JPS6152104A - Load power control circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a load power control circuit, and particularly to a load power control circuit that cuts off power supply to the load when a control element that controls power to the load is destroyed and becomes conductive. This invention relates to a load power control circuit.

[Prior art]

Generally, in copying machines equipped with a fuser heater, if fuser heat control becomes impossible due to a thermistor disconnection, continuity breakdown of a triac or 5SR (solid state relay) static control element, or a defect in the control system, the fuser heater will overheat. However, there is also the risk of melting of surrounding parts, smoke generation, and fire, which is very dangerous. Therefore, in order to keep the fuser heater from overheating, a temperature fuse or thermal protector is usually installed in series with the fuser heater, near the fuser roller, etc. However, the failure rate of temperature fuses, etc. is high, and sometimes they do not work properly. Not only is this not the case, but even if the temperature fuse reaches the set temperature and blows out, at that time the fixing row 2 or separation tab will melt and the fixing device must be replaced. Furthermore, if the fixing heater becomes uncontrollable with paper wrapped around the fixing roller, the paper may burn before reaching the temperature set by the fuse, so there is a need for a very safe protection circuit.

Among them, countermeasures are taken by adding a thermistor disconnection detection circuit for thermistor disconnection, and a runaway detection circuit for the OPu runaway, but triac,
No countermeasures have been taken for control elements such as SSRs, even though they have a high failure rate because they control loads with large instantaneous currents.

〔the purpose〕

The present invention eliminates these drawbacks, and greatly reduces the risk of abnormalities in the control element that controls the power supply to the load, making it possible to control the power supply to the load with extremely high safety. The purpose of the present invention is to provide a load power control device that is capable of controlling load power.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

1 and 2 are circuit diagrams showing one embodiment of the present invention.

As shown in FIG. 1, terminal A1. A temperature fuse F'u1, a triac TR, and a cutoff relay contact Ry1-a are connected in series to the fixing heater H1 between A2 and A2.

Furthermore, abnormal voltage absorbing spark quenchers FJQ, i and BQ, 2 are connected to both ends of the relay contact Ry1-a and the triac TR.

In FIG. 2, 1 is a Hall element, and a constant current element 2 and a variable resistor VR1 are connected to a terminal (2). Further, the output side of the operational amplifier Op,1 is connected to the terminal (2), and the terminal (2) is connected to one input end of the operational amplifier Op,1.

Further, the input side of the operational amplifier op, 1 is grounded. Furthermore, the terminal ■ of the Hall element 1 is connected to the input side of the operational amplifiers Op and 2, and the - input terminal is connected to the resistors R17 and R1.
The output side of the operational amplifier Op2, to which 8 is connected and whose value is determined so that the output of the Hall element is about 100 times, is connected to the 10 input side of the comparator COm, 1 via a resistor R19, and - Input is grounded.

In the above, Zener diodes zD1 to ZD5 and transistors Q, 2. Q, 4. For Q5, use the same one, and below, Zener diodes ZD1 to ZD5 (
D'): r-f- potential to Vz, Q2. Q4. Let the pace and emitter potential of Q5 be "BE".

The fixing heater is controlled using a Tri Book TR engineer, and full-wave and half-wave energization is controlled based on the fixing heater control signal. During full-wave energization control, a control signal with a positive pulse waveform synchronized with the zero cross is output as shown in FIG. 2a. In addition, during half-wave energization control, the pulse in Figure 2 a is
Outputs every other item. Now, when the fixing heater control pulse is output as shown in FIG. 2a, the pulse is applied to the gate of the triac TRI, and the fixing heater H1 is energized. (Normally, the relay contact Ry1-a is closed.) At this time, as shown in FIG. Hall element 1 is arranged in. Hall element 1 has four terminals, and terminal ■
A constant current is passed between terminals ■ and ■, and a Hall voltage is output between terminals ■ and ■. Also, on the output side of comparator CQm, there are a pull amplifier resistor R20, resistors R21, R22, and transistor Q6.
A switching circuit consisting of the following is connected. On the output side of the transistor Q6, there is a charge/discharge circuit consisting of a resistor It10, R11, a capacitor C2, and a Zener diode).
' Zn2, resistors R12, R13, transistor Q4
A switching circuit consisting of the following is connected. On the other hand, the heater control signal is connected to the switching circuit of resistors R1, R2 and transistor q1, and further connected to the switching circuit of transistor Q1.
On the output side, there is a charge/discharge circuit consisting of resistors R3, R4, capacitor C1, Zener diode ZD1, resistors R5, R6, R7, R8, and transistors Q, 2, Q3.
A current supply circuit to the capacitor C3 is connected thereto. Further, a charging/discharging circuit including resistors R9, R14 and a capacitor 03, and a switching circuit including an rf-tie auto ZD3, resistors R15, R16, and a transistor Q5 are connected to the output side of the transistor Q4,
A fuse resistor FR1, a relay Ry1, and a reverse voltage prevention diode D2 are connected to the output side of the transistor Q5.

Constant voltage construction 02 is, for example, AD5 from Analog Devices.
By using 80 and adjusting the variable resistor VR1, you can determine the constant current IC to be passed between terminals ■ and ■.In the case of AD580, IC = 2.5 x 105
/VR1+ 1 (mA).

In order to remove the common mode voltage generated in the Hall element 1, the operational amplifier Opi controls the terminal (2) to have the same potential as the ground potential (Ov). The Hall voltage vH is VH=, I
c, B (mV) Yes. Here, K is also called product sensitivity and is a constant determined by the type of Hall element (unit: mV/mA, expressed in KG). Further, B is a magnetic field applied perpendicularly to the semiconductor piece of the Hall element (unit: KG). This Hall voltage vH is generated between the terminals ■ and ■, but since the terminal ■ is at 0 potential, the potential of the terminal ■ becomes its Oh/L/voltage vH. The Hall voltage vH is amplified approximately 100 times by the operational amplifier Op2. This voltage waveform is almost the same as the fourth diagram, but the comparator Ca
By comparing m, 1 with 0 potential, a waveform as shown in FIG. 2d is obtained.

The output of the comparator Oom,1 is the resistor R20, R21
.

It is inverted by a switching circuit including R22 and transistors Q and 6, and smoothed by a charging/discharging circuit including resistors R10 and R11 and a capacitor C2.

At this time, the transistor Q, Since no current flows into the base of 40, transistor Q4 has no ONL, but the potential of e becomes (VZ+VI1
1), transistor Q4 is turned on. I cut it,
The heater control signal a is connected to the resistor R via the transistor Q1.
11, R4, and a charging/discharging circuit consisting of capacitor C1.
, is smoothed as shown in FIG. 2, and as explained earlier, when the potential of the capacitor C1 terminal voltage S reaches (v2+VBz), the transistors Q and 2 are turned on. Transistor Q2
When Q3 turns on, transistor Q3 also turns on. In other words, while the heater control pulse is being output, transistor Q3 is OFF, so transistor Q4 is ON.
, OFF, the capacitor C5 is not charged. However, when the fixing heater control pulse is not output and the transistor Q4 is OFF, that is, when the fixing heater is conductive, the capacitor C5 is charged. Further, when the transistor Q3 is turned on when the heater control pulse is not output, that is, when the fixing heater is non-conductive (normal state), the transistor Q4 is turned on and the capacitor C3 is discharged. Capacitor C
Even when the potential of the terminal voltage f of No. 3 is normal, the capacitor 03 is charged due to signal delays, etc., and as shown in the waveform shown in FIG. 2 f, before and after the fixing heater control pulse output, Although the potential of capacitor C3 may rise, f
As long as the potential does not exceed (Vz+vBK), transistor Q5 is not ON.

However, if the triac TR has broken continuity and the fuser heater becomes conductive even though it is not outputting the fuser heater control pulse, capacitor C3
is gradually charged, and after a certain period of time, (vz+V-nx)
Since the potential is higher than that, transistor Q5 turns ON L,
By setting the input terminals of relay RY1 to almost the same potential,
Contact Ry1-a is opened to shut off the fixing heater. Also,
At this time, the fuse resistor FR,1 is blown because several tens of times the rated power is applied to the fuse resistor FR,1.

This keeps the fuser heater shut off, so even if you turn the power switch off and then turn it on again, the fuser heater will still shut off! It is safe because it is cohesive.

In this way, by comparing the fixing heater control signal and the signal detected by using a magnetic sensor such as a Hall element to detect the current flowing through the fixing heater, at least the try book, S
By detecting continuity breakdown in control elements such as SR, forcibly shutting off the fixing heater, and maintaining that state,
This makes it possible to significantly eliminate damage and danger caused by overheating of the fixing heater.

In the above embodiment, since a control method using full-wave and half-wave energization is adopted, the heater control waveform is a pulse waveform synchronized with zero cross. However, if the control method is based only on full-wave energization, for example, the heater A control waveform based on a level such that O1' is output when the heater is ON at 11'' may be used. In this case, the pace Km contact control signal of the transistor Q2 may be input.

Further, in the above embodiment, a fuse resistor is used to keep the heater shut off in the event of an abnormality, but the relay Ry
1, a latching relay or the like may be used to maintain the heater cutoff, and a cutoff holding means such as a breaker or a fuse may be used instead of the fuse resistor.

Further, in the above embodiment, the fusing heater is shut off in the event of an abnormality, but other components other than the fusing heater, such as the drive motor and the lighting lamp, may be shut off at the same time. However, the present invention is not limited to fixing heaters, but can also be applied to other heaters, lamps, and other devices that control power to loads.

[Effect J As described above, according to the present invention, by comparing the load power control signal and the signal corresponding to the magnetic field generated by the load current, it is possible to detect an abnormality in the control element that controls the power supply to the load. The risk of injury caused by this can be greatly reduced, and extremely safe load power control can be performed.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams in an embodiment of the present invention,
FIG. 3 is a diagram for explaining the installation position of the Hall element, and FIG. 4 is a timing diagram for explaining Mizumoto and Akira. 1... Hall element 2... Constant current construction C 3... Ferrite core 4... Fixing heater lead θ R1-R22... Resistance 01-C3... Capacitor zD1-ZD3... Zener diode DI, D2
...Diode DBl...Diode bridge Q, 1 to Q6 ...Transistor Op, i-〇p, 2...Operational amplifier Com1 ...Comparator VRl ...Variable resistor FRl ...Fuse resistance

Claims (3)

[Claims] (1) A control element for controlling the electric power supplied to the load based on the load power control signal, a detection circuit for detecting the magnetic field generated by the load current flowing through the load, a load power control signal, and a detection circuit for detecting the magnetic field generated by the load current flowing through the load. 1. A load power control circuit comprising: a control circuit that compares signals corresponding to load currents and cuts off load power when the respective relationships are in a state that does not normally occur. (2) The load power control circuit according to claim 1, wherein the control circuit includes an element for maintaining a cut-off state. (3) Load power control according to claim 1, wherein the control circuit cuts off the load only when the load is energized even though the load power signal is an off signal. circuit.