JPS635993B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a constant voltage power supply device equipped with a series resonant DC-DC converter. As a conventional constant voltage power supply device, a switching regulator that uses a pulse width control method for on/off operation of a switching element is particularly popular. Switching regulators are highly efficient and are useful for making devices smaller and lighter. However, in principle, there is a period of time during which voltage and current change rapidly, that is, switching time. It has disadvantages such as high loss, high unnecessary radiation noise, and high conduction noise. Therefore, the scope of use of switching regulators is limited, and especially when used as a power source for audio equipment, it is necessary to insert a filter with a large amount of noise attenuation into the input/output section, or to apply a completely sealed shield. Countermeasures have to be taken, and there are problems such as increased costs and decreased reliability. As shown in Figure 1, one solution is to connect a resonant coil and a resonant capacitor in series, and by alternately turning on and off a switch element, a series resonance system is used to obtain a predetermined output energy via a transformer. A type DC-DC converter has been proposed. In Fig. 1, 1 and 2 are DC power supplies, 3,
4 is a switching element such as a transistor or thyristor, 5 is a resonant capacitor, 6 is a resonant coil, and 7 is the primary winding of an ideal converter transformer 9 without leakage inductance, which is connected to the resonant capacitor 5 described above. It is connected in series with the resonance coil 6. 8 is a secondary winding of the converter transformer 9, the output of which is connected to a smoothing electrolytic capacitor 11 via a rectifying diode 10. 1
2 is a load resistance. Switch elements 3 and 4 are designed to switch alternately, and switch element 3
is on and switch element 4 is off, DC power supply 1
→ Switch element 3 → Primary winding 7 of converter transformer 9 → Resonant coil 6 → Resonant capacitor 5 →
A sinusoidal current flows in a loop called DC power supply 1. On the other hand, when switch element 3 is off and switch element 4 is on, a sinusoidal waveform is generated in the loop of DC power supply 2 → resonance capacitor 5 → resonance coil 6 → primary winding 7 → switch element 4 → DC power supply 2. Current flows. The period is determined by the capacitance _C5 of the resonant capacitor 5 and the inductance of the resonant coil 6.
2π√ _{5 6} determined by L ₆ . The operating waveforms are shown in FIG. In FIG. 2, a and b show timing charts of the switch elements 3 and 4, and c shows a corresponding current waveform. As is clear from Fig. 2, when the switch elements 3 and 4 are switched, the current becomes zero, so the switching loss is significantly reduced, resulting in not only high efficiency but also unnecessary radiation noise and conduction noise. It is possible to reduce the However, a series resonant DC as shown in Figure 1
In DC converters, it is difficult to stabilize the output in response to large changes in input and load, and a major problem remains as to how to control the output voltage at a constant level. The present invention aims to provide a high-efficiency, low-noise constant voltage power supply device that is easy to control and has a wide range of control functions in such a series resonant DC-DC converter. FIG. 3 shows a circuit diagram of the first embodiment of the present invention. In this figure, the same parts as those explained in FIG. 1 are given the same reference numerals. The difference between the configuration in FIG. 3 and the configuration in FIG. 1 is that the primary winding 13 of the control converter transformer 14 is connected in parallel with the resonant capacitor 5, and the secondary winding 15 is This is because it is connected to the electrical load resistor 12. A control circuit 17 is composed of an error amplification circuit, an oscillation circuit, a distribution circuit, a drive circuit, etc., and turns the switch elements 3 and 4 on and off alternately at appropriate intervals. Next, before explaining the operation of the embodiment of the present invention,
First, the control principle of a series resonant DC-DC converter will be explained with reference to FIG. In FIG. 1, switch element 3 (or 4)
The sinusoidal current i ₁ flowing through the primary winding 7 of the converter transformer 9 when the switch element 4 (or 3) is on and the switch element 4 (or 3) is off is expressed by the following equation. Here, 0tπ√ _{5 6} , α=R _S /2L ₆ ,

[Formula] E _c ; Voltage of DC power supply 1 or 2 V _p ; Output voltage converted to the primary side V _c ; Initial charging voltage value R _s of resonance capacitor 5 ; Equivalent series loss resistance in Fig. 1 Above formula The average value of the resonant current represented by is the current transmitted to the secondary side through the ideal converter transformer 9 with an appropriate primary-secondary winding ratio, that is, the load current. (E _c − V _p )≪V _c By controlling the initial charging voltage value V _c of the resonance capacitor 5, the resonance current i ₁ (t) is controlled, and as a result, the load current is controlled. . The present invention applies this principle, and attempts to stabilize the output DC voltage by controlling the initial charging voltage value of the resonance capacitor 5 using a control converter transformer 14 added in parallel with the resonance capacitor 5. It is. Now, the operation of the embodiment of the present invention shown in FIG. 3 will be explained with reference to FIG. 4, which shows operational waveforms of each part of FIG. 3, which is an embodiment of the present invention. In Fig. 4, a and b indicate the timing charts of the switch elements 3 and 4, i ₁ (t) in c indicates the current flowing in the primary winding 7 of the converter transformer 9, and i ₂ (t) indicates the current flowing in the primary winding 7 of the converter transformer 9. υ _cp (t) represents the current flowing through the primary winding 13 of the converter transformer 14, and the voltage across the resonance capacitor 5. In FIG. 3, at time _t1 , the initial charging voltage value of the resonance capacitor 5 is −υ _cp3 . time t ₁
From _t4 , switch element 3 is on and switch element 4 is off, then the positive side of DC power supply 1 → switch element 3 → primary winding 7 of converter transformer 9 → resonance coil 6 → resonance capacitor 5 → Resonant current i ₁ (t) in the negative side loop of DC power supply 1
flows. The current i ₂ (t) flowing through the primary winding 13 of the control converter transformer 14 serves as the exciting current of the control converter transformer 14 during t ₁ tt ₂ . Voltage of resonance capacitor 5 υ _cp (t)
increases due to the resonance current i ₁ (t) and the above excitation current, and the voltage of the secondary winding 15 of the control converter transformer 14 also increases, and at time t ₂ the output voltage + rectifier diode increases. 16, the rectifying diode 16 turns on and current flows toward the output. As this current flows, the control converter transformer 14
The direction of the current flowing through the primary winding 13 of is reversed,
That is, the charge in the resonance capacitor 5 starts discharging. The period of this discharge current i ₂ (t) is determined by the capacitance C ₅ of the resonance capacitor 5 and the leakage inductance L _l of the control converter transformer 14, and has a value of approximately π√ _{5 l} . Next, at t ₂ tt ₃ , the resonance capacitor 5
A resonance current i ₁ (t) flows into the , and at the same time a discharge current i ₂ (t) flows through the control converter transformer 14.
will flow in. In this period |i ₁ (t)|>|
Since i ₂ (t)|, the voltage of the resonant capacitor 5 increases and reaches the maximum value υ _cp1 when |i ₁ (t)|=|i ₂ (t)|, that is, at time t ₃ . Motsu. Next, in the period t ₃ tt ₅ | resonant current i ₁
Since (t)|<|discharge current i ₂ (t)|, the voltage of the resonance capacitor 5 begins to fall below υ _cp1 . Furthermore, during the period t ₅ tt ₆ , the voltage of the resonance capacitor 5 further decreases due to the exciting current component i ₂ (t) of the control converter transformer 14.
At time t ₆ , υ _cp2 . At time _t6 , the switch element 4 sets υ _cp2 as the initial charging voltage value of the resonance capacitor 5, and the resonance current i ₁ (t) shown by the above equation starts to flow. When repeating the above operation, by changing the period T of the switch elements 3 and 4, the initial charging voltage value υ _cp2 of the resonance capacitor 5 can be changed, as is clear from the above operation description. That is, by changing the period T of the switch elements 3 and 4, it becomes possible to change the resonance current i ₁ (t) shown by the above equation, and the output can be controlled. From the above, the output can be controlled by lengthening the period T when the output increases and by shortening the period T when the output decreases. A second embodiment of the invention is shown in FIG. In FIG. 5, the same parts as those explained in FIG. 3 are given the same reference numerals. In FIG. 5, diodes 18 and 19 are added in parallel with the switch elements 3 and 4, allowing current to flow in the direction opposite to that flowing through the switch elements 3 and 4. This fifth
The circuit shown in the figure is connected to the DC power source 1 through the diode ₁₈ (or 19) during t ₂ tt ₅ in FIG. By flowing a feedback current i ₃ (t) to (or 2), the voltage υ _cp (t) of the resonant capacitor 5 is intended to be greatly changed. That is, in the circuit of FIG. 3, the only element that changes the voltage of the resonant capacitor 5 is the current i ₂ (t) flowing through the primary winding 13 of the control converter transformer 14, but in the circuit of FIG. In addition to i ₂ (t) in the circuit, the feedback current i ₃ (t)
I am trying to add . Therefore, the embodiment of FIG. 5 has the advantage that the range of change in the period T required for control is smaller than that of the embodiment of FIG. 3.
6a, b, and c show the operating waveforms of FIG. 5. A third embodiment of the invention is shown in FIG. In FIG. 7, the same parts as those explained in FIG. 3 are given the same reference numerals. In the embodiment of FIG. 5 described above, the feedback current i ₃ (t) is
However, in the embodiment shown in FIG. 5, a feedback current i ₃ (t) is made to flow to the DC power supply 1 (or 2). For this purpose, in FIG. 7, a series connection circuit of another diode 20 and another resonance coil 21 is connected to the positive side of the DC power supply 1 with respect to the series circuit of the DC power supply 1 and the resonance capacitor 5. Connect as if the cathode side is connected, and also connect another diode 22 and another resonance coil 23.
is connected to the series circuit of the DC power supply 2 and the resonant capacitor 5 such that the anode side of the diode 22 is connected to the negative side of the DC power supply 2. With this configuration, the feedback current i ₃ (t) can be directly returned to the DC power supply 1 (or 2) via the diversion capacitor 5. In addition, in the embodiment shown in FIG. 5, the period of the feedback current i ₃ (t) is equal to the resonant current i ₁
(t), but in the embodiment shown in FIG. 7, by changing the inductance value of the resonant coil 21 (or 23), the feedback current i ₃
The period of (t) can be changed as necessary. In the above, an example of a half-bridge series resonant type DC-DC converter with two switch elements has been shown, but a full bridge series resonant type converter with four switch elements has been described.
Of course, a similar effect can be expected in a DC-DC converter, and by providing the converter transformer 7 with a leakage inductance of the same value as the resonant coil 6 instead of the ideal converter transformer 9, The resonance coil 6 can also be omitted. As described above, the present invention has the excellent effect of stabilizing the output voltage over a wide range of input/output fluctuations with a simple configuration while taking advantage of the features of the series resonant DC-DC converter. There are things you can do.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional series resonant DC-DC converter, Fig. 2 a, b, and c are operation waveform diagrams of each part in Fig. 1, and Fig. 3 is a circuit diagram of the first embodiment of the present invention. Figures 4a, b, and c are operation waveform diagrams of each part in the embodiment of Figure 3, and Figure 5 is a diagram of the second embodiment of the present invention.
FIGS. 6a, b, and c are operation waveform diagrams of various parts in the embodiment of FIG. 5, and FIG. 7 is a circuit diagram of a third embodiment of the present invention. 1, 2...DC power supply, 3, 4...Switch element, 5...Resonance capacitor, 6...Resonance coil, 7...Primary winding, 8...Secondary winding, 9...Converter Transformer, 10... rectifier diode,
11...Smoothing electrolytic capacitor, 12...Electrical load resistance, 13...Primary winding, 14...Control converter transformer, 15...Secondary winding, 16...
Rectifier diode, 17... Control circuit, 18, 1
9, 20, 22...diode, 21, 23...
Resonant coil.

Claims (1)

[Scope of Claims] 1. A switch element that performs on/off operation, a resonant capacitor, and a primary winding of a first conversion transformer are connected in series with respect to an input DC power supply, and a secondary winding of the conversion transformer is connected in series. Connect a rectifier/smoothing circuit to the wire,
A series resonant DC-DC converter configured to supply a DC voltage to an electrical load connected to the output terminal thereof, and a primary winding of another second conversion transformer in parallel with the resonant capacitor. 1. A constant voltage power supply device, characterized in that the constant voltage power supply device is configured such that the secondary winding of the second conversion transformer is connected to the electrical load of the output terminal via a rectifier. 2. A constant voltage power supply device as set forth in claim 1, wherein a diode is connected in parallel to the switch element so as to conduct in a direction opposite to the conduction direction of the switch element. 3 In the statement of claim 1, a series connection circuit of a diode and another resonance coil is connected to a series circuit of an input DC power supply and a resonance capacitor so that the diode is biased in the opposite direction. A constant voltage power supply device characterized by being connected.