JP2006340429A - Apparatus equipped with switching regulator and micro controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption by performing control excellent in power conversion efficiency at low cost in two or more states such as, for example, an operating state, a waiting state, an energy saving mode state, etc. of an apparatuses. <P>SOLUTION: The voltage of a power source is divided with a resistor R6 and a resistor R7, and the obtained divided voltage, that is, the voltage of the A/D port of CPU110 is detected with the CPU110, and based on this detected voltage, the output of the feedback of the power source is controlled compulsively by the CPU110 thereby reducing the number of times of switching of the MOSFET Q1 of the power source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a device including a switching regulator and a microcontroller.

  As a technique for reducing power consumption during device standby, for example, a technique described in Patent Document 1 is known. According to this technique, the following control is performed depending on whether the printer is in a printing state or a non-printing state. That is, in an image forming apparatus including a first power supply unit that supplies power to a control unit that is used even during non-printing, and a second power supply unit that supplies power to a drive unit used during printing. The output voltage of the second power supply means can be switched and controlled, and the output voltage of the second power supply means is lowered in the non-printing state.

  Moreover, according to the technique described in Patent Document 2, the following control is performed when the device is stopped. In other words, when the device is inactive, the current of the optocoupler in the feedback unit of the power supply device is intermittently forcibly increased from the microcontroller to stop the operation of the power supply device intermittently, thereby increasing the oscillation frequency. This prevents a reduction in conversion efficiency of the power supply.

  This is a means for increasing the efficiency by reducing the switching loss of the switching element provided in the power supply device. When the equipment is not in operation, the loss is reduced by preventing the switching frequency of the switching element from decreasing or increasing, although the load on the power supply device is reduced.

JP 2002-19232 A JP 2003-284340 A JP 2004-153871 A

  Combining these individual means makes the circuit complex and not economical. For example, Patent Document 3 proposes means for lowering the output voltage of the power supply means and intermittently stopping the operation of the power supply apparatus when the device is stopped, but the circuit is complicated.

  Therefore, the present invention solves the above-described problems and is a device equipped with a switching regulator and a microcontroller, and the switching regulator can be made inexpensive in a load operating state, a standby state, a non-operating state, etc. An object of the present invention is to provide a device capable of controlling power supply conversion efficiently.

  According to a first aspect of the present invention, there is provided a transformer having a primary winding and a secondary winding that are insulated from each other, a switching element that switches a current flowing through the primary winding of the transformer, and a secondary winding of the transformer. Rectifying / smoothing means for rectifying and smoothing the output, a phototransistor having a phototransistor on the primary winding side of the transformer, a light emitting means connected to the secondary winding side, and a secondary winding side of the transformer A reference power supply, an error amplifier that compares the reference voltage with the secondary output voltage obtained by rectifying and smoothing of the rectifying and smoothing means and outputs an error signal, and the duty of the switching element are supplied via the photocoupler. A switching regulator having a duty control means for controlling based on the error signal, a load driven by a secondary output voltage of the switching regulator, A microcontroller driven by the voltage generated by the further voltage conversion means for the secondary output voltage of the switching regulator, the microcontroller monitoring the voltage value of the secondary output voltage of the switching regulator; and The microcontroller controls the operation of the load, and the microcontroller has a function in which the duty control means forcibly changes the error signal for setting the duty of the switching element to zero. The duty control means operates based on the error signal when the load state is in operation, and the secondary output voltage is a first desired voltage when the load state is not in operation. From this point on, the duty of the switching element becomes zero until the voltage drops below the second desired voltage. The error signal is forcibly changed such that the duty control means operates based on the error signal until it becomes equal to or higher than the first desired voltage after being lower than or equal to the second desired voltage. To do.

  Further, in claim 2, in addition to claim 1, there are a plurality of load states under the control of the microcontroller, and the microcontroller determines the first desired voltage and the first state according to the load state. The desired voltage of 2 is changed.

  According to a third aspect of the present invention, a transformer having a primary winding and a secondary winding insulated from each other, a switching element for switching a current flowing through the primary winding of the transformer, and a secondary winding of the transformer Rectifying / smoothing means for rectifying and smoothing the output of the output, a phototransistor having a phototransistor connected to the primary winding side of the transformer, a light emitting means connected to the secondary winding side, and a secondary winding side of the transformer. A reference power source, a secondary output voltage obtained by rectifying and smoothing by the rectifying and smoothing means, an error amplifier for comparing the reference voltage and outputting an error signal, and a duty of the switching element via the photocoupler. A switching regulator having duty control means for controlling based on the supplied error signal, and a load driven by a secondary output voltage of the switching regulator; And a microcontroller driven by the voltage generated by the voltage conversion means for converting the secondary output voltage of the switching regulator, the microcontroller monitoring the voltage value of the secondary output voltage of the switching regulator, And the microcontroller controls the operation of the load, and the microcontroller has a function in which the duty control means forcibly changes the error signal that makes the duty of the switching element zero. When the load state is in operation, the duty control means operates based on the error signal, and when the load state is not in operation, the microcontroller periodically cycles the duty control means to the error signal. Based on the operation period and the duty of the switching element is zero During periodically repeated, and the microcontroller, characterized in that the secondary output voltage to control the ratio of the period of the two to not less than the desired value.

  In addition to claim 3, in claim 4, there are a plurality of load states under the control of the microcontroller, and the microcontroller changes the desired voltage according to the load state. Features.

  According to a fifth aspect of the present invention, in addition to the first to fourth aspects, the microcontroller provides a low-pass filter in a means for monitoring the voltage value of the secondary output voltage of the switching regulator, and the low-pass filter is provided on the secondary side. The time constant for a change in which the output voltage increases is set to be larger than the time constant for a change in which the output voltage decreases.

  According to the present invention, since it is configured as described above, in a device including a switching regulator and a microcontroller, the switching regulator is inexpensive and has high power conversion efficiency in a load operating state, a standby state, a non-operating state, and the like. Can be controlled.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 101 denotes a rectifying / smoothing circuit, which converts an AC voltage input from a commercial power source AC into a DC voltage using rectifying diodes D1 to D4 and a smoothing capacitor C1.

  Reference numeral 102 denotes a switching regulator. Q1 is a MOSFET as a main switching element, T1 is an insulation transformer, and 103 is a control circuit for the MOSFET Q1. The control circuit 103 determines the length of the on-time of the MOSFET Q1 according to the transistor current of the phototransistor 1021. If the transistor current of the phototransistor 1021 is small, the on-time is long. When the transistor current of the phototransistor 1021 is large, the on-time is shortened. When the phototransistor 1021 exceeds a predetermined value, the on-time is not turned on. The off time is a period during which the stored energy of the insulating transformer T1 is released. The output of the insulation transformer T1 is rectified and smoothed by the diode D5 and the capacitor C2. The voltage across the capacitor C2 becomes the secondary output voltage V1 of the switching regulator 102. The present embodiment is an example of a flyback power supply, but is not particularly limited to this example.

  A feedback circuit 104 amplifies an error between the output voltage V1 of the switching regulator 102 and the input voltage of the Ref terminal of the shunt regulator IC1, and is configured via a photocoupler (configured by an LED 1041 and a phototransistor 1021). Feedback to the primary side. The secondary output voltage V1 is divided by the resistors R1 and R2 and input to the Ref terminal of the shunt regulator IC1. The shunt regulator IC1 compares the built-in reference voltage with the voltage at the Ref terminal and reflects it in the cathode voltage. A current determined by the difference voltage between the output voltage V1 of the switching regulator 102 and the cathode voltage of the shunt regulator IC1 and the resistor R3 flows through the LED 1041 as a diode current, and a current corresponding to the diode current is generated between the LED 1041 and the light. It flows through the coupled phototransistor 1021 (of the switching regulator 102). The cathode voltage of the shunt regulator IC1 operates so as to decrease when the voltage at the Ref terminal is higher than the built-in reference voltage and increase when it is lower. The capacitor C3 and the resistor R4 are provided for phase compensation.

  The output voltage V1 of the switching regulator 102 is controlled by the feedback circuit 104 to (R1 + R2) / R2 of the built-in reference voltage of the shunt regulator IC1.

  A step-down DC-DC converter 121 steps down the output voltage V1 of the switching regulator 102 to V2 that is the power supply voltage of the CPU 110.

  Reference numerals 105 and 106 denote loads of the switching regulator 102. The load 105 is a load that needs to be supplied with power only while the device is operating. For example, a paper conveyance motor in the case of a printer can be used. The load 106 is a load that requires power supply both when the device is in operation and in standby, and includes an operation panel, for example. Some devices do not require power supply to both the load 105 and the load 106 when the device enters the energy saving mode.

  The CPU 110 controls the device. Vcc is a drive power supply terminal, Gnd is a ground terminal, Po2 and Po3 are output ports, and controls the load 105 and the load 106. A / D is an analog-digital conversion port (hereinafter referred to as “A / D port”), and a voltage obtained by dividing the output voltage V1 of the switching regulator 102 by the resistor R6 and the resistor R7 is input. Po1 is an output port.

  When the output port Po1 of the CPU 110 is at a logic low level (hereinafter referred to as “L”), the transistor Q2 is off, and the feedback circuit 104 uses the output voltage of the switching regulator 102 as the internal reference voltage (R1 + R2) of the shunt regulator IC1. ) / R2. On the other hand, when the output port Po1 is at a logic high level (hereinafter referred to as “H”), the transistor Q2 is turned on and the cathode voltage of the shunt regulator IC1 becomes the ground voltage. As a result, the shunt regulator IC1 does not operate, but the diode current of the LED 1041 increases because it flows through the transistor Q2, and the transistor current of the phototransistor 1021 that is optically coupled to the LED 1041 increases. The current value of the transistor current is set to a value that prevents the control circuit 103 from turning on the MOSFET Q1.

  Next, operations in each state of the circuit of FIG. 1 will be described with reference to FIGS. 2 to 4 show, in order from the top, the state of the output port Po1 of the CPU 110, the gate voltage waveform of the MOSFET Q1, the drain voltage waveform, the drain current waveform, the voltage waveform of the output voltage V1 of the switching regulator 102, and the A of the CPU 110. The input voltage of / D port and the output current waveform of the switching regulator 102 are shown. 2 to 4 show a series of time-series movements. The following description will be made according to the illustrated state 1 to state 5.

  State 1: The device is in an operating state, and both the load 105 and the load 106 are operating. At this time, the switching regulator 102 is in the maximum output state. Depending on the diode current determined by the difference voltage between the output voltage V1 of the switching regulator 102 and the cathode voltage of the shunt regulator IC1 and the resistor R3, that is, the phototransistor 1021 that is optically coupled to the LED 1041 has a transistor current. Flows. The control circuit 103 controls the on-duty of the MOSFET Q1 according to the transistor current, and controls the output voltage V1 of the switching regulator 102.

  State 2: The device is in a standby state, and only the load 106 operates and the load 105 does not operate. Therefore, the output current of the switching regulator 102 is smaller than that in the state 1. By the action of the feedback circuit 104, the cathode voltage of the shunt regulator IC1 increases, the diode current of the LED 1041 decreases, and the transistor current of the phototransistor optically coupled to the LED 1041 decreases, so the on-time of the MOSFET Q1 is short. Become. Since the number of times of switching of the MOSFET Q1 is larger than that in the state 1, it is a period in which the loss increases.

  State 3: As with state 2, the device is in a standby state. The CPU 110 intermittently sets the output port Po1 to H. While the output port Po1 is H, the transistor Q2 is turned on, and the cathode voltage of the shunt regulator IC1 becomes the ground voltage. Then, the shunt regulator IC1 does not operate, but the diode current of the LED 1041 flows through the transistor Q2, and thus increases, and the transistor current of the phototransistor 1021 optically coupled to the LED 1041 increases. While the output port Po1 is H, the MOSFET Q1 is turned off, and the output voltage V1 is lowered by the load current of the load 106.

  On the other hand, the shunt regulator IC1 operates while the output port Po1 is L. When the output port Po1 shifts from H to L, the output voltage V1 is lower than the built-in reference voltage (R1 + R2) / R2, so that the diode current of the LED 1041 is smaller than that in the state 2 and is optically coupled to the LED 1041. The transistor current of the phototransistor is reduced. Therefore, the on-time of MOSFET Q1 is longer than in state 2.

  The CPU 110 monitors the voltage input to the A / D port, that is, the voltage obtained by dividing the output voltage V1 by the resistor R6 and the resistor R7. The CPU 110 increases the H duty of the output port Po1 until it falls below a predetermined value Vmin1 set by the program code. Vmin1 × (R6 + R7) / R7 must be set to a voltage at which the load 106 can operate sufficiently.

  State 4: As with state 2, the device is in a standby state. The H duty of the output port Po1 of the CPU 110 is larger than that in the state 3. A period during which the voltage of the A / D port of the CPU 110 falls below a predetermined value Vmin1 occurs. The CPU 110 maintains this state unless the state of the device changes. Compared to state 2, the number of switchings of MOSFET Q1 is greatly reduced, and switching regulator 102 is more efficient than state 2. Although not shown, when the CPU 110 transitions from this state to the operation state of the device, the CPU 110 fixes the output port Po1 to the L state and then transitions the device state.

  State 5: The device enters the energy saving mode, and the load 105 and the load 106 are not operating. In this state 5, the output of the switching regulator 102 supplies power only to the step-down DC-DC converter 121. The step-down DC-DC converter 121 can operate if the input voltage is Vmin2 × (R6 + R7) / R7 or higher in the figure, and the lower the input voltage, the better the efficiency. The CPU 110 sets the output port Po1 to H until the input voltage of the A / D port falls below Vmin2, and sets the output port Po1 to L until Vmin2 exceeds Vmax2.

  The number of switchings of the MOSFET Q1 is greatly reduced as compared with the state 4, and the efficiency of the step-down DC-DC converter 121 is also increased, so that the loss is extremely small.

  State 5 → State 1: This is a transition state when the device is shifted from the energy saving mode to the operating state. The CPU 110 maintains the output port Po1 in the L state in order to shift the device to the operating state. However, since the output voltage V1 is in the vicinity of Vmin2 and Vmax2, the load 105 and the load 106 cannot be operated immediately. The CPU 110 monitors the voltage at the A / D port, confirms that the voltage has exceeded Vmin1, operates the load 105 and the load 106, and shifts the device to the operating state.

  As described above, in the present embodiment, control can be performed so that the number of switchings of MOSFET Q1 does not increase according to the operating state of the device, and loss of switching regulator 102 can be suppressed.

  Note that the setting of the output port Po1 of the CPU 110 may be sequentially specified by a program code, or a frequency and a duty may be specified like PWM output.

  In this embodiment, the analog-digital conversion function is a built-in type of the CPU 110. However, another analog-digital circuit may be used and the output thereof may be input to the CPU 110.

<Second Embodiment>
FIG. 5 shows a second embodiment of the present invention. The present embodiment is different from the first embodiment in the configuration of a circuit connected to the A / D port of the CPU 110.

  That is, in the first embodiment, a voltage obtained by dividing the secondary output voltage V1 by the resistors R6 and R7 is input to the A / D port of the CPU 110. Further, the conversion speed of the analog-digital conversion function in the CPU 110 is required to be high, and when the switching frequency of the switching regulator is generally several tens of kHz, a conversion cycle of at least several tens of kHz is necessary. .

On the other hand, in the present embodiment, a resistor R8, a diode D6, and a capacitor C4 form a filter circuit having different charge / discharge time constants.
A voltage obtained by dividing the voltage between the capacitors C4 by the resistor R9 and the resistor R10 is input.

  The operation of each state of the circuit will be described with reference to FIGS. Each of the waveforms in FIGS. 6 to 8 is the same waveform as in FIGS.

  State 1 to State 3: Same as in the first embodiment. The input voltage of the A / D port of the CPU 110 has a waveform biased toward the low voltage side of the secondary output voltage V1 due to the influence of the filter circuit.

  State 4: Same as in the first embodiment. Since the input voltage of the A / D port of the CPU 110 is biased toward the low voltage side of the secondary side output voltage V1 due to the influence of the filter circuit, the period of time below Vmin1 is long. Therefore, the CPU 110 can detect that the A / D port of the CPU 110 is below Vmin1 at the latest.

  State 5: The state of the device is the same as in the first embodiment. The input voltage of the A / D port of the CPU 110 is biased toward the low voltage side of the secondary output voltage V1 due to the influence of this filter circuit. Therefore, Vmin2 can be detected, but the voltage corresponding to Vmax2 in the first embodiment cannot be detected. The CPU 110 controls the voltage at which the input voltage of the A / D port of the CPU 110 is reduced to Vmin2 by adjusting the H period by setting the L period of the output port Po1 to a predetermined time.

  State 5 → State 1: The state of the device is the same as in the first embodiment. The CPU 110 maintains the output port Po1 in the L state in order to shift the device to the operating state. However, since the secondary output voltage V1 is in the vicinity of Vmin2 and Vmax2, the load 105 and the load 106 cannot be operated immediately.

  In addition, the input voltage of the A / D port of the CPU 110 does not easily increase due to the influence of the filter circuit.

  Therefore, when the input voltage of the A / D port of the CPU 110 is monitored and the state 5 is shifted to the state 1, it takes more time in the present embodiment than in the first embodiment. In order to shorten the time, the completion of the state transition can be performed at a predetermined time regardless of the input voltage of the A / D port of the CPU 110.

1 is a circuit diagram showing a circuit according to a first embodiment of the present invention. FIG. 2 is an operation waveform diagram of the circuit of FIG. 1. FIG. 2 is an operation waveform diagram of the circuit of FIG. 1. FIG. 2 is an operation waveform diagram of the circuit of FIG. 1. It is a circuit diagram which shows the circuit which concerns on the 2nd Embodiment of this invention. FIG. 6 is an operation waveform diagram of the circuit of FIG. 5. FIG. 6 is an operation waveform diagram of the circuit of FIG. 5. FIG. 6 is an operation waveform diagram of the circuit of FIG. 5.

Explanation of symbols

101 Smoothing rectifier circuit 102 Switching regulator 103 Control circuit 104 Feedback circuit 105, 106 Load 110 CPU
121 DC-DC converter 1021 Phototransistor 1041 LED
Q1 MOSFET
T1 transformer IC1 shunt regulator

Claims (5)

A transformer having a primary winding and a secondary winding insulated from each other;
A switching element for switching a current flowing through the primary winding of the transformer;
Rectifying and smoothing means for rectifying and smoothing the output of the secondary winding of the transformer;
A phototransistor having a phototransistor on the primary winding side of the transformer and a light emitting means connected to the secondary winding side;
A reference power source disposed on the secondary winding side of the transformer;
An error amplifier that compares the secondary output voltage obtained by the rectifying and smoothing of the rectifying and smoothing means with the reference voltage and outputs an error signal;
A switching regulator having duty control means for controlling the duty of the switching element based on the error signal supplied through the photocoupler;
A load driven by the secondary output voltage of the switching regulator;
A microcontroller that drives the secondary output voltage of the switching regulator by a voltage generated by a further voltage conversion means;
The microcontroller monitors the voltage value of the secondary output voltage of the switching regulator;
And the microcontroller controls the operation of the load;
Further, the microcontroller has a function in which the duty control means forcibly changes the error signal that makes the duty of the switching element zero,
The microcontroller operates based on the error signal when the load condition is in operation,
When the load state is not operating, the microcontroller sets the duty of the switching element to zero until the secondary output voltage becomes equal to or higher than the first desired voltage and then becomes equal to or lower than the second desired voltage. The error signal is forcibly changed so that the duty control means operates based on the error signal until it becomes equal to or higher than the first desired voltage after being lower than or equal to the second desired voltage. Equipment with switching regulator and microcontroller. In claim 1, there are a plurality of load states under the control of the microcontroller,
An apparatus comprising a switching regulator and a microcontroller, wherein the microcontroller changes the first desired voltage and the second desired voltage in accordance with a load state. A transformer having a primary winding and a secondary winding insulated from each other;
A switching element for switching a current flowing through the primary winding of the transformer;
Rectifying and smoothing means for rectifying and smoothing the output of the secondary winding of the transformer;
A phototransistor having a phototransistor on the primary winding side of the transformer and a light emitting means connected to the secondary winding side;
A reference power source disposed on the secondary winding side of the transformer;
An error amplifier that compares the secondary output voltage obtained by the rectifying and smoothing of the rectifying and smoothing means with the reference voltage and outputs an error signal;
A switching regulator having duty control means for controlling the duty of the switching element based on the error signal supplied through the photocoupler;
A load driven by the secondary output voltage of the switching regulator;
A microcontroller that drives the secondary output voltage of the switching regulator by a voltage generated by a further voltage conversion means;
The microcontroller monitors the voltage value of the secondary output voltage of the switching regulator;
And the microcontroller controls the operation of the load;
Further, the microcontroller has a function in which the duty control means forcibly changes the error signal that makes the duty of the switching element zero,
The microcontroller operates based on the error signal when the load condition is in operation,
When the load is not operating, the microcontroller periodically repeats a period in which the duty control means operates based on the error signal and a period in which the duty of the switching element is zero, and the A device comprising a switching regulator and a microcontroller, wherein the microcontroller controls the ratio of both periods so that the secondary output voltage does not fall below a desired value. In claim 3, there are a plurality of load states under the control of the microcontroller,
A device comprising a switching regulator and a microcontroller, wherein the microcontroller changes the desired voltage in accordance with a load state. In any of claims 1 to 4,
The microcontroller is provided with a low-pass filter in the means for monitoring the voltage value of the secondary output voltage of the switching regulator,
An apparatus comprising a switching regulator and a microcontroller, wherein the low-pass filter is set to be larger than a time constant for a change in which the time constant for a change in which the secondary output voltage increases.

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