JP3052254B2 - Resonant DC power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type DC power supply, and more particularly to a resonance type DC power supply capable of performing stable operation regardless of a load state.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a resonance type DC power supply which has been widely used in the past. The resonance type DC power supply includes a DC power supply 1 and first and second switching elements connected between one end and the other end of the DC power supply 1.
And second FETs (field effect transistors) 2, 3;
An output transformer 4 having first and second primary windings 4a and 4b and a secondary winding 4c, and an output transformer 4 connected in series to each of the first and second FETs 2 and 3 A resonance circuit 6 including a first primary winding 4a, a resonance capacitor 5 and a resonance reactor including an inductance formed integrally with the first primary winding 4a;
Of the first and second FETs 2 and 3 operated by the load 8 connected to the secondary winding 4c of the output transformer 4 via the rectifying and smoothing circuit 7 and the voltage of the second primary winding 4b of the output transformer 4. A control circuit 9 for applying a control signal to a gate terminal (control terminal) to control on / off of the first and second FETs 2 and 3; Although not shown, the control circuit 9 has frequency control means for controlling the frequency of a control signal applied to each gate terminal of the first and second FETs 2 and 3 according to the terminal voltage of the load 8. The rectifying / smoothing circuit 7 includes diodes 10 and 11 and a smoothing capacitor 12.
The voltage induced in the next winding 4b is supplied to the power supply terminal 9a of the control circuit 9 via the rectifier 13 and the smoothing capacitor 14. Reference numerals 15 and 16 denote light emitting diodes and light receiving transistors constituting a photocoupler, 17 denotes an operational amplifier, and 18 denotes a reference voltage source. The light receiving transistor 16 of the photocoupler is connected to a current detection terminal 9b of the control circuit 9 via a protection resistor.

In the resonance type DC power supply device shown in FIG. 4, when the terminal voltage of the load 8 is low, the control applied to each gate terminal of the first and second FETs 2 and 3 is controlled by the frequency control means in the control circuit 9. When the signal frequency decreases and the terminal voltage of the load 8 is high, the frequency of the control signal applied to each gate terminal of the first and second FETs 2 and 3 increases. Thereby, the DC output voltage of the resonance type DC power supply is stabilized. Further, since the rising and falling of the switching voltage waveform or the switching current waveform of the first and second FETs 2 and 3 become sinusoidal by the resonance action of the resonance circuit 6, the first and second FETs 2 and 3 are turned on. In addition, zero voltage switching (ZVS) or zero current switching (ZCS) at the time of turn-off is achieved, and there is an advantage that switching loss can be reduced.

FIGS. 5A to 5G show the waveform of the gate terminal voltage V _G1 of the first FET 2 and the second F, respectively, of the circuit of FIG.
The waveform of the gate terminal voltage V _G2 of ET3, the waveform of the voltage V _DS1 between the drain and source terminals of the first FET ₂ , the first F
The waveform of the drain current _ID1 of the ET2, the waveform of the voltage _VDS2 between the drain and source terminals of the second FET 3, the second FE
Waveform of drain current _ID2 of T3, first of output transformer 4
_Shows the waveform of the current I _N1 of the primary winding 4a. In the circuit of FIG. 4, when the load 8 is a light load, the resonance current flowing through the resonance circuit 6 decreases, so that the waveforms of the currents I _D1 , I _D2 and I _N1 are shown in FIGS. 5 (D), (F) and (F). The waveform is as shown by the broken line G). FIG. 6 shows the voltage E ₁ of the DC power supply ₁ and the load 8.
Power supply voltage V _CC of the control circuit 9 in various cases of
6 is a graph showing a relationship between the control frequency and a control frequency f of the control circuit 9. 6, curve A when the voltage E ₁ of the DC power source 1 in the light load state is minimal, if the curve B the voltage E ₁ of the DC power source 1 in the light load state of the maximum, the curve C is a direct current in the overload condition If the voltage E ₁ of the power supply 1 is minimum, if the curve D is the voltage E ₁ of the DC power source 1 in the overload condition is maximum, the curve E in the case of constant output voltage at light load conditions, the curve F is overloaded Shows a case where the output voltage is constant. Usually, control of the frequency of the control signal applied to each gate terminal of the first and second FETs 2 and 3 in the range indicated by the curves E and F is performed by the frequency control means in the control circuit 9.

[0005]

By the way, in the resonance type DC power supply device shown in FIG.
_{Since MAX} is constant regardless of the state of the load 8, when the voltage E1 of the DC power supply ₁ is low and the load 8 is in a light load state,
As shown by a curve A in FIG. 6, the power supply voltage V _CC of the control circuit 9 may be lower than the minimum allowable operating voltage V _MIN . Therefore, there is a disadvantage that the operation of the control circuit 9 stops and the power supply device does not operate. Also, if the power supply voltage V _CC is set higher to ensure the minimum allowable operating voltage V _MIN or higher, the power supply voltage V _CC exceeds the maximum allowable operating voltage V _MAX of the control circuit 9 shown in FIG. As a result, the control circuit 9 may be burned.

Accordingly, an object of the present invention is to provide a resonance type DC power supply that can operate stably regardless of the state of a load.

[0007]

A resonance type DC power supply according to the present invention comprises a DC power supply (1) and a first switching element connected in series between one end and the other end of the DC power supply (1). (2)
And a second switching element (3) and a first primary winding (4
a), an output transformer (4) having a second primary winding (4b) and a secondary winding (4c); and any one of a first switching element (2) and a second switching element (3). A first primary winding (4a) of an output transformer (4), a resonance circuit (6) comprising a resonance capacitor (5) and a resonance reactor connected in parallel to one of the output transformers, and an output transformer (4). ), A load (8) connected to a secondary winding (4c) through a rectifying and smoothing circuit (7), and an output transformer (4).
Operating by the voltage of the second primary winding (4b), and applying a control signal to each control terminal of the first switching element (2) and the second switching element (3) to provide a first switching element.
(2) and a control circuit (9) for controlling ON / OFF of the second switching element (3 ) . The resonance reactor comprises an inductance or an independent inductance formed integrally with the first primary winding (4a) of the output transformer (4),
The control circuit (9) increases the frequency of the control signal when the terminal voltage of the load (8) increases and decreases the frequency of the control signal when the terminal voltage of the load (8) decreases.
(23). In this resonance type DC power supply, the control circuit
Voltage detection means (22) for detecting a voltage applied to (9),
A control frequency limiting means (24) connected to the voltage detecting means (22) and the frequency controlling means (23) is provided in the control circuit (9), and the control voltage is reduced when the voltage detected by the voltage detecting means (22) decreases. When the minimum allowable operating voltage (V _MIN ) of (9) is _reached , the control frequency limiting means (2
4) The current flowing in the frequency control means (23) is reduced by flowing a current through the
(f _MAX ) is reduced. In the embodiment of the present invention, the resonance circuit (6)
The overcurrent detection resistor (40) is inserted in the circuit, and when the load (8) is overloaded, the overcurrent flowing to the resonance circuit (6) is detected by the overcurrent detection resistor (40) and the frequency control means is The control frequency of (23) is increased. Furthermore, when photocouplers (15, 16) are connected between the secondary side of the output transformer (4) and the control circuit (9), the photocouplers (15, 16) are connected when the terminal voltage of the load (8) rises. A large current flows through (15, 16) to increase the frequency of the control signal, and when the terminal voltage of the load (8) drops, the current flowing through the photocoupler (15, 16) decreases, reducing the frequency of the control signal. I do.

[0008]

[Function] The voltage applied to the control circuit (9) is detected by a voltage detecting means.
(22), the maximum control frequency of the frequency control means (23) is set when the detection voltage of the voltage detection means (22) decreases and becomes the minimum allowable operating voltage (V _MIN ) of the control circuit (9). By reducing the control frequency by the control frequency limiting means (24), the control circuit (9) of the resonance type DC power supply can be operated stably regardless of the state of the load.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a resonance type DC power supply according to the present invention will be described below with reference to FIGS. The resonance type DC power supply device of the present embodiment is such that the control circuit 9 of the resonance type DC power supply device shown in FIG. 4 is configured as shown in FIG. That is, the control circuit 9 of the resonance type DC power supply according to the present invention includes:
As shown in FIG. 1, a voltage detecting means 22 comprising two voltage dividing resistors 20 and 21 and detecting a voltage induced in the second primary winding 4b of the output transformer 4 of FIG. 22 is the minimum allowable operating voltage V of the control circuit 9.
A control frequency limiting means 24 for limiting the maximum control frequency of the frequency control means 23 when it becomes equal to or less than _MIN (FIG. 6); a waveform shaping circuit 25 for shaping the output voltage waveform of the frequency control means 23 into a rectangular pulse waveform; and a control signal generating circuit 26 for generating a control signal V _G1, V _G2 to impart a rectangular pulse output of the waveform shaping circuit 25 to the gate terminals of the first and second FET2,3 in FIG. Waveform shaping circuit 2
For example, M51841P (timer IC, manufactured by Mitsubishi Electric Corporation) or the like can be used as 5. The control signal generation circuit 26 includes a flip-flop 27 and two AND gates 28 and 29.
It consists of. The frequency control means 23 includes a constant voltage regulator 30 for generating a reference voltage V _REF as a minimum allowable operating voltage V _MIN of the control circuit, and a constant current circuit comprising two transistors 31 and 32 and connected to the constant voltage regulator 30. 33, and a capacitor 34 connected to the constant current circuit 33. The control frequency limiting means 24 comprises a transistor 35 and is connected between the voltage detecting means 22 and the frequency control means 23.
The configuration other than the control circuit 9 is the same as the circuit of FIG. 2 (A) to 2 (D) show voltage waveforms at points A to D in FIG. 1, respectively.

In the above configuration, when the load 8 shown in FIG. 4 enters a light load state, the terminal voltage of the load 8 increases, and the current flowing through the light receiving transistor 16 of the photocoupler increases. At this time, the constant current circuit 3 in the control circuit 9 shown in FIG.
3 operates, the current flowing through the capacitor 34 increases, and the control frequency of the frequency control means 23 increases accordingly. As a result, the waveform at the point A (FIG. 1) shown in FIG. Changes to Conversely, when the terminal voltage of the load 8 decreases and the current flowing through the light receiving transistor 16 of the photocoupler decreases, the control frequency of the frequency control means 23 decreases accordingly. Therefore, the pulse width of the rectangular wave pulse at points B to D in FIG. 1 shown in FIGS. 2B to 2D is reduced and the frequency is increased, and the first and second FETs shown in FIG.
The frequency (switching frequency) of the control signal applied to each of the second and third gate terminals increases. When the switching frequency of each of the FETs 2 and 3 increases, the output transformer 4
The voltage of the secondary winding 4c decreases, and the second
The voltage induced in the next winding 4b also decreases. Accordingly, the power supply voltage V _CC of the control circuit 9 also decreases. Control circuit 9
The power supply voltage V _CC is detected by the voltage detecting means 22, when the detection voltage of the DC power supply 1 voltage E ₁ and a low voltage detector 22 becomes equal to or lower than the reference voltage V _REF of Ryakujo voltage regulator 30, the control frequency limit Transistor 3 of means 24
5 is turned on. At this time, the current flowing through the transistor 31 of the constant current circuit 33 in the frequency control means 23 is shunted to the transistor 35 of the control frequency limiting means 24,
The current flowing through the capacitor 34 also decreases. As a result, the control frequency of the frequency control means 23 decreases,
The waveform at point A (FIG. 1) shown in FIG. 2A is as shown by the solid line, and the pulse width of the rectangular wave pulse at points B to D in FIG. 1 shown in FIGS. At the same time, the frequency decreases. When the frequency (switching frequency) of the control signal applied to each gate terminal of the first and second FETs 2 and 3 shown in FIG. 4 decreases, the voltage of the secondary winding 4c of the output transformer 4 increases, and 4, the voltage induced in the second primary winding 4b also increases. Therefore, the power supply voltage V _CC of the control circuit 9 becomes higher than the minimum allowable operating voltage V _MIN .

As described above, in the present embodiment, the voltage induced in the second primary winding 4b of the output transformer 4 is detected by the voltage detecting means 22, and the detected voltage of the voltage detecting means 22 is used for the control circuit. Since the maximum control frequency of the frequency control means 23 is limited by the control frequency limiting means 24 when the voltage becomes equal to or lower than the minimum allowable operating voltage V _MIN , that is, the reference voltage V _{REF of the} constant voltage regulator 30, the load 8 may be in a light load state In such a case, the control circuit 9 can be operated stably.

In the above description, only the case where the load 8 is in the light load state has been described. However, depending on the type of the load 8, the load 8 may be in the overload state. For this reason, in the circuit of the embodiment shown in FIG. 3, an overcurrent detection resistor 40 is inserted in the resonance circuit 6 shown in FIG. 4, and the current of the control circuit 9 is supplied via the operational amplifier 41, the reference voltage source 42 and the protection resistor. By connecting to the detection terminal 9b, an overcurrent flowing through the resonance circuit 6 when the load 8 is in an overload state is detected. In the circuit of FIG. 3, when the load 8 is overloaded, the overcurrent detection resistor 4
When 0 is detected, an overcurrent is detected, the current of the constant current circuit 33 in the control circuit 9 increases, and the current flowing to the capacitor 34 increases. Accordingly, since the control frequency of the frequency control means 23 increases, the switching frequency of the first and second FETs 2 and 3 increases, and the secondary winding 4 of the output transformer 4
The voltage of c decreases. Therefore, even when the load 8 is overloaded, the same problem as that when the load 8 is lightly loaded occurs. Therefore, in the circuit of the embodiment shown in FIG. 3, the overcurrent detection resistor 40 is inserted to detect the overcurrent flowing when the load 8 is in the overload state. Thus, the control circuit 9 can be operated stably.

The embodiments of the present invention are not limited to the above-described embodiments, and various modifications are possible. For example, in the above-described embodiment, an example has been described in which the resonance reactor forming the resonance circuit 6 is configured by an inductance formed integrally with the first primary winding 4a of the output transformer 4, but the resonance reactor is independent. May be used. In the above embodiment, an example in which an FET is used as a switching element has been described. However, another switching element such as a bipolar transistor or an SCR (reverse blocking three-terminal thyristor) may be used. Also, two half-bridge capacitors are connected in parallel with the first and second FETs 2 and 3 connected between one end and the other end of the DC power supply 1, and the first and second FEs are connected.
The primary circuit of the output transformer 4 may be configured as a half-bridge type by connecting the resonance circuit 6 between the connection point of T2 and T3 and the connection point of the two half-bridge capacitors. Further, the two voltage dividing resistors 20 and 21 and the capacitor 34 constituting the voltage detecting means 22 may be provided outside the control circuit 9.

[0014]

As described above, according to the present invention, the voltage induced in the second primary winding of the output transformer is detected by the voltage detecting means, and the detected voltage of the voltage detecting means is used by the control circuit. Since the maximum control frequency of the frequency control means is limited by the control frequency limiting means when the voltage becomes equal to or lower than the operating voltage, the control circuit of the resonance type DC power supply can always be operated stably regardless of the state of the load. Therefore, there is an advantage that a stable output voltage can be obtained even when used as a power source of an electronic device having a remarkable load variation such as a printer of a personal computer.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a control circuit of a resonance type DC power supply device according to the present invention.

FIG. 2 is a waveform chart showing voltages of respective parts of the circuit of FIG.

FIG. 3 is an electric circuit diagram showing a modified embodiment of the present invention.

FIG. 4 is an electric circuit diagram showing a conventional resonance type DC power supply device.

FIG. 5 is a waveform chart showing the voltage and current of each part of the circuit of FIG.

FIG. 6 is a graph showing a relationship between a power supply voltage and a control frequency of the control circuit of FIG. 4;

[Explanation of symbols]

1. . . DC power supply, 2, 3,. . . First and second FET
(First and second switching elements); . . Output transformer, 4a. . . A first primary winding, 4b. . . Second primary winding, 4c. . . 4. secondary winding; . . 5. a capacitor for resonance; . . 6. resonance circuit, . . Rectifying and smoothing circuit,
8. . . Load, 9. . . Control circuit, 22. . . Voltage detection means, 23. . . Frequency control means, 24. . . Control frequency limiting means

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (3)

(57) [Claims] 1. A DC power supply, a first switching element and a second switching element connected in series between one end and the other end of the DC power supply, a first primary winding and a second switching element. 1
An output transformer having a secondary winding and a secondary winding;
A resonance circuit comprising a first primary winding, a resonance capacitor, and a resonance reactor of the output transformer connected in parallel to one of the switching element and the second switching element; The first transformer operates by a load connected to a secondary winding via a rectifying and smoothing circuit, and a voltage of a second primary winding of the output transformer;
A control circuit that applies a control signal to each control terminal of the switching element and the second switching element to control the first switching element and the second switching element to be on / off. The control circuit increases the frequency of the control signal when the terminal voltage of the load increases, and comprises an inductance formed integrally with the first primary winding of the output transformer or an independent inductance. A resonance type direct-current power supply having frequency control means for reducing the frequency of the control signal when the terminal voltage of the control circuit decreases; voltage detection means for detecting a voltage applied to the control circuit; A control frequency limiting unit connected to the frequency control unit is provided in the control circuit; When the minimum allowable operating voltage of the control circuit is reached, a current flowing through the frequency control means is reduced by flowing a current through the control frequency limiting means, and a maximum control frequency of the frequency control means is reduced. Resonant DC power supply. 2. An overcurrent detection resistor is inserted into the resonance circuit, and when the load is in an overload state, an overcurrent flowing through the resonance circuit is detected by the overcurrent detection resistor and the frequency control means is provided. The resonance type direct-current power supply device according to claim 1, wherein the control frequency is increased. 3. When a terminal voltage of the load increases, a large current flows through a photocoupler connected between a secondary side of the output transformer and the control circuit to increase the frequency of the control signal. 3. The resonance type DC power supply device according to claim 1, wherein a current flowing through the photocoupler when the terminal voltage of the load decreases decreases the frequency of the control signal.