JP2005253261A - Power supply system and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simultaneously achieve a high withstand voltage and a small voltage drop by devising a circuit configuration to realize low loss/high efficiency of a power supply system. <P>SOLUTION: A silicon diode 5 having a high withstand voltage as electric performance and a Schottky diode 6 having a small voltage drop and a small power loss are combined to reduce power loss with the silicon diode 5 which suffers from a big power loss, when the voltage applied to the diodes 5, 6 is in a forward direction. While a relay contact point 8 is controlled opening and closing with a control element 9 corresponding to the magnitude of a fuel battery 1 and a constant voltage power supply 3 so as not to apply a reverse direction voltage to the Schottky diode 6, when the voltage applied to the diodes 5, 6 is in a reverse direction. Thereby, the high withstand voltage and the small voltage drop regarding a rectifying element are simultaneously achieved to realize the low loss/high efficiency of the power supply system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power supply system using a fuel cell or the like and an electronic apparatus such as a copying machine including the power supply system.

  Patent Document 1 discloses a fuel power generation apparatus using a fuel cell. In addition to the fuel cell, there is a proposal example related to an image forming apparatus using a power generation device including a secondary battery and a charging device (see, for example, Patent Document 2).

JP-A-8-50902 Japanese Patent No. 3310767

  Since the output voltage of the fuel cell is unstable, the voltage is generally stabilized by a constant voltage power supply and then supplied to the load. A large-capacity capacitor for absorbing fluctuations in the input voltage is connected in parallel to the input terminal of the constant voltage power supply.

  Here, the fuel cell is a power source that takes out the energy when water is produced by chemically reacting hydrogen and oxygen in the form of electric power, and conversely, when current is supplied to the fuel cell, hydrogen is electrolyzed to produce hydrogen. In addition to the generation of oxygen, the characteristics of the fuel cell are deteriorated. Therefore, it is necessary to prevent the reverse current from the capacitor on the input side of the constant voltage power source by a rectifying element, for example, a diode. That is, if the fuel cell cannot catch up with the fuel cell due to some trouble, the voltage of the capacitor of the constant voltage power supply becomes higher than the generated voltage, and the current flows into the fuel cell. A diode is inserted to prevent this.

  However, there is no diode that can achieve both high withstand voltage and low voltage drop, and silicon diodes with high withstand voltage of 1000V or higher have a forward voltage drop of about 1V, and the power loss is about twice that of Schottky diodes. End up. A Schottky diode with a forward voltage drop as small as about 0.5 V has little power loss, but has a withstand voltage of up to about 100 V, and cannot be used in a place with a very high voltage.

  For this reason, a diode with a low voltage drop cannot be used in a power supply system with a high voltage. For example, when a silicon diode having a high withstand voltage is used, a loss of 10 A × 1 V = 10 W was large when a current of 10 A was passed.

  An object of the present invention is to achieve both a high withstand voltage and a low voltage drop by devising a circuit configuration, and to achieve low loss and high efficiency of a power supply system.

  The power supply system according to claim 1 is a power supply system in which a constant voltage power source is connected to an output side of a battery or a power generator, and is connected in the same rectification direction between the battery or the power generator and the constant voltage power source. A plurality of rectifying elements having different electrical capabilities.

  According to a second aspect of the present invention, there is provided a power supply system in which a constant voltage power source is connected to the output side of the fuel cell, the electric power system connected in the same rectification direction between the fuel cell and the constant voltage power source. A plurality of different rectifying elements are provided.

  According to a third aspect of the present invention, in the power supply system according to the first or second aspect, one of the plurality of rectifying elements is a rectifying element having an electrical capability with a lower voltage drop than the other rectifying elements.

  According to a fourth aspect of the present invention, in the power supply system according to the third aspect, the rectifying element having an electrical capability with a lower voltage drop than other rectifying elements is a Schottky diode.

  According to a fifth aspect of the present invention, there is provided a power supply system in which a constant voltage power source is connected to the output side of the fuel cell, the first rectifier element and the switch connected between the fuel cell and the constant voltage power source. And a second rectifier element connected in series to the parallel circuit and having an electrical capability with a voltage drop lower than that of the first rectifier element.

  According to a sixth aspect of the present invention, there is provided a power supply system in which a constant voltage power source is connected to the output side of the fuel cell, the first rectifier element and the switch connected between the fuel cell and the constant voltage power source. And a second rectifying element connected in series to the switch in the parallel circuit and having an electrical capability with a voltage drop lower than that of the first rectifying element.

  According to a seventh aspect of the present invention, in the power supply system according to the fifth or sixth aspect, the control element that turns on the switch when the input terminal voltage of the constant voltage power supply becomes smaller than a certain value from the output voltage of the fuel cell. Is provided.

  According to an eighth aspect of the present invention, in the power supply system according to any one of the fifth to seventh aspects, the switch is turned on when the input terminal voltage of the constant voltage power source becomes larger than a certain value than the output voltage of the fuel cell. A control element to be turned off is provided.

  According to a ninth aspect of the present invention, in the power supply system according to any one of the fifth to eighth aspects, the switch is an FET.

  According to a tenth aspect of the present invention, in the power supply system according to any one of the fifth to ninth aspects, a resistor connected in parallel to the second rectifying element is provided.

  An electronic apparatus according to an eleventh aspect includes the power supply system according to any one of the first to tenth aspects, and each load operates with electric power supplied from the power supply system.

  According to a twelfth aspect of the present invention, in the electronic device according to the eleventh aspect, the power supply system is incorporated.

  According to the present invention, for example, a plurality of rectifying elements having different electrical capacities such as a combination of a silicon diode having a high withstand voltage as an electrical capability and a Schottky diode with a low voltage drop and low power loss are provided. When the voltage applied to the rectifying element is in the forward direction, the power loss in the silicon diode having a large power loss is eliminated. On the other hand, when the voltage applied to these rectifying elements is in the reverse direction, the reverse voltage is applied to the Schottky diode. By preventing the voltage from being applied, it is possible to achieve both high withstand voltage and low voltage drop, and to achieve low loss and high efficiency of the power supply system.

  The best mode for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
A first embodiment of the present invention will be described with reference to FIG. The present embodiment shows an application example to a power supply system PS using a fuel cell 1 as a battery or a power generation device. Connected to the output side of the fuel cell 1 is a constant voltage power supply 3 that stabilizes the output voltage of the fuel cell 1 and supplies it to the target load 2. A large-capacitance capacitor 4 is connected between the input terminals of the constant voltage power supply 3 to absorb fluctuations in the input voltage.

  Between the output side of the fuel cell 1 and the input side of the constant voltage power source 3, a plurality of, for example, two rectifying elements 5 and 6 align the rectification direction from the fuel cell 1 side to the constant voltage power source 3 side. Connected. Here, as the rectifying element, for example, a silicon diode, an SCR, a Schottky diode, a fast recovery diode, a germanium diode, an ore detector, a selenium rectifier, a vacuum tube, a mercury rectifying tube, or the like can be used. However, the rectifying elements 5 and 6 are different in electric capacity. In the present embodiment, for example, a high-breakdown-voltage silicon diode (hereinafter referred to as silicon diode 5) is used as the rectifying element (first rectifying element) 5, and the rectifying element (second rectifying element) 6 is rectified. A Schottky diode (hereinafter referred to as a Schottky diode 6) having an electrical capability with a voltage drop lower than that of the element 5 is used. Here, a relay contact 8 as a switch opened and closed by a relay coil 7 is connected in parallel to the silicon diode 5 to constitute a parallel circuit, and the Schottky diode 6 is connected in series to the parallel circuit. . Further, the magnitude relationship between the output voltage of the fuel cell 1 and the input terminal voltage of the constant voltage power source 3 is compared, and the energization to the relay coil 7 is controlled according to the magnitude relationship, and the relay contact 8 is controlled to be opened and closed (ON / OFF). A differential amplifier 10 is provided as a control element to be controlled. The differential amplifier 10 energizes the relay coil 7 to close (ON) the relay contact 8 when the input terminal voltage of the constant voltage power supply 3 is smaller than a certain value than the output voltage of the fuel cell 1, thereby closing (ON) the relay contact 8. When the input terminal voltage of the constant voltage power supply exceeds a certain value from the output voltage of 1, the relay coil 7 is deenergized and the relay contact 8 is opened (OFF). Reference numeral 10 denotes a drive power supply battery for operating the differential amplifier 9.

  In such a configuration, when the output voltage of the fuel cell 1 is higher than the input terminal voltage of the constant voltage power supply 3 (when the voltage applied to the diodes 5 and 6 is forward), the output of the differential amplifier 9 is L (Low). Since the current flows through the relay coil 7, the relay contact 8 is closed (turned ON), and the anode and cathode of the silicon diode 5 are short-circuited. Therefore, when power is extracted from the fuel cell 1, there is no voltage drop at the silicon diode 5, but only at the Schottky diode 6, so that power loss can be reduced.

  Conversely, when the output voltage of the fuel cell 1 is lower than the input terminal voltage of the constant voltage power supply 3 (when the voltage applied to the diodes 5 and 6 is in the reverse direction), the output of the differential amplifier 9 becomes H (High). Since no current flows through the relay coil 7, the relay contact 8 is opened, which is the same as when there is nothing electrically between the anode and the cathode of the silicon diode 5. Therefore, even if a current flows backward from the input terminal of the constant voltage power supply 3 to the output terminal of the fuel cell 1, it is blocked by the silicon diode 5 having a high withstand voltage, so that a large reverse voltage is applied to the Schottky diode 6 having a low withstand voltage. It is never applied.

  As more detailed operation control, when the output voltage of the fuel cell 1 is higher than the input terminal voltage of the constant voltage power supply 3, for example, when the supply of fuel or air suddenly decreases, the output voltage of the fuel cell 1 decreases. The output voltage of the fuel cell 1 becomes lower than the input terminal voltage of the constant voltage power supply 3. At this time, as described above, the relay contact 8 that has been closed opens and is the same as when there is nothing electrically between the anode and the cathode of the silicon diode 5, but the voltage drops more than the operation of the relay contact 8. If this is earlier, the silicon diode 5 having a high withstand voltage does not function, but can be blocked by the Schottky diode 6 having a low withstand voltage while the voltage difference is not so large. If the relay contact 8 is fully opened while the Schottky diode 6 is dammed, the silicon diode 5 having a high withstand voltage will function, so that a large reverse voltage is applied to the Schottky diode 6 having a low withstand voltage. No current flows from the constant voltage power supply 3 to the fuel cell 1.

  Incidentally, in the case of a circuit configuration in which the relay contact 8 is short-circuited so as to bypass all the rectifying elements 5 and 6, there is nothing to prevent reverse current until the contacts are fully opened, so this transient period is Current flows from the constant voltage power source 3 to the fuel cell 1, which damages the expensive fuel cell 1. This has been described in the operation example of the relay contact 8, but even if this is changed to a non-contact semiconductor element to be described later and the switching operation time is shortened, the current flows from the voltage power source to the fuel cell for a short time. End up.

  As a modification of the present embodiment, a contactless semiconductor element, for example, an FET 11 may be used instead of the relay contact 8 that is opened and closed by the relay coil 7 as shown in FIG. The above-described relay (relay coil 7 & relay contact 8) has a feature that the operation circuit is simple and the leakage current is small. On the other hand, the operation time of the FET 11 is much shorter than that of the relay. Since the reverse voltage can be prevented from being applied to the fuel cell 1 even when the voltage drops, and since it is a non-contact switch, there is a feature that it can be used semipermanently without any contact roughening or foreign matter adhesion. The FET 1 is connected in parallel to the silicon diode 5 between S (source) and D (drain) to form a parallel circuit, and the output of the differential amplifier 9 is connected to G (gate). The ± input terminal of the differential amplifier 9 is opposite to that in FIG.

  In operation, when the output voltage of the fuel cell 1 is higher than the input terminal voltage of the constant voltage power supply 3, the output of the differential amplifier 9 becomes H (High), contrary to the case of FIG. Since the (gate) voltage becomes higher than the S (source) voltage, the FET 11 is turned ON, and the anode and cathode of the silicon diode 5 are short-circuited. Therefore, when power is extracted from the fuel cell 1, there is no voltage drop at the silicon diode 5, but only at the Schottky diode 6, so that power loss can be reduced.

  On the contrary, when the output voltage of the fuel cell 1 is lower than the input terminal voltage of the constant voltage power supply 3, the output of the differential amplifier 9 becomes L (Low) and the G (gate) voltage of the FET 11 is equal to the S (source) voltage. Therefore, the FET 11 is turned OFF, and it is the same as that there is nothing electrically between the anode and the cathode of the silicon diode 5. Therefore, even if a current flows backward from the input terminal of the constant voltage power supply 3 to the output terminal of the fuel cell 1, it is blocked by the silicon diode 5 having a high withstand voltage, so that a large reverse voltage is applied to the Schottky diode 6 having a low withstand voltage. It is never applied.

  Another modification is shown in FIG. In this modification, a resistor 12 is connected in parallel to the Schottky diode 6. This resistor 12 is for preventing reverse voltage from being applied to the Schottky diode 6 through the leakage resistance of the silicon diode 5 and the relay contact 8 connected in series with the Schottky diode 6.

For example, when the leakage resistance of the silicon diode 5 is 10 MΩ, the leakage resistance of the Schottky diode 6 is 100 KΩ, the output terminal voltage of the fuel cell 1 is 0 V, and the input terminal voltage of the constant voltage power supply 3 is 100 V in the circuit configuration shown in FIG. The reverse voltage Vs applied to the Schottky diode 6 is
Vs = 100V * 100KΩ / (10MΩ + 100KΩ)
And is 0.99V. Since this value is much smaller than the reverse breakdown voltage of the Schottky diode 6, it is not always necessary to insert the resistor 12 in parallel with the Schottky diode 6. However, the leakage resistance varies greatly and varies greatly depending on the environment. If the performance of the Schottky diode 6 is improved and the leakage resistance value is significantly improved, the reverse breakdown voltage may be exceeded. By inserting, it can prevent reliably.

  As shown in FIG. 4, the resistor 12 may be connected in parallel to the Schottky diode 6 in the configuration example shown in FIG.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIG. The same parts as those shown in FIGS. 1 to 4 are denoted by the same reference numerals, and the description thereof is also omitted. The basic configuration is the same as the case of FIG. 1, but in this embodiment, a rectifier Schottky diode 6 is connected in series with the relay contact 8 with respect to the parallel circuit of the silicon diode 5 and the relay contact 8. It is.

  In such a configuration, when the output voltage of the fuel cell 1 is higher than the input terminal voltage of the constant voltage power supply 3 (when the voltage applied to the diodes 5 and 6 is forward), the output of the differential amplifier 9 is L (Low). ) And the current flows through the relay coil 7, the relay contact 8 is closed, and a parallel circuit of the silicon diode 5 and the Schottky diode 6 is formed. Accordingly, when the power is taken out from the fuel cell 1, the current flows only through the Schottky diode 6 having a small forward voltage drop, so that the power loss can be reduced.

  Conversely, when the output voltage of the fuel cell 1 is lower than the input terminal voltage of the constant voltage power supply 3 (when the voltage applied to the diodes 5 and 6 is in the reverse direction), the output of the differential amplifier 9 becomes H (High). Since no current flows through the relay coil 7, the relay contact 8 is opened, and the Schottky diode 6 is electrically disconnected from the cathode of the silicon diode 5, so that a large reverse voltage is applied to the Schottky diode 6 having a low withstand voltage. Never happen.

  As a modification of the present embodiment, a contactless semiconductor element, for example, an FET 11 may be used instead of the relay contact 8 that is opened and closed by the relay coil 7 as shown in FIG. This is the same as in the case of the relationship between FIG. 1 and FIG. 2 described above, and the description of the operation and the like is omitted.

  As in the case of FIG. 3 and FIG. 4 described above, in this embodiment, as another modification, a resistor 12 is connected in parallel to the Schottky diode 6 as shown in FIG. 7 and FIG. May be.

[Third embodiment]
A third embodiment of the present invention will be described with reference to FIG. The present embodiment shows an application example in which the power supply system PS configured as described above is used as a power supply for an electronic apparatus such as a copying machine, a facsimile machine, a multifunction peripheral (MFP), and various printers. . The image forming apparatus 21 includes various well-known loads such as an image forming unit 22, a communication control unit 23, a mechanical drive unit 24, an electronic control unit 25, and a fixing unit 26, and serves as a power source for these various loads. The power supply system PS is provided so as to be built in the image forming apparatus 21, and is configured to be supplied with electric power after being converted into an appropriate high voltage or the like by the inverter circuit 27.

  Of course, the electronic apparatus provided with the power supply system PS is not limited to such an image forming apparatus, but can be applied to various apparatuses such as an electronic blackboard.

It is a schematic circuit diagram which shows the power supply system of 1st embodiment of this invention. It is a schematic circuit diagram which shows the modification. It is a schematic circuit diagram which shows another modification. It is a schematic circuit diagram which shows another modification. It is a schematic circuit diagram which shows the power supply system of 2nd embodiment of this invention. It is a schematic circuit diagram which shows the modification. It is a schematic circuit diagram which shows another modification. It is a schematic circuit diagram which shows another modification. It is a schematic block diagram which shows the image forming apparatus of 3rd embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell, battery 3 Constant voltage power supply 5 Silicon diode, 1st rectifier 6 Schottky diode, 2nd rectifier 8 Switch 9 Control element 11 FET, switch 12 Resistance

Claims (12)

In a power supply system in which a constant voltage power supply is connected to the output side of a battery or power generator,
A power supply system comprising a plurality of rectifier elements connected in the same rectification direction between the battery or the power generation device and the constant voltage power supply and having different electrical capabilities. In a power supply system where a constant voltage power supply is connected to the output side of the fuel cell,
A power supply system comprising a plurality of rectifier elements connected in the same rectification direction between the fuel cell and the constant voltage power supply and having different electrical capabilities.   3. The power supply system according to claim 1, wherein one of the plurality of rectifying elements is a rectifying element having an electrical capability with a lower voltage drop than other rectifying elements.   The power supply system according to claim 3, wherein the rectifying element having an electrical capability with a lower voltage drop than other rectifying elements is a Schottky diode. In a power supply system where a constant voltage power supply is connected to the output side of the fuel cell,
A parallel circuit of a first rectifier element and a switch connected between the fuel cell and the constant voltage power source, and an electric circuit connected in series to the parallel circuit and having a voltage drop lower than that of the first rectifier element. A power supply system comprising: a second rectifying element having capacity. In a power supply system where a constant voltage power supply is connected to the output side of the fuel cell,
A parallel circuit of a first rectifying element and a switch connected between the fuel cell and the constant voltage power source, and a voltage drop than the first rectifying element connected in series to the switch in the parallel circuit And a second rectifying element having a low electrical capacity.   The power supply system according to claim 5, further comprising a control element that turns on the switch when an input terminal voltage of the constant voltage power supply becomes smaller than a certain value from an output voltage of the fuel cell.   The control element according to any one of claims 5 to 7, further comprising a control element that turns off the switch when an input terminal voltage of the constant voltage power source becomes larger than a certain value than an output voltage of the fuel cell. Power system.   The power supply system according to claim 5, wherein the switch is an FET.   The power supply system according to any one of claims 5 to 9, further comprising a resistor connected in parallel to the second rectifier element.   An electronic apparatus comprising the power supply system according to claim 1, wherein each load operates with electric power supplied from the power supply system. The electronic device according to claim 11, wherein the power supply system is incorporated.

Images