, and a normal energizing current is supplied to the halogen lamp 22. The normal energizing operation is performed after T6 in FIG.

[0022]

As described above, according to the present invention, an expensive power thermistor can be eliminated with an inexpensive phase control circuit configuration. Also, the mounting area can be reduced, so that downsizing and cost reduction can be achieved. In addition, since control by software is reduced and a current limiting method by phase control is made possible by a hardware circuit configuration, measures against noise and runaway of software can be reduced, and cost reduction and improvement in reliability can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a current limiting circuit according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing control timing, voltage, and current limiting waveforms according to the first embodiment of the present invention.

FIG. 3 is a current limiting circuit diagram according to a second embodiment of the present invention.

FIG. 4 is a conventional current limiting circuit diagram.

FIG. 5 is a conventional current waveform diagram.

FIG. 6 is a conventional current waveform diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Resistance for phase determination 5, 6, 12 Zero cross opto-isolation energizing element driver 7, 8 Rectifier diode 10 Trigger element 11, 19 Capacitor 14 Energizing element (triac) 15 Surge absorber 16 Selection control block 20, 21 Power thermistor 22 Halogen lamp 26 Timer control unit 27 Temperature sensor 28 Temperature comparison unit

Claims (2)

[Claims] 1. A phase control energizing circuit for energizing an AC voltage to a load in a period from more than 1/4 to less than 1/2 of one cycle from a zero crossing point of an AC voltage waveform, comprising: A zero-cross opto-isolation energizing element driver, a phase-determining resistor and a capacitor connected thereto, and a zero-cross opto-isolation energizing element driver connected in parallel to this capacitor; and the opto-isolation energizing element driver or A selection control block for controlling ON / OFF of an output of a zero-cross opto-isolation energizing element driver, a trigger element connected to the capacitor, and an energizing element for turning on and off energization to a load by a trigger signal from the trigger element It is characterized by comprising Flow-limiting circuit. 2. The current according to claim 1, further comprising a function of controlling the operation of the phase control energizing circuit based on a temperature of a predetermined portion, and a timer control unit for controlling an operation time of the phase control energizing circuit. Limit circuit.