JP2011139569A - Rectifying smoothing circuit and electronic apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rectifying smoothing circuit which uses an element used for a 100 V power supply, can commonly be used in a 100 V area and a 200 V area, and dispenses with the exchange of a circuit caused by a voltage, and an electronic apparatus using the rectifying smoothing circuit. <P>SOLUTION: In order to solve the problem, there are provided: a commercial AC power supply AC; a diode bridge which rectifies commercial AC power into a direct current; a voltage comparison means which is arranged at the rectifying smoothing circuit having a smoothing capacitor C1 which smoothes a DC voltage of the diode bridge in parallel with the smoothing capacitor between the output end of the diode bridge and the smoothing capacitor, and compares a voltage of the output end of the diode bridge and a reference voltage; and a power supply control means which is arranged at the smoothing capacitor in series thereto between the output end of the diode bridge and the smoothing capacitor, and controls the connection state of a current supply passage between the output end of the diode bridge and the smoothing capacitor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rectifying / smoothing circuit that converts commercial AC power into DC and an electronic device using the same.

  Commercial AC power supplies are broadly classified into regions that employ AC 100V to 127V (hereinafter referred to as “100V region”) and regions that use AC 220V to 240V (hereinafter referred to as “200V region”).

  Many electronic devices are provided with a rectifying / smoothing circuit and a voltage conversion circuit for converting a commercial AC power source into DC in order to generate DC used for operation and control of the device.

However, since the voltage of the commercial AC power supply varies depending on the country or region, the following three methods are used for DC generation in electronic devices.
Method 1) Electronic devices having different rectifying / smoothing circuits and voltage conversion circuits are provided for the 100V region and the 200V region, respectively.
Method 2) An electronic device including a rectifying / smoothing circuit that can be switched between a 100V region and a 200V region is provided.
Method 3) An electronic device including a rectifying / smoothing circuit and a voltage conversion circuit common to the 100V region and the 200V region is provided.

  In general, regardless of whether the electronic device is used in a 100V region or a 200V region, the power required in the electronic device is the same. Therefore, in the case of the method 1, the elements used in the rectifying / smoothing circuit and the voltage conversion circuit of the electronic device for the 100V region and the 200V region generally have the following specification differences. That is, with respect to the withstand voltage of the device, the device for the 100V region is about half that for the 200V region, and the allowable current of the device is about twice that for the 200V region. .

  In the case of Method 2, for example, as shown in Patent Document 1, two smoothing capacitors constituting a rectifying and smoothing circuit are provided, and for 200 V region, full-wave rectification is used, and the capacitors are used in series as they are, and for 100 V region. The switch is used for voltage doubler rectification using a switch.

  In the case of the method 3, it is common to use an element whose withstand voltage is adapted for a 200V region and whose allowable current is adapted for a 100V region.

Japanese Patent Laid-Open No. 11-113258

  However, the methods 1 to 3 have the following problems.

  For example, in the case of the method 1, if an electronic device for a 100V region is mistakenly used in a 200V region, an element in the electronic device is destroyed due to overvoltage resistance, resulting in a failure of the device.

  On the other hand, in the case of the method 2, a function of switching circuits depending on the area where the electronic device is used is necessary. Furthermore, since two capacitors are required, it becomes expensive, and it takes time and effort to switch depending on the voltage in the area where it is used.

  Moreover, since the withstand voltage is adjusted for the 200V region and the allowable current is adjusted for the 100V region, the device used in Method 3 is larger and more expensive than the device adapted to one of the voltages. become. In particular, the smoothing capacitor used in the rectifying and smoothing circuit has a large effect on the price and size because its withstand voltage and allowable current directly affect the volume of the capacitor itself.

  The present invention has been made in view of the above situation, and a rectifying / smoothing circuit that can be used in common in the 100V region and the 200V region, does not require circuit switching by voltage, and can reduce the size of the smoothing capacitor, and uses the same. The purpose is to provide electronic devices.

  In order to solve the above problems, in the present invention, a rectifying / smoothing circuit is configured as described in (1) below, and an electronic device using the rectifying / smoothing circuit is configured as described in (2) below.

(1) A commercial AC power supply, a diode bridge connected to the commercial AC power supply and rectifying an AC voltage from the commercial AC power supply into a DC voltage, and a DC connected in series to the diode bridge and output from the diode bridge In a rectifying / smoothing circuit including a capacitor for smoothing voltage,
Between the output terminal of the diode bridge and the capacitor, connected in parallel with the capacitor, voltage comparison means for comparing the voltage of the output terminal of the diode bridge with a reference voltage, the output terminal of the diode bridge, and the A rectifying / smoothing circuit comprising a current supply control unit that is connected in series with the capacitor and controls a connection state of a current supply path between the output terminal of the diode bridge and the capacitor.

  (2) The electronic device including the rectifying / smoothing circuit according to (1), further including a control unit that controls the electronic device, wherein the voltage comparison unit is configured to obtain a voltage between the output voltage of the diode bridge and the reference voltage. An electronic device having notification means for notifying the control means of the comparison result, wherein the control means stops the operation of the device when the voltage at the output terminal of the diode bridge is higher than the reference voltage.

  According to the present invention, there is no need to switch circuits by voltage, a rectifying / smoothing circuit that can be used commonly in the 100V region and 200V region, and the size of the smoothing capacitor can be reduced by using an element used for a 100V power supply, and the same are used. Can be provided.

Rectification smoothing circuit diagram of Example 1 Waveform diagram when AC100V is input in the circuit of FIG. Waveform diagram when AC200V is input in the circuit of FIG. Rectification smoothing circuit diagram of Example 2 Circuit diagram of electronic device including rectifying / smoothing circuit of embodiment 3

  Hereinafter, the form for implementing this invention is demonstrated in detail by an Example.

  FIG. 1 shows a circuit diagram of the rectifying / smoothing circuit of this embodiment.

  In FIG. 1, AC is a commercial AC power source. D1, D2, D3, and D4 are rectifier diodes that are connected to the commercial AC power source AC and rectify the AC voltage from the input commercial AC power source to generate a DC voltage, and constitute a diode bridge.

  C1 is a smoothing capacitor, which is connected in series between the output ends of the diode bridge.

  ZD1 is a Zener diode, Q2 is a transistor (second switching element), R1 and R2 are resistors that bias the transistor Q2, and are connected in parallel to C1 between the output terminal of the diode bridge and the smoothing capacitor C1. ing. Q1 is an N channel MOS type field effect transistor (FET), which is a switching element (first switching element) inserted in series between the diode bridge and the smoothing capacitor C1. R3 and R4 are resistors that bias the gate of the field effect transistor Q1.

  When the voltage between the output terminals of the diode bridge becomes higher than the Zener voltage of the Zener diode ZD1, a current flows through the Zener diode ZD1, resistors R1 and R2, and as a result, the transistor Q2 is turned on. Conversely, when the voltage between the output terminals of the diode bridge is lower than the Zener voltage of the Zener diode ZD1, no current flows through the Zener diode ZD1 and the resistors R1 and R2, and the transistor Q2 is turned off. Therefore, the Zener diode ZD1, the transistor Q2, and the resistors R1 and R2 constitute voltage comparison means that compares the voltage applied to the two output terminals of the diode bridge with the Zener voltage of the Zener diode that is the reference voltage.

  The field effect transistor Q1 is connected in series to a current supply path constituted by one end and the other end of the output end of the diode bridge via the smoothing capacitor C1. When the transistor Q2 is in an off state, the voltage between the output terminals of the diode bridge is divided by resistors R3 and R4 and applied to the gate of the field effect transistor Q1. Thereby, Q1 is turned on, and the current supply path between the output terminal of the diode bridge and the smoothing capacitor C1 is connected.

  However, when the transistor Q2 is on, the current flowing through the resistor R3 flows to the transistor Q2 side, so that no voltage is applied to the gate of the field effect transistor Q1. As a result, Q1 is turned off, and the current supply path between the output terminal of the diode bridge and the smoothing capacitor C1 is disconnected. Therefore, the field effect transistor Q1 determines whether the current supply path is connected (connected or disconnected) based on the comparison result between the voltage across the output terminal of the diode bridge and the Zener voltage of the Zener diode ZD1 that is the reference voltage. Current supply control means for controlling.

  In FIG. 1, the withstand voltage of the smoothing capacitor C1 is 200V. This is a withstand voltage of a capacitor generally used for an electronic device for a 100V region. For this reason, it is desirable to set the Zener voltage of the Zener diode ZD1 to 200V.

  Next, the operation waveforms of the circuit in FIG. 1 when AC 100 V is applied and when AC 200 V is applied as the commercial AC power supply AC will be described.

  First, FIG. 2 shows operation waveforms when AC 100 V is applied as the commercial AC power supply AC.

  2A is an input voltage waveform of AC 100V, FIG. 2B is a voltage waveform of the gate of the field effect transistor Q1, FIG. 2C is a drain inflow current waveform of Q1, and FIG. 2D is a smoothing capacitor C1. It is a both-ends voltage waveform.

  In the case of AC100V, the maximum voltage applied to the Zener diode ZD1 is 141V. Since the Zener voltage of the Zener diode ZD1 is 200V, the voltage applied to the Zener diode does not exceed 200V, and the transistor Q2 is always off. Therefore, as shown in FIG. 2B, a voltage obtained by dividing the output voltage of the diode bridge by the resistors R3 and R4 is always applied to the gate of the field effect transistor Q1, and Q1 is always other than near the zero cross of AC100V. Turns on. As a result, the drain inflow current of Q1 has a waveform as shown in FIG. 2C, which is a normal capacitor input type current waveform. As shown in FIG. 2D, the voltage across the smoothing capacitor C1 becomes a direct current having ripple with the maximum voltage 141V of AC100V as the upper limit.

  On the other hand, FIG. 3 shows operation waveforms when AC 200 V is applied as the commercial AC power supply AC.

  3A is a voltage waveform of AC 200V, FIG. 3B is a voltage waveform of the gate of the field effect transistor Q1, FIG. 3C is a drain inflow current waveform of Q1, and FIG. 3D is a smoothing capacitor C1. It is a voltage waveform at both ends.

  In the case of AC200V, the maximum value of the output voltage of the diode bridge is 282V. Accordingly, when the Zener diode ZD1 exceeds the Zener voltage of 200V, the Zener diode ZD1 is turned on, the voltage divided by the resistors R1 and R2 is applied to the base of the transistor Q2, and the transistor Q2 is turned on. As a result, the gate voltage waveform of the field effect transistor Q1 is as shown in FIG. In this case, since the gate voltage of Q1 is lowered, Q1 is turned off. Therefore, the field effect transistor Q1 is turned off when the input AC 200V is in the vicinity of the zero cross and while the output of the diode bridge exceeds 200V. Therefore, as shown in FIG. 3C, the drain inflow current of Q1 flows immediately before the zener diode ZD1 is turned on and immediately after it is turned off. Then, as shown in FIG. 3D, the voltage across the smoothing capacitor C1 becomes a DC voltage having a ripple whose maximum value is the Zener voltage 200V of the Zener diode ZD1.

  Therefore, the maximum voltage applied to the smoothing capacitor C1 depends on the Zener voltage of the Zener diode ZD1. Accordingly, by appropriately selecting the Zener voltage of the Zener diode ZD1, even if AC 200V is applied, an excessive voltage exceeding 200V is not applied to the smoothing capacitor C1, and the element is not destroyed.

  As described above, by using the rectifying / smoothing circuit of the present invention, it is possible to use a capacitor with a withstand voltage of 200 V, which is originally used for an electronic device for 100 V region, regardless of whether it is AC 100 V or AC 200 V. Usually, a switching power supply is provided at the subsequent stage of the rectifying / smoothing circuit, and the voltage is stepped down to a constant voltage necessary for a device equipped with the rectifying / smoothing circuit. In the design of the switching power supply, by designing the input voltage as DC200V, it is possible to realize a device that can use either AC100V or AC200V without a switching function by the input voltage even when a 200V withstand voltage capacitor is used.

  FIG. 4 shows a circuit diagram of the rectifying / smoothing circuit of this embodiment.

  In FIG. 4, the same symbols as those in FIG. 1 have the same functions. The difference from FIG. 1 is that a circuit for biasing the gate of the field effect transistor Q1 is composed of resistors R53, R54, and R55.

  In the case of the first embodiment, when the field effect transistor Q1 is in the OFF state, the charge of the smoothing capacitor C1 is discharged through the body diode that is a built-in diode between the source and drain of Q1 and the resistors R3 and R4. Therefore, an increase in power consumption of the electronic device including the rectifying / smoothing circuit according to the first embodiment is caused.

  Therefore, in this embodiment, by taking the gate bias of the field effect transistor Q1 not from the output end of the diode bridge but from the input end side, it is possible to prevent useless discharge of the smoothing capacitor C1 when Q1 is OFF. it can.

  FIG. 5 shows a circuit diagram of an electronic device including the rectifying / smoothing circuit of this embodiment.

  The electronic device in FIG. 5 is a device that controls the temperature of the heater using a microcontroller. An example of such an apparatus is an image recording apparatus provided with a heat fixing device. The electronic device illustrated in FIG. 5 is a device having an input voltage of AC 100V.

  In FIG. 5, 101 is a rectifying / smoothing circuit to which the present invention is applied, 102 is an insulating flyback switching power supply, and 103 is a heater and a heater control circuit.

  In the rectifying and smoothing circuit 101, the light emitting diode side of the photocoupler PC1 is added in series with the Zener diode ZD1 of the circuit of FIG. Similar to the first embodiment, the Zener voltage of the Zener diode ZD1 is set to 200V.

  If the voltage of the commercial AC power supply AC is 100 V AC, no current flows through the Zener diode ZD1, and the light emitting diode of the PC 1 is not lit. If the commercial AC power supply AC is 200V AC, the Zener diode ZD1 is turned on when the input voltage exceeds the Zener voltage of 200V, and the light emitting diode of the PC1 is turned on. The light emitting diode is turned off. As a result, the light-emitting diode is turned on every half cycle of the commercial AC power supply, and thus blinks repeatedly at a cycle twice the AC power supply frequency.

  Reference numeral 102 denotes a general insulated flyback switching power supply that steps down the output voltage of the rectifying and smoothing circuit 101 to a desired constant voltage.

  The CPU in FIG. 5 is a microcontroller that controls the electronic apparatus. Po1 is an input terminal, Po2 is an input terminal to which an analog-to-digital conversion function is added, and Po3 is an output terminal.

  Reference numeral 103 denotes a heater and a heater control circuit. H1 is a heat generating heater and TH1 is a thermistor. The heat generating heater H1 and the thermistor TH1 are thermally coupled. The thermistor TH1 is a resistor that exhibits a very large change in resistance value with respect to a change in temperature. The resistance value change of the thermistor TH1 is converted into a voltage change by the pull-up resistor R13 and inputted to the input terminal Po2 of the CPU, and the CPU monitors the temperature of the heat generating heater H1. Then, the CPU performs output control of the output terminal Po3 so that the temperature of the heat generating heater H1 becomes a desired temperature, performs ON / OFF control of the triac Q4 via the phototriac coupler PC3, and supplies power to the heat generating heater H1. Control.

  The phototransistor side of the photocoupler PC1 is pulled up by the resistor R5, and a signal transmitted from the light emitting diode side is input to the input terminal Po1 of the CPU. As described above, when the voltage of the commercial AC power supply AC is 100V AC, a high signal is always input to the input terminal Po1, and when the voltage is 200V AC, a pulse signal having a cycle twice the frequency of the commercial AC power supply is input. The Since the comparison result between the voltage between the output terminals of the diode bridge and the Zener voltage that is the reference voltage is notified via the input terminal Po1, the CPU monitors the terminal state of the input terminal Po1 so that the commercial AC power supply is AC100V. Or AC200V.

  Note that the signal input to the input terminal Po1 may contain noise. Therefore, in order to distinguish between noise and a normal pulse signal, the CPU measures the period of the signal at the input terminal Po1, and confirms that the frequency is twice the frequency of the commercial AC power supply, thereby AC200V. Is determined to have been entered.

  With the above configuration, the CPU can normally operate the device when the commercial AC power supply is AC100V, and can stop the operation of the device when AC200V, and stop the energization of the heater. Normally, the heater is composed of a resistor, and the current is doubled and the amount of heat generated is four times when AC200V is input compared to when AC100V is input. For this reason, when the current rating becomes unacceptable when AC200V is input or when temperature control becomes difficult, it is important for safety to stop energizing the heater.

  By providing the electronic device with the rectifying / smoothing circuit of the present invention, it is possible to prevent damage to the device even if AC200V is accidentally applied to the device for AC100V.

  In addition, for the convenience of the user, when AC200V is accidentally applied and the electronic apparatus is in an operation stop state, the user can be notified as necessary. For example, the LED 1 in FIG. 5 is a display element for that purpose, and not only the LED but also a liquid crystal display element or the like may be used as the display element.

AC commercial AC power supply C1 smoothing capacitor D1, D2, D3, D4 rectifier diode Q1 field effect transistor Q2 transistor ZD1 Zener diode

Claims (6)

Commercial AC power supply,
A diode bridge connected to the commercial AC power source and rectifying an AC voltage from the commercial AC power source into a DC voltage;
In a rectifying and smoothing circuit including a capacitor connected in series to the diode bridge and smoothing a DC voltage output from the diode bridge,
A voltage comparing means connected in parallel with the capacitor between the output end of the diode bridge and the capacitor, and compares the voltage at the output end of the diode bridge with a reference voltage;
Current supply control means connected in series with the capacitor between the output end of the diode bridge and the capacitor, and controlling a connection state of a current supply path between the output end of the diode bridge and the capacitor; A rectifying and smoothing circuit characterized by:   The current supply control means is turned on to connect a current supply path between the output end of the diode bridge and the capacitor when the voltage at the output end of the diode bridge is lower than the reference voltage. 2. The first switching element that is turned off to cut off a current supply path between the output terminal of the diode bridge and the capacitor when the voltage at the output terminal is higher than the reference voltage. The rectifying / smoothing circuit described. The voltage comparison means includes a Zener diode and a second switching element,
The voltage at the output terminal of the diode bridge is compared with the Zener voltage of the Zener diode that is the reference voltage. When the voltage at the output terminal of the diode bridge is lower than the reference voltage, the first switching element is turned on. The rectifying / smoothing circuit according to claim 2, further comprising: the second switching element that turns off the first switching element when a voltage at an output terminal of the diode bridge is higher than the reference voltage. In the electronic device provided with the rectification smoothing circuit according to any one of claims 1 to 3,
A control means for controlling the electronic device;
The voltage comparison means has a notification means for notifying the control means of the comparison result between the voltage at the output terminal of the diode bridge and the reference voltage;
The control device stops the operation of the device when the voltage at the output terminal of the diode bridge is higher than the reference voltage.   The electronic device according to claim 4, further comprising a notifying unit that notifies that the electronic device is in an operation stop state when a voltage at an output terminal of the diode bridge is higher than the reference voltage.   The electronic device according to claim 5, wherein the notification unit is an LED or a liquid crystal display element provided in the electronic device.

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