JPH05304775A - Power supply circuit - Google Patents

Abstract

PURPOSE:To provide a low-noise and high-efficiency power supply circuit using a switching inverter circuit. CONSTITUTION:The title circuit is constituted of a DC-DC converter 11, a switching inverter circuit 12, and an output circuit 13 for rectifying, smoothing, and then taking out the output. An inductance element Ls is connected in series to an output terminal or an input terminal in the converter 11, the switching inverter circuit 12 includes a switching element S12 and a timing control circuit 14 which turns it on or off, and then a voltage resonance circuit according to a capacitor Cp and a current resonance circuit according to a capacitor Cs are formed at the primary side of an output transformer T. The inductance element Ls of the converter 11 is also used as an inductance element for preventing interference which is normally used for the switching inverter circuit 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type switching inverter type power supply circuit.

[0002]

2. Description of the Related Art In the conventional DC power supply circuit configuration, a large power supply transformer is generally used, a commercial AC power supply is connected to its primary winding, and the secondary side output is rectified and smoothed.
In addition to this, there was a small and lightweight power supply called a switching power supply. There were switching inverter power supplies of half bridge, full bridge, push-pull type using switching elements such as transistors and thyristors. However, the conventional switching inverter type power supply has a square wave for both the operating current and the operating voltage.
There was a lot of switching noise. In addition, since it basically operates at a high frequency, power loss is large during the recovery time of the rectifying diode and the turn-off time of the switching transistor, which causes heat generation. In recent years, in such a switching power supply, it has been proposed to use resonance to bring a current or voltage waveform close to a sine wave to reduce noise and improve efficiency (for example, Japanese Patent Laid-Open No. 64-43).
062, JP-A-1-91659, etc.).

[0003]

However, in the conventionally proposed resonance type switching power supply, it is difficult to set the ON / OFF timing of the switching element, and if this setting is insufficient, the efficiency cannot be improved. In addition, even if it is a resonance type, most of the current or voltage waveforms actually approach a sine wave due to resonance, and the noise generated from these switching circuits can be both due to voltage and due to current. Considering this, there was a limit to noise reduction. It is possible to stabilize the output by combining a resonance type switching power supply and a switching converter. Normally, these circuits prevent resonance, smoothing, and mutual interference between circuit elements. It contains many passive elements such as inductance elements and capacitors for interference prevention (isolation), and when simply combined, the configuration becomes complicated,
Miniaturization becomes difficult. The present invention has been made in view of the above points, and an object of the present invention is to provide a power supply circuit of a switching inverter type which can be miniaturized with extremely high efficiency and low noise.

[0004]

A power supply circuit according to the present invention includes a DC-DC converter having an inductance element inserted in at least one of an input terminal and an output terminal, and an output smoothing connected to the output terminal of the converter. The switching inverter circuit has an inductance element for use, and an output means coupled to the output of the switching inverter circuit through a transformer to rectify and smooth the AC output to take out the DC output. Switching device including a switching element for converting an input voltage to convert into an alternating current and outputting the current, and a current resonance formed in series with a current provided at a primary side of the transformer and flowing to an output terminal of the switching device. Means and the switching provided on the primary side of the transformer The voltage resonance means formed in parallel with the voltage generated at the output terminal of the stage and the switching element of the switching means are turned off when the main current is zero, and are turned on when the voltage between both ends is zero. Timing converter means, and the inductance element of the converter also serves as the output smoothing inductance element of the switching inverter circuit.

[0005]

According to the present invention, in the switching inverter circuit in the subsequent stage, the current resonance and the voltage resonance are used, both the current waveform and the voltage waveform are sinusoidal, and the switching element is driven off in the state where the current is zero. It is driven on when the voltage is zero. As a result, the loss in the switching element becomes extremely small, and extremely high efficiency can be obtained. Also, switching noise is greatly reduced, and unnecessary radiation such as harmonics is extremely small. Further, according to the present invention, the inductance element of the DC-DC converter in the front stage also serves as the inductance element for preventing interference with the front stage of the resonance means of the switching inverter circuit in the rear stage, and as a result, the configuration is simplified and a small switching power supply is provided. can get.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration of a switching power supply circuit according to an embodiment of the present invention. As shown in the figure, this power supply circuit is a DC-D including a switching element S11 in the preceding stage.
A C converter 11 is provided, and a resonance type switching inverter circuit 12 for converting the output of the converter 11 into an alternating current and an output circuit 13 for rectifying and smoothing the output thereof are provided in the subsequent stage. DC-DC converter 11
Is assumed to have an inductance element Ls in series with the output terminal (or input terminal). The switching inverter circuit 12 includes a switching element S12 and its ON,
A timing control circuit 14 for performing off control is included, and a voltage resonance circuit formed by a capacitor Cp provided in parallel with the switching element S12 and a current resonance circuit formed by a capacitor Cs provided in series are formed on the primary side of the output transformer T. There is. In the figure, the primary self-inductance of the transformer T is used as the inductance of the voltage resonance circuit, and the leakage inductance of the transformer T is used as the inductance of the current resonance circuit. By the way, in the switching inverter circuit 12, as shown in FIG. 11, the current resonance capacitor Cs is directly exposed between the input terminals. If the switching inverter circuit 12 is solely used, the isolation means is naturally provided on the input side.
For example, it is useless unless a line filter or the like for preventing interference is provided separately. That is, all the impedance components existing between the output terminals of the preceding circuit connected to this input terminal are added in parallel to the current resonance capacitor Cs of the switching inverter circuit 12, and the resonance condition changes greatly or the resonance ability is lost. There is a risk that However, by arranging the DC-DC converter 11 as shown in FIG. 1 in the front stage, the inductance element Ls of the converter 11 has not only the function of the original smoothing inductance, but also the current resonance capacitor Cs in the rear stage as the other circuit. This means that it can be isolated from the element, that is, it can also function as an inductance element for interference prevention.

FIG. 2 shows a power supply circuit configuration of an embodiment embodying FIG. Current continuous mode DC-DC converter 2
1 is an NPN transistor Q as a switching element
It has a basic circuit in which a capacitor C1 is connected in parallel to a series circuit of 1 and a diode D1. Its input terminal N
A first inductance element L1 is inserted in 1 and a second inductance element L2 is inserted between the connection node of the diode D1 and the capacitor C1 and the reference terminal N2. In this embodiment, the first and second inductance elements L1 and L2 are wound around one core and integrated. The first starting circuit 22 is a circuit for starting the transistor Q1 which is the switching element when an input DC voltage (for example, obtained by rectifying a commercial AC power source by a rectifying circuit) is supplied to the converter 21. .. The first starter circuit 22 has a collector connected to the input terminal N1 and an emitter connected to the converter 21 via the diode D2.
Is formed of an NPN transistor Q2 connected to the base of the transistor Q1, a Zener diode ZD1 for biasing the same, and a resistor R1.

Output terminal N3 of the DC-DC converter 21
A current-voltage resonance type switching inverter circuit 24 that receives the output voltage thereof is connected to the. This switching inverter circuit 24 controls the ON / OFF timing of a second starting circuit 26 consisting of an NPN transistor Q6 as a switching element, a resistor R8 connected between the base of the transistor Q6 and a terminal N3, and the transistor Q6. It has a timing control circuit 27 and the like composed of an inductive element L3 and a capacitor C7. In addition, the capacitor C4 provided between the terminal N3 and the reference terminal N2 and the leakage inductance of the output transformer T form a current resonance circuit (series resonance circuit) that enters in series with the output current of the inverter, and the collector of the transistor Q6. The capacitor C4 connected between the emitters and the self-inductance of the primary winding tap P1 of the transformer T form a voltage resonance circuit (parallel resonance circuit) that is in parallel with the output voltage of the inverter. That is, the transformer T is equivalently represented by an ideal transformer and a leakage inductance and a self-inductance as shown in FIG. 3, and the leakage inductance and the self-inductance are used in a current resonance circuit and a voltage resonance circuit, respectively. A capacitor C6 provided between the base and emitter of the transistor Q6
, And diode D7 are for timing adjustment and overvoltage protection, respectively. An additional tap P4 is provided on the primary winding of the output transformer T, and a clamping diode D6 is connected between this and the reference terminal N2.

Output terminal N3 of the DC-DC converter 21
Further, there is provided a pulse width modulation (PWM) circuit 23 for controlling the ON / OFF time of the NPN transistor Q1 which is the switching element. PWM circuit 23
Are NPN transistors Q3, Q4, resistors R2, R3,
It is based on a drive circuit section consisting of R4, diode D4 and the like. This drive circuit section rectifies the AC voltage extracted from the tap P3 portion of the transformer T by the diode D5 and smoothes the DC voltage of the terminal N4 smoothed by the capacitor N4 and the voltage similarly extracted from the primary winding tap P3. Obtained by integrating with an integrating circuit consisting of R7 and capacitor C3,
It is controlled by the triangular wave voltage at the terminal N5. The voltage at terminal N4 is the resistance R2 and diode D3.
Is supplied to the collector of the switching transistor Q1 of the converter 21 via the resistor R2 and the capacitor D4 to the base of the switching transistor Q1. These diodes D3 and D4 are connected to the switching transistor Q1 of the converter 21. Are provided to always operate in the unsaturated region. PWM
The circuit 23 also includes a transistor Q4 in its drive circuit section.
Is controlled according to the voltage of the terminal N3, the NPN transistor Q5, the Zener diode ZD2, the resistors R5 and R6
Is provided.

The output of the switching inverter circuit 24 is coupled to the output circuit 25 via the output transformer T. In the output transformer T of this embodiment, the number of turns n1 of the primary winding and the number of turns n2 of the secondary winding are n1> n2. That is, the primary side has high voltage and small current, and the secondary side has low voltage and large current. In this embodiment, the output circuit is
In addition to the rectifier diode D8 and the smoothing capacitor COUT, a Zener diode ZD3 and a photocoupler P for checking the output voltage of the capacitor for feedback control
Has H. The light emitting portion of the photocoupler PH is connected in series with the Zener diode ZD3 between two output terminals, and the light receiving transistor portion is provided between the emitter of the transistor Q5 of the PWM circuit 23 and the reference terminal N2.
2 shorted together. As a result, when the output voltage on the secondary side exceeds a certain value, feedback is applied to the PWM circuit 23 in order to lower it.

The current resonance capacitor C4 is directly exposed between the input terminals of the switching inverter circuit 24. Whatever circuit is connected to the input side, it is necessary to provide an isolation means for preventing other circuits from interfering with the current resonance capacitor C4. In this embodiment, the first inductance element L1 forming the preceding DC-DC converter 21 also serves as an inductance element for preventing interference with the current resonance means of the switching inverter circuit 24. That is, this inductance element has a sufficiently large impedance in the resonance frequency region determined by the current resonance capacitor C4, and prevents the current resonance capacitor C4 from being substantially coupled to other impedance components in the preceding stage. This inductance element is also used for the purpose that the resonance circuit of the switching inverter circuit 24 of this embodiment is provided on the primary side of the transformer T and that D is provided for the purpose of ripple removal.
This is possible because the value of the inductance element L1 of the C-DC converter 21 is suitable for presenting an impedance at the resonance frequency of the switching inverter 24 that is large enough to separate the other from the resonance means. ..

Next, a schematic operation of the power supply circuit of the embodiment shown in FIG. 2 will be described. When an input voltage is applied between the terminals N1 and N2, the first start-up circuit 22 first operates and DC
-The DC converter 21 is started. That is, when the input voltage is applied, the resistance R1 and the Zener diode ZD1
The transistor Q2 of the first start-up circuit 22 is turned on by the bias determined by, and the voltage determined by the diode D2 is applied to the base of the transistor Q1 of the converter 21. As a result, the potential of the output terminal N2 of the converter 21 rises. When the voltage of this output terminal N2 reaches a certain value,
A base bias is applied to the transistor Q6 by the resistor R8 in the second starting circuit 26, that is, the switching inverter circuit, and oscillation is started by the tap P3 of the transformer. The oscillation frequency wave is generated by the timing control circuit 27.
Is determined by the time constants of the inductance element L3 and the capacitor C7 that form At this time, the inductance of the transformer T and the values of the capacitors C4 and C5 are optimally set so that the voltage resonance and the current resonance are established.
Detailed operation of the switching inverter circuit 24 utilizing this voltage-current resonance will be described later.

When the on / off operation of the transistor Q6 starts, the voltage obtained at the tap P3 of the transformer is rectified by the diode D5 and smoothed by the capacitor C2. That is, the voltage of the terminal N4 is given as the power supply voltage of the PWM circuit 23. The voltage of the tap P3 is converted into a triangular wave by the integrating circuit composed of the resistor R7 and the capacitor C3, and the voltage of the terminal N5 is given to the base of the transistor Q4. The base of the transistor Q4 has a terminal N4
A base bias is applied from the resistor R4 to the resistor R4, and the values of the resistors R4 and R7 are set so that the transistor Q4 is always on when the transistor Q5 is off. When the transistor Q4 turns on, the transistor Q3 turns off and the transistor Q1 of the converter 21 turns on. When the output terminal N3 of the converter 21 reaches a specified voltage, the resistors R5, R6 and the Zener diode ZD2 turn on the transistor Q5, which works to lower the base potential of the transistor Q4. Therefore, the PWM modulation for controlling the ON period of the transistor Q1 of the converter 21 is performed according to the potential relationship between the terminals N5 and N3, and the potential of the terminal N3 is stabilized.

After the PWM operation is started and the voltage of the output terminal N3 of the converter 21 is stabilized, the first starting circuit 2
2 should not work, so it will automatically stop working. That is, in the case of the embodiment, the constant voltage VD of the Zener diode ZD1 which determines the base bias of the transistor Q2 is selected so as to be lower than the stabilizing voltage of the output terminal N3 of the converter 21, and when the stable operation starts. The first starting circuit 22 does not participate in the circuit operation.

The output of the switching inverter circuit 24 is coupled to the output circuit 25 by a transformer T, and rectified,
The output is smoothed. When the secondary side output voltage exceeds a certain value, the Zener diode ZD3 is turned on, the photocoupler PH is activated, and the PWM circuit 23 is fed back. That is, the light receiving transistor of the photocoupler is in parallel with the Zener diode ZD2 inserted in the emitter of the transistor Q5 of the PWM circuit,
When it turns on, transistor Q5 is forward biased. When the transistor Q5 turns on, the transistor Q4
Is turned off when the base potential is lowered, and the transistor Q
3 is turned on and the transistor Q1 of converter 21
Is driven off. P by such feedback
The voltage at the output terminal N3 of the converter 21 is adjusted downward by the WM control. At this time, the constant voltage of the Zener diode ZD2 is selected to be lower than the voltage of the terminal N3 which is finally operating.

Next, the configuration and operation of each part of the embodiment shown in FIG. 2 will be described in detail. The continuous current mode converter 21 used in the embodiment of FIG. 2 is represented as shown in FIG. That is, the first inductance element L1 is inserted in series to the input terminal of the converter circuit body, and the second inductance element L1 is connected to the reference terminal.
Inductance element L2 is inserted. The part of the converter circuit body is specifically shown in FIGS. 4 (b) to 4 (d). FIG. 4B shows a switching circuit S1 connected in parallel to a series circuit of a capacitor C1 and a diode D1, which is shown in the embodiment of FIG. FIG. 4 (c) shows a diode D1 connected in parallel with a series circuit of a switching element S1 and a capacitor C1, and FIG. 4 (d) shows a switching element S1 and a diode D1.
The capacitor C1 is connected in parallel to the series circuit of 1, and these are also functionally equivalent to FIG. 4 (b), and the circuit of the embodiment of FIG. 2 can be replaced with these. 5 (a) to 5 (d) show that the first inductance element L1 of FIGS. 4 (a) to 4 (d) is brought to the output terminal side. These are also functionally equivalent to those of FIG. 4, and the circuit of the embodiment of FIG. 2 can be replaced with these.

The operation of the DC-DC converter in the continuous current mode as described above will be described with reference to the circuit of the embodiment of FIG.
The circuit configuration of (b) will be described below with reference to FIG. FIG. 6 shows voltage and current waveforms at various parts of the circuit of FIG. 4 (b). The impedance of the capacitor C1 is sufficiently small at the switching frequency. Under this condition, when switching element S1 is turned on and off,
Output current IOUT is obtained alternately through switching element S1 when switching element S1 is on, and through diode D1 when switching element S1 is off. At this time, the current flowing through the diode D1 is supplied from the second inductance element L2 and the capacitor C1. However, in terms of direct current, the current is supplied only from the second inductance element L2. Therefore, the value of the output current IOUT is the second inductance value. It becomes the current IL2 of the element L2.

When the switching element S1 is turned on, the current IL1 (equal to the input current IIN) flowing in the first inductance element L1 flows to the output side, but at this time, the diode D1 is in the reverse biased off state, and The current IL2 flowing through the second inductance element L2 is also the capacitor C1.
And through the switching element S to the output side. Therefore, the output current IOUT becomes IOUT = IL1 + IL2. On the other hand, when the switching element S1 is turned off,
The diode D1 turns on and the second inductance element L
The current IL2 flowing through 2 flows through the diode D2 to the output side. At this time, the current IL1 flowing through the first inductance element L1 also flows to the output side through the capacitor C1 and the diode D1 since the switching element S1 is off. Therefore, also at this time, the output current is IOUT IOUT = IL1 + IL2.

In this way, the output current IOUT of the DC-DC converter is in the continuous mode. Further, the current IC1 of the capacitor C1 alternates, and the voltage across it becomes almost equal to the input voltage VIN. In this circuit, the maximum voltage across switching element S1 and diode D1 is input voltage VIN, and the current is equal to output current IOUT.
This is the same as the conventional BUCK type converter. Since the duty can be used up to 100%, it has all the advantages of the BUCK type.

On the other hand, in the circuit configuration of FIG. 4B, the first inductance element L1 and the second inductance element L2
The voltage across both ends is always the same. The situation is shown in FIG.
FIG. 7 shows the case where 10V, 1A is converted to 5V, 2A as an example.
1 and the voltage V1, V across the second inductance element L2
2 vibrates as shown. Therefore, these inductance elements L1 and L2 can be wound around one core to be integrated, and FIG. 2 shows the configuration in that case. 5 (b), the first and second inductance elements L1 and L2 can be shared by the core for the same reason.

Next, the operation of the switching inverter circuit 24 shown in FIG. 2 will be described in detail with reference to FIG. When the converter 21 is activated and a voltage is obtained at the terminal N3 as described above, the switching circuit 24 is activated by the second activation circuit 26 to convert the obtained output voltage into an alternating current. When the transistor Q6 turns on,
A current flows through this, but at this time, a series resonance circuit due to the leakage inductance of the capacitor C4 and the transformer T operates to generate a sinusoidal oscillating current as shown in FIG. Then, when the main current of the transistor Q6 is almost zero, the transistor Q6 is driven off. When the transistor Q6 is turned off, a parallel resonance circuit due to the self-inductance of the capacitor C5 and the tap P1 of the transformer T operates, and the terminal voltage of the transistor Q6 oscillates in a sine wave shape as shown in FIG. Then, the transistor Q6 is driven off when the voltage across the transistor Q6 is substantially zero.

In this way, the series resonance circuit (current resonance circuit) and the parallel resonance circuit (voltage resonance circuit) are driven off so that the current of the transistor Q6 is off when the current is substantially zero and on when the voltage across the transistor Q6 is almost zero. Circuit) and timing control circuit 2
Each time constant of 7 is set. As a result, in the switching inverter circuit 24, both the current waveform and the voltage waveform are sinusoidal, and an AC output without harmonics can be obtained. The base current of the transistor Q6 is similar to the collector resonance current waveform due to LC resonance, and high efficiency is realized. The capacitor C6 provided between the base and the emitter of the transistor Q6 makes the base voltage negative at the time of turning off the transistor Q6 to secure a turn-off current and enables high-speed turn-off.

As described above, according to this embodiment, the DC-DC converter 21 in the preceding stage is in the continuous current mode, and the noise is small. Since the switching inverter circuit 24 in the latter stage is also turned on and off at zero voltage and zero current due to current-voltage resonance, noise is reduced. Therefore, a switching power supply with extremely low noise can be obtained as a whole. Further, in the switching inverter circuit 24, the transistor Q6 which is a switching element is used.
Is turned on and off at zero voltage and zero current, resulting in a highly efficient power source with little loss and little heat generation.

In this embodiment, the switching inverter circuit 24 has a voltage resonance circuit on the primary side of the transformer T,
It constitutes a current resonance circuit. In general, a small-sized switching power source has a high voltage and a small current on the primary side and a low voltage and a large current on the secondary side, as in this embodiment. In this case, if the leakage inductance of the transformer is used on the secondary side to configure the current resonance circuit, the capacitance value of the capacitor becomes large. This is because, depending on the turns ratio, the leakage inductance seen from the secondary side is smaller than that seen from the primary side. Moreover, since this is influenced by the square of the winding ratio, the capacitance value of the current resonance capacitor C4 becomes as large as, for example, about 10 μF when the transformer secondary side leakage inductance is used. As this kind of current resonance capacitor, a film capacitor or the like is desirable from the viewpoint of ripple current characteristics, high frequency characteristics, or change over time, but a film capacitor having such a capacitance value has an extremely large shape and dimension. Will end up. If a chemical capacitor is used, it is convenient to use a capacitor having such a capacity because of its small size and shape, but it is inferior in ripple current characteristics and high frequency characteristics, and it cannot be used because it has a large change over time. On the other hand, on the primary side, since the leakage inductance is large, the required resonance capacitance is small, and the operating conditions are high voltage and small current. Therefore, a film capacitor can be used as the current resonance capacitor C4. As a result, the Q of resonance can be increased and the entire power supply can be downsized.

Further, in this embodiment, the first inductance element L1 provided in the preceding DC-DC converter is used.
However, as it is, it is used as an interference prevention inductance element for preventing the current resonance circuit of the switching inverter circuit from interfering with others. This is possible as a result of the switching inverter circuit 24 of this embodiment forming a current resonance circuit on the primary side. This is extremely advantageous when a multi-output power supply is constructed as shown in FIG. If the multi-output power supply circuit as shown in FIG. 9 is configured by bringing a current resonance circuit on the secondary side, each output circuit on the secondary side needs an interference preventing and smoothing inductance. This hinders downsizing of the switching power supply. Therefore, in this embodiment, when the number of outputs is increased, the power source can be effectively downsized.

In the embodiment shown in FIG. 2, a DC-DC converter in which a continuous current mode is set by adding an inductance element is used, but a switching converter of another type can also be used in the present invention. That is, if the output impedance has a value equivalent to the interference prevention inductance required for the switching inverter circuit in the subsequent stage, the inductance element for interference prevention to the current resonance circuit may be omitted to combine them, and Similar to the embodiment described above, the circuit can be simplified and downsized.

In the embodiment shown in FIG. 2, the switching inverter circuit 24 is a so-called monolithic type using one transistor, and both the current resonance circuit and the voltage resonance circuit are transformers T.
Formed on the primary side. The one-stone switching inverter circuit may have a configuration as shown in FIGS. 10 to 13. Among these, the one that can be used in the present invention is
It is a structure of FIG. 12 and FIG. That is, FIG.
The voltage resonance circuit is constructed on the primary side by the capacitor C5 and the self-inductance of the primary winding of the transformer, and the current resonance circuit is constructed on the secondary side by the leakage inductance of the transformer and the capacitor C4. In this case, an interference prevention and smoothing inductance element LF is provided on the secondary side. FIG. 11 is based on the configuration of FIG. 10 and is provided with a clamping diode D6 on the primary side. These require an inductance element LF for interference prevention and smoothing on the secondary side.
It cannot be shared with the inductance element of the DC converter. FIG. 12 shows an example in which both the current resonance circuit and the voltage resonance circuit are configured on the primary side of the transformer T. in this case,
The interference prevention inductance element LF is provided on the primary side. In FIG. 13, a clamping diode D6 is provided on the primary side based on the configuration of FIG. That is, the configuration of FIG. 13 corresponds to that of the embodiment of FIG.
That is, when the configurations of FIGS. 12 and 13 are used, the inductance element LF can be shared.

A clamping diode D6 is provided on the primary side of the transformer of the switching inverter circuit 24 in the embodiment of FIG. 2 in order to suppress the peak voltage determined by the voltage resonance. This has the following meanings. First, if there is nothing that suppresses the peak voltage, it may cause element breakdown due to component variations, design errors, and the like. By providing the clamp diode, such damage is prevented and reliability is improved.
Second, the on-time of transistor Q6 can be made relatively long. That is, as shown in comparison with FIGS. 14 (a) and 14 (b), in the case of FIG. 14 (a) in which the peak voltage Vp is not suppressed, it is difficult to increase the ratio of the ON period for a large peak voltage. .. On the other hand, when the peak voltage Vp is determined by the clamp as shown in FIG. 14 (b),
The ON period of the transistor Q6 can be lengthened.
This is because the areas of the positive half-wave and the negative half-wave of the resonance voltage waveform are equal, and in FIG. 14 (a), S1 = S2,
In (b), S1 '= S2'. This is because the area S1 when the peak value is Vp and the area S1 'when the peak value is Vp is the same as the sine wave, S1'> S1 and therefore S2 '> S2. And since the ON period of the transistor Q6 can be lengthened,
The peak of the resonance current can be reduced.

The present invention can also use a so-called Futashi type switching inverter circuit using two switching elements. The Futashi type switching inverter circuit is configured as shown in FIGS. 15 to 17. Of these, the one that can be used in the present invention is shown in FIG.
And the configuration of FIG. In FIG. 15, two switching elements S1 and S2 are used, and a current resonance capacitor C4 is used.
, The voltage resonance capacitor C5 is a half-bridge type switching inverter circuit arranged on the primary side of the transformer T. FIG. 16 is based on the configuration of FIG.
This is a half-bridge type switching inverter circuit in which a current resonance capacitor C4 is arranged on the secondary side of a transformer T. Of these FIG. 15 and FIG. 16, the one in FIG.
Since the interference preventing inductance element LF is provided on the primary side, it becomes possible to share this with the preceding-stage inductance element as in the previous embodiment. FIG. 17 shows a push-pull type in which both the voltage resonance circuit and the current resonance circuit are formed on the primary side of the transformer T. In FIG. 18, the current resonance circuit is formed on the secondary side of the transformer T also in the push-pull type. Of these FIGS. 17 and 18, the one shown in FIG. 17 has the interference preventing inductance element LF on the primary side, so that it can be shared with the preceding stage inductance element as in the previous embodiment.

Next, some modifications of the timing control circuit 27 and the second starting circuit 26 in the switching inverter circuit 24 in the embodiment of FIG. 2 will be described. FIG. 19 shows an example in which an oscillation circuit using a transistor Q10, resistors R10 and R11, capacitors C10 and C11, and a diode D10 is used as a timing control circuit for driving the transistor Q6, instead of the LC circuit of the embodiment shown in FIG. is there. FIG. 20 shows a modification of the second starting circuit 26 portion which is composed of only the resistor R8 in the embodiment of FIG. Here, the second
A PNP transistor Q11 is added to the starting circuit 26 of the diode D11 and D11 for giving a predetermined bias thereto.
A bias circuit composed of 12, D13, a resistor R12 and a capacitor C12 is provided. When the preceding DC-DC converter is activated and the potential of the terminal N3 rises to a certain value, P
The NP transistor Q11 is turned on to supply a large base current to the transistor Q6, which is a switching element of the switching inverter circuit, to activate it. That is, the startup is strengthened. Once in a stable state, the capacitor C12
The voltage of turns off the PNP transistor Q11,
The second activation circuit 26 stops its function. As a result, it is possible to suppress heat generation in the starting resistor when the base current is increased to enhance the starting. FIG. 21 is a modification of the second starting circuit 26 as well. Here, two PNP transistors Q13, Q14 and resistors R13, R14, R
A bias circuit is constituted by 15 and the Zener diode ZD10. In this case, when the potential of the terminal N3 rises to some extent, the PNP transistor Q13 is turned on to supply the base current to the transistor Q6. When the potential of the terminal N3 further rises, the PNP transistor Q14 turns on, the forward bias of the transistor Q13 becomes shallow, and the base current supplied to the transistor Q6 is suppressed. That is, the base current for the transistor Q6 is controlled in accordance with the input voltage, and it is possible to suppress the increase in heat generation due to the enhanced start-up as in FIG.

[0031]

As described above in detail, according to the present invention, the voltage-current resonance type switching inverter circuit in which the current resonance circuit is formed on the primary side of the output transformer is used, and the inductance element of the preceding stage DC-DC converter is used. Is used as an inductance element for preventing interference with the resonance circuit of the switching inverter circuit in the subsequent stage, it is possible to obtain a low-noise, high-efficiency switching power supply that is downsized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a power supply circuit according to an embodiment.

FIG. 2 is a diagram showing a specific configuration of a power supply circuit according to an embodiment.

FIG. 3 is a diagram showing an equivalent circuit of a transformer.

FIG. 4 is a diagram showing a configuration of a current continuous mode DC-DC converter.

FIG. 5 is a diagram showing a configuration of a current continuous mode DC-DC converter.

FIG. 6 is a diagram showing operation waveforms of a continuous current mode DC-DC converter.

FIG. 7 is a diagram for explaining core sharing of an inductance element.

FIG. 8 is a diagram showing operating waveforms of a switching inverter circuit.

FIG. 9 is a diagram showing a multiple output power supply configuration.

FIG. 10 is a diagram showing a one-stone switching inverter for primary side voltage resonance and secondary side current resonance.

FIG. 11 is a diagram showing a one-step switching inverter for primary side voltage resonance and secondary side current resonance.

FIG. 12 is a diagram showing a one-step type switching inverter of primary side voltage resonance and primary side current resonance.

FIG. 13 is a diagram showing an integrated switching inverter of primary side voltage resonance and primary side current resonance.

FIG. 14 is a diagram for explaining the effect of voltage clamping.

FIG. 15 is a diagram showing a two-stone half-bridge type switching inverter with primary-side voltage resonance and primary-side current resonance.

FIG. 16 is a diagram showing a two-stone half-bridge type switching inverter with primary-side voltage resonance and secondary-side current resonance.

FIG. 17 is a diagram showing a two-stone push-pull type switching inverter having primary-side voltage resonance and primary-side current resonance.

FIG. 18 is a diagram showing a two-stone push-pull type switching inverter with primary-side voltage resonance and secondary-side current resonance.

FIG. 19 is a diagram showing a modification of the timing control circuit.

FIG. 20 is a diagram showing a modification of the second starting circuit.

FIG. 21 is a diagram showing a modification of the second starting circuit.

[Explanation of symbols]

11 ... Current continuous mode DC-DC converter, 12 ... Current-voltage resonance type switching inverter circuit, 13 ... Output circuit, 14 ... Timing control circuit, T ... Output transformer,
S11, S12 ... Switching element, Cs ... Current resonance capacitor, Cp ... Voltage resonance capacitor, 21 ... DC-D
C converter, 22 ... First starting circuit, 23 ... PWM circuit, 24 ... Resonant switching inverter circuit, 25 ...
Output circuit, 26 ... Second start circuit, 27 ... Timing control circuit, L1 ... First inductance element, L2 ... Second
Inductance element, Q1 ... Npn transistor (switching element), Q6 ... Npn transistor (switching element), C4 ... Current resonance capacitor, C5 ... Voltage resonance capacitor.

Claims (2)

[Claims] 1. A DC-DC converter having an inductance element inserted in at least one of an input terminal and an output terminal, a switching inverter circuit connected to the output terminal of this converter, and a transformer for the output of this switching inverter circuit. And an output unit coupled together to rectify and smooth the AC output to take out the DC output. The switching inverter circuit includes a switching element capable of on / off control, switches an input voltage, converts the AC voltage into an AC voltage, and outputs the AC voltage. Switching means, a current resonance means provided on the primary side of the transformer and formed in series with a current flowing through the output terminal of the switching means, and generated at the output terminal of the switching means provided on the primary side of the transformer A voltage resonance means formed in parallel with a voltage, and And a timing control means for driving the switching element of the switching means off when the main current is zero, and for driving the switching element on when the voltage across the switching element is zero, and at the input side of the switching inverter circuit, the resonance of the resonance means. A power supply circuit, wherein the inductance element of the DC-DC converter is also used as an interference prevention inductance element for preventing the element from interfering with other circuit elements. 2. In the DC-DC converter, a series circuit of a capacitor and a diode is connected between an input terminal and an output terminal via a first inductance element, and a switching element is connected in parallel to the series circuit. The power supply circuit according to claim 1, wherein a second inductance element is connected between a connection terminal of the capacitor and the diode and a reference terminal.