JPS6353790B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a constant voltage power supply, especially a series resonant DC power supply.
-Relates to a constant voltage power supply device equipped with a control function to stabilize the output voltage of a DC converter. As is well known, a DC-DC converter converts an input DC voltage into an output voltage value that is different from the input voltage value. Conventionally, a DC-DC converter converts an input DC voltage into an output voltage value that is different from the input voltage value. Conventionally, the desired conversion is achieved by controlling the duty ratio of the on/off operation of a switching element. DC-DC converters with duty ratio control are common. The disadvantages of the duty ratio control type DC-DC converter (for example, chopper type or flyback type) are that unnecessary radiation is large due to sudden changes in voltage and current during conversion operation, and the switching element is turned on and off. The switching loss during OFF operation is large. The first method that can significantly improve the shortcomings of the above-mentioned duty ratio control method is
A series resonant DC-DC converter has been proposed that utilizes series resonance between a capacitor and a coil, as shown in the figure. Series resonant DC-DC converters have the advantage that the current during the conversion operation has a sinusoidal waveform, so there is little unnecessary radiation and the switching loss of the switching elements is extremely small. However, the series resonant DC-DC converters that have been proposed in the past still have problems with the means to stably control the output voltage, and it is difficult to stabilize the output against large fluctuations in input voltage and load. I couldn't do it. The present invention provides a constant voltage power supply device in a series resonant DC-DC converter that has a control function with simple control operation and a wide control range. 1st
The figure shows a basic circuit configuration diagram of a conventional series resonant DC-DC converter, FIG. 2 shows an equivalent circuit diagram of FIG. 1, and FIG. 3 shows a resonant current waveform of a resonant circuit. In FIG. 1, switching elements 3 and 4 that perform on/off operations are connected in series between both terminals of two input DC power supplies 1 and 2 connected in series, and between the midpoint of the input DC power supply and the switching element. A resonance capacitor 5, a resonance coil 6, and a primary winding 8 of a conversion transformer 7 are connected in series between the midpoints. Secondary winding 9 of the conversion transformer 7
A rectifying circuit 10 and a smoothing capacitor 11 are connected to the rectifying circuit 10, and an electrical load 12 (for example, a resistor) is connected to the output terminal thereof. The series resonant DC-DC converter configured as described above is already known, and the details of its operation will be omitted, but for reference, the secondary circuit of the conversion transformer 7 will be converted to the primary circuit. This will be briefly explained using FIG. 2, which is an equivalent circuit obtained by The voltage values of the input DC power sources 1 and 2 are equal, and the voltage value is EC, and the two switching elements 3 and 4 can be equivalently replaced as one switching element 13. The capacitor 11 and the electrical load 12 are converted to the primary side and are shown as 10', 11', and 12', respectively, and the secondary output DC voltage V _O becomes V _O '. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. When the switching element 13 is connected to the input DC power supply 1, the input DC power supply 1 is connected to the resonance capacitor 5, the resonance coil 6, the rectifier circuit 10', and the smoothing capacitor 1.
A sinusoidal current determined by the resonance capacitor 5 and the resonance capacitor 6 flows in the direction of 1', and when the switching element 13 is connected in the direction of the input DC power supply 2, the input DC power supply flows in the direction opposite to the current direction. The same sinusoidal current as above flows toward the point 2. When the switching of the switching element 13 is made to match the resonant frequency, a continuous sinusoidal current as shown in FIG. 3 flows. The time for 1/2 cycle of the resonance cycle is π√ ₅・₆ . Here, C ₅ : Capacitance value of the resonant capacitor 5 L ₆ : Inductance value of the resonant coil 6 The secondary output DC voltage V _O is the rectified and smoothed sine wave current in Figure 3, and the output DC Voltage V _O
In order to stabilize the input DC power supply against fluctuations in the electrical load, it is necessary to control the magnitude of the above-mentioned sine wave current, that is, the average current value. The average current value of the resonant circuit can be calculated from the equivalent circuit diagram shown in FIG. By the operation of the switching element 13, a voltage of ±EC is applied to the resonant circuit in cycles that match the resonant period, and the output DC voltage V _O ' is kept constant.
Assuming that the equivalent series loss resistance of the circuit is R (second
(not shown in the diagram) Average current value of the resonant circuit
I _O ′ is determined by the following formula: I _O ′∝(EC−V _O ′)/R (1). Therefore, the average current value I _O ′
In order to stabilize the output DC voltage V _O by controlling the Eq _. If R is controlled, the conversion efficiency will deteriorate.
It is possible to equivalently control the equivalent series loss resistance R, that is, the Q of the circuit, without deteriorating the conversion efficiency. In the equivalent circuit of Figure 2, the resonant current i(t) in steady state is O≦t≦π√ ₅・₆ α=R/2L ₆ ,

[Formula] (V _C : initial charge voltage value of resonance capacitor 5). The average value of the resonant current obtained by equation (2) is the above average current value I _O ′, and from the relationship (EC−V _O ′)≪V _C , the above resonant current value is A method of controlling the initial charging voltage V _C of the capacitor 5 can be considered. The constant voltage control device of the present invention transfers the charging energy of the resonance capacitor 5 to the resonance coil 6, or transfers the charging energy to another coil connected in parallel with the resonance capacitor 5. Initial charging voltage value of resonance capacitor 5 V _C
is controlled to stabilize the output DC voltage _VO . FIG. 4 shows an embodiment of the present invention. In FIG. 4, the same components as those explained in FIG. 1 are designated by the same reference numerals.
In order to control the charging voltage value V _C of the resonance capacitor 5, a switching element 13 that performs on/off operation is connected in parallel to the resonance capacitor 5 and the resonance capacitor 6, and the switching elements 3 and 4 are connected in parallel to each other. They are driven by a control circuit in synchronization with each other. The configuration and operation of the control circuit will be explained with reference to the operational waveform diagram of FIG. 7. 4 and 7, the current detection winding 14 detects the resonant current flowing through the primary winding 8 of the conversion transformer 7, and the synchronous circuit 15 rectifies the resonant current of the current detection winding 14. The zero cross is detected and the oscillation frequency of the sawtooth wave oscillation circuit 16 is synchronized with the resonant current. A in FIG. 7 is a resonant current waveform rectified by the synchronization circuit 15, and a in B is an oscillation waveform of the sawtooth wave oscillation circuit 16 synchronized by the output signal of the synchronization circuit 15. 17 is an error amplification circuit to which the output DC voltage of the electrical load 12 is applied to one input terminal, a predetermined reference voltage E _S is applied to the other input terminal, and amplifies the difference voltage between them;
The output signal (indicated by b in FIG. 7B) is applied to a comparison circuit 18 for comparison with the output signal of the sawtooth wave oscillation circuit 18. The comparison circuit 18 compares the output signal of the sawtooth wave oscillation circuit 16 and the output signal of the error amplification circuit 17 as shown in FIG. 7B, and sends a signal shown in FIG. 7D to one output terminal. At the same time, output the signal shown in C in FIG. 7, which is an inversion of the above output signal, to the other output terminal,
It is supplied to the distribution circuit 19. The distribution circuit 19 is a well-known circuit composed of a flip-flop circuit, an AND circuit, etc., and in order to convert the signal shown in FIG. 7C into a signal for driving the two switching elements 3 and 4, Separate as shown in E and F in the figure. The signal at one output terminal of the distribution circuit 19 [E in FIG. 7] drives the switching element 3, and the signal at the other output terminal [F in FIG. 7] drives the switching element 4. . Also, the output signal of the comparison circuit 18 [D in FIG. 7]
drives the switching element 13. In the above circuit configuration, the operation in a steady state will be explained using an equivalent circuit diagram. The equivalent circuit diagram of the resonant circuit when the switching elements 3 and 4 are both off and the switching element 13 is on shows that the resonant capacitor 5 is discharged by the resonant coil 6 via the switching element 13. The voltage waveform v _C (t) and current waveform i(t) of the resonance capacitor 5 at that time are shown in FIG. 5b. If the charging voltage value charged to the resonance capacitor 5 by the resonance current of the resonance circuit constituted by the switching element 3 or 4 is V _C 1, then the switching element 13 turns on, causing the resonance to occur. The resonant current i(t) determined by the resonant capacitor 5 and the resonant coil 6 flows as shown by the dotted line in _FIG . At t ₂ , it becomes V _C 2. The V _C 2 changes depending on the on period (t ₂ -t ₁ ) of the switching element 13, and the on period (t ₂ -t ₁ ) is controlled by the pulse width shown in FIG. 7D. When the switching element 13 is turned off at the time _t2 , the charging voltage value of the resonance capacitor 5 becomes V _C 2 and the current value of the resonance coil 6 becomes I _O as described above. When switching element 13 is turned off, switching element 3 or 4 is turned on at the same time, and an equivalent circuit diagram at that time is shown in FIG. FIG. 6a is an equivalent circuit diagram when switching element 3 is turned on, and the concept of operation when switching element 4 is turned on is exactly the same. As shown in FIG. 6a, a resonant circuit is created by the input DC power supply 1, the resonant capacitor 5, the resonant coil 6, and the DC power supply having the voltage V _O ', and the initial voltage of the resonant capacitor 5 is The charging voltage value is V _C 2, the initial current of the resonant coil 6 is I _O , and the DC power supply having the above voltage V _O ' has the output DC voltage at the voltage between both terminals of the primary winding 8 of the conversion transformer 7. It shows the value obtained by converting V _O to the primary side. The resonance current i(t) shown in the equivalent circuit of FIG. 6a and the voltage waveform v _C (t) of the resonance capacitor 5 are shown in FIG. 6b. Since the initial current of the resonant coil 6 is I _O , the resonant current i(t) has a resonant waveform (shown by the dotted line) with the initial value of I _O , and the voltage waveform of the resonant capacitor 5 changes from V _C 2 to the above-mentioned waveform. The charging voltage value of V _C
It is charged to a voltage value (-V _C 1) having a magnitude equal to 1. The period (t ₃ -t ₂ ) of the resonant current is controlled by the pulse width of FIG. 7E. Figure 6b
The operation during the period (t ₄ -t ₃ ) is the same as that shown in FIG. The resonant current shown in FIG. 6b is rectified and smoothed by the rectifier circuit 10 and the smoothing capacitor 11 through the conversion transformer 7, and the voltage becomes the output DC voltage V _O. The magnitude of the resonant current is determined by the initial charging voltage value of the resonant capacitor 5. Therefore, in order to keep the output DC voltage constant against fluctuations in the input DC power supply or load, the switching element 13 must be adjusted. The driving pulse width may be controlled. When the output DC voltage of the smoothing capacitor 11 tries to increase, the differential voltage at the input of the error amplification circuit 17 increases, and the output signal level of the error amplification circuit 17 becomes higher than b in FIG. 7B.
As a result, the pulse width of the output signal of the comparator circuit 18 shown in FIG. limit the rise of Here, the sawtooth wave oscillation circuit 1
In the oscillation waveform No. 6 [a in FIG. 7B], the lower level is fixed at a constant value, and the upper level varies depending on the output level of the error amplification circuit 17. When the output DC voltage tries to decrease,
Contrary to the above-described operation, the output signal level of the error amplification circuit 17 is lower than b in FIG. 7B, and as a result, the pulse width of the output signal of the comparator circuit 18 in FIG. As a result, the ON period of the switching element 13 becomes shorter, the resonance current becomes larger, and the drop in the output DC voltage is limited. As described above, the embodiment of the present invention shown in FIG.
By adding a control switching element and a relatively simple control circuit to a series resonant DC-DC converter, the output DC voltage can be stabilized. FIG. 8 is a circuit connection diagram showing another embodiment of the present invention, in which elements having the same functions as those explained in FIG. 4 are given the same reference numerals. In the embodiment shown in FIG. 4, the charging voltage value of the resonance capacitor 5 is discharged and controlled by the resonance coil 6, whereas in the embodiment shown in FIG. Connect another coil 21 in parallel,
The coil 21 is controlled to discharge the charging voltage of the resonance capacitor 5. In FIG. 8, the control switching element 13 used in FIG. 4 is not used, and the control operation is performed by the switching elements 3 and 4. Therefore, the fourth
The comparison circuit 18 shown in the figure has an output terminal for outputting a signal for driving the switching element 13, but the comparison circuit 20 shown in FIG. 8 does not have the above output. However, the functions of both are exactly the same. The other circuit configurations are the same as in FIG. 4. In the above circuit configuration, the operation shown in FIG.
This will be explained using the diagram and the equivalent circuit diagram in FIG. FIG. 9 is an equivalent circuit diagram when the switching elements 3 and 4 are in the off state, in which a resonant current determined by the resonant capacitor 5 and the coil 21 flows, and the charging voltage of the resonant capacitor 5 is is time t ₁
It is discharged from the value V _C 1 at time t ₂ to V _C 2 at time t 2 . An operating waveform diagram when the inductance of the coil 21 is made larger than the inductance of the resonance coil 6 is shown in FIG. 10b. At time t ₂ , when the switching element 3 or 4 is turned on, the resonant capacitor 5 receives a resonance current i ₂ (t) from the coil 21 as well as the input DC power supply 1 or 2. A resonant current i ₁ (t) of the resonant circuit flows. The current value I _a of the coil 21 at time t ₂ is assumed. An equivalent circuit diagram when the switching element 3 is turned on is shown in FIG.
It is shown as a resonant circuit with a DC power supply having V _O ′. The DC power supply having the above-mentioned voltage V _O ' indicates a value obtained by converting the output DC voltage to the primary side with the voltage between both terminals of the primary winding 8 of the conversion transformer 7. The resonant currents i ₁ (t) and i ₂ (t) shown in FIGS. 9 and 10a and the voltage waveform v _C (t) of the resonance capacitor 5 are shown in FIG. 10b. In FIG. 10a, the initial charging voltage value of the resonance capacitor 5 is V _C 2,
The initial current value of the coil 21 is I _a , and the initial current value of the resonance coil 6 is zero. Since the operation is shown in a steady state, the above-mentioned V _O ' is constant. The period during which the switching element 3 is turned on becomes (t ₃ -t ₂ ) as shown in FIG. 10b due to the operations of the synchronization circuit 15 and the sawtooth wave generation circuit 16. The charging voltage of the resonance capacitor 5 is determined from the V _C 2,
−V _C with a magnitude equal to the above charging voltage value V _C 1
Charged to 1. -V _C 1 is reached at time t ₄ instead of at time t ₃ . The period from time t ₃ to t ₅ is as explained earlier in the operation using the equivalent circuit in FIG. 9, and the charging voltage value of the resonance capacitor 5 at time t ₅ is equal to the previous voltage value V _C 2. with -
V _C 2, and at this time, the switching element 4
turns on. The operation when switching element 4 is on is similar to that of switching element 3. In addition, in Fig. 10b, the current waveform indicated by the dotted line is
i ₁ (t), and the current waveform shown by the dotted line is i ₂ (t)
It is. Resonant current i ₁ (t) shown by the dotted line in Figure 10b
The rectifier circuit 1 is connected to the rectifier circuit 1 via the conversion transformer 7.
0 and the voltage rectified and smoothed by the smoothing capacitor 11 becomes the output DC voltage V _O. The magnitude of the resonant current i ₁ (t) is determined by the magnitude of the resonant current i 1 (t) of the switching element 3
and 4. Since the operation of the control circuit shown in FIG. 8 is completely similar to the operation of the control circuit shown in FIG. 4, the explanation here will be omitted. In addition, the time of 1/2 cycle of the resonance cycle of the above-mentioned resonance current i ₁ (t) is π・√
It is smaller than the value determined by C ₅ and L ₆ and is not constant. In addition, in FIGS. 4 and 8, the conversion transformer 7 is assumed to be an ideal transformer, and the resonant coil 6 is provided separately, but leakage inductance exists in an actual conversion transformer, and this value cannot be ignored. . Therefore, in this case, one of the conversion transformers is adjusted so that the effective leakage inductance of the conversion transformer 7 becomes the same value as the inductance of the resonance coil 6.
By adjusting the coupling of the next secondary winding, the resonance coil 6 can be omitted. Further, in the above embodiments of the present invention, a so-called half-bridge circuit series resonant DC-DC converter using two switching elements has been described, but the present invention can also be applied to other series resonant DC-DC converters. is clear. As described above, according to the present invention, the output voltage of a series resonant DC-DC converter can be stabilized with a relatively simple configuration, and its effects are extremely large.

[Brief explanation of drawings]

Figure 1 is a basic circuit diagram of a conventional series resonant DC-DC converter, Figure 2 is its equivalent circuit diagram, Figure 3 is a resonant current waveform diagram, and Figure 4 is a circuit connection showing an embodiment of the present invention. Figures 5a and 5b, 6a and 6b, and 7A, B, C, D, E, and F are equivalent circuit diagrams and their operations for explaining the operations of the embodiments of the present invention. A waveform diagram, FIG. 8 is a circuit connection diagram showing another embodiment of the present invention, and FIGS. 9 and 10 a and b are equivalent circuit diagrams and their operations to explain the operation of the embodiment of the present invention. FIG. 1, 2... Input DC power supply, 3, 4, 13... Switching element, 5... Resonance capacitor, 6, 21...
Resonance coil, 7... Conversion transformer, 10... Rectifier circuit, 11... Smoothing capacitor, 12... Electrical load, 14... Current detection winding, 15... Synchronous circuit, 16
...Sawtooth wave oscillation circuit, 17...Error amplification circuit, 1
8, 20...Comparison circuit, 19...Distribution circuit.

Claims (1)

[Claims] 1. Input DC power source, first source for on/off operation
A switching element, a resonant circuit including a resonance capacitor and an inductance element, and a primary winding of a conversion transformer are connected in series, a rectifier/smoothing circuit is connected to the secondary winding of the conversion transformer, and the output terminal In a series resonant DC-DC converter configured to supply a DC voltage by connecting an electrical load to the resonant circuit, a second switching element is connected in parallel to the resonant circuit, and a predetermined reference voltage is connected to the resonant circuit. The output signal of the circuit that compares and amplifies the DC voltage of the electric load and the oscillation output of the sawtooth wave oscillation circuit that oscillates in synchronization with the resonant current waveform is compared by a comparison circuit, and one of the comparison circuits The signal obtained from the output terminal of the comparator circuit drives the second switching element, and has a level that is inverted with respect to the signal obtained from the other output terminal of the comparator circuit that drives the second switching element. 1. A constant voltage power supply device characterized in that a signal is applied to the first switching element via a distribution circuit to drive it and stabilize the DC voltage of the electrical load. 2. The constant voltage power supply device according to claim 1, characterized in that the effective leakage inductance of the conversion transformer is used as the inductance element. 3 Input DC power supply, switching element for on/off operation, resonance circuit including resonance capacitor and inductance element, and conversion transformer 1
The second winding of the conversion transformer is connected in series with the next winding.
In a series resonant DC-DC converter configured to supply a DC voltage by connecting a rectifier/smoothing circuit to the next winding and connecting an electrical load to its output terminal, a predetermined reference voltage and the A comparator circuit compares the output signal of a circuit that compares and amplifies the DC voltage of an electrical load with the oscillation output of a sawtooth wave oscillation circuit that oscillates in synchronization with the resonant current waveform. A constant voltage power supply device characterized in that the obtained signal is applied to the switching element via a distribution circuit to drive it and stabilize the DC voltage of the electrical load. 4. The constant voltage power supply device according to claim 3, wherein the resonant circuit includes a coil connected in parallel to the capacitor.