JP2941547B2 - Resonant switching 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 switching power supply. In particular, a high-frequency voltage generated on the secondary side of the output transformer is changed to a DC voltage, the capacitor is charged, and then when the battery is charged to a certain voltage, the battery is discharged to a load. The present invention also relates to a device that repeatedly performs this charge and discharge.

[0002]

2. Description of the Related Art Conventionally, as a circuit for repeatedly charging and discharging a capacitor by a switching power supply, a circuit based on pulse width modulation (hereinafter referred to as PWM) is generally used. For example, one example is shown in FIG. This circuit uses a flash lamp as a load. In FIG. 1, 1 is an AC power supply, 2 is a diode bridge, 3,
Reference numeral 4 denotes an electrolytic capacitor connected in series for smoothing and dividing a DC obtained by rectifying an AC voltage, 5 denotes an inductance, 6 denotes a voltage conversion transformer (hereinafter referred to as a transformer), and 61 denotes a primary winding thereof. , 62 indicate secondary windings, respectively. 7 is a current detection circuit, 8 and 9 are diodes,
Reference numerals 10 and 11 denote switching elements, in this case MOS
I use FET. 13 is a high-frequency rectifier diode bridge, 14 is a main capacitor, 15 is an inductance for optimizing the discharge current waveform of the capacitor 14, 16
Is a flash lamp as a load, and 17 is a switch which receives the output of the current detection circuit 7 and turns on the switching elements 10 and 11.
A drive signal generation circuit for turning off is shown.
Vi indicates the output voltage of the diode 2, and the voltage across each of the electrolytic capacitors 3 and 4 is (半 分) × V
i. The charging voltage of the main capacitor 14 is set to V0.

FIG. 2 is a time chart of the circuit shown in FIG. The current flowing through the inductance 5 is defined as Ip, and the drive signals for the switching elements 10 and 11 are defined as Vg1 and Vg2, respectively. In FIG. 2, the drive signals Vg1 and Vg2 have an appropriate dead time DT so that they do not overlap with each other in time.
Generated from. The timing at which each drive signal is turned off is when the current value Ip detected by the current detection circuit 7 reaches the preset limit values Ic and -Ic. The ON timing is when the set dead time has elapsed after the other signal is turned OFF at the above timing.

(1) Description of current Ip in period in FIG. 2 Now, drive signal Vg1 is given to switching element 10. At this time, electric field capacitor 3 → switching element 10 → primary winding 61 → inductance 5 → A current Ip flows through a closed circuit formed by the electrolytic capacitor 3. Assuming that the turn ratio of the transformer 6 is n (n is the primary winding 61 of the transformer 6 / the secondary winding 62 of the transformer 6), nV0 back electromotive force is generated at both ends of the primary winding 61. (However, the voltage drop due to the diode bridge 13 is ignored.) At this time, the inductance 5 has (１ ／) × Vi−nV0.
Is applied. If the self-inductance of the inductance 5 is L, the current Ip increases linearly at a slope (dIp / dt) determined by L × (dIp / dt) = (1/2) Vi─nV0. (However, a voltage change due to the discharge of the electrolytic capacitor 3 and a voltage drop when the switching element 10 is turned on are ignored.)

(2) Description of Current Ip in Period in FIG. 2 When the current Ip reaches the limit value Ic, the switching element 10 is turned off as described above. Then, the energy stored in the inductance 5 is released, and the current Ip is commutated to the diode 9. Thereafter, the current Ip flows through a closed circuit formed by the diode 9 → the primary winding 61 → the inductance 5 → the electrolytic capacitor 4 → the diode 9 to charge the electrolytic capacitor 4. At this time, the voltage across the electrolytic capacitor 4 and the primary winding 61 has a polarity opposite to that of the current Ip, and the current Ip has a slope determined by L × (dIp / dt) = − ((１ ／) Vi + nV0). Decrease. As can be seen from the figure, the period decreases at a larger rate of change than the period.
Since the current flows through the diode 9 until the current Ip becomes zero, the current does not flow even if the drive signal Vg2 is applied to the switching element 11 on the way.

(3) Description of the current Ip in the period in FIG. 2 After all the energy stored in the inductance 5 is released, the current Ip shown in the period starts to flow through the switching element 11. The operation at this time is the same as the period, although the polarity is different, and the description is omitted. In this manner, the main capacitor 14 is charged and energy is stored by repeating the period. When the charged energy reaches a certain value, a trigger (not shown) is triggered to discharge the charged energy at once. This causes the lamp to emit light. This light emission is performed, for example, at 2 to 5 Hz.
The operation of the circuit shown in FIG. 1 has been described above. The charging voltage V0 of the output capacitor 14 changes by a factor of 10 or more before and after the flash lamp 16 emits light. Therefore, the back electromotive force nV0 generated in the primary winding 61
Also vary greatly.

[0007] In the case of a conventional switching circuit based on PWM control, the following problems occur. (1) Since the switching elements 10 and 11 turn off at the maximum point of the triangular waveform based on the current value Ip, extremely large switching loss and switching noise are generated. For this reason, a large and expensive switching element and a noise filter are required. (2) In the waveform of the current Ip shown in FIG. 2, the period is a time during which the energy stored in the inductance 5 is released. Part of this energy is charged to the main capacitor 14 via the transformer 6. However, most returns to the electrolytic capacitor 4 without being used as charging energy. The ratio between the energy used as the charging voltage and the energy fed back to the electrolytic capacitor corresponds to the ratio between the voltage nV0 across the primary winding 61 and the voltage across the electrolytic capacitor 4. The rate at which the stored energy is used as charging energy in the main capacitor 14 is just before the light emission of the lamp 16 (when V0 is high), about half, and almost completely after the light emission (when V0 is low). Not done. As described above, it is very inefficient that the energy that is not effectively used is stored and released by the inductance 5. That is, the energy supplied from the AC power supply is
Returning again without using it for the load increases the loss of the elements constituting the circuit.

Therefore, recently, as a method for solving such a problem, use of a resonant switching power supply has been studied. An example is shown in FIG. In the drawing, reference numeral 30 denotes a smoothing electrolytic capacitor. Reference numerals 31 and 32 denote resonance capacitors. Reference numerals 33 and 34 denote diodes for clamping the voltage across the resonance capacitor to a value equal to or lower than the voltage across the smoothing capacitor 30. 35 indicates a resonance inductance. Reference numeral 36 denotes a resonance tank including the resonance capacitors 33 and 34 and the resonance inductance 35. In the figure, V
s indicates the voltage across the diode 9, and Vc indicates the voltage across the resonance capacitor 32. The current Ip indicates a current flowing through the resonance inductance 35 and the primary winding 61. Others
The same numbers are the same as those in FIG.

This circuit is commonly referred to as an improved series resonant converter. Since the flash lamp 16 is used as a load similarly to the circuit shown in FIG. 1, the charging voltage V0 of the main capacitor 14 fluctuates greatly each time the lamp emits light. FIG. 4 shows a time chart corresponding to FIG. FIG.
(A) shows each value immediately after the light emission of the lamp and when the charging voltage V0 is small. FIG. 4 (b)
Each value is shown immediately before the light emission of the lamp and when the charging voltage V0 is large. An ordinary resonant converter operates with a waveform as shown in FIG. 4 (b), but in the case where the charging voltage V0 changes greatly, the operation as shown in FIG. 4 (a) also occurs. Vg1 and Vg2 are drive signals from the drive signal generation circuit 17, but in the case of a resonance type circuit, the pulse width during the ON period is about 1.
Fixed to 2x. That is, the output control is performed by PWM
In general, instead of changing the pulse width as described above, the frequency (hereinafter referred to as the operating frequency) is changed. The series resonance tank 36 composed of the resonance capacitors 6 and 7 and the resonance inductance 8 resonates at a resonance frequency fr.

(1) Period in FIG. 4A and FIG.
Description of Period ′ in FIG. 4B In FIG. 4A, in the period, the switching element 1
0 is on. At this time, the capacitor 30 → the switching element 10 → the primary winding 61 → the resonance inductance 35
→ Resonant capacitor 32 → Resonant current flows in a closed circuit of capacitor 30. Then, the resonance capacitor 32 is charged up to Vi. On the other hand, a resonance current also flows through a closed circuit formed by the resonance capacitor 31 → the switching element 10 → the primary winding 61 → the resonance inductance 35 → the resonance capacitor 31 to discharge the resonance capacitor 31 from Vi to zero. The current Ip obtained by combining the two resonance currents is the switching element 1
0, the primary winding 61, and the resonance inductance 35. In the section of the above, if the time when the current Ip starts to flow is t0, the self-inductance of the resonance inductance 35 is L, and the capacitance of the resonance capacitors 31 and 32 is C, the current Ip becomes

[0011]

(Equation 1)

## EQU1 ## From this equation, it can be seen that the smaller the charging voltage V0, the larger the current Ip. That is, immediately after the lamp emits light, the charging voltage Vc of the resonance capacitor 32 is small in the resonance half cycle.
Reaches the voltage Vi across the capacitor 30 at an early point. On the other hand, in FIG. 4B, the charging voltage V0 is
Since the current is higher than in the case of FIG. 4A, the current Ip has a small value. Therefore, the charging voltage Vc of the resonance capacitor 32 becomes
The timing of reaching the voltage Vi across the capacitor 30 is also
It is slower than that of FIG.

(2) Period in FIG. 4A and FIG.
Description of period 'b' in (b) When the charging voltage Vc of the resonance capacitor 32 reaches the voltage Vi across the capacitor 30, the current Ip changes from the period to the period. This time is defined as t1. Then, the resonance stops, and the current flowing through the resonance capacitors 31 and 32 is commutated to the diode 33. In the period,
The voltage Vc and the voltage Vs are both Vi, and the primary winding 6
The value obtained by adding the back electromotive force generated at 1 and the voltage of the resonance inductance 35 becomes zero. Then, since the back electromotive force generated in the primary winding 61 is nV0, nV0 + L × (dI
(p / dt) = 0 and (dIp / dt) =-(n / L) V0 Since V0 immediately after the lamp 16 emits a very small value, the absolute value of (dIp / dt) becomes a small value. ,
Ip slowly decreases and the energy stored in the inductance 35 slowly releases during this time via the transformer 6 to charge the capacitor 14. On the other hand, the basic operation in the period ′ in FIG. 4B is the same as that in the period, but the rate of decrease in the current Ip is large because the value of the charging voltage V0 is large. That is, before the switching element 10 is turned off, the current Ip becomes zero, and all the energy stored in the resonance inductance 35 is used for charging the main capacitor 14 via the transformer 6.

(3) Period in FIG. 4A and FIG.
Description of Period ′ in (b) When the switching element 10 is turned off (t2), the operation mode shifts from the period to the period. When the switching element 10 is turned off, the current Ip flowing in the state of the period
Commutates to the diode 9. Then, the diode 9 → the primary winding 61 → the resonance inductance 35 → the diode 33
→ The capacitor 30 → flows in a closed circuit of the diode 9. If the voltage drop in the diode 33 and the diode 9 is ignored, the sum of the voltages in the closed circuit becomes zero.
i + L × (dIp / dt) + nV0, and
(DIp / dt) =-(1/2) (Vi + nV0), which indicates that the current Ip decreases more rapidly during the period than during the period. Then, at time t3, the current Ip becomes zero. The period is a time when the energy stored in the resonance inductance 35 is released,
Part of the charge is charged to the main capacitor 14 via the transformer 6, but most of the charge returns to the electrolytic capacitor 30. More specifically, the ratio of the charging energy to the main capacitor 14 and the charging energy fed back to the electrolytic capacitor 30 is nV0 to Vi. That is, when the charging voltage V0 is small immediately after light emission, most of the energy is not effectively used. When the current Ip becomes zero (t3 in FIG. 4), all the energy stored in the resonance inductance 35 is released, and the half cycle of the resonance operation ends. Hereinafter, the period, the period, and the operation of the period are essentially the same as the period, the period, and the operation of the period, and the description thereof is omitted.

That is, as described in FIGS. 3 and 4,
In the case of the resonant switching power supply, when the charging voltage V0 of the capacitor 14, which is a load, is large (that is, immediately before light emission of the lamp 16), the current Ip becomes zero as shown in FIG. Since the switching element performs the turn-off operation at the timing of the switching, the switching loss and the switching noise can be suppressed low.
Furthermore, since all the stored energy of the resonance inductance 35 is used for charging the main capacitor 14 via the transformer 6, the stored energy can be used effectively. On the other hand, as can be seen in FIG. 4A, when the charging voltage V0 of the capacitor 14 is low (immediately after the lamp 16 emits light), when the switching element 10 is turned off (t2), the current Ip is at the highest point. No, but quite expensive. Therefore, the problems of switching loss and switching noise still remain. Furthermore, since the turn-off is performed while the stored energy of the inductance is being discharged, the stored energy is mostly returned to the electrolytic capacitor. That is, since the energy supplied from the AC power supply is returned to the load again without using it as in the PWM method, the loss of the elements constituting the circuit increases. Generally, such a resonance circuit sets the winding of the transformer for a high voltage state when the load voltage fluctuation is large. (That is, in this case, when the charging voltage of the main capacitor 14 is high.) This is because if the winding is set for a low voltage, the resonance operation does not occur when the voltage is high. For this reason, when a resonance circuit is used, there is no problem when the voltage value is high, but when the voltage value is low, the same problem as in the PWM method still remains.

[0016]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the following problems in a resonance type switching power supply used for repeatedly charging and discharging a capacitor even when a charging voltage is low. It is in. (1) An object of the present invention is to use a small and inexpensive switching element or noise filter by reducing switching noise and switching loss due to the switching element. (2) Turn off the switching element with as little stored energy as possible to prevent or reduce the stored energy of the resonant inductance from being fed back to the primary side electrolytic capacitor without being used at the load. It is in.

[0017]

In order to solve such a problem, a resonance type switching power supply according to the present invention periodically performs an operation of storing energy in a main capacitor and discharging the energy to a load. It is a repetitive resonant switching power supply. And the power supply is a voltage conversion transformer, a resonance tank composed of a resonance inductance and a resonance capacitor connected to the primary winding of the transformer,
A secondary winding on the secondary side of the transformer, a divided secondary winding, a charging circuit connected to each of the secondary windings for charging the main capacitor, and a resonance operation state of the resonance tank; And a resonance stop detection circuit that outputs a signal when the resonance operation stops, and a signal from the resonance stop detection circuit turns on the output to maintain that state and discharge the signal when the main capacitor is discharged. A signal holding circuit whose output is reset and turned off, and a switching circuit driven by a signal of the signal holding circuit, wherein the switching circuit causes the plurality of charging circuits to operate in parallel immediately after the main capacitor is discharged. After the main capacitor has been charged to a chargeable voltage, a means for switching to series operation and charging is provided.

[0018]

With the circuit having such a configuration, even if the charging voltage of the capacitor fluctuates greatly, the operation of the secondary winding and the charging circuit is switched from parallel to series, so that the operation is hardly affected by the fluctuation. Can resonate.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 5 is an example of a resonance type switching power supply according to the present invention. The secondary winding of the transformer 6 is divided into two windings 51 and 51 '. Each number of turns is shown in FIG.
１ ／ of the number of turns of the secondary winding 62 shown in FIG. Winding 5
1. High-frequency rectifier diode bridges 52, 52 'are connected to the winding 51', respectively. Reference numerals 53 and 54 denote diodes. The positive terminal of the diode bridge 52 ′ is connected to the anode of the diode 53, and the cathode of the diode 53 is connected to the positive terminal of the diode bridge 52 and the positive terminal of the capacitor 14. . The negative terminal of the diode bridge 52 is connected to the cathode of the diode 54, and the anode of the diode 54 is connected to the negative terminal of the diode bridge 52 ′ and the negative terminal of the main capacitor 14. One charging circuit is constituted by the secondary winding 51, the diode bridge 52, and the diode 54, and the secondary winding 51 ', the diode bridge 52', and the diode 53
Constitute another charging circuit. Switching element 55 (IGBT is used in this embodiment)
Has its collector connected to the anode of diode 53 and its emitter connected to the cathode of diode 54.
Reference numeral 84 denotes a current transformer for detecting a current flowing through the resonance inductance 35. Reference numeral 80 denotes a resonance stop detection circuit that outputs a resonance stop signal according to a change in the output of the current transformer 84 when the resonance operation stops.
A trigger circuit 83 generates a trigger pulse for causing the flash lamp 16 to emit light. Reference numeral 82 denotes a trigger signal generation circuit for operating the trigger circuit 83. 81 is based on the signal of the resonance stop detection circuit 80,
A signal holding circuit is shown in which the output is turned on, the state is held, and the output is reset and turned off by a signal from the trigger signal generation circuit 82. Reference numeral 58 denotes a switching signal generation circuit that generates a drive signal for the switching element 55 based on the output of the signal holding circuit 81. In this circuit, when the switching element 55 is off, the two charging circuits operate in parallel. When it is on, it operates in series. Reference numeral 63 denotes a switching circuit including a diode 53, a diode 54, and a switching element 55. Reference numeral 64 denotes a charging circuit including the winding 51 and the diode bridge 52, and reference numeral 65 denotes a charging circuit including the winding 51 'and the diode bridge 52'.

On the other hand, the resonance operation by the resonance tank 36 is as follows.
When the charging voltage V0 of the main capacitor 14 rises and the voltage across the primary winding 61 becomes 1/2 of the DC voltage Vi, the operation naturally stops. The charging voltage V of the main capacitor 14 at this time
0 indicates when the two charging circuits 64 and 65 operate in parallel,
It differs when operating in series. In the parallel operation, when the charging voltage V0 is (1 / (4n)). Times.Vi, the resonance operation of the resonance tank 6 stops. In the case of serial operation, the resonance operation of the resonance tank 6 stops when the charging voltage V0 is (1 / (2n)). Times.Vi. * However, Vi indicates a DC input voltage, and n indicates (the number of turns of the primary winding 61 of the transformer 6) / (the sum of the number of turns of the winding 51 and the winding 51 'of the transformer 6).
Next, the operation of this circuit will be described. When the trigger circuit 83 operates according to the signal of the trigger signal generation circuit 82,
When the flash lamp 16 emits light, the charging voltage V0 of the main capacitor 14 decreases. At the same time, the signal holding circuit 81 is reset, and the charging circuit 63 and the charging circuit 64 operate in parallel to start the charging operation. Then, when the main capacitor 14 is charged to (1 / (4n)) × Vi, the resonance operation naturally stops as described above. At this time, the output current of the current transformer 84 drops significantly. In response to this decrease, the resonance stop circuit 80 operates, the signal holding circuit 81 operates, and the switching signal generation circuit 58 operates to turn on the switching element 55. by this,
The operation of the two charging circuits switches from parallel to series. At the same time, the voltage between both ends of the primary winding 61 is reduced by half, the stopped resonance operation is restarted, and the main capacitor 14 is charged. When the charging voltage V0 of the main capacitor 14 reaches the set voltage of the voltage limiting circuit 85 from this state, a signal is sent to the drive signal generating circuit 17 to stop the entire switching circuit. That is, the resonance operation of the resonance tank 36 also stops. Also at this time, the resonance stop circuit 80 operates, but since the signal holding circuit 81 is reset only by a signal from the trigger signal generating circuit 82, the states of the charging circuit 63 and the charging circuit 64 are maintained as being connected in series. Then, when the trigger circuit 83 operates by the trigger signal generation circuit 82, the lamp 16 emits light. Hereinafter, this procedure is repeated.

Here, even if the input voltage Vi fluctuates, the main capacitor 14 must be charged up to the set voltage of the voltage limiting circuit 85. For this reason, even when the input voltage Vi is the lowest, the turns ratio of the transformer 6 is set such that the charging voltage of the main capacitor 14 when the resonance due to the series operation naturally stops becomes larger than the maximum value of the set voltage. You. The set voltage can be changed according to the purpose of use. Also, the charging voltage V0 may decrease due to leakage current from the completion of charging to the light emission of the lamp. In this case, charging and stopping are repeated while keeping the series operation. In this way, the problem that occurs when V0 is small in the initial stage of charging is solved by switching the series or parallel connection of a plurality of charging circuits, thereby reducing the primary winding 6.
1 is designed to increase the voltage between both ends. 86 is a comparator between the reference voltage V0 and the set voltage, and 87 is a reference value of the comparator 86 for determining the set voltage. For example, before and after the flash lamp 16 emits light, the charging voltage V0 changes about 10 times. At this time, in the case of the conventional circuit, the back electromotive force generated in the primary winding 61 also changes 10 times, but in the case of the present invention, the change can be suppressed to about 5 times.
Therefore, the amplitude of the current Ip at the beginning of charging can be made closer to the waveform at the end of charging. That is, the current due to the release of the stored energy when the switching element is turned off can be considerably reduced. For this reason, switching loss and switching noise in the switching element can be suppressed low, and further, the amount of energy that is fed back without using the load can be suppressed.

In this embodiment, the stop of the resonance operation is detected by a change in the current of the resonance inductance 35. However, the present invention is not limited to this. A method of detecting the voltage across the resonance capacitor 31 or 32, or Other methods of detecting a current value or a voltage value that changes due to the stop of resonance may be considered. Further, the signal of the trigger signal generation circuit 82 is used as the reset signal of the signal holding circuit 81,
In this case, the discharge current or the terminal voltage of the main capacitor 14 or another signal generated when the flash lamp 16 emits light may be used as the reset signal.

According to the present invention, the back electromotive force generated in the primary winding of the transformer is suppressed to a considerably small fluctuation range even if the charging voltage of the capacitor fluctuates greatly, for example, due to the emission of the flash lamp. Can be. For this reason, switching loss and switching noise due to the switching element can be suppressed to a considerably low level. In addition, since the switching element is turned off in a state where the energy stored in the inductance forming the resonance tank is as small as possible, the amount of energy that is fed back can be reduced without using it for a load. For this reason, the loss of the elements constituting the circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a PWM type switching power supply.

FIG. 2 is a time chart according to a circuit diagram of a PWM type switching power supply.

FIG. 3 is a circuit diagram of a resonance type switching power supply.

FIG. 4 is a time chart diagram of a circuit diagram of a resonance type switching power supply.

FIG. 5 is a circuit diagram of the resonance type switching power supply of the present invention.

[Explanation of symbols]

 6 Transformer 10 Switching element 11 Switching element 14 Main capacitor 30 Electrolytic capacitor 31 Resonance inductance 35 Resonance capacitor 36 Resonance tank 51 Secondary winding 52 Diode bridge 53 Diode 51 ′ Secondary winding 52 ′ Diode bridge 54 Diode 55 Switching element 58 Switching Signal generating circuit 61 Primary winding of transformer 62 Secondary winding of transformer 63 Switching circuit 64 Charging circuit 65 Charging circuit 80 Resonance stop detection circuit 81 Signal holding circuit 82 Trigger signal generating circuit 83 Trigger circuit

Claims (1)

(57) [Claims] 1. A resonance type switching power supply that periodically repeats an operation of storing energy in a main capacitor and discharging the energy to a load, comprising: a voltage conversion transformer; and a resonance converter connected to a primary winding of the transformer. A resonance tank composed of an inductance and a resonance capacitor; a secondary winding on the secondary side of the transformer, divided into a plurality of windings; and a charging unit connected to each of the secondary windings to charge the main capacitor. A circuit, a resonance stop detection circuit that monitors a resonance operation state of the resonance tank and outputs a signal when the resonance operation stops, and an output is turned on by a signal from the resonance stop detection circuit, and the state is turned on. A signal holding circuit that holds and resets its output when the main capacitor is discharged and turns off, and is driven by the signal of this signal holding circuit Immediately after discharging the main capacitor, the plurality of charging circuits are operated in parallel, the main capacitor is charged to a chargeable voltage, and then switched to series operation. A resonance type switching power supply having charging means.