JP6365488B2 - Electrical equipment - Google Patents

Description

  The present invention relates to an electrical apparatus such as an MFP having a fixing device that thermally fixes a toner image onto a recording sheet.

  As shown in FIG. 4, the electrical apparatus 1 such as an image forming apparatus such as a copying machine, a facsimile machine, or a multifunction machine includes a power supply unit 3 that supplies power to a load 21 such as a motor provided in the main body 2.

  The power supply unit 3 is an AC / DC converter that converts electric power supplied from a commercial AC power supply AC into a DC voltage. Referring to FIG. 4, a rectifier circuit DB, smoothing capacitors C1, C2, a transformer T, a power supply A control IC 31, a rectifier diode D1, a switching element Q1, and a current detection resistor R1 are provided.

  A commercial AC power supply AC is connected to the AC input terminals ACL and ACN of the rectifier circuit DB having a diode bridge configuration, and the AC voltage input from the commercial AC power supply AC is full-wave rectified and output from the rectifier circuit DB. A smoothing capacitor C1 is connected between the rectified output positive terminal and the rectified output negative terminal of the rectifier circuit DB. Further, the rectified output negative terminal of the rectifier circuit DB is connected to the ground terminal. As a result, a DC voltage obtained by rectifying and smoothing the commercial AC power supply AC using the rectifier circuit DB and the smoothing capacitor C1 is obtained.

  The power supply control IC 31 incorporates a control circuit for performing on / off control of a switching element Q1 such as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The power supply control IC 31 outputs a drive signal to the gate terminal of the switching element Q1, and controls the switching element Q1 on and off. The positive terminal of the rectified output of the rectifier circuit DB is connected to one end of the primary winding P of the transformer T, the other end of the primary winding P of the transformer T is connected to the drain terminal of the switching element Q1, and the switching element The source terminal of Q1 is connected to the ground terminal via the current detection resistor R1. Thus, the power applied to the primary winding P of the transformer T is transmitted to the secondary winding S of the transformer T by performing on / off control of the switching element Q1. The current detection resistor R1 detects the current Id flowing through the switching element Q1 as a voltage signal. The voltage signal detected by the current detection resistor R1 is input to the power supply control IC 31. When the current Id reaches the overcurrent detection point, the power supply control IC 31 limits the power supplied to the main body unit 2.

  A smoothing capacitor C2 is connected between both terminals of the secondary winding S of the transformer T via a rectifier diode D1. The voltage induced in the secondary winding S of the transformer T is rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C2. Then, the inter-terminal voltage of the smoothing capacitor C2 is output as the output voltage Vo from the power supply output terminals T3a and T3b, and is supplied to the load 21 via the power supply input terminals T2a and T2b of the main body 2 connected by a connector or the like.

JP-A-6-308785 JP 2006-296159 A JP 2014-154669 A

  In an image forming apparatus such as a copying machine, a facsimile machine, or a multifunction machine, a plurality of models having different printing speeds are prepared, and a common power supply unit 3 is used for the plurality of models in order to reduce component costs. In this case, since the load 21 is greatly different among a plurality of models, as shown in FIGS. 5A and 5B, the current Id flowing through the switching element Q1 varies depending on the model (when the load is model A <model B). The current Id is also model A <model B). Further, even in the same model, under a low temperature environment, the load 21 increases due to an increase in driving torque, and flows through the switching element Q1 depending on the temperature of the main body 2 as shown in FIGS. 5 (b) and 5 (c). The current Id is also different (low temperature> high temperature). Therefore, when the common power supply unit 3 is used, it is necessary to set the overcurrent detection point according to the highest condition as shown in FIG.

  However, in a model with a small load, even if a part of the output is short-circuited due to a machine abnormality, the current Id does not rise up to the overcurrent detection point, and the partial short-circuit state may continue and cause damage. The same can be said for the same model because the load is reduced under high temperature conditions.

  Patent Document 1 discloses a technique for setting an overcurrent detection point suitable for a standby state, an operation state, and a load current at the start of operation, and Patent Documents 2 and 3 describe an excessive current according to the temperature characteristics of the switching element. Although technologies for changing the current detection conditions are disclosed, they do not solve the above-described problems.

  An object of the present invention is to solve the above problems and to provide an electric device that can reliably detect a state such as a partial short circuit even in a model with a small load.

The electrical device of the present invention is an electrical device having a power supply unit that generates power by on / off control of a switching element, and a main body that operates by the power supplied from the power supply unit, and the power supply unit includes the switching unit. A control circuit that performs on / off control of an element; and a current output terminal that outputs a current flowing through the switching element; and the main body is connected to the current output terminal of the power supply unit and flows through the switching element And an overcurrent detection circuit that is connected between the current input terminal and the ground terminal and converts a current flowing through the switching element into a voltage signal using a resistor. The control circuit is configured to detect the voltage signal detected by the overcurrent detection circuit as a preset overcurrent value. Upon reaching the cement, to limit the power supplied to the main body portion, an overcurrent detecting circuit of the main body portion, comprises a thermistor having a connected positive temperature characteristic between the ground terminal and the current input terminal It is characterized by doing .
Et al is in electrical equipment of the present invention, the overcurrent detection circuit of the main body portion, the connected between the current input terminal and the ground terminal, the resistance value comprises a modifiable current detecting variable resistor May be.

  According to the present invention, even when a common power supply unit is used for models with different loads, the overcurrent detection point can be apparently changed in conjunction with the load fluctuation due to the model difference, and the model with a small load Even so, there is an effect that a state such as a partial short circuit can be reliably detected.

It is a figure which shows the structure of 1st Embodiment of the electric equipment which concerns on this invention. It is a graph which shows the relationship between the overcurrent point and the electric current which flows through a switching element in 1st Embodiment of the electric equipment which concerns on this invention. It is a figure which shows the structure of 2nd Embodiment of the electric equipment which concerns on this invention. It is a figure which shows the structure of the conventional electric equipment. It is the graph which compared the electric current which flows through a switching element in a different model and different temperature. It is a graph which shows the relationship between the overcurrent point in the conventional electric equipment, and the electric current which flows through a switching element.

  Next, embodiments of the present invention will be specifically described with reference to the drawings.

(First embodiment)
An electrical apparatus 10 according to the first embodiment is an image forming apparatus such as a copying machine, a facsimile machine, or a multifunction machine. Referring to FIG. 1, a main body 20 having various configurations for image formation, And a power supply unit 30 that supplies power to a load 21 such as a motor provided in the main body 20.

  The power supply unit 30 is an AC / DC converter that converts electric power supplied from a commercial AC power supply AC into a DC voltage. Referring to FIG. 4, a rectifier circuit DB, smoothing capacitors C1, C2, a transformer T, and a power supply A control IC 31, a rectifier diode D1, and a switching element Q1 are provided.

  A commercial AC power supply AC is connected to the AC input terminals ACL and ACN of the rectifier circuit DB having a diode bridge configuration, and the AC voltage input from the commercial AC power supply AC is full-wave rectified and output from the rectifier circuit DB. A smoothing capacitor C1 is connected between the rectified output positive terminal and the rectified output negative terminal of the rectifier circuit DB. Further, the rectified output negative terminal of the rectifier circuit DB is connected to the ground terminal. As a result, a DC voltage obtained by rectifying and smoothing the commercial AC power supply AC using the rectifier circuit DB and the smoothing capacitor C1 is obtained.

  The power supply control IC 31 incorporates a control circuit for performing on / off control of a switching element Q1 such as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The power supply control IC 31 outputs a drive signal to the gate terminal of the switching element Q1, and controls the switching element Q1 on and off. The positive terminal of the rectified output of the rectifier circuit DB is connected to one end of the primary winding P of the transformer T, the other end of the primary winding P of the transformer T is connected to the drain terminal of the switching element Q1, and the switching element The source terminal of Q1 is connected to the current output terminal T3c.

  The current output terminal T3c of the power supply unit 30 is connected to the current input terminal T2c of the main body 20 by a connector or the like. Thereby, the current Id flowing through the switching element Q1 is output from the current output terminal T3c of the power supply unit 30 and input from the current input terminal T2c of the main body unit 20. In the main body 20, the current input terminal T2c is connected to the ground terminal via a parallel circuit including a thermistor TH1 and a current detection resistor R2. A parallel circuit composed of the thermistor TH1 provided in the main body 20 and the current detection resistor R2 functions as an overcurrent detection circuit 22.

  By turning on / off the switching element Q1, the power applied to the primary winding P of the transformer T is transmitted to the secondary winding S of the transformer T. The overcurrent detection circuit 22 detects the current Id flowing through the switching element Q1, that is, the current Id input from the current input terminal T2c as a voltage signal. The voltage signal detected by the overcurrent detection circuit 22 is input to the power supply control IC 31 via the current input terminal T2c and the current output terminal T3c. When the current Id reaches the overcurrent detection point, the power supply control IC31 The power supplied to 20 is limited.

  A smoothing capacitor C2 is connected between both terminals of the secondary winding S of the transformer T via a rectifier diode D1. The voltage induced in the secondary winding S of the transformer T is rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C2. The inter-terminal voltage of the smoothing capacitor C2 is output as the output voltage Vo from the power supply output terminals T3a and T3b, and is supplied to the load 21 via the power supply input terminals T2a and T2b of the main body 20 connected by a connector or the like.

  At the same temperature, the resistance of the overcurrent detection circuit 22, that is, the combined resistance of the thermistor TH1 connected in parallel with the current detection resistor R2, is smaller in the model with the smaller load 21 than the model with the larger load 21. It is set to be large. Therefore, the voltage signal detected by the overcurrent detection circuit 22 is larger in the model A with the small load 21 than the model B with the large load 21 even if the current Id flowing through the switching element Q1 is the same. Become. Accordingly, when the overcurrent detection point to be compared with the voltage signal is constant, as shown in FIG. 2, the overcurrent detection point of the model A having the smaller load 21 is detected by the overcurrent detection point of the model B having the larger load 21. It looks smaller than the point. That is, the overcurrent detection point apparently fluctuates in conjunction with load fluctuations due to model differences, so even a model with a small load can reliably detect a state such as a partial short circuit and can be used more safely.

  Further, the thermistor TH1 uses a PTC (Positive Temperature Coefficient) having a positive temperature characteristic in which the resistance increases as the temperature increases. Therefore, the voltage signal detected by the overcurrent detection circuit 22 is larger at a high temperature than at a low temperature even if the current Id flowing through the switching element Q1 is the same. Accordingly, when the overcurrent detection point to be compared with the voltage signal is constant, the high temperature overcurrent detection point is apparently smaller than the low temperature overcurrent detection point as shown in FIG. In other words, the overcurrent detection point apparently fluctuates in conjunction with load fluctuations due to temperature differences, so even if the temperature is high and the load is small, it is possible to reliably detect a state such as a partial short-circuit and use it more safely .

As described above, the first embodiment is an electric device 10 having the power supply unit 30 that generates power by the on / off control of the switching element Q1 and the main body 20 that operates by the power supplied from the power supply unit 30. The power supply unit 30 includes a power supply control IC 31 that performs on / off control of the switching element Q1 and a current output terminal T3c that outputs a current Id that flows through the switching element Q1. A current input terminal T2c connected to the output terminal T3c, to which a current Id flowing through the switching element Q1 is input, and connected between the current input terminal T2c and the ground terminal. And an overcurrent detection circuit 22 for converting the power supply unit 30 into a power supply control I. 31, the voltage signal detected by the overcurrent detection circuit 22 reaches a preset over-current point, to limit the power supplied to the main body portion 20.
With this configuration, by changing the resistance value of the overcurrent detection circuit 22 according to the model load, even if the common power supply unit 30 is used for different models of the load, it is linked with the load fluctuation due to the model difference. Thus, the overcurrent detection point can be apparently changed. Therefore, even a model with a small load can reliably detect a state such as a partial short circuit and can be used more safely.

Furthermore, in the first embodiment, the overcurrent detection circuit 22 of the main body 20 includes a thermistor TH1 having a positive temperature characteristic connected between the current input terminal T2c and the ground terminal.
With this configuration, the overcurrent detection point can be apparently changed in conjunction with the load change due to the temperature difference.

(Second Embodiment)
In the second embodiment, referring to FIG. 3, the overcurrent detection circuit 22a provided in the main body 20 is configured by a parallel circuit of a thermistor TH1 and a current detection variable resistor R3 whose resistance value can be changed. This is different from the first embodiment. Therefore, in the second embodiment, the resistance value of the current detection variable resistor R3 can be changed according to the size of the model load 21, and the resistance value of the overcurrent detection circuit 22a can be set. That is, the overcurrent detection circuit 22a of the main body 20 can be shared.

As described above, in the second embodiment, the overcurrent detection circuit 22a of the main body unit 20 is connected between the current input terminal T2c and the ground terminal, and the current detection variable resistor R3 whose resistance value can be changed. It has.
With this configuration, the overcurrent detection circuit 22a can be shared.

  Note that the present invention is not limited to the above-described embodiments, and it is obvious that the embodiments can be appropriately changed within the scope of the technical idea of the present invention. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a number, position, shape, and the like that are suitable for implementing the present invention. In each figure, the same numerals are given to the same component.

DESCRIPTION OF SYMBOLS 1,10 Electric equipment 2,20 Main-body part 21 Load 22,22a Overcurrent detection circuit 3,30 Power supply unit 31 Power supply control IC
AC commercial AC power supply C1, C2 smoothing capacitor D1 rectifier diode DB rectifier circuit R1, R2 current detection resistor R3 current detection variable resistor Q1 switching element T transformer T2a, T2b power input terminal T2c current input terminal T3a, T3b power output terminal T3c current output Terminal TH1 Thermistor

Claims (2)

An electric device having a power supply unit that generates electric power by on / off control of a switching element, and a main body that operates by electric power supplied from the power supply unit,
The power supply unit is
A control circuit for performing on / off control of the switching element;
A current output terminal for outputting a current flowing through the switching element;
The main body is
A current input terminal connected to the current output terminal of the power supply unit, to which a current flowing through the switching element is input;
An overcurrent detection circuit which is connected between the current input terminal and the ground terminal and converts a current flowing through the switching element into a voltage signal by a resistor;
When the voltage signal detected by the overcurrent detection circuit reaches a preset overcurrent point, the control circuit of the power supply unit limits power supplied to the main body ,
The overcurrent detection circuit of the main body includes an electrical device having a positive temperature characteristic connected between the current input terminal and the ground terminal . Overcurrent detection circuit of the main body portion, the current said input terminal being connected between a ground terminal, an electric according to claim 1, characterized by comprising a modifiable current detecting variable resistor the resistance value machine.

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