JP2013158211A - Discharge circuit and power source with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of an apparatus in a stand-by state and quickly discharge an electric charge remaining in an X capacitor at the time of extraction of a plug.SOLUTION: A discharge circuit includes: electric charge storage means for reducing noise generated in a line to which an AC voltage is input; voltage detection means for detecting whether or not the AC voltage is input; and zero cross detection means which includes discharge means for discharging the electric charge of the electric charge storage means and detects zero cross of the AC voltage using the discharge means. In a case that the input of the AC voltage is cut off when the discharge means is in a non-conductive state, the discharge circuit discharges the electric charge of the electric charge storage means by conducting the discharge means by the voltage detection means according to the cut-off of the input of the AC voltage.

Description

  The present invention relates to a discharge circuit of a power supply device that supplies electric power to an electronic device.

  A discharge circuit in an electronic apparatus having a power source as a converter that receives an AC voltage from a commercial AC power source and converts the AC voltage will be described with reference to FIG.

  In an electronic device that operates with an AC voltage from a commercial AC power supply as an input, a capacitor 40 commonly called an across-the-line capacitor is generally used for the purpose of preventing normal mode noise generated between lines from the commercial AC power supply 1. (Hereinafter referred to as X capacitor) is connected. In addition, after the plug of the electronic device is pulled out (when supply of AC voltage from the commercial AC power supply is cut off), it is obliged to discharge the electric charge remaining in the X capacitor to a predetermined voltage or less within 1 second. ing. When the X capacitor 40 is used to satisfy this requirement, a discharge resistor 20 is generally provided as a discharge circuit for discharging the charge in parallel with the X capacitor 40 as shown in FIG. In general, the AC voltage is full-wave rectified by a rectifier circuit 8 connected to a subsequent stage of the discharge circuit, converted to a desired voltage by a converter 9, and supplied to an electronic device. Some electronic devices have a circuit that detects a zero cross of an AC voltage in order to determine the frequency of the AC voltage of the commercial AC power supply and detect an instantaneous power failure. In such an electronic device, a circuit that detects zero crossing may be used also as a discharge circuit.

  On the other hand, recent electronic devices are required to further reduce power consumption during standby when the electronic device is not operating. When the capacitance of the X capacitor is 1.0 μF, the resistance value of the discharge resistor for reducing the voltage to a predetermined voltage within 1 second is about 1 MΩ. When the voltage of the commercial AC power supply is AC 230V, the power consumption of the discharge resistor is about 52.9 mW. This power consumption is not a negligible power consumption when the power consumption during standby of the electronic device is further reduced.

  In the conventional circuit, the circuit for detecting the discharge resistance and the zero crossing has a configuration that always consumes electric power because a current flows regardless of the operating state of the electronic device. On the other hand, in Patent Document 1, a circuit for zero cross detection is turned on / off during standby, the ratio of the on period is reduced, and a circuit for zero cross detection indicates that the plug has been pulled out. A configuration is proposed in which the ratio of the ON period is detected and the ratio of the ON period is made higher than that in the standby state or is always turned ON to accelerate the discharge of the charge remaining in the X capacitor. Thereby, the power consumption of the circuit for the zero cross detection at the time of standby can be reduced.

  As another method, as shown in FIG. 7, the standby power source 11 is provided in parallel with the main power source 12, and the commercial power line of the main power source 12 is turned off during standby so that the X capacitor 44 is not connected. Is also possible. In FIG. 7, 20 and 30 are discharge resistors, and 40 and 44 are X capacitors. The standby dedicated power supply 11 includes a rectification unit 8a and a converter 9a, and the main power supply 12 includes a rectification unit 8b and a converter 9b. Electric power is supplied from the main power supply 12 during normal operation, and the main power supply 12 is turned off by the switch 73 during standby, and power is supplied from the dedicated power supply 11 during standby. Since the power required for the electronic device during standby is small, the capacity of the X capacitor 40 can be made smaller than that of the X capacitor 44. Therefore, the resistance value of the discharge resistor 20 is set larger than the resistance value of the discharge resistor 30, and Power consumption can be reduced.

  Further, a configuration as shown in FIG. 8 is proposed in Patent Document 2, which has a resistor 41 and a capacitor 21 as a circuit for monitoring the voltage from the commercial AC power supply. The circuit monitors the voltage and pulls out the plug. Is detected. As a configuration in which the switch 70 is turned on when pulling out of the plug is detected, a discharge circuit that suppresses power consumption when a voltage is input from the commercial AC power supply 1 has also been proposed.

JP2005-201587 JP2011-010295A

  However, in the configuration of Patent Document 1, since the plug extraction is detected by the zero-cross detection circuit and the zero-cross detection circuit is also used as the discharge circuit, the zero-cross detection circuit cannot be turned off for the entire period during standby. That is, power is still consumed during the ON period of the zero cross detection means. In addition, when the AC voltage from the commercial AC power source is distorted by external noise or the like, or when the frequency of the AC voltage of the commercial AC power source fluctuates, there is a problem that the zero cross is erroneously detected.

  Further, in the configuration in which the dedicated power source 11 is provided as shown in FIG. 7, an X capacitor is required even during standby, and the capacity of the X capacitor of the dedicated power source 11 can be reduced to, for example, 0.22 μF. However, the resistance value of the discharge resistor for making the voltage lower than the predetermined voltage within 1 second is about 4.5 MΩ. When the AC voltage of the commercial AC power supply is AC 230 V, the power consumption due to the discharge resistance is about 11.8 mW. Although power consumption can be reduced as compared with the configuration of FIG. 6, it is difficult to further reduce power consumption. Further, in the configuration provided with the dedicated power supply, there are problems that the number of parts of the power supply circuit is increased, the circuit scale is increased, and the cost of the power supply is increased.

  Further, in the configuration of Patent Document 2, in a standby state that does not require zero-cross detection, a separate high-breakdown-voltage switch element that shuts off the zero-cross detection circuit is required, which may increase the cost.

  The present invention has been made in view of the above-described problems, and further reduces the power consumption during standby of the device, and can discharge the residual charge of the X capacitor quickly when the plug is pulled out. An object is to provide a power supply including a circuit and a discharge circuit.

  A discharge circuit for solving the above problems includes a charge storage unit for reducing noise generated in a line to which an AC voltage is input, a voltage detection unit for detecting whether or not the AC voltage is input, A discharge means for discharging the electric charge of the charge storage means; a zero cross detection means for detecting a zero cross of the AC voltage using the discharge means; and an input of the AC voltage when the discharge means is non-conductive. If the AC voltage is interrupted, the electric charge storage means is discharged by conducting the discharge means with the voltage detecting means in response to the input of the AC voltage being cut off.

The power source of the present invention is a power source that converts and outputs an input AC voltage, a rectifier that rectifies the AC voltage, a converter that converts a voltage rectified by the rectifier, and the AC voltage is Charge storage means for reducing noise generated in the input line, voltage detection means for detecting whether or not the AC voltage is input, and discharge means for discharging the charge of the charge storage means And a zero cross detecting means for detecting a zero cross of the AC voltage using the discharging means, and when the AC voltage input is cut off while the discharging means is non-conductive, the AC voltage input is cut off. And a discharge circuit that discharges the charge of the charge accumulating means by causing the voltage detecting means to conduct the discharge means in response to sagging.

  As described above, according to the present invention, it is possible to reduce the power consumption during standby of the device, and to quickly discharge the charge remaining in the X capacitor when the plug is pulled out.

A circuit diagram showing a discharge circuit in Example 1 Timing chart of discharge circuit in embodiment 1 The circuit diagram which shows the discharge circuit in Example 2 The circuit diagram which shows the discharge circuit in Example 3 Timing chart of discharge circuit in embodiment 3 Block diagram showing the configuration of a conventional discharge circuit Block diagram showing the configuration of a conventional discharge circuit provided with a dedicated standby power supply The block diagram which shows the structure of the discharge circuit which provided the conventional commercial power supply voltage monitoring means Diagram showing application example of discharge circuit and power supply

  Hereinafter, specific configurations of the present invention for solving the above-described problems will be described based on the following examples. In addition, the Example shown below is an example, Comprising: It is not the meaning which limits the technical scope of this invention only to them.

Example 1
FIG. 1 shows a discharge circuit according to Embodiment 1 of the present invention. The discharge circuit according to the first embodiment includes a zero-cross detection circuit for zero-cross detection, and is a circuit that combines zero-cross detection and discharge. The discharge circuit of FIG. 1 includes a commercial AC power supply 101, an X capacitor 140, and filter circuits 104 and 105, and detects a plug being pulled out (an AC voltage input has been cut off). And a zero-cross detection unit 103 that includes discharge resistors 121 and 122 and detects the zero-cross of the AC voltage input from the commercial AC power supply 101. As described above, the X capacitor 104 is a charge storage unit for suppressing the influence of normal mode noise generated between the input lines of the AC voltage of the commercial AC power supply 101. Note that a power supply device including a rectification unit 108 configured by a diode bridge circuit and a converter 109 that converts a voltage rectified by the rectification unit 108 supplies electric power to the control unit 110. Further, plugs are connected to the contacts a and b, and an AC voltage is input from the commercial AC power supply 101.

  The rectifier 108 is connected to a diode bridge circuit composed of diodes 160, 161, 162, and 163. The AC voltage input by the diode bridge circuit is full-wave rectified and then smoothed by the smoothing capacitor 142. The In addition, the capacitor C164 is connected to the anode side of the smoothing capacitor 142, the capacitor C165 is connected to the cathode side, and the connection point between the capacitors C164 and C165 is grounded. The capacitors C164 and 165 are provided with a capacitor of about several thousand pF between the line of the commercial AC power supply and the ground (hereinafter referred to as GND) as a countermeasure against terminal noise. The capacitors C164 and C165 are commonly called “Y capacitors”. The Y capacitor of this embodiment is configured to be connected to the output terminal of the rectifying unit 108. The Y capacitor may be connected to the input side of the alternating current with respect to the rectifying unit 108, but the configuration of the present embodiment is more effective in preventing terminal noise.

  Next, the operation of the AC detection unit 102 will be described. Since the filter circuits 104 and 105 of the AC detection unit 102 perform the same operation according to the polarity of the AC voltage from the commercial AC power supply 101, the operation of the filter circuit 104 will be described (description of 105 is omitted).

  An AC voltage from the commercial AC voltage 101 is applied to both ends of the filter circuit 104 including the resistor 111 and the capacitor 112. If the time constant of the resistor 111 and the capacitor 112 is set sufficiently longer than the period of the AC voltage from the commercial AC power supply 101, the voltage at both ends of the capacitor 112 becomes sufficiently lower than the AC voltage. When the voltage value at both ends of the capacitor 112 is at a peak, the FET 171 is turned off by making the voltage lower than the threshold voltage for turning on the FET 171 which is the switch element of the zero cross detection unit 103. Accordingly, the resistor 111 is simply connected to both ends of the X capacitor 140. If the resistance value of the resistor 111 is sufficiently larger than the resistance value of the normal discharge resistor 121, the power consumption by the discharge resistor can be reduced as compared with the conventional case.

  On the other hand, when the plug is pulled out, it is necessary to set the voltage across the insertion blade (voltage based on the residual charge of the X capacitor) to a predetermined voltage or less within 1 second. At the moment when the plug is pulled out, the electric charge accumulated in the X capacitor 140 is present, and the voltage across the X capacitor 140 is attenuated according to the capacitance of the X capacitor 140 and the time constant of the resistor 111. As described above, since the resistance value of the resistor 111 is set larger than the resistance value of the normal discharge resistor 121, the voltage across the X capacitor 140 is substantially DC.

  On the other hand, the voltage across the capacitor 112 rises exponentially with time, and when the threshold voltage for turning on the FET 171 is exceeded, the discharge resistor 121 becomes conductive, and the residual charge in the X capacitor 140 is discharged. The resistance value of the resistor 111, the capacitance of the capacitor 112, and the resistance of the discharge resistor 121 are set so that the time until the FET 171 is turned on and the residual charge of the X capacitor 140 is discharged to a predetermined voltage or less by the discharge resistor 121 is within one second. The value relationship (constant) is set as described below.

  Next, the operation of the zero cross detection unit 103 will be described. The zero-cross detector 103 detects the zero-cross of the input AC voltage only when the switch element 145 in the normal operation state is made conductive, and the commercial power supply voltage is detected by the voltage at the connection point c (hereinafter referred to as the node c). Determine the zero-cross point. On the other hand, in the power saving state that is a standby state, the switch element 145 is turned off to reduce power consumption. The switch element 145 may be a semiconductor element such as an FET, or may be configured to stop one output of the multi-output converter.

  When the AC voltage from the commercial AC power supply 101 is lower at the contact b than the cathode of the smoothing capacitor 142, no current flows through the base of the transistor 139, so that the transistor 139 becomes non-conductive. Since the transistor 139 is non-conductive, the photocoupler 144 is turned on by the electric charge supplied from the converter 109, and the node c has a low voltage.

  At the same time, the FET 171 is turned on by supplying a voltage from the converter 109 to the FET 171 via the diode 113. The resistors 121 and 133 and the FET 171 are elements that operate normally even if the Y capacitors 164 and 165 are provided, and stably perform zero-cross detection even when the commercial AC power supply shows an abnormal waveform. When the potential of the contact a is higher than that of the contact b and the potential of GND is lower than the cathode of the smoothing capacitor 142, if the resistor 121 is not provided, the current flows to the Y capacitor except for the charging period of the smoothing capacitor 142. The current flows through resistor 122 and into the base of transistor 139. As a result of the current flowing through the base of the transistor 139, the transistor 139 becomes conductive, so that the zero cross point is erroneously detected. In order to prevent such erroneous detection, by providing the resistor 121, the current flowing through the Y capacitor can be flowed from the resistor 121, and the current generated when the Y capacitor is installed does not flow through the resistor 122, and is stable. Thus, the zero cross point can be detected.

  On the other hand, when the contact point b is higher than the cathode of the smoothing capacitor 142 in the voltage of the commercial AC power supply 101, the FET 172 is turned on by supplying a voltage from the converter 109 to the FET 172 that is a switching element via the diode 118. Further, when a current flows from the resistor 122 to the base of the transistor 139, the transistor 139 is turned on and the photocoupler 144 is turned off, so that the node c becomes a high voltage. The diode 138 is a protection diode for preventing backflow.

Next, the reduction in power consumption by the discharge circuit of this embodiment will be described with reference to the timing chart of FIG. First, in the operation state in which the zero cross point is detected, a current is passed through the discharge resistors 121 and 122 to stably detect the zero cross point. Thereafter, the state transits to a standby state at the timing of t _zero and the switch element 145 is turned off. This standby state is a state where it is not necessary to detect the zero cross point because the electronic device is not operating. By making the switch element 145 non-conductive, the discharge resistors 121 and 122 can be made non-conductive as described in the operation of the AC detection unit 102, so that power consumption can be reduced. t The plug is pulled out at _AC-OFF timing. After the plug is pulled out, the residual charge of the X capacitor 140 is discharged after waiting for the voltage rise of the capacitor 112 until the timing of t _det .

  Next, a method for discharging the residual charge of the X capacitor within 1 second will be described by taking as an example a case where the contact b is lower than the cathode of the smoothing capacitor 142 in the voltage from the commercial AC power supply 101.

The voltage across the capacitor 112 of the filter circuit 104 after the plug is pulled out is V _C1 (t) as a function of time t, the capacitance of the capacitor 112 is C ₁ , the resistance value of the resistor 111 is R ₁ , and the plug is pulled out. _Assuming that the voltage across the X capacitor 140 at the instant (t = t _AC−OFF = 0) is V _dc , V _c1 (t) is given by equation (1).

If the time until the FET 171 is turned on is t = t _det and the voltage at both ends of the capacitor 112 at this time is V _C1 (t _det ) = V _C1th , t _det is given by equation (2).

From this equation, it can be seen that t _det can be set by R ₁ , C ₁ , and V _C1th .
Further, the voltage across the X capacitor 140 after the FET 171 is turned on, that is, the voltage between the lines from the commercial AC power supply 101 is expressed as a function of time V _{CX (t)} , where the capacitance of the X capacitor is C _X and the discharge resistance 121 Assuming that the resistance value of R ₀ is R ₀ , it is approximately given by Equation 3.

However, Equation 2 is assumed to hold in the period from t = t _det until the FET 171 is turned off again.

Since V _{CX (t)} needs to be equal to or lower than the predetermined voltage V _reg within 1 second, R ₀ and t _det should be set so that V _{CX (1)} ≦ V _{reg under} any V _dc condition. That's fine.

  Thus, according to the present embodiment, the circuit for detecting the zero cross point can also be used as the discharge circuit.

  For example, when the AC voltage from the commercial power supply voltage 101 is 230 V AC, the capacitance of the X capacitor 140 is 1.0 μF, and the threshold voltage at which the FET 172 is turned on is 5 V, the resistance value of the resistor 111 is 20 MΩ and the capacitance of the capacitor 112 is 0.1 μF. The resistance value of the resistor 121 may be 960 kΩ or less. For example, when the capacitance of the X capacitor 140 is 1.0 μF, the resistance value of the discharge resistor 20 required to discharge below a predetermined voltage within 1 second is 1 MΩ, and the input AC voltage is AC 230V. The power consumption by the discharge resistor 20 is about 52.9 mW. On the other hand, in this embodiment, the power consumption of the resistors 111 and 116 when the capacitance of the X capacitor 140 is 1.0 μF, the resistance values of the resistors 111 and 116 are 20 MΩ, and the input AC voltage is 230 V AC is as follows: The total is about 5.3 mW. Therefore, the effect of reducing power consumption according to this embodiment is about 47.6 mW.

  As described above, according to this embodiment, it is possible to reduce the power consumption when the device is on standby, and to quickly discharge the charge remaining in the X capacitor when the plug is pulled out.

  Further, in this embodiment, it is detected that the plug is pulled out by an RC integration circuit (filter circuits 104 and 105) using resistors and capacitors, and the RC integration circuit functions as a filter. Compared to a configuration in which the zero-cross point is detected by narrowing the detection timing, the zero-cross point can be detected with high accuracy even with respect to external noise and frequency fluctuations of the input AC voltage.

(Example 2)
FIG. 3 shows a discharge circuit of the second embodiment. The description of the same parts as those of the discharge circuit of FIG. For each part of the overlapping circuit, the first digit of the three-digit code is changed from 1 to 2 (for example, the commercial AC power supply 101 is changed to 201), but the configuration is the same. This embodiment is different in that the configuration of the AC detection unit is changed according to the operation of the zero-cross detection circuit.

  In FIG. 3, the filter 204 of the AC detection unit 202 includes a circuit in which a resistor 214 and a transistor 213 as a switch element are connected in series, and is connected in parallel to the resistor 211. In the filter 205, a circuit in which a resistor 219 and a transistor 218 as a switch element are connected in series is connected in parallel to the resistor 216. In this embodiment, when the transistors 213 and 218 are non-conductive, the power consumption due to the discharge resistance can be reduced by turning off the FETs 271 and 272 as in the first embodiment.

  The operation of the zero cross detection circuit 203 in this embodiment is as described below. When the contact b is lower than the cathode of the smoothing capacitor 242 in the AC voltage from the commercial AC power supply 201, no current flows through the base of the transistor 239, so that the transistor 239 becomes non-conductive. Since the transistor 239 is non-conductive, the photocoupler 244 is turned on by the electric charge supplied from the converter 209, and the node c becomes a low voltage. On the other hand, when the contact b is higher than the cathode of the smoothing capacitor 242 in the AC voltage from the commercial AC power supply 201, the transistor 218 is turned on by passing a current from the converter 209 to the base of the transistor 218. The voltage of the capacitor 217 is increased by the resistor 219, and the FET 272 is turned on by setting the voltage higher than the threshold voltage for turning on the FET 272. Further, when a current flows from the resistor 222 to the base of the transistor 239, the transistor 239 is turned on and the photocoupler 244 is turned off, so that the node c becomes a high voltage.

  In this embodiment, the transistors 213 and 218 in the AC detection unit are turned on to change the configuration of the AC detection unit, thereby boosting the voltages of the capacitors 212 and 217 to drive the FETs 271 and 272 from the converter 209. It is also possible to suppress the current required for the operation.

  As described above, according to this embodiment, it is possible to reduce the power consumption during standby of the device and to quickly discharge the charge remaining in the X capacitor when the plug is pulled out.

  In the present embodiment as well, as in the first embodiment, the zero cross point can be detected with high accuracy even with respect to external noise and frequency fluctuations of the input AC voltage, as compared with the zero cross detection means disclosed in Patent Document 1 described above. be able to.

(Example 3)
FIG. 4 shows a discharge circuit of the third embodiment. The description of the same configurations as those in the first and second embodiments is omitted. In addition, about each part of the circuit which overlaps, although the top number of the code | symbol of 3 digits is changed into 1 => 3 (the commercial alternating current power supply 101 is changed into 301 as an example), the structure is the same. The present embodiment is different in that the detection result of the AC detection unit is output to the control unit, and the control unit discharges the charge of the X capacitor based on the output.

  In FIG. 4, the AC detection unit 302 outputs the voltage between the resistor 311 and the resistor 312 to the control unit 310 via the diode 313. The control unit 310 compares the threshold voltage set therein and the output obtained via the diode, and detects whether the threshold voltage is higher (High signal) or lower than the threshold voltage (Low signal). When the rising or falling of the High signal and the Low signal is not detected for a predetermined time or more, it is detected that the plug is pulled out, and the FET 372 that is a switch element is turned on to discharge the residual charge of the X capacitor 340.

  The controller 310 may be configured to turn on the FET 372 using a CPU, or may be configured to turn on the FET 372 with a control circuit (such as an ASIC) configured using a semiconductor element such as a transistor or FET.

  The zero cross point is detected by turning on the FET 372 to detect the zero cross point based on the voltage at the node c. When the commercial power supply voltage is in the vicinity of the zero cross point, a sufficient current cannot flow through the base of the transistor 339, so that the transistor 339 becomes non-conductive, the photocoupler 344 becomes conductive, and the node c becomes a low voltage. Outside the vicinity of the zero-cross point, when a sufficient current flows through the base of the transistor 339, the transistor 339 becomes conductive, the photocoupler 344 becomes non-conductive, and the node c becomes a high voltage.

Next, how power consumption is reduced will be described with reference to the timing chart of FIG.
In a normal operation state that requires zero-cross detection, the FET 372 is turned on, a current is passed through the discharge resistor 322, and the zero-cross point is detected. Thereafter, the state transits to a standby state at t _zero and the FET 372 is turned off. The standby state is a state that does not require detection of a zero cross point. Since the discharge resistor 322 can be made non-conductive by turning off the FET 372, power consumption can be reduced. After the plug is pulled out at t _AC-OFF , it is detected at t _det that there is no change in the cathode voltage of the diode 313, and the residual charge of the X capacitor 340 is discharged.

  According to this embodiment, it is possible to reduce the power consumption during standby of the device and to quickly discharge the charge remaining in the X capacitor when the plug is pulled out.

  In addition, according to the present embodiment, the residual charge of the X capacitor is discharged by outputting from the AC detection unit to the control unit 310, so that the resistor 311 does not depend on the threshold voltage for turning on the FET as the switch element. And the detection voltage between the resistor 312 can be set. Further, since the discharge can be started without depending on the variation in the threshold voltage at which the FET is turned on, it is possible to perform a stable discharge operation by reducing the variation in the timing of the discharge time.

(Application example of a power source provided with the discharge circuit of the present invention)
A power supply equipped with the above-described discharge circuit can be applied as a low-voltage power supply in an image forming apparatus such as a printer, a copying machine, a facsimile, or the like. The present invention can be applied as a power source for supplying power to a controller as a control unit in the image forming apparatus.

  FIG. 9A shows a schematic configuration of a laser beam printer which is an example of an image forming apparatus. The laser beam printer 200 includes a photosensitive drum 211 as an image carrier on which a latent image is formed as an image forming unit 210, and a developing unit 212 that develops the latent image formed on the photosensitive drum with toner. The toner image developed on the photosensitive drum 211 is transferred to a sheet (not shown) as a recording material supplied from the cassette 216, and the toner image transferred to the sheet is fixed by the fixing device 214 and discharged to the tray 215. . FIG. 9B shows a power supply line from a power source to a controller as a control unit of the image forming apparatus. A power source equipped with the above-described discharge circuit can be applied as a low-voltage power source that supplies power to the controller 300 having the CPU 310 that controls the image forming operation of the image forming apparatus, or the motors 312 and 313 as the drive unit. As illustrated in FIG. 9B, when there are a plurality of targets to which power is supplied, a DCDC converter 312 that converts the voltage from the switching power supply may be provided and supplied to the controller 300.

  In response to an instruction from the controller 300, the output voltage of the power supply is reduced and the image forming apparatus transitions to a standby state. In such a standby state, a power supply equipped with the above-described discharge circuit can reduce the power consumption in the standby state of the apparatus, and quickly discharge the charge remaining in the X capacitor when the plug is pulled out. be able to.

  Further, the detection result of the zero cross point in the above-described embodiment can be used for controlling the operation of the fixing unit of the image forming apparatus. Specifically, it can be used to control the current flowing through the fixing device 214. This current control is an operation for fixing the image on the recording material appropriately according to the type of the recording material, the environment in which the apparatus is placed, and the like. The apparatus to which the present invention is applied is not limited to such an image forming apparatus, and can be applied as a low-voltage power source for other electronic devices having an operating state and a standby state.

101 AC power supply 102 AC detection unit 103 Zero cross detection unit 104, 105 Filter circuit

Claims (10)

Charge storage means for reducing noise generated in a line to which an AC voltage is input;
Voltage detecting means for detecting whether or not the AC voltage is input;
A discharge means for discharging the charge of the charge storage means, and a zero cross detection means for detecting a zero cross of the AC voltage using the discharge means;
When the input of the AC voltage is cut off while the discharge unit is in a non-conductive state, the charge detecting unit is turned on by the voltage detection unit in response to the input of the AC voltage being cut off. A discharge circuit for discharging an electric charge of a storage means.   The voltage detection means includes filter means including a capacitor connected between lines to which the AC voltage is input, and the discharge means of the zero-cross detection means in response to a voltage across the capacitor exceeding a threshold voltage. The discharge circuit according to claim 1, wherein the discharge circuit is made conductive. The filter means further includes a switch connected in series with the capacitor,
3. The discharge circuit according to claim 2, wherein a voltage at both ends of the capacitor is controlled to exceed the threshold voltage by turning on the switch.   The voltage detection means has two resistors connected between lines to which the AC voltage is input, and makes the discharge means conductive based on a voltage between the two resistances. 2. The discharge circuit according to 1. In the power supply that converts and outputs the input AC voltage,
A rectifying unit for rectifying the AC voltage;
A converter that converts the voltage rectified by the rectifier;
Charge storage means for reducing noise generated in a line to which the AC voltage is input;
Voltage detecting means for detecting whether or not the AC voltage is input;
A discharge means for discharging the charge of the charge storage means, and a zero cross detection means for detecting a zero cross of the AC voltage using the discharge means;
When the input of the AC voltage is cut off while the discharge unit is in a non-conductive state, the charge detecting unit is turned on by the voltage detection unit in response to the input of the AC voltage being cut off. A power supply comprising a discharge circuit for discharging the charge of the storage means.   The voltage detection means includes filter means including a capacitor connected between lines to which the AC voltage is input, and the discharge means of the zero-cross detection means in response to a voltage across the capacitor exceeding a threshold voltage. The power supply according to claim 5, wherein the power supply is made conductive. The filter means further includes a switch connected in series with the capacitor,
The power supply according to claim 6, wherein a voltage across the capacitor is controlled so as to exceed the threshold voltage by turning on the switch.   The voltage detection means has two resistors connected between lines to which the AC voltage is input, and makes the discharge means conductive based on a voltage between the two resistances. 5. The power supply according to 5. An image forming apparatus comprising the power source according to any one of claims 5 to 8 and forming an image on a recording material.
An image forming apparatus comprising: an image forming unit; and a driving unit that is driven by a voltage supplied from the power source. The image forming unit includes a fixing device that fixes an image formed on the recording material to the recording material,
The image forming apparatus according to claim 9, wherein an operation of the fixing device is controlled based on a detection result of the zero-cross detection unit.

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