WO2006003951A1 - スイッチング電源装置 - Google Patents
スイッチング電源装置 Download PDFInfo
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- WO2006003951A1 WO2006003951A1 PCT/JP2005/011985 JP2005011985W WO2006003951A1 WO 2006003951 A1 WO2006003951 A1 WO 2006003951A1 JP 2005011985 W JP2005011985 W JP 2005011985W WO 2006003951 A1 WO2006003951 A1 WO 2006003951A1
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- Prior art keywords
- synchronous rectification
- voltage
- period
- switch
- capacitor
- Prior art date
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Definitions
- the present invention relates to a switching power supply device having a synchronous rectifier circuit.
- a typical switching power supply device including a flyback type DC-DC conversion circuit includes a pair of DC power supply terminals, a transformer having primary and secondary power wires, and a pair of DC power supply terminals. It consists of a main switch connected via the secondary winding and a smoothing capacitor connected via a rectifier diode to the secondary winding.
- a voltage drop of about 0.8 V occurs in the rectifier diode connected to the secondary winding, resulting in power loss.
- a technique for connecting a synchronous rectifier switch in parallel to the rectifier diode and turning on the synchronous rectifier switch during the conduction period of the rectifier diode is disclosed in, for example, Japanese Patent Laid-Open No. 9 1637. It is known from No. 36 publication.
- the voltage drop here is about 0.2 V, which is lower than that of the rectifier diode, and the voltage drop and power on the secondary side of the transformer Loss can be reduced.
- Patent Document 1 Japanese Patent Laid-Open No. 9-163736
- the problem to be solved by the present invention is that the optimum control of the synchronous rectification switch cannot be performed accurately and easily, and the object of the present invention is a switching power supply capable of solving the above problems. Is to provide a device.
- DC voltage input means for supplying a DC input voltage
- An intermittent voltage supply means connected between the DC voltage input means and the inductance means for intermittently supplying a voltage to the inductance means and having a main switch for interrupting the DC input voltage;
- a switch control circuit connected to a control terminal of the main switch and having a function of on / off controlling the main switch;
- a smoothing capacitor connected between the pair of DC voltage output terminals
- a synchronous rectification switch connected in parallel to the series circuit of the inductance means and the smoothing capacitor;
- a switching power supply comprising: a parasitic or individual rectifier diode connected in parallel to the synchronous rectification switch; and a synchronous rectification control circuit connected to a control terminal of the synchronous rectification switch,
- the synchronous rectification control circuit includes:
- a synchronous rectification period determining unit for determining an on period of the synchronous rectification switch
- a second current source connected to the synchronous rectification period determining capacitor and having a function of flowing a discharge current having a value corresponding to the DC output voltage;
- a conduction allowable period detecting means connected to a location where a signal indicating the on / off state of the main switch is obtained and having a function of detecting a conduction allowable period of the synchronous rectification switch;
- the charging current having a value corresponding to the voltage of the inductance means in the present invention becomes larger when the voltage of the inductance means becomes higher than a predetermined value, and the voltage of the inductance means becomes lower than the predetermined value. It means a charging current that changes so as to become smaller.
- the charging current having a value corresponding to the voltage of the inductance means in the present invention means a charging current that changes according to a change in the voltage of the inductance means.
- the voltage of the inductance means means, for example, the voltage of the secondary winding of the transformer or the voltage of the smoothing inductor.
- the discharge current having a value corresponding to the DC output voltage in the present invention becomes larger when the DC output voltage becomes higher than the rated DC output voltage, and the DC output voltage becomes lower than the rated DC output voltage. It means the discharge current that changes so as to decrease.
- the discharge current having a value corresponding to the DC output voltage in the present invention means a discharge current that changes according to a change in the DC output voltage.
- the inductance means is a transformer having a primary winding and a secondary winding
- the intermittent voltage supply means is a main switch connected between the DC voltage input means and the primary winding.
- the switch for synchronous rectification is connected in series to a current path from the secondary winding to the smoothing capacitor, and the rectifier diode is induced in the secondary winding during the ON period of the main switch. It is desirable to have a direction that is reverse-biased by voltage.
- the intermittent voltage supply means includes a primary winding connected to the DC voltage input means, a secondary winding electromagnetically coupled to the primary winding, the DC voltage input means, and the primary winding.
- a main switch connected between the secondary winding and a current path connected in series from the secondary winding to the smoothing capacitor, and a voltage induced in the secondary winding during the ON period of the main switch.
- the inductance means is a smoothing inductor connected in series to the current path from the secondary winding to the smoothing capacitor, and the synchronous rectification switch is It is desirable that the smoothing inductor and the smoothing capacitor are connected in parallel to each other and connected to the secondary winding in parallel via the rectifying element.
- the inductance means is a smoothing inductor connected in series to a current path from the DC voltage input means to the smoothing capacitor, and the intermittent voltage supply means is provided between the DC voltage input means and the smoothing inductor.
- the synchronous rectification switch is connected to the smoothing capacitor in parallel via the smoothing inductor.
- the first current source supplies a first current (11) to the synchronous rectification period determining capacitor during an ON period of the main switch
- the second current source is provided in the main switch.
- a second current (12) for discharging the synchronous rectification period determining capacitor during an off period, and a ratio between the first current (II) and the second current (12) ( ⁇ 2) is a value (V2 + Vo) obtained by adding the output voltage (Vo) between the pair of DC voltage output terminals to the voltage (V2) of the inductance means in the ON period of the main switch and the output voltage. It is desirable that the ratio of pressure (Vo) to ⁇ (V2 + Vo) / Vo ⁇ is U, etc.
- the first current source supplies a first current (11) to the synchronous rectification period determining capacitor during an ON period of the main switch
- the second current source is provided in the main switch.
- a second current (12) for discharging the synchronous rectification period determining capacitor during an off period, and a ratio between the first current (II) and the second current (12) ( ⁇ 2) is a value (Vds ⁇ Vz) obtained by subtracting a predetermined level shift voltage (Vz) from the voltage (Vds) force between the main terminals of the pair of synchronous rectifier switches during the ON period of the main switch and the output voltage ( It is desirable to equal the ratio ⁇ (Vds-Vz) / Vo ⁇ to Vo).
- the first current source supplies a first current (11) to the synchronous rectification period determining capacitor during an ON period of the main switch
- the second current source is provided in the main switch.
- a second current (12) for discharging the synchronous rectification period determining capacitor during an off period, and a ratio between the first current (II) and the second current (12) ( ⁇ 2) Force U is preferably equal to the ratio (V2ZVo) between the voltage (V2) between the pair of terminals of the inductance means and the output voltage (Vo) during the ON period of the main switch.
- the first current source supplies a first current (II) to the combination of the synchronous rectification period determining capacitor and the second current source during an ON period of the main switch.
- the second current source is configured to flow a second current (12) for discharging the capacitor for determining the synchronous rectification period in both the ON period and the OFF period of the main switch.
- the ratio ⁇ (II 12) ZI2 ⁇ of the value (11 -12) obtained by subtracting the second current (12) from the current (II) and the second current (12) is the ON period of the main switch.
- Voltage (Vds) force between the main terminals of the pair of synchronous rectification switches A value obtained by subtracting the output voltage (Vo) between the pair of DC voltage output terminals (Vds—Vo) and the output voltage (Vo) It is desirable to be equal to the ratio ⁇ (Vds—Vo) / Vo ⁇ .
- the first current source is a first current mirror circuit and the second current source is a second current mirror circuit.
- the first current source includes a first transistor having an emitter connected to one main terminal of the synchronous rectification switch and a collector connected to one end of the synchronous rectification period determining capacitor;
- the emitter connected to the emitter of the first transistor and the front
- a second transistor having a base and a collector connected to the base of the first transistor, and a second transistor connected between the collector of the second transistor and the other main terminal of the synchronous rectification switch
- it consists of a first collector resistor.
- the first current source includes a first transistor having an emitter connected to one main terminal of the synchronous rectification switch and a collector connected to one end of the synchronous rectification period determining capacitor; A second transistor having an emitter connected to the emitter of the first transistor and a base and a collector connected to the base of the first transistor; the collector of the second transistor; and the synchronous rectifier A first collector resistor connected between the other main terminal of the switch and one main terminal of the synchronous rectification switch and the emitter of the first transistor and the output voltage ( It is desirable to have the same Zener voltage as Vo) and to work with a Zener diode.
- the first current source includes a first transistor having an emitter connected to one main terminal of the synchronous rectification switch and a collector connected to one end of the synchronous rectification period determining capacitor; A second transistor having an emitter connected to the emitter of the first transistor, a base and a collector connected to the base of the first transistor, and one end connected to the collector of the second transistor; And a first collector resistor having the other end connected to one of the pair of direct current voltage output terminals.
- the second current source includes a third transistor having an emitter connected to one end of the smoothing capacitor, a collector connected to one end of the synchronous rectification period determining capacitor, and one end of the smoothing capacitor.
- a fourth transistor having an emitter connected to the base and a base and a collector respectively connected to a base of the third transistor, and connected between the other end of the smoothing capacitor and the collector of the fourth transistor. Desirable to consist of a second collector resistor, U, made.
- the discharge prohibiting means includes a selective discharge diode connected between one end of the synchronous rectification period determining capacitor and a collector of the third transistor, one main terminal of the synchronous rectification switch, and the Desirably, consisting of a biasing diode connected between the collector of the third transistor.
- the discharge prohibiting means may include a discharge blocking switch connected in parallel to the fourth transistor, and a discharge blocking control circuit that controls the discharge blocking switch to be on during the main switch on period. Hope.
- the first current source includes a first transistor having an emitter connected to one main terminal of the synchronous rectification switch and a collector connected to one end of the synchronous rectification period determining capacitor; A second transistor having an emitter connected to the emitter of the first transistor and a base and a collector connected to the base of the first transistor; the collector of the second transistor; and the synchronous rectifier A first collector resistor connected between the other main terminal of the switch, and the second current source includes an emitter connected to one end of the smoothing capacitor and a synchronous rectification period determining capacitor.
- a third transistor connected to one end and having a collector; an emitter connected to one end of the smoothing capacitor; and a base of the third transistor.
- a fourth transistor having a base and a collector connected to each other, and a second collector resistor connected between the other end of the smoothing capacitor and the collector of the fourth transistor. It is desirable to further have a discharge adjustment resistor connected in parallel to the synchronous rectification period determining capacitor.
- the conduction allowable period detecting means is preferably means for detecting a voltage between a pair of main terminals of the synchronous rectification switch.
- the comparison and pulse forming circuit is connected to a reference voltage source that supplies a predetermined reference voltage as the predetermined voltage value, a first input terminal connected to the synchronous rectification period determining capacitor, and the reference voltage source.
- a comparator having a second input terminal, a first input terminal connected to the permissible conduction period detecting means, and a second input terminal connected to the comparator, and the permissible conduction period.
- the comparison and pulse forming circuit has a threshold value that functions as the predetermined reference value. And the first level output is generated when the voltage of the synchronous rectification period determining capacitor is higher than the threshold value, and the synchronous rectification period determining capacitor voltage is lower than the threshold value.
- a first logic circuit that sometimes generates a second level output; a first input terminal connected to the conduction-permissible period detecting means; and a second input terminal connected to the first logic circuit.
- the synchronous rectification control circuit preferably has a semiconductor integrated circuit capability.
- the synchronous rectification switch, the rectifier diode, and the synchronous rectification control circuit are accommodated in the same enclosure.
- Another invention of the present application provides a DC voltage input means for supplying a DC input voltage, an inductance means, and the DC voltage input means and the inductance means for intermittently supplying a voltage to the inductance means. And an intermittent voltage supply means for connecting and disconnecting the DC input voltage, and a switch control connected to the control terminal of the main switch and having a function of on / off controlling the main switch.
- a synchronous rectifying switch, a parasitic or individual rectifying diode connected in parallel to the synchronous rectifying switch, and the synchronous rectifying switch.
- a synchronous rectification control circuit connected to a control terminal, wherein the synchronous rectification control circuit includes a synchronous rectification period determining capacitor for determining an ON period of the synchronous rectification switch; A charging circuit connected to the synchronous rectification period determination capacitor and having a function of charging the synchronous rectification period determination capacitor during an on period of the main switch; and connected to the synchronous rectification period determination capacitor; A discharge circuit having a function of flowing a discharge current of the synchronous rectification period determining capacitor; and a conduction allowable period of the synchronous rectification switch connected to a location where a signal indicating the on / off state of the main switch is obtained.
- a conduction permissible period detecting means having a function of detecting; Determining whether the voltage of the synchronous rectification period determining capacitor is higher than a predetermined reference value and connected to the synchronous rectification period determination capacitor, the conduction allowable period detecting means, and the control terminal of the synchronous rectification switch.
- the synchronous rectification period determining capacitor voltage is higher than the predetermined reference value and at the same time the conduction allowable period is formed, an on-control pulse of the synchronous rectification switch is formed to control the synchronous rectification switch.
- a comparison and pulse formation circuit a forced discharge switch connected in parallel to the synchronous rectification period determining capacitor, and a time when the on-control of the synchronous rectification switch ends or the main
- a control circuit for controlling the on / off switch for forced discharge for a predetermined time in synchronization with the on-control start time of the switch.
- Still another invention of the present application is directed to a DC voltage input means for supplying a DC input voltage, an inductance means, and between the DC voltage input means and the inductance means for intermittently supplying a voltage to the inductance means.
- an intermittent voltage supply means connected to the main switch for connecting the DC input voltage, and a function connected to the control terminal of the main switch and controlling the on / off of the main switch.
- a switch control circuit ; a pair of DC voltage output terminals for outputting a DC voltage; a smoothing capacitor connected between the pair of DC voltage output terminals; and a series circuit of the inductance means and the smoothing capacitor in parallel.
- a synchronous rectifying switch connected thereto, a parasitic or individual rectifying diode connected in parallel to the synchronous rectifying switch, and the synchronous rectifying switch;
- a signal indicating an on / off state of the main switch, and a charging circuit connected to the capacitor for determining the synchronous rectification period and having a function of flowing a discharge current of the capacitor for determining the synchronous rectification period Connected to a location where the rectification switch is obtained and has a function of detecting a conduction allowable period of the synchronous rectification switch, a conduction allowable period detection means, the synchronous rectification period determining capacitor, the conduction allowable period detection means, and the It is determined whether or not the voltage of the synchronous rectification period determination capacitor
- the present invention relates to a synchronous rectification period determining capacitor for determining an ON period of the synchronous rectification switch, and the main switch connected to the synchronous rectification period determination capacitor and to the synchronous rectification period determination capacitor.
- the ON period of the synchronous rectification switch is determined, so that the energy of the inductance means due to the ON / OFF of the main switch is determined.
- the on-period of the synchronous rectification switch can be made to substantially coincide with the energy release period of the inductance means to maximize the effect of synchronous rectification, and the synchronous rectification switch and the main switch can be turned on simultaneously. It is possible to suppress adverse effects such as noise generation and circuit destruction due to the state.
- the synchronous rectification period determining capacitor can be easily charged under the optimum conditions.
- a desired discharge current of the synchronous rectification period determining capacitor can be easily and accurately passed. Further, according to still another preferred embodiment of the present invention, it is possible to easily achieve the prohibition of discharge of the capacitor for determining the synchronous rectification period during the ON period of the main switch.
- the allowable conduction period of the synchronous rectification switch can be easily detected.
- the comparison and pulse forming circuit can be easily configured.
- the synchronous rectification control circuit since the synchronous rectification control circuit includes a special adjustment circuit, semiconductor integration can be easily achieved.
- the number of parts of the synchronous rectification circuit is reduced by the integrated circuit of the synchronous rectification control circuit, and a plurality of circuit elements (for example, transistors) constituting the synchronous rectification control circuit.
- the characteristics can be aligned.
- the number of parts of the synchronous rectification circuit can be reduced by integrating the synchronous rectification control circuit, the synchronous rectification switch, and the rectifier diode.
- FIG. 1 is a circuit diagram showing a switching power supply device according to a first embodiment of the present invention.
- FIG. 2 is a circuit diagram showing in detail the secondary side of the transformer of FIG.
- FIG. 3 is a waveform diagram showing the state of each part in FIG.
- FIG. 4 is a circuit diagram showing a part of the switching power supply unit of Example 2 according to the present invention in the same manner as FIG.
- FIG. 5 is a circuit diagram showing a part of the switching power supply device of Example 3 according to the present invention in the same manner as FIG. [Fig. 6]
- Fig. 6 is a circuit diagram showing a part of the switching power supply unit of Example 4 according to the present invention in the same manner as Fig. 2.
- FIG. 7 is a circuit diagram showing a part of the switching power supply unit of Example 5 according to the present invention in the same manner as FIG.
- FIG. 8 is a circuit diagram showing a part of the switching power supply unit of Example 6 according to the present invention in the same manner as FIG.
- FIG. 9 is a circuit diagram showing the state of each part of the switching power supply device of Example 6 in the same manner as FIG.
- FIG. 10 is a circuit diagram showing a part of the switching power supply device of Embodiment 7 according to the present invention in the same manner as FIG.
- FIG. 11 is a circuit diagram showing a part of the switching power supply device according to the eighth embodiment of the present invention in the same manner as FIG.
- FIG. 12 is a circuit diagram showing a part of the switching power supply device of Embodiment 9 according to the present invention in the same manner as FIG.
- FIG. 13 is a circuit diagram showing a switching power supply device according to Embodiment 10 in accordance with the present invention.
- FIG. 14 is a circuit diagram showing a comparison of a modified example and a pulse forming circuit.
- FIG. 15 is a circuit diagram showing a comparison and pulse forming circuit of another modified example.
- FIG. 16 is a circuit diagram showing a comparison and pulse forming circuit of still another modified example. Explanation of symbols
- the switching power supply that also has a flyback type DC-DC conversion of the first embodiment according to the present invention shown in FIG. 1 has a pair of DC power supply terminals la, lb as DC voltage input means connected to the DC power supply 1.
- the DC power source 1 is constituted by a rectifying / smoothing circuit or a battery connected to a commercial AC power source, and supplies a DC input voltage Vin to a pair of DC power source terminals la and lb.
- the transformer 2 as an inductance means is composed of a primary winding N1 and a secondary winding N2 wound around a magnetic core 6 and electromagnetically coupled to each other.
- the primary and secondary windings Nl and N2 have opposite polarities.
- the transformer 2 has a tertiary winding for forming a power supply circuit for the switch control circuit 5.
- the primary feeder N1 is connected between the pair of DC power supply terminals la and lb via the main switch Q1.
- Primary winding N1 has a first power Np and has an inductance Lp.
- Secondary winding N2 has a second power Ns and has an inductance Ls.
- One end of secondary shoreline N2 Is connected to one end of a smoothing capacitor Co as a smoothing circuit and one DC output terminal 4a, and the other end is connected to the other end of the smoothing capacitor Co and the other DC output terminal 4b via a synchronous rectifier circuit 3. .
- the main switch Q1 as the intermittent voltage supply means is composed of an insulated gate field effect transistor.
- the main switch Q1 can be another semiconductor switch such as a bipolar transistor or IGBT.
- the drain as the first main terminal of the main switch Q1 is connected to the primary wire N1, and the source as the second main terminal is connected to the DC power supply terminal lb on the ground side. Therefore, the main switch Q1 intermittently supplies the DC input voltage to the transformer 2 intermittently.
- the synchronous rectification circuit 3 is roughly composed of a synchronous rectification element Q2 composed of an insulated gate field effect transistor and a synchronous rectification control circuit 7 having a semiconductor integrated circuit configuration.
- the synchronous rectification element Q 2 and the synchronous rectification control circuit 7 are accommodated in the same enclosure, that is, a package.
- the synchronous rectification element Q2 and the synchronous rectification control circuit 7 may be the same semiconductor integrated circuit.
- the synchronous rectification element Q2 includes a synchronous rectification switch 8 and a diode Do connected in parallel thereto.
- the synchronous rectification switch 8 is a main body of an insulated gate field effect transistor (FET), and has a drain electrode as one main terminal, a source electrode as the other main terminal, and a gate electrode as a control terminal. Is connected in series to the line between the secondary feeder N2 and the negative DC output terminal 4b.
- the diode Do is a parasitic diode, that is, a body diode of the synchronous rectifying element Q2, which is an insulated gate field effect transistor, and is formed in the same semiconductor substrate as the synchronous rectifying switch 8 such as silicon.
- This diode Do can be an individual diode with a separate structure from the synchronous rectification switch 8 with FET structure.
- the synchronous rectifying element Q2 or the synchronous rectifying switch 8 can be another semiconductor switch such as a bipolar transistor or IGBT.
- the voltage drop voltage when the synchronous rectifier switch 8 is on is about 0.2 V, for example, and the voltage drop when the diode Do is on is for synchronous rectification. For example, about 0.8V higher than switch 8. Therefore, when the synchronous rectification switch 8 is turned on to rectify the voltage of the secondary winding N2, the voltage drop and Power loss is reduced.
- the synchronous rectification control circuit 7 is used to turn on the synchronous rectification switch 8 of the synchronous rectification element Q2, and includes a synchronous rectification period determining capacitor C1 (hereinafter simply referred to as a capacitor C1), a charging circuit A first current source 9 as a discharge circuit, a second current source 10 as a discharge circuit, a switch 11 as a discharge prohibiting means, and a pulse forming circuit 12.
- a first current source 9 shown schematically is connected between the other end of the secondary winding N2, that is, between the drain of the synchronous rectifier Q2 and one end of the capacitor C1, 10 is connected in parallel to the capacitor C1 through the switch 11 as a discharge prohibiting means.
- the other end of the capacitor C1 is connected to the DC output terminal 4b on the ground side.
- the first and second current sources 9 and 10 have the first and second current sources 9 and 10 so that the discharge time TcT of the capacitor C1 and the discharge time Td of the stored energy of the transformer 2 are the same or substantially the same. Currents II and 12 are set.
- the first discharge time is set to be the same as the discharge time ⁇ ( ⁇ and the discharge time Td. It is desirable to set the second currents II and 12 so that they have the following relationship.
- V2 indicates the voltage of the secondary winding N2 of the transformer 2 as the inductance means.
- the first and second currents II and 12 are expressed by the following equations in order to make the discharge time Td 'and the discharge time Td coincide with each other. Set.
- the stored energy Ws of the transformer 2 during the ON period Ton of the main switch Q1 can be expressed by the following equation.
- the stored energy Ws release time Td during the off period of the main switch Ql can be expressed by the following equation.
- Td ⁇ (Ns Vin) / (Np Vo) ⁇ Ton (4)
- the charging time of the capacitor CI is the same as the ON period Ton of the main switch Ql.
- the discharge time Td 'of the capacitor C1 can be expressed by the following equation.
- the energy storage time of the transformer 2 that is, the on-time Ton of the main switch Ql and the ratio of the energy release time Td of the transformer 2 Is ideal, so it is desirable that
- the ratio of the first current II and the second current 12 can be expressed by the following equation.
- equation (8) which is the same as equation (1), the powers Np and Ns of the primary and secondary windings Nl and N2 are constant, and the input voltage Vin and the output voltage Vo are constant.
- the ratio II / 12 of the first and second currents II and 12 is set to (Ns Vin) / (Np Vo). Since the first and second currents II and 12 are supplied from the first and second current sources 9 and 10 having a constant current source configuration, a desired synchronous rectification period can be obtained easily and accurately. Details of the first and second current sources 9 and 10 will be described later.
- the pulse forming circuit 12 of FIG. 1 is roughly composed of a conduction allowable period detecting means 13 and a comparison and pulse forming circuit 14, and forms a pulse for driving the synchronous rectification switch 8.
- the conduction allowable period detecting means 13 detects a period during which the conduction of the synchronous rectification switch 8 is permitted.
- the drain of the synchronous rectifier element Q2 in order to detect a signal indicating the off period of the main switch Q1.
- the drain of the synchronous rectifier element Q2 'The series circuit of the first and second voltage dividing resistors 15 and 16 connected between the sources via the conductors 18 and 19 and the voltage dividing conductor 17 and the force for obtaining the divided output Become. Therefore, a voltage proportional to the drain-source voltage of the synchronous rectifier Q2 is obtained in the voltage dividing conductor 17 connected to the interconnection point of the first and second voltage dividing resistors 15, 16. Since the drain-to-source voltage of the synchronous rectifier Q2 changes according to the on / off state of the main switch Q1, the conduction allowable period detecting means 13 is called the on / off detecting means of the main switch Q1.
- the switch state signal of the voltage dividing conductor 17 indicates the conduction allowable period of the rectifying switch 8.
- the comparison and pulse formation circuit 14 may also be referred to as a comparison and conduction period determination circuit.
- the synchronous rectification period determining capacitor CI, the conduction allowable period detecting means 13 and the control terminal of the synchronous rectification switch 8 are connected.
- This comparison and pulse formation circuit 14 has a function for determining whether or not the voltage Vcl of the synchronous rectification period determining capacitor C1 is higher than a predetermined reference value (reference voltage value Vr), and the voltage of the synchronous rectification period determining capacitor C1.
- the comparison and pulse formation circuit 14 of FIG. 1 comprises a comparator 20, a reference voltage source 21, and a negative OR circuit or NOR circuit 22.
- One input terminal of the comparator 20 is connected to one end of the capacitor C 1, and the other input terminal is connected to the reference voltage source 21.
- the reference voltage source 21 provides a reference voltage value Vr that is the lowest voltage (ground) of the capacitor C1 or slightly higher than this.
- This reference voltage value Vr is preferably in the range of 0 to 20% of the maximum value of voltage Vcl of capacitor C1 at the rated load.
- the comparator 20 compares the voltage Vcl of the capacitor C1 with the reference voltage value Vr, and during the period t2 to t4 when the voltage Vcl of the capacitor C1 is lower than the reference voltage value Vr.
- high level output V20 is generated.
- the ON period of the synchronous rectification switch 8 is preferably 80 to L00 percent, more preferably 90 to L00 percent of the energy discharge time Td of the transformer 2 as the inductance means.
- the NOR circuit 22 determines the ON period of the synchronous rectification switch 8 and forms a pulse corresponding to the ON period.
- One input terminal of the NOR circuit 22 is connected to the comparator 20 and the other input terminal Is connected to a voltage dividing conductor 17.
- the NOR circuit 22 outputs a high level (logic 1) only when the two input pins are simultaneously low (logic 0). Therefore, as shown in the period from tl to t2 in Fig. 3, the output V22 of the NOR circuit 22 is shown in Fig. 3 (G) when the output V20 of the comparator 20 is low while the main switch Q1 is off. As shown in the figure, the synchronous rectification switch 8 is turned on.
- the comparator 20 and the NOR circuit 22 are connected to a known DC power source for driving them.
- the NOR circuit 22 is shown as including a known drive circuit.
- a known drive circuit can be provided independently, and this drive circuit can be connected between the NOR circuit 22 and the gate of the synchronous rectifier Q2.
- the first current source 9 as the charging circuit in FIG. 1 has a value corresponding to the DC input voltage Vin during the ON period of the main switch Q1 with respect to the capacitor C1, that is, the secondary winding N2 of the transformer 2 as an inductance means. It has a function of supplying a charging current having a value corresponding to the voltage V2.
- the first current source 9 can be called a current mirror circuit. As shown in detail in FIG.
- the pnp-type first and second transistors Q11 and Q12 and the first collector resistor R1 The first and second diodes Dl and D2 for backflow prevention and the Zener diode 23 as a voltage source are used.
- the emitter of the first transistor Q11 is connected to the drain electrode (first main terminal) of the synchronous rectifier Q2 via the first diode D1, the Zener diode 23, and the conductor 18.
- the collector of the first transistor Q1 is connected to one end of the capacitor C1 through the second diode D2.
- the emitter of the second transistor Q12 is connected to the emitter of the first transistor Q11 to form a current mirror circuit.
- the collector of the second transistor Q12 is connected to the source electrode (second main terminal) of the synchronous rectifier Q2 via the first collector resistor R1 and the conductor 19.
- the bases of the first and second transistors Qll, Q12 are connected to each other and to the collector of the second transistor Q12.
- the Zener diode 23 has a function of making the first current II proportional to the input voltage Vin to satisfy the equation (8), and has the same Zener voltage Vz as the output voltage Vo of the smoothing capacitor Co.
- the first collector resistor R1 has the voltage Vz of the Zener diode 23 and the forward voltage of the first diode D1 from the sum of the voltage V2 of the secondary winding N2 and the output voltage Vo. V and the collector of the second transistor Q12 'source voltage V and
- the voltage of the first collector resistor R1 is V2—V-V.
- V and V are integers
- the first and second transistors Qll and Q12 are current mirrors Since the circuit is configured, the first current II flowing through the collector of the first transistor Q11 is the same as the current flowing through the first collector resistor R1, and can be expressed by the following equation.
- the first current II has a value proportional to the input voltage Vin.
- the current flowing through the first collector resistor R1 and the first current II flowing through the collector of the first transistor Q11 can be expressed by the following equations.
- V and V are sufficiently smaller than V2.
- the value of the first current II is V compared to the case where the Zener diode 23 is provided. Vo must be taken into account when setting II / 12. However, even if the Zener diode 23 is omitted, it is possible to set II / 12. Therefore, the Zener diode 23 can be omitted when a simple circuit configuration is required.
- the second current source 10 as a discharge circuit is connected to the capacitor C1 and has a function of flowing a discharge current having a value corresponding to the DC output voltage Vo of the pair of DC output terminals 4a and 4b.
- the second current source 10 can also be called a second current mirror circuit, and includes npn-type third and fourth transistors Q13 and Q14, and a second resistor R2.
- the collector of the third transistor Q13 is connected to one end of a capacitor C1 through a selective discharge diode 1la having the same function as the switch 11 of FIG.
- the emitter of the third transistor Q13 is connected via a conductor 19 to the source electrode of the synchronous rectifier Q2 and the negative DC output terminal 4b.
- the collector of the fourth transistor Q14 is connected to the positive DC output terminal 4a via the second collector resistor R2.
- the emitter of the fourth transistor Q14 is the conductor 1 9 is connected to the source electrode of the synchronous rectifier Q2 and the negative DC output terminal 4b.
- the bases of the third and fourth transistors Q13, Q14 are connected to each other and to the collector of the fourth transistor Q14.
- FIG. 1 lb bias diode In order to obtain the same function as the switch 1 1 of FIG. 1 as a means for prohibiting the discharge of the capacitor C 1 of FIG. 1 during the ON period of the main switch Q 1, FIG. There is a 1 lb bias diode!
- the bias diode 1 lb is for turning on the selective discharge diode 11a only during the OFF period of the main switch Q1, and its anode is connected to the drain electrode of the synchronous rectifier Q2 via the conductor 18.
- the force sword is connected to the force sword of the selective discharge diode 11a.
- the bias diode l ib is forward-biased by the sum of the output voltage Vo and the voltage V2 of the secondary winding N2, and the power sword potential of the selective discharge diode 1 1a becomes the capacitor C.
- V2 + Vo -V which is higher than the voltage Vcl of 1, and the selective discharge diode 1 1a
- the battery enters a suspended state and no discharge current flows.
- the above V is the bias diode l ib
- the second collector resistor R2 of the second current source 10 is applied with a voltage Vo — V obtained by subtracting the collector-emitter voltage V of the fourth transistor Q 14 from the output voltage Vo force.
- the collector-emitter voltage V is extremely small compared to the output voltage Vo.
- the ratio II / 12 of the first and second currents II and 12 is roughly expressed by the following equation while ignoring V and V. Can do.
- Zener diode 23 is not provided, ignoring V and V,
- the first current II can be expressed by the following equation according to the above equation (11).
- TonZTd Ton / Td 'is ideal.
- TonZTd Ton / Td 'according to the same method as equations (7) to (12) above.
- the Zener diode 23 In the case where the Zener diode 23 is not provided, if the input voltage Vin and the output voltage Vo are constant, Vin and Vo can be regarded as constants. Therefore, the first and second collector resistors Rl and R2 are ideal. A simple ratio can be set easily.
- This switch control circuit 5 has a feedback signal forming circuit 5a, a sawtooth generator 5b, and a comparator 5c, and forms a PWM (pulse width modulation) control signal Vg for the main switch Q1 by a well-known method. Is.
- the feedback signal forming circuit 5a is connected to the DC output terminals 4a and 4b by lines 24 and 25, and forms a feedback control signal for keeping the output voltage Vo at a desired value.
- the feedback control signal is a signal indicating a voltage between the pair of DC output terminals 4a and 4b.
- the feedback control signal is a voltage signal proportional to the output voltage Vo between the DC output terminals 4a and 4b.
- a voltage that is inversely proportional to the output voltage Vo can be used as the feedback signal.
- the sawtooth wave generator 5b as a carrier wave generator generates a sawtooth wave with a high repetition frequency of, for example, 20 to: LOOkHz.
- This sawtooth generator 5b can be replaced with a triangular generator.
- the negative input terminal of the comparator 5c is connected to the feedback signal forming circuit 5a, and the positive input terminal is connected to the sawtooth generator 5b. Therefore, a high level pulse is generated from the comparator 5c when the sawtooth wave is higher than the feedback signal.
- the output line 26 of the comparator 5c is connected to the control terminal or gate of the main switch Q1. Note that the control signal Vg consisting of a PWM pulse cover is applied between the gate and source of the main switch Q1.
- FIG. Figure 3 (A) shows the control signal Vg, which is the PWM pulse force output from the switch control circuit 5.
- the main switch Q1 is turned on during the high level period of the control signal Vg in Fig. 3 (A) and turned off during the low level period.
- the switch control circuit 5 is connected to the DC output terminals 4a and 4b. Instead of this, it can be connected to a tertiary winding or the like in which the transformer 2 is not shown.
- the feedback signal forming circuit 5a may be connected anywhere as long as it shows a voltage proportional to the output voltage of the DC output terminals 4a and 4b. Further, a well-known optical coupling transmission line can be included in the feedback signal forming circuit 5a.
- the operation of the switching power supply device of FIG. 1 will be described with reference to FIG.
- the voltage of the DC power source 1 is applied to the primary winding N1, and the current Id shown in FIG. 3 (C) flows through the primary winding N1 and the main switch Q1.
- the synchronous rectification switch 8 and the diode Do of the synchronous rectification element Q2 are non-conductive, energy is stored in the transformer 2.
- the smoothing capacitor Co is already charged, the voltage V2 of the secondary winding N2 and the output voltage Vo of the smoothing capacitor Co during the on period Ton of the main switch Q1 shown in FIG.
- the capacitor C1 is charged based on the voltage Vds between the main terminals of the pair of synchronous rectifier elements Q2 shown in Fig. 3 (B), which has a value corresponding to the sum voltage of The voltage Vcl increases with a slope.
- the Zener diode 23 is provided as shown in FIG. 2
- the capacitor C1 is charged with the first current II having a value proportional to V2 + Vo ⁇ Vz, and the Zener diode 23 is provided. If not, the capacitor C1 is charged with the first current II having a value proportional to V2 + Vo.
- the output of the comparator 20 is changed to a low level as shown in FIG.
- the output of the comparator 20 changes from low level to high level, which causes the output V22 of the NOR circuit 22 to have low high level power.
- the level is switched to ON, and the on-control of the synchronous rectification switch 8 ends. Even if the on-control of the synchronous rectification switch 8 is completed, the current Is flows through the diode Do. Since the current Is only flows through the diode Do only for a very short time and the value of the current is small, the diode Do will not be destroyed.
- the energy of the transformer 2 can be reduced by turning the main switch Q1 on and off. It is possible to easily and accurately set the correspondence between the ratio between the accumulation time and the discharge time and the ratio between the charging time and the discharging time of the capacitor C1, and to set the ideal ON period of the synchronous rectification switch 8. Can do. In other words, the on-period of the synchronous rectification switch 8 is almost matched with the energy release period of the transformer 2 to maximize the efficiency improvement effect of the synchronous rectification. In addition, it is possible to suppress the occurrence of noise, circuit damage, and the like caused by the synchronous rectification switch 8 and the main switch Q1 being simultaneously turned on.
- the first and second current sources 9 and 10 are current mirror circuits in the circuit of FIG. 2, the first and second currents II and 12 can be easily and accurately set to a desired ratio. it can.
- the Zener diode 23 having the same voltage Vz as the output voltage Vo is provided in the circuit of FIG. 2, when the output voltage Vo is constant, the values of the first and second collector resistors R1 and R2 Is set to be the same, the ideal on-period of the synchronous rectification switch 8 is set.
- the selective discharge diode 11a and the bias diode l ib function as a means for inhibiting the discharge of the capacitor C1 during the ON period of the main switch Q1, so the capacitor during the ON period of the main switch Q 1 Disabling discharge of C 1 can be easily achieved.
- the semiconductor integration of the synchronous rectification control circuit 7 can be easily achieved.
- the synchronous rectification control circuit 7 Since the synchronous rectification control circuit 7 is integrated in a semiconductor, the number of parts of the synchronous rectification control circuit 7 is increased, and the cost can be reduced.
- the first and second transistors Qll and Q12 constituting the current mirror circuit are formed on the same semiconductor substrate, these characteristics can be easily aligned, and a desired current can be accurately supplied. Can do.
- the third and fourth transistors Q1 3 and Q14 constituting the current mirror circuit are formed on the same semiconductor substrate, these characteristics can be easily aligned and the desired current can be accurately obtained. It can flow.
- the synchronous rectification control circuit 7 and the synchronous rectification element Q2 are housed in the same enclosure, that is, the package, the synchronous rectification circuit 3 becomes a component, and the increase in the number of components and cost can be suppressed.
- Example 2 Next, a switching power supply device according to the second embodiment shown in FIG. 4 will be described.
- FIG. 4 and FIGS. 5 to 16 to be described later substantially the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. Also, refer to FIG. 1 and FIG. 3 in the description of FIG. 4 to FIG.
- the switching power supply device of FIG. 4 is formed in the same manner as FIGS. 1 and 2 except that it has a modified synchronous rectifier circuit 3a. Further, the modified synchronous rectification circuit 3a of FIG. 4 is formed in the same manner as FIG. 2 except for the modified synchronous rectification control circuit 7a.
- the synchronous rectification control circuit 7a of FIG. 4 is formed in the same manner as FIG. 2 except for the modified first current source 9a.
- the first collector resistor R1 in the first current source 9a in FIG. 4 is connected between the collector of the second transistor Q12 and one end of the secondary winding N2.
- the first current source 9a in FIG. 4 is formed in the same way as in FIG. 2 except that the Zener diode 23 is omitted and the connection location of the first collector resistor R1 is changed.
- the modified first current source 9a has a function of optimally charging the capacitor C1 regardless of the change of the output voltage Vo. That is, the voltage Vz of the Zener diode 23 in FIG. 2 is fixed and does not change following the change of the output voltage Vo. Therefore, the circuit of FIG. 2 cannot supply the optimum charging current to the capacitor C1 when the output voltage Vo changes.
- the first current source 9a in FIG. 4 supplies the optimum charging current to the capacitor C1 regardless of the change in the output voltage Vo.
- the optimum charging current can be supplied to the capacitor C1 by the first current source 9a of FIG. 4 regardless of the change of the output voltage Vo.
- the voltage V2 of the secondary winding N2 is applied to the first collector resistor R1 via the first diode D1 and the second transistor Q12. Therefore, the current flowing through the first collector resistor R1 is (V2 -V -V
- the first and second transistors Qll and Q12 are current mirror circuits.
- the current II flowing through the collector of the first transistor Q11 is the same as the current flowing through the first collector resistor R1, and can be expressed by the following equation.
- This equation (14) is the same as the aforementioned equation (10), and has a value unrelated to the output voltage Vo. Therefore, according to the second embodiment of FIG. 4, an optimum synchronous rectification period can be obtained regardless of the change of the output voltage Vo. Further, since the Zener diode 23 is not used, the cost can be reduced by this amount.
- the second current source 10 the selective discharge diode l la, the diode for diode l ib, and the pulse forming circuit 12 of the second embodiment of FIG. 4 are configured in the same manner as those of the first embodiment of FIG. Therefore, the same effects as those of the first embodiment can be obtained.
- the switching power supply according to Embodiment 3 shown in FIG. 5 has the same configuration as that of FIGS. 1, 2, and 4 except for the modified synchronous rectifier circuit 3b. Further, the synchronous rectification circuit 3b of FIG. 5 is formed in the same manner as FIG. 4 except for the modified synchronous rectification control circuit 7b.
- the synchronous rectification control circuit 7b in FIG. 5 omits the selective discharge diode 11a and the bias diode l ib in FIG. 4 and instead uses two voltage dividing resistors 31 and 32 and a comparator 33 as discharge prohibiting means.
- a reference voltage source 34 and a discharge control switch Q5 are provided, and the others are formed in the same manner as in FIG.
- the third transistor Q13 is directly connected in parallel to the capacitor C1.
- a discharge control switch Q5 composed of an FET is connected in parallel to the fourth transistor Q14.
- the positive input terminal of the comparator 33 for determining the ON period of the main switch Q1 is connected to the voltage dividing point of the two voltage dividing resistors 31, 32, and the negative input terminal is connected to the reference voltage source 34. It is.
- the series circuit of the voltage dividing resistors 31 and 32 is connected between the drain and the source of the synchronous rectifier Q2 via conductors 18 and 19. Therefore, as shown in Fig.
- the discharge control switch Q5 Since the output terminal of the comparator 33 is connected to the control terminal (gate) of the discharge control switch Q5, the discharge control switch Q5 is turned on while the main switch Q1 is on, and the third and fourth transistors Q13 Q14 is prohibited from turning on and capacitor C1 is prevented from discharging. As a result, the third and fourth transistors Q13 and Q14 conduct only during the off period Toff of the main switch Ql and pass the second current 12.
- the voltage dividing resistors 31 and 32 are independently provided for the input of the comparator 33. However, the voltage dividing resistors 31 and 32 are omitted, and the voltage dividing resistors 15 and 15 of the conduction allowable period detecting means 13 are omitted. Sixteen voltage dividing points can be connected to the positive input terminal of comparator 33. Further, the comparator 33 can be omitted, and the output of the switch control circuit 5 in FIG. 1 can be supplied to the control terminal of the discharge control switch Q5 in FIG. 5 instead. In short, the control circuit of the discharge control switch Q5 is not limited to the voltage dividing resistors 31, 32, the comparator 33, and the reference voltage source 34. Any circuit that can do this is acceptable.
- Example 3 of FIG. 5 has the same function as the selective discharge diode 11a of FIG. 4, Example 3 of FIG. 5 has the same effect as Example 2 of FIG. Have.
- the switch 11 in FIG. 1 and the selective discharge diode 11a in FIG. 2 may be omitted, and a switch corresponding to the discharge control switch Q5 in FIG. 5 may be provided instead.
- the switching power supply device is formed in the same manner as in FIGS. 1, 2 and 5 except for the modified synchronous rectifier circuit 3c.
- the modified synchronous rectification control circuit 7c in FIG. 6 has a discharge resistor Rd in parallel with the capacitor C1 in FIG. 5, and the others are synchronized in FIG. It is formed in the same manner as the rectification control circuit 7b.
- the discharge resistor Rd in Fig. 6 is provided to prevent the discharge of the capacitor C1 from ending within the off period Toff of the main switch Q1 when the output voltage Vo abnormally decreases. As shown in Fig.
- the switch control circuit 5 that feedback-controls the output voltage Vo is provided, the switch control circuit is switched into a short-circuited state, that is, an impedance short-circuited state between the pair of DC output terminals 4a and 4b. 5 works to limit the ON width of the main switch Q1, and the output voltage Vo drops abnormally. Also, as shown in FIG. 1, the output voltage Vo abnormally decreases when a well-known overcurrent protection circuit is activated. When the output voltage Vo decreases in this way, the on-period Ton of the main switch Q1 becomes longer than that at normal load in order to compensate for this decrease. As a result, the peak value of the voltage Vcl of the capacitor C1 increases. On the other hand, when the output voltage Vo decreases as described above, the base-emitter voltage V power of the fourth transistor Q14 of the second current source 10 decreases.
- Embodiment 4 in FIG. 6 is the same as FIG. 5 except for the discharge resistor Rd, the same effect as Embodiment 3 in FIG. 5 can be obtained. Note that the same discharge resistor Rd as shown in FIG. 6 can be connected in parallel to the capacitor C1 shown in FIGS.
- the switching power supply apparatus is formed in the same manner as in FIGS. 1, 2 and 5 except for the modified synchronous rectifier circuit 3d. Further, the synchronous rectification circuit 3d in FIG. 7 is formed in the same manner as FIG. 5 except for the modified synchronous rectification control circuit 7d.
- the synchronous rectification control circuit 7d in FIG. 7 includes the modified first current source 9b and the synchronous rectification in FIG. 5 except that the forced discharge switch 40 and the forced discharge logic circuit 41 are provided.
- Control circuit 7 It is formed the same as b.
- the first current source 9b in FIG. 7 is connected to the first emitter resistor R11 in place of the first diode D1 of the first current source 9a in FIG. 5, and the emitter of the second transistor Q12 is connected.
- FIG. 5 instead of connecting to the emitter of the first transistor Q11, it is connected to the drain electrode of the synchronous rectifier Q2 via the second emitter resistor R12 and the conductor 18, and the others are connected to the first current source of FIG. It corresponds to the one formed in the same way as 9a.
- R2 R12Z ⁇ R11 (R12 + R1) ⁇ is set in the above equation, it becomes the same as the above equation (9), and ideal synchronous rectification can be obtained easily and accurately.
- first current source 9b in FIG. 7 can be connected in place of the first current source 9 in FIG. 2 or the first current source 9a in FIGS.
- the forced discharge switch 40 shown as a field effect transistor is connected in parallel to the capacitor C1.
- the logic circuit 41 as the forced discharge control circuit is composed of an inhibit AND gate, and is connected to the non-inverting input terminal connected to the output terminal of the comparator 20 and the voltage dividing points of the two voltage dividing resistors 15 and 16. It has an inverting input terminal and an output terminal connected to the control terminal (gate) of the forced discharge switch 40.
- the logic circuit 41 composed of an inhibit AND gate outputs an output having the same logic as the signal at the non-inverting input terminal only when the inverting input terminal is at logic 0, that is, at a low level.
- the logic circuit 41 can be an AND gate, and a NOT circuit can be connected between the voltage dividing points of the voltage dividing resistors 15 and 16 and one input terminal of the AND gate.
- the logic circuit 41 includes the drain and source of the synchronous rectifier Q2 in FIG. 3B shown in t3 to t4 in FIG.
- a high level output is generated when the inter-terminal voltage Vds is low and the output V20 of the comparator 20 shown in FIG. 3 (F) is high.
- the forced discharge switch 40 is turned on during the period from t2 to t4 in FIG. 3, and the charge of the capacitor C1 is forcibly released.
- capacitor C1 is forcibly discharged at the same time that synchronous rectifier Q2 is turned off.
- the charge of the capacitor C1 is zero at the start of the ON period Ton of the main switch Q1, and this state force also means that charging starts.
- the forced discharge circuit of capacitor C1 is provided to cope with the case where the current of transformer 2 switches from discontinuous mode to continuous mode.
- the main switch Q1 When the main switch Q1 is on / off controlled at a constant frequency, the load condition Depending on the situation, the main switch Q1 may be turned on before the stored energy of the transformer 2 is released, and a continuous mode in which the current of the transformer 2 continuously flows may occur. If the forced discharge circuit composed of the forced discharge switch 40 and the logic circuit 41 in FIG.
- the fifth embodiment of FIG. 7 has the same effect as that of the first to fourth embodiments of FIGS. 1 to 6 and the above-described forced discharge circuit.
- a forced discharge circuit composed of the forced discharge switch 40 and the logic circuit 41 can be added to the synchronous rectification control circuits 7, 7a, 7b, and 7c in FIGS. 1, 2, 4, 4, 5, and 6. .
- a forced discharge circuit similar to that in FIG. 7 is provided in the synchronous rectification control circuit in which the first and second current sources 9b and 10 in FIG. 7 are replaced with a charging circuit and a discharging circuit other than a current mirror circuit having a constant current characteristic. be able to.
- another comparator having the same function as that of the comparator 20 can be provided, and the output of this other comparator can be sent to the logic circuit 41 instead of the output of the comparator 20. Further, instead of sending the output of the comparator 20 to the logic circuit 41, the output of the discharge control comparator 33 can be inverted and sent to the logic circuit 41.
- the inverting input terminal of the logic circuit 41 can be connected to the voltage dividing point of the voltage dividing resistors 31 and 32 for discharge control, or can be connected to the output line of the switch control circuit 5 in FIG. Example 6
- the switching power supply device of Example 6 in FIG. 8 is formed in the same manner as in FIG. 1, FIG. 2 and FIG. 7 except for the modified synchronous rectifier circuit 3e. Further, the synchronous rectification circuit 3e of FIG. 8 is formed in the same manner as FIG. 7 except for the modified synchronous rectification control circuit 7e.
- the synchronous rectification control circuit 7e in FIG. 8 is provided with a pulse forming circuit 41a as a forced discharge control circuit instead of the forced discharge logic circuit 41 in FIG. 7, and the rest is the same as the synchronous rectification control circuit 7d in FIG. Formed.
- FIG. 9 shows the state of each part of the switching power supply device of Example 6 in FIG. 8 as in FIG. However, the output V41a of the pulse forming circuit 41a is shown in FIG. 9 (F) instead of V20 in FIG. 3 (F).
- the pulse forming circuit 41a in FIG. 8 forms a pulse with a time width sufficiently shorter than the on period Ton in synchronization with the end of turning off of the main switch Q1, that is, the start of turning on, to the forced discharge switch 40.
- the noise forming circuit 41a is connected to the voltage dividing points of the voltage dividing resistors 15 and 16, and is turned on in synchronization with the on-start time t2 of the main switch Ql as indicated by t2 to t3 in FIG.
- a very narrow pulse is generated sufficiently shorter than the period Ton.
- the pulse forming circuit 41a can be formed by a timer or a differentiating circuit triggered at the on-start time t2.
- the forced discharge switch 40 is turned on in response to the pulse of the pulse forming circuit 41a to forcibly discharge the capacitor C1.
- a forced discharge circuit composed of the pulse forming circuit 41a and the forced discharge switch 40 of FIG. 8 can be added to the circuits of FIGS. 1, 2, and 4 to 6.
- the pulse forming The input terminal of the line 4 la can be connected to the voltage dividing point of the voltage dividing resistors 31 and 32, or can be connected to the output line 26 of the switch control circuit 5 in FIG.
- a charging / discharging circuit and a discharging circuit having no constant current characteristic can be provided.
- the switching power supply device is formed in the same manner as FIG. 1 except for the modified synchronous rectifier circuit 3f. Further, the synchronous rectifier circuit 3f in FIG. 10 has the same configuration as that in FIG. 2 except for the modified synchronous rectifier control circuit 7f. The synchronous rectifier circuit 7f shown in FIG. 10 has the same configuration as that shown in FIG. 2 except that a modified first current source 9c is provided and the selective discharge switch 11a and the bias diode ib are omitted.
- the first current source 9c in FIG. 10 corresponds to the first current source 9 in FIG. 2 in which the Zener diode 23 is omitted.
- the third transistor Q13 of the second current source 10 in FIG. 10 is directly connected in parallel with the capacitor.
- the first current II supplied from the first current source 9c in FIG. 10 is the same as the above-described equation (11), and can be expressed as follows.
- the second current 12 of the second current source 10 can be expressed by the following equation.
- the charging current Ic of the capacitor C1 can be expressed by the following equation.
- the charging current Ic in Eq. (15) is the capacitor charging current as in the first current II in Eq. (10), and has a value unrelated to the output voltage Vo as in Eq. (10).
- the switching power supply device has the same configuration as that of FIG. 1 except for the modified synchronous rectifier circuit 3g.
- the synchronous rectifier circuit 3g in FIG. 11 is the same as FIG. 5 except for the modified synchronous rectifier control circuit 7g.
- the synchronous rectification control circuit 7g of FIG. 11 is formed in the same manner as FIG. 5 except for the modified pulse forming circuit 12a.
- the pulse forming circuit 12a of FIG. 11 is formed in the same manner as FIG. 5 except for the modified comparison and pulse forming circuit 14 ′.
- the comparison and pulse formation circuit 14 in FIG. 11 and the comparison and pulse formation circuit 14 in FIG. 5 are added with a light load determination comparator 50, a light load determination reference voltage source 51, and an RS flip-flop 52.
- the synchronous rectification control circuit 7g in FIG. 11 has the function of turning on the synchronous rectification switch 8 during the off period of the main switch Q3 and the load 4 connected between the pair of DC voltage output terminals 4a and 4b is rated load. And a function for determining whether or not the load 4 is lower than the predetermined load level, and a function for prohibiting the on-control of the synchronous rectification switch 8 when the load 4 is lower than the predetermined load level.
- a function for determining whether or not the load 4 is lower than the predetermined load level
- a function for prohibiting the on-control of the synchronous rectification switch 8 when the load 4 is lower than the predetermined load level are examples of the load 4 is lower than the predetermined load level.
- the added comparator 50, reference voltage source 51, and RS flip-flop 52 are such that the load connected between the pair of DC power supply terminals 4a and 5b is significantly lighter than the rated load (normal load). It is used to judge whether or not there is a certain force, and to prohibit the on-drive of the synchronous rectification switch 8 under light load conditions. If the on-drive of the synchronous rectification switch 8 is prohibited at light load, the efficiency of the switching power supply at light load is improved. That is, when the synchronous rectification switch 8 is turned on, the power loss in the diode Do on the output side of the secondary winding N2 is reduced as described above.
- the current on the secondary side at a load lighter than the rated load is smaller than the secondary current at the rated load, and the amount of power loss reduced by the synchronous rectification switch 8 is also reduced.
- it is shown as having the drive function of the switch 8 for synchronous rectification When the synchronous rectifier switch 8 is turned on by the NOR circuit 22, power loss occurs. This power loss during on-drive is almost constant regardless of the load change. For this reason, when the load is light, the amount of power loss due to the driving of the synchronous rectification switch 8 is larger than the loss reduction amount based on the synchronous rectification switch 8. Therefore, in the eighth embodiment of FIG. 11, the driving of the synchronous rectification switch 8 is prohibited at light load.
- the positive input terminal of the light load determination comparator 50 in FIG. 11 is connected to the capacitor C1, and the negative input terminal is connected to the reference voltage source 51 indicating a predetermined light load.
- the reference voltage V51 of the reference voltage source 51 is the difference between the maximum value of the voltage Vc 1 of the capacitor C 1 at normal load and the reference voltage value Vr of the reference voltage source 21 for synchronous rectification as shown by the chain line in FIG. It is set to a value higher than the maximum value of the voltage Vcl of the capacitor C1 at the time of light load.
- a preferable value of the reference voltage V51 of the reference voltage source 51 is 5 to 30% of the maximum value of the voltage Vcl at the normal load, that is, at the rated load.
- the reference voltage V51 of the reference voltage source 51 is obtained by reducing the amount of power loss due to the driving of the synchronous rectifying switch 8 and the amount of power loss caused by the driving of the synchronous rectifying switch 8 when the load amount is equal to the capacitor C1. It is desirable to be equal to the maximum value of voltage Vcl.
- the set input terminal S of the RS flip-flop 52 is connected to the comparator 20 for determining the synchronous rectification period, the reset input terminal R is connected to the light load determination comparator 50, and the output terminal Q is connected to the NOR circuit 22.
- the voltage Vcl of the capacitor C1 is proportional to the on-time width of the main switch Q1 in FIG.
- the ON time width of the main switch Q1 becomes narrower than that at the normal load. Therefore, the voltage of capacitor C1 becomes low at light load.
- the output of the comparator 50 continuously goes low, making it impossible to reset the RS flip-flop.
- the RS flip-flop 52 maintains the state set by the output of the synchronous rectification comparator 20, and the output of the RS flip-flop 52 becomes continuously high.
- the load is light, the output of the NOR circuit 22 continuously becomes a low level, and the on-drive of the synchronous rectification switch 8 is prohibited.
- the light load determination means can be configured other than the circuit of FIG. For example, instead of inputting the voltage Vcl of the capacitor C1 to the comparator 50, a means for generating a signal indicating the light load mode by linking with the switching of the size of the load 4 is provided. A low level signal can be input to the comparator 50. Further, the comparator 50 can be omitted, and a signal indicating the light load mode can be directly input to the reset terminal of the RS flip-flop 52.
- a drive prohibiting switch for prohibiting the on-drive of the synchronization organizing switch 8 can be provided.
- This drive prohibiting switch is connected to, for example, a power supply line (not shown) of the NOR circuit 22 and is on / off controlled by the output of the comparator 50.
- a drive circuit is provided at the output stage of the NOR circuit 22 and the above-mentioned drive prohibition switch is connected to the power supply line of this drive circuit, and this drive prohibition switch is controlled to be turned off at light load. 8 can be prohibited.
- the comparator 20 of FIG. 10 can have a known hysteresis.
- the lower trigger level of the comparator 20 hysteresis is set to the reference voltage value Vr in Fig. 3 (E)
- the upper trigger level is set to the reference voltage value Vr and the maximum value of the normal voltage Ccl of the capacitor C1.
- the reference voltage V51 has a value higher than the maximum value of the voltage Vc1 of the capacitor C1 at light load.
- the on-drive of the synchronous rectification switch 8 can be prohibited. Therefore, the same effect as the circuit of FIG. 11 can be obtained by providing the comparator 20 with hysteresis.
- the lower trigger level in hysteresis operation is a comparator having hysteresis
- the 20 means that the output of the comparator 20 changes when the lower trigger level crosses the lower trigger level from the high level to the low level.
- the upper trigger level means that the input of the comparator 20 is higher than the upper trigger level. This means the level at which the output of comparator 20 changes when the trigger level crosses the low level side force to the high level side.
- the discharge circuit 10a in FIG. 11 is shown as including the second current source 10, the resistors 31, 32, the comparator 33, the reference voltage source 34, and the switch Q5 in FIG.
- Example 8 of FIG. 11 has the same effect as Examples 1-7 in addition to the effect based on prohibiting synchronous rectification at light load.
- the reference voltage source 51, the RS flip-flop 52, and the means for prohibiting synchronous rectification at the time of a light load or those having the same function as those of FIG. 11, FIG. 2, FIG. 4, FIG.
- the circuit of FIG. 7, FIG. 8, and FIG. 10 can also be applied.
- FIG. 12 shows the secondary winding N 2 and the output side circuit of the switching power supply device according to the ninth embodiment.
- the primary side circuit of the switching power supply of Example 9 is the same as that shown in FIG.
- the switching power supply of Example 9 is configured as a forward type DC-DC converter, and the polarity of the secondary winding N2 in FIG. 12 is set opposite to that in FIG.
- Secondary winding N2 is connected to DC output terminals 4a and 4b via rectifier diode 60, smoothing circuit 3h and smoothing capacitor Co.
- the smoothing capacitor Co is shown with the force shown outside the smoothing circuit 3h.
- the smoothing circuit 3h in FIG. 12 is connected in parallel to the inductor L1 connected in series to the line between the secondary winding N2 and the smoothing capacitor Co, and to the inductor L1 and the smoothing capacitor Co. And a synchronous rectification control circuit 7d.
- Synchronous rectification element Q2 is a force generally called a commutation rectification element, a flywheel element, or a smoothing rectification element.
- Q2 is also synchronous rectification in FIG. It will be called an element.
- the synchronous rectifying device Q2 in Fig. 12 has the same configuration as in Examples 1 to 8, and is connected in parallel to the secondary winding N2 via a diode 60 as a rectifying device.
- Figure 12 Synchronous rectification control circuit 7d has the same configuration as that shown by the same reference numerals in FIG.
- the rectifier diode 60 Since the rectifier diode 60 is conductive during the ON period of the main switch Q1, energy is stored in the inductor L1 during the ON period of the main switch Q1. As is well known, the energy stored in the inductor L1 is released through a path including the inductor L1, the smoothing capacitor Co, and the synchronous rectifier Q2.
- the operation in which the synchronous rectifier element Q2 in FIG. 12 conducts during the discharge period of the stored energy of the inductor L1 is the same as the operation in which the synchronous rectifier element Q2 conducts in the discharge period of the stored energy of the transformer 2 in Examples 1-8.
- the circuit consisting of the main switch Q1, the transformer 2 and the diode 60 can be called an intermittent voltage supply means or an intermittent voltage supply switching means for supplying voltage to the inductor L1 intermittently. .
- the synchronous rectification switch 8 of the synchronous rectification element Q2 is turned on so as to substantially coincide with the discharge period of the stored energy of the inductor L1. It becomes possible to drive the synchronous rectification switch 8 and to reduce the power loss in the smoothing circuit 3h.
- Capacitor CI in Figure 12 ignores diodes Dl, D2 V, transistors Qll, Q12 V
- the maximum value of voltage Vcl of capacitor C1 is as follows.
- Vcl (V2-Vo) Ton / (R1C1)
- the capacitor C1 is discharged by the second current 12 expressed by the following equation.
- the discharge time of the capacitor C1 is the same as the discharge time Td of the stored energy of the inductor L1. Therefore, if the resistors R1 and R2 are set to the same value in the ninth embodiment, the synchronous rectification switch 8 can be turned on for an optimum time as in the first to eighth embodiments.
- the force that allows continuous current to flow through inductor L1 is because capacitor C1 is discharged every period by forced discharge switch 40, so the charge / discharge time of capacitor C1 is limited to the change in current in inductor L1. Can be matched.
- FIG. 13 shows a chopper type switching power supply apparatus according to the tenth embodiment.
- the main switch Q1 as an intermittent voltage supply means is connected in series between the DC power supply terminal la and the output terminal 4a, and is turned on / off by a control signal output from the switch control circuit 5a.
- DC output terminals 4a and 4b are connected to the output side of the main switch Q1 through the same smoothing circuit 3h and smoothing capacitor Co as in Fig. 12.
- the input voltage Vin of the DC power supply terminals la and lb is intermittently input to the smoothing circuit 3h by the main switch Q1. Therefore, with the smoothing inductor L1 as a reference, the main switch Q1 can be called an intermittent voltage supply means or an intermittent voltage supply switching means for supplying voltage to the inductor L1 intermittently.
- the synchronous rectification switch 8 in the circuit of FIG. 13 operates equivalently when the voltage V2 of the secondary winding N2 of FIG. 12 is replaced with the voltage of the smoothing inductor L1, and has the same effect as the embodiment 9 of FIG. be able to.
- the NOT circuit 20a shown in FIG. 14 is used instead of the comparator 20 and the reference voltage source 21 in the comparison and pulse forming circuit 14 shown in FIG. 1, FIG. 2, FIG. 4 to FIG. Can be provided.
- the NOT circuit 20a in Fig. 14 has a threshold value similar to the reference voltage value Vr, shapes the voltage Vcl of the capacitor C1 into a binary waveform, and outputs the same pulse as in Fig. 3 (F). .
- an input inverting AND circuit 22a can be provided instead of the NOR circuit 22 of each of the embodiments described above.
- NOR circuit 20b connected to the capacitor C1 can be provided instead of the NOT circuit 20a in FIG.
- the two inputs of NOR circuit 20b are short-circuited, it functions in the same way as the NOT circuit.
- a NOT circuit 22b and an AND circuit 20c can be provided instead of the comparator 20, the reference voltage source 21 and the NOR circuit 22 in FIG. it can.
- One input terminal of the AND circuit 20c is connected to the voltage dividing conductor 17 via the NOT circuit 22b, and the other input terminal is connected to the capacitor C1.
- the input terminal connected to the capacitor of the AND circuit 20c has a threshold value corresponding to the reference voltage value Vr in Fig. 1 and shapes the voltage Vcl of the capacitor C1. Generate output.
- the present invention can be applied to other switching power supply devices such as a well-known step-up DC-DC converter.
- the first and second emitter resistors Rl l and R12 in FIGS. 7 and 8 can be omitted.
- the present invention can be used for a DC power supply device.
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US11/614,474 US7262977B2 (en) | 2004-07-02 | 2006-12-21 | Switching-mode power supply having a synchronous rectifier |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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JP2004-196685 | 2004-07-02 | ||
JP2004196685A JP4126558B2 (ja) | 2004-07-02 | 2004-07-02 | スイッチング電源装置 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US11/614,474 Continuation US7262977B2 (en) | 2004-07-02 | 2006-12-21 | Switching-mode power supply having a synchronous rectifier |
Publications (1)
Publication Number | Publication Date |
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WO2006003951A1 true WO2006003951A1 (ja) | 2006-01-12 |
Family
ID=35782758
Family Applications (1)
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PCT/JP2005/011985 WO2006003951A1 (ja) | 2004-07-02 | 2005-06-29 | スイッチング電源装置 |
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US (1) | US7262977B2 (ja) |
JP (1) | JP4126558B2 (ja) |
CN (1) | CN100505497C (ja) |
WO (1) | WO2006003951A1 (ja) |
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CN105305844B (zh) * | 2015-10-21 | 2017-11-21 | 深圳市芯茂微电子有限公司 | 一种隔离型同步整流控制电路及其装置与控制方法 |
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- 2005-06-29 WO PCT/JP2005/011985 patent/WO2006003951A1/ja active Application Filing
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Also Published As
Publication number | Publication date |
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CN1965466A (zh) | 2007-05-16 |
JP2006020444A (ja) | 2006-01-19 |
CN100505497C (zh) | 2009-06-24 |
JP4126558B2 (ja) | 2008-07-30 |
US20070103946A1 (en) | 2007-05-10 |
US7262977B2 (en) | 2007-08-28 |
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