1. Field of the Invention
The present invention relates to a power source apparatus for providing a DC voltage, and particularly, to a technique of balancing currents in such a power source apparatus.
2. Description of the Related Art
A secondary winding S of the transformer T is connected to a rectifying-smoothing circuit consisting of an output diode D5 and a capacitor C51. The output diode D5 consists of a diode D51 and a diode D52 that are connected in parallel with each other. The rectifying-smoothing circuit rectifies an AC voltage induced on the secondary winding S of the transformer T, smoothes the rectified voltage, and outputs the smoothed voltage to output terminals +Vout and −Vout.
Between the output terminals +Vout and −Vout, resistors R53 and R54 are connected as voltage dividing resistors for dividing the output voltage Vo. Also between the output terminals +Vout and −Vout, an error detector is connected. The error detector has a light emitting diode of a photocoupler PC1, a resistor R52, and a shunt regulator Z51 that are connected in series. The shunt regulator Z51 has a reference terminal R connected to a connection point of the resistors R53 and R54. Between a connection point of the resistors R53 and R54 and a connection point between the resistor R52 and the shunt regulator Z51, a capacitor C52 is connected.
The transformer T has an auxiliary winding C that is connected to a rectifying-smoothing circuit composed of a diode D4 and a capacitor C2. The rectifying-smoothing circuit rectifies an AC voltage induced on the auxiliary winding C of the transformer T, smoothes the voltage into a DC voltage, and supplies the DC voltage as a source voltage to a controller CONT.
The light emitting diode of the photocoupler PC1 in the error detector sends a feedback signal to a phototransistor of the photocoupler PC1. The feedback signal is an error voltage (a difference between the output voltage Vo and a reference voltage) based on which the controller CONT generates a control signal to turn on/off the switching element Q1. By controlling a duty factor of the control signal, the controller CONT maintains the output voltage Vo at a predetermined value.
Operation of the power source apparatus according to the related art of
When the switching element Q1 is turned on, a current passes through a path extending along the capacitor C1, the primary winding P of the transformer T, the switching element Q1, and the capacitor C1, to accumulate energy in the transformer T. When the switching element Q1 is turned off, the energy accumulated in the transformer T is rectified and smoothed through the secondary winding S of the transformer T, the output diode D5 (composed of the diodes D51 and D52), and the capacitor C51 into a DC voltage. The DC voltage is provided as the output voltage Vo from the output terminals +Vout and −Vout.
The output voltage Vo from the output terminals +Vout and −Vout is divided by the resistors R53 and R54 and is sent to the reference terminal R of the shunt regulator Z51. The shunt regulator Z51 compares the voltage at the reference terminal R with an internal reference voltage of the shunt regulator Z51. If the voltage (proportional to the output voltage Vo) at the reference terminal R is higher than the reference voltage, the shunt regulator Z51 sets a cathode terminal K thereof to low. This results in passing a current through a path extending along the output terminal +Vout, the light emitting diode of the photocoupler PC1, the resistor R52, the shunt regulator Z51, and the output terminal −Vout, to transmit a feedback signal to the primary side through the photocoupler PC1.
The feedback signal transmitted to the primary side is received by the phototransistor of the photocoupler PC1 and is sent to a feedback terminal FB of the controller CONT. According to the feedback signal, the controller CONT controls the duty factor of a drive voltage supplied to the gate terminal of the switching element Q1. In this way, whenever the switching element Q1 is turned on/off, energy accumulated in the transformer T is adjusted to maintain the output voltage Vo at a predetermined value.
If the power source apparatus of
The power source apparatus of the related art employs standard silicon (Si) diodes as the output diodes D51 and D52.
The first DC-DC converter DD1 converts a DC voltage supplied to input terminals +IN and −IN into a second DC voltage. Similarly, the second DC-DC converter DD2 converts the DC voltage supplied to the input terminals +IN and −IN into the second DC voltage. The first and second DC-DC converters DD1 and DD2 are connected in parallel with each other with the use of a diode OR configuration.
Namely, a first output terminal of the first DC-DC converter DD1 is connected through the reverse-current preventing diode D1 to the output terminal +Vout and a second output terminal thereof is connected through the current detecting resistor RS1 to the output terminal −Vout. Similarly, a first output terminal of the second DC-DC converter DD1 is connected through the reverse-current preventing diode D2 to the output terminal +Vout and a second output terminal thereof is connected through the current detecting resistor RS2 to the output terminal −Vout.
The output terminal −Vout is connected to the first and second DC-DC converters DD1 and DD2. The first and second DC-DC converters DD1 and DD2 are connected to each other through respective current balance terminals. The current detecting resistor RS1 provides a detected voltage, which is amplified by an amplifier. The amplified voltage is passed through an impedance element and is outputted from the current balance terminal of the first DC-DC converter DD1. Similarly, the current detecting resistor RS2 provides a detected voltage, which is amplified by an amplifier. The amplified voltage is passed through an impedance and is outputted from the current balance terminal of the second DC-DC converter DD2.
Each of the first and second DC-DC converters DD1 and DD2 is configured like, for example,
The diode OR structure usually employs silicon diodes. When passing a current, the silicon diode generates heat to decrease a forward voltage Vf and further increase an output current, thereby causing a current unbalance between the diodes that form the diode OR structure. To avoid the problem, the power source apparatus of the related art shown in
Another current balancing technique is disclosed in Japanese Unexamined Patent Application Publication No. H06-339263. This disclosure is an output current balancing DC-DC converter capable of balancing output currents and stabilizing operation even if the output voltage of one power source abnormally increases. According to this DC-DC converter, an output voltage corrector is arranged between the anode and cathode of an OR diode. The output voltage corrector includes a first amplifier. An inverting terminal of the first amplifier is connected to a voltage detecting resistor that is connected to the cathode of the OR diode, and a non-inverting terminal of the first amplifier is connected to a voltage detecting resistor that is connected to the anode side of the OR diode. An output terminal of the first amplifier is connected through a correction resistor to a connection point between two output voltage detecting resistors. A connection point between the two output voltage detecting resistors is connected to an input terminal of a second amplifier arranged in a controller. The second amplifier compares an output voltage of the output voltage corrector with a reference voltage and sends a comparison result to a power source adjusting feedback circuit.
The related art shown in
The related art shown in
According to the present invention, a power source apparatus capable of minimizing losses and the number of parts and balancing currents can be provided.
According to a first aspect of the present invention, provided is a power source apparatus having a series circuit connected between output terminals of a DC power source and including a primary winding of a transformer and a switching element; a controller configured to control an ON/OFF operation of the switching element; and an output diode connected between terminals of a second winding of the transformer and configured to rectify an alternating current that is induced on the secondary winding when the controller turns on/off the switching element. The output diode includes a plurality of diodes that are connected in parallel with one another and are made of wide-gap semiconductor.
According to a second aspect of the present invention, provided is a power source apparatus having a first power source unit configured to output a direct current; a second power source unit configured to output a direct current; a first diode made of wide-gap semiconductor and having an anode connected to an output terminal of the first power source unit; and a second diode made of the wide-gap semiconductor and having an anode connected to an output terminal of the second power source unit and a cathode connected to a cathode of the first diode.
Embodiments of the present invention will be explained in detail with reference to the accompanying drawings.
In
In
The power source apparatus according to the first embodiment of the present invention shown in
In
Unlike the diodes D51 and D52 of the related art shown in
The SiC or GaN diode increases the forward voltage Vf thereof as the forward current If thereof increases. The forward voltage Vf of the SiC or GaN diode also increases as the temperature thereof increases. When devices (for example, the diodes D53 and D54) made of wide-gap semiconductor are connected in parallel with each other, the forward voltage Vf of each device increases as the forward current If thereof increases, thereby balancing currents passing through the parallel devices.
In
The first embodiment has other advantages that no thermal coupling is required between the two diodes D53 and D54 and that these diodes can easily be operated in parallel. Variations in the forward voltages Vf of the diodes D53 and D54 are compensated by temperature increase, and therefore, currents passing through these diodes can ideally be balanced. The currents are balanced while the output voltage Vo is being kept at a constant value, and therefore, the output power of the diodes is balanced. Even if the diodes D53 and D54 are operated at a bias point where the forward current If is low in
According to the first embodiment, the diodes D53 and D54 are made of wide-gap semiconductor such as gallium nitride (GaN) and silicon carbide (SiC). The diodes D53 and D54 may each have a Schottky barrier diode structure.
In this way, the power source apparatus according to the present embodiment employs the output diode for rectifying an alternating current induced on a secondary winding of a transformer from a plurality of wide-gap-semiconductor diodes that are connected in parallel with one another. Due to a forward voltage drop occurring in each wide-gap-semiconductor diode, currents passing through the diodes are balanced. The apparatus according to the present embodiment employs no special circuit for balancing currents, and therefore, causes no loss. Namely, the apparatus of the present embodiment can balance currents with a small number of parts, and therefore, is highly efficient, inexpensive, and reliable.
Compared with the power source apparatus of the related art shown in
Instead of the reverse-current preventing diodes D1 and D2 of the related art of
The power source apparatus according to the second embodiment employs wide-gap-semiconductor diodes as the reverse-current preventing diodes D6 and D7 for the parallel DC-DC converters DD1 and DD2. These diodes each increase a forward voltage Vf in proportion to an increase in a load current. Accordingly, the apparatus of the second embodiment can balance output currents of the two DC-DC converters without employing current detecting circuits or current balancing circuits.
Any variation in the forward voltages Vf of the diodes D6 and D7 is compensated by a temperature increase, to realize an ideal current balance. The current balance is achieved with an output voltage Vo being kept at a constant value, and therefore, output power is naturally balanced.
According to the present embodiment, the diodes D6 and D7 are made of wide-gap semiconductor such as gallium nitride (GaN) and silicon carbide (SiC). The diodes D6 and D7 may each have a Schottky barrier diode structure.
In this way, the power source apparatus according to the present embodiment includes the first wide-gap-semiconductor diode D6 having an anode connected to an output terminal of the first power source unit DD1 and the second wide-gap-semiconductor diode D7 having an anode connected to an output terminal of the second power source unit DD2 and a cathode connected to a cathode of the first diode D6. Due to a forward voltage drop occurring in each wide-gap-semiconductor diode, currents passing through the first and second diodes are balanced. The apparatus according to the present embodiment employs no special circuit for balancing currents, and therefore, causes no loss. Namely, the apparatus of the present embodiment can balance currents with a small number of parts, and therefore, is highly efficient, inexpensive, and reliable.
The present invention is applicable to switching power source apparatuses of high output power and power source systems that drive a plurality of power source units in parallel.
This application claims benefit of priority under 35USC §119 to Japanese Patent Application No. 2006-291505, filed on Oct. 26, 2006, the entire contents of which are incorporated by reference herein. Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.
Number | Date | Country | Kind |
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2006-291505 | Oct 2006 | JP | national |