JPH06113534A - Power supply - Google Patents

Abstract

PURPOSE:To provide a power supply comprising a switching element, withstand voltage of which may be exceeded due to the effect of electromotive force induced in an inductance element, wherein the induced electromotive force is decreased under heavy load or at the time of rising without increasing power loss of snubber circuit during steady operation. CONSTITUTION:Constants of a snubber circuit 2 are switched through a switching element Q2 such that the surge voltage absorbing power of the snubber circuit 2 is enhanced if a high electromotive force is induced in an inductance element upon turn OFF of a switching element Q1. Consequently, the switching element Q1 is protected against application of a surge voltage exceeding the withstand voltage thereof by increasing the constants of the snubber circuit 2 upon generation of a high electromotive force. When the induced electromotive force is low, power loss of the snubber circuit 2 can be lowered by decreasing the constants of the snubber circuit 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device using an inductance element and a switching element, such as a step-up chopper circuit and a one-stone separately-excited DC-DC converter circuit, and for example, lighting a high-intensity discharge lamp. It is used in the field of devices and the like.

[0002]

2. Description of the Related Art FIG. 9 shows a conventional lighting device for a general HID lamp (high-intensity discharge lamp). The lighting device is H
Inverter unit 13 for controlling the output characteristics of the ID lamp 15
And an igniter 14 for discharging the HID lamp 15,
It is composed of a power supply unit 12 that stably supplies electric power from the battery 11 to the inverter unit 13. Generally, H
Since the ID lamp has a low pressure inside the discharge tube immediately after the start of discharge and the vapor pressure of the metal that emits light due to the discharge energy is low,
The luminous flux is small. After that, as the temperature of the discharge tube rises, the metal vapor pressure in the tube rises, the luminous flux increases, and stable lighting is achieved.

FIG. 10 shows load characteristics of a general HID lamp. A general HID lamp lighting device gradually moves on the output characteristic curve of FIG. 10 from an operating point A immediately after lighting to a stable point B. The lamp output W is HI
It gradually increases as the D-lamp stabilizes. Further, since the discharge tube temperature gradually rises with the passage of time, the luminous flux Φ of the lamp is, as shown in FIG.
Gradually rises with the progress of. However, with such a rising characteristic of the luminous flux, since the lighting of the lamp is very slow, there is a problem that it cannot be used as, for example, a vehicle headlight.

In order to solve such a problem, it can be considered to design the output characteristic of the inverter section 13 as shown in FIG. In the output characteristic of FIG. 12, by increasing the output characteristic from the operating point A immediately after lighting to the stable point B,
By supplying an excessive current to the HID lamp, the temperature inside the tube is rapidly increased, the luminous flux is rapidly increased, and the time until stable lighting is shortened. in this case,
The rising characteristic of the luminous flux of the HID lamp is as shown in FIG. With such output characteristics, it can be used as a vehicle-mounted headlight, for example. By the way, if the inverter unit 13 of the lighting device has the output characteristic shown by the solid line in FIG. 12, the lamp power W has the characteristic shown by the broken line in FIG. 12, and an excessive lamp current I immediately after the lamp is lit.
It is necessary to have a lamp output W that can flow the light. To obtain this lamp output W, the power supply unit 12 is required to have an excessive output power immediately after the lamp is turned on.

Therefore, it is conceivable to use a boost chopper circuit as shown in FIG. In this circuit, an inductor L1 is connected to a DC power supply V1 via a switching element Q1, and a smoothing capacitor C2 is connected to both ends of the switching element Q1 via a diode D1, and both ends of the DC power supply V1 are connected. A capacitor C1 for smoothing the input voltage is connected in parallel. When the switching element Q1 is turned on, a current flows from the DC power supply V1 to the inductor L1 and electromagnetic energy is stored in the inductor L1. When the switching element Q1 is turned off, an induced electromotive voltage due to electromagnetic energy is generated at both ends of the inductor L1, superposed on the voltage of the DC power source V1, and the output voltage V2 boosted to the smoothing capacitor C2 via the diode D1. can get. In this step-up chopper circuit, for example, a drive signal subjected to PWM control is supplied to the control circuit 1.
From the above, the output voltage V2 can be controlled by giving it to the switching element Q1, and the output voltage V2 can be increased immediately after the lamp is turned on. However, if a general boost chopper circuit as shown in FIG. 14 is used as the power supply unit of the lighting device, for example, when used as a vehicle headlight, the input voltage V1 becomes the voltage of the vehicle battery. ,
The step-up ratio of the power supply section becomes very large, and the withstand voltage, current rating, etc. required of the switching element Q1 become large, leading to an increase in size or cost. Further, as described above, since an excessive output current is required, the input current becomes large and the power loss in the inductor and the like becomes large.

In order to solve such a problem, conventionally, a step-up chopper circuit using an auto transformer T1 as shown in FIG. 15 has been adopted. As described above, in the method using the auto transformer T1, even if the step-up ratio is large,
The switching element Q1 is not required to have a large withstand voltage, and the power loss due to the inductance element is small.
However, when such an autotransformer T1 is used, a leakage inductance Lt is generated between the primary side and the secondary side, as shown in FIG. 16, and the kick voltage immediately after the switching element Q1 is turned off. The generated voltage Vds between the drain and source of the switching element Q1 is shown in FIG.
As shown in 7. The peak value of this voltage Vds increases in proportion to the energy stored in the leakage inductance Lt. FIG. 17A shows a waveform at the time of rising of the output voltage V2 immediately after the power is turned on, or at the time of excessive output in the initial stage of lamp lighting, and FIG. 17B shows a waveform at the steady state. That is, the larger the input current I1 shown in FIG. 15, the larger the peak value of the voltage Vds. As described above, there are two states in which the input current of the power supply unit becomes large: when excessive power is required when the lamp is lit and when the output potential rises. In the transient two states, if the peak value of the voltage Vds exceeds the withstand voltage, there is a problem that the switching element Q1 is destroyed. Therefore, conventionally, the snubber circuit 2 as shown in FIG. This is intended to reduce the peak value of the voltage Vds. However, in this way, the voltage Vd
In order to reliably reduce the peak value of s, it is necessary to sufficiently increase the capacitance of the capacitor C3. When the capacitance of the capacitor C3 is increased, the power consumption by the resistor R3 is increased and the power loss of the snubber circuit 2 is increased.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention, for example, from a light load to a heavy load such as a lighting device for an HID lamp. , When the load condition changes drastically,
In a power supply device in which the withstand voltage of the switching element may be exceeded due to the influence of kick voltage, etc. due to the energy accumulated in the leakage inductance, a heavy load or startup may occur without increasing the power loss of the snubber circuit at steady state. The switching element is protected by switching the constant of the snubber circuit so as to reduce the kick voltage.

[0008]

According to the present invention, in order to solve the above problems, as shown in FIG. 1, a series circuit of an inductance element and a first switching element Q1 is provided between input terminals. When the switching element Q1 is turned on, energy is stored in the inductance element, and when the switching element Q1 is turned off, the energy of the inductance element is released to output an output voltage V2 different from the input voltage V1 to the smoothing capacitor C2 between the output terminals. In the obtained power supply device, the snubber circuit 2 connected in parallel with the first switching element Q1 has a second switching element Q2 for constant switching.
And a second switching for constant switching of the snubber circuit 2 so that the surge voltage absorbing power of the snubber circuit 2 increases when the induced electromotive voltage generated by the inductance element when the first switching element Q1 is off is large. Element Q2
Is provided with a means for controlling.

Although the leakage inductance of the autotransformer T1 is used as the inductance element in the circuit of FIG. 1, the inductance component of the primary winding of the high frequency transformer T2 may be used as shown in the circuit of FIG. Absent.

[0010]

In the present invention, as described above, the second switching element Q2 for switching the constant of the snubber circuit 2 is provided, and the first switching element Q2 is provided.
When the induced electromotive force generated by the inductance element when the switching element Q1 is off is large, the constant of the snubber circuit 2 is switched by the second switching element Q2 so that the surge voltage absorbing power of the snubber circuit 2 increases. Therefore, it is possible to prevent a surge voltage exceeding the withstand voltage of the switching element Q1 from being applied to both ends of the switching element Q1. Further, when the induced electromotive voltage generated by the inductance element when the first switching element Q1 is off is small, the surge voltage absorption capacity of the snubber circuit 2 is not set unnecessarily large, so the first switching element Q1 It is possible to prevent the power loss of the snubber circuit 2 from increasing due to the switching.

[0011]

1 is a circuit diagram of a first embodiment of the present invention.
The circuit configuration will be described below. The smoothing capacitor C1 is connected to the input terminal of the power supply device. One end of the auto transformer T1 is connected to the positive electrode of the smoothing capacitor C1. The other end of the autotransformer T1 is connected to the positive electrode of the smoothing capacitor C2 via the anode / cathode of the diode D1. The negative electrode of the smoothing capacitor C2 is connected to the negative electrode of the smoothing capacitor C1.
The center tap of the autotransformer T1 is connected to the drain of the switching element Q1 composed of a MOS transistor. The source of the switching element Q1 is connected to the negative electrode of the smoothing capacitor C1. A parasitic reverse diode is connected in parallel between the drain and source of the switching element Q1. In addition, the switching element Q
In order to absorb the kick voltage generated across 1, the resistance R
3 and capacitor C3 in series circuit is switching element Q1
It is connected between the drain and source of. Also, the resistance R
4 and the capacitor C4 are connected in series with the switching element Q2.
Is connected in parallel to the series circuit of the resistor R3 and the capacitor C3 via. The switching element Q2 is composed of a MOS transistor, and a parasitic reverse diode is connected in parallel between its drain and source.

Next, the control circuit 1 uses the switching element Q1.
A square wave drive signal Va subjected to PWM control is supplied to the gate of the. The drive signal Va is also input to the duty detection circuit 4 including a CR integration circuit including a resistor R5 and a capacitor C5. The duty detection circuit 4 compares the signal Vb obtained by integrating the drive signal Va with the comparison circuit 3
Is applied to the first input terminal of the comparator CMP. A reference voltage Vc obtained by dividing the control power supply voltage by the resistors R1 and R2 is applied to the second input terminal of the comparator CMP. Output signal Vd of comparator CMP
Are supplied to the gate of the switching element Q2.

FIG. 2 is an operation waveform diagram of this embodiment. In the figure, Va is a drive signal for the switching element Q1, Vb is an output signal from the duty detection circuit 4, and Vc is a comparator C.
The reference voltage of MP, Vd is the output signal of the comparator CMP. Cs is the capacitance of the snubber circuit 2.
Now, assume that the load of the chopper changes and the control signal Va of the switching element Q1 changes as shown in FIG. 2 in order to maintain the potential of the output voltage V2. At this time,
The duty of the drive signal Va is detected as a voltage signal Vb proportional to the duty width by charging / discharging the CR time constant of the duty detection circuit 4. This voltage signal Vb is
It is compared with the reference voltage Vc by the comparator CMP.
Here, the reference voltage Vc is a kick voltage between the drain and source of the switching element Q1 (induced electromotive voltage generated by the leakage inductance of the auto transformer T1).
Is set to the potential of the output signal Vb of the duty detection circuit 4 in the duty width immediately before the withstand voltage of the switching element Q1 is exceeded. The magnitude of the drain-source voltage Vds of the switching element Q1 changes depending on the energy of the leakage inductance. Since the energy of the leakage inductance is determined by the energy stored in the auto transformer T1 when the switching element Q1 is turned on, the duty width of the switching element Q1 determines the magnitude of the drain-source voltage Vds. When the output signal Vb of the duty detection circuit 4 is larger than the reference voltage Vc, the energy of the leakage inductance becomes large and the switching element Q2
Control signal Vd becomes high level. This allows
The switching element Q2 is turned on, the capacitance Cs of the snubber circuit 2 becomes (C3 + C4), and the drain-source voltage Vds of the switching element Q1 is reduced. By the above operation, the constant of the snubber circuit 2 can be appropriately changed and the switching element Q1 can be protected from breakdown voltage only when the duty width of the switching element Q1 is large and the voltage Vds is large.

FIG. 3 is a circuit diagram of the second embodiment of the present invention, and FIG. 4 is an operation waveform diagram of the present embodiment. In this embodiment, at both ends of the capacitor C3 in the snubber circuit 2,
The capacitor C4 is connected via the switching element Q2. A timer signal Vt is supplied from the timer circuit 5 to the gate of the switching element Q2. After the power is turned on, the timer signal Vt from the timer circuit 5 is Hi.
The gh level is reached, and the switching element Q2 is turned on. After that, the control circuit 1 rises to operate the switching element Q1. As shown in FIG. 4, the timer signal Vt from the timer circuit 5 becomes High level and continues to turn on the switching element Q2 for a period of time until the lamp is stably lit after the power is turned on. Meanwhile, the capacitance Cs of the snubber circuit 2 is the sum (C3 + C4) of the capacitors C3 and C4. Further, when the load becomes stable and the output voltage V2 enters the stable period, the timer signal Vt from the timer circuit 5 becomes Low level, and the switching element Q2 is turned off. As a result, the capacitance Cs of the snubber circuit 2 becomes only the capacitance of the capacitor C3. By the above operation, the power loss in the steady state can be reduced and the switching element Q in the transient state can be reduced.
The kick voltage appearing in the drain-source voltage Vds of 1 can be reduced.

FIG. 5 is a circuit diagram of the third embodiment of the present invention, and FIG. 6 is an operation waveform diagram of the present embodiment. In this example,
The present invention is applied to a DC-DC converter of the one-stone separate excitation type. The voltage V1 between the input terminals is the current detection circuit 6
Is applied to the series circuit of the primary winding of the high frequency transformer T2 and the switching element Q1 via. The switching element Q1 is composed of a MOS transistor, and a parasitic reverse diode is connected in parallel between its drain and source. The gate of the switching element Q1 has a PWM
A controlled square wave drive signal is supplied from the control circuit 1. A smoothing capacitor C2 is connected to the secondary winding of the high frequency transformer T2 via a rectifying diode D1 and a smoothing inductor L1. A diode D2 is connected to the series circuit of the inductor L1 and the smoothing capacitor C2 with the polarity shown. Switching element Q1
When is turned on, a current flows in the primary winding of the high frequency transformer T2, an induced electromotive voltage is generated in the secondary winding, and the capacitor C2 is charged via the diode D1 and the inductor L1. When the switching element Q1 is turned off, the energy stored in the inductor L1 is discharged to the smoothing capacitor C2 via the diode D2, and the smoothing capacitor C2 is discharged.
Is a DC voltage V2.

Next, the snubber circuit 2 will be described.
The configuration of the snubber circuit 2 in this embodiment is similar to that of the second embodiment shown in FIG. 3, and the resistor R3 and the capacitor C3 are included.
In the snubber circuit 2 composed of the serial circuit of, a capacitor C4 for changing the constant is connected in parallel with the capacitor C3 via the switching element Q2. The comparison circuit 3 for controlling the switching element Q2 includes a comparator CMP and resistors R1 and R2 for generating a reference voltage.
And has the same configuration as that of the first embodiment shown in FIG. The detection signal Vi that is compared with the reference voltage Vc by the comparator CMP is obtained from the current detection circuit 6. The current detection circuit 6 includes a resistor R5 for current-voltage conversion.
And resistors R6 and R7 for voltage division, and outputs the detection signal Vi corresponding to the current flowing from the input terminal.

In this embodiment, HID is used as the load circuit.
When a lighting circuit such as a lamp is connected, the input current increases immediately after the power is turned on to raise the output voltage V2,
Also, due to the load characteristics of the HID lamp, the input current becomes large immediately after the start of lighting because of a heavy load. Therefore, as shown in FIG. 6, the detection signal Vi from the current detection circuit 6 becomes small immediately after the power is turned on (section t1) and immediately after lighting (section t2). The detection signal Vi is compared with the reference voltage Vc by the comparator CMP, and when the input current is large, the control signal Vd which becomes High level is obtained. By this control signal Vd, the switching element Q
2 becomes ON only when the input current is large, and the capacitance Cs of the capacitor of the snubber circuit 2 becomes (C3 + C4) in the sections t1 and t2 where the input current is large, and changes to C3 in the other sections. When the input current is large, the energy of the high frequency transformer T2 is large, so that the kick voltage appearing in the drain-source voltage Vds of the switching element Q1 also becomes large, but at that time, the snubber circuit 2
Also, the capacitance Cs of is increased, so that the kick voltage can be reduced. Further, in a section where the input current is not large, the capacitance Cs of the snubber circuit 2 can be reduced to reduce power loss, heat generation, etc. of the circuit.

FIG. 7 is a circuit diagram of the fourth embodiment of the present invention, and FIG. 8 is an operation waveform diagram of the present embodiment. In this embodiment, the voltage detection circuit 7 is connected to the smoothing capacitor C2 on the output side of the chopper circuit to detect the output voltage V2.
The voltage detection circuit 7 outputs a detection signal Vo obtained by dividing the output voltage V2 by the resistors R8 and R9. This detection signal Vo is input to the comparison circuit 3 and the comparator C
It is compared with the reference voltage Vc by MP, and when the output voltage V2 is high, it operates so as to turn on the switching element Q2 of the snubber circuit 2. In addition, the detection signal Vo
Is also input to the control circuit 1 of the switching element Q1 and compared with the triangular wave signal Ve of the CR oscillator 8 by the comparator CMP2, and is also used for PWM control of the drive signal Va of the switching element Q1.

In the present embodiment, assuming that the load of the chopper circuit is, for example, a lighting circuit of a HID lamp or the like, the detection signal Vo of the voltage detection circuit 7 is generated at the time of rising or a heavy load (initial lighting of the lamp). As shown by the solid line in FIG. 8A, the switching element Q1 is turned on.
Due to the charging / discharging of the capacitor C2 due to / OFF, it fluctuates significantly up and down. When the load is heavy, the output voltage V2 drops. As a result, as shown in FIG. 8B, the duty of the control signal Va of the switching element Q1 is increased, the stored energy of the high frequency transformer T1 is increased, and the output voltage V2 is increased. On the other hand, when the load is light, the output voltage V2 does not fluctuate up and down and the output voltage V2 does not drop sharply as in the case of the heavy load. Therefore, as shown in FIG. The duty of the signal Va is small. By the above-described operation, the control circuit 1 of the chopper operates so as to keep the constant output voltage V2 in response to the changing load. Further, the comparison circuit 3 compares the detection signal Vo of the voltage detection circuit 7 with the reference voltage Vc, as shown in FIG. The solid line in the figure indicates the detection signal Vo when the load is heavy.
And the broken line shows the detection signal Vo when the load is light. Only when the load is heavy, the detection signal Vo becomes lower than the reference voltage Vc, and at that time, as shown in FIG. 8E, the output signal Vd of the comparator CMP becomes the high level. The output signal Vd of this comparator CMP is H
At the high level, the capacitance Cs of the snubber circuit 2 becomes C
3 to (C3 + C4), switching element Q1
It is possible to effectively reduce the kick voltage that appears in the drain-source voltage Vds. As described above, when the duty of the switching element Q1 is large, the energy accumulated in the leakage inductance of the auto transformer T1 increases and the kick voltage of the switching element Q1 increases, but as in the present embodiment, the output voltage V2 is increased. By increasing the capacitance Cs of the snubber circuit 2 only when the duty is large, the power loss in the steady state does not change, and moreover, when the output voltage V2 of the chopper rises, for example, when the lamp is turned on. The kick voltage of the switching element Q1 can be effectively reduced under a heavy load such as time.

[0020]

According to the present invention, in the power supply device using the inductance element and the first switching element, the constant of the snubber circuit connected in parallel with the first switching element can be switched by the second switching element. , The constant of the snubber circuit is switched by the second switching element so that the surge voltage absorbing power of the snubber circuit increases when the induced electromotive force generated by the inductance element when the first switching element is off is large. , The effect of preventing the voltage across the first switching element from exceeding the withstand voltage, and the surge voltage of the snubber circuit when the induced electromotive voltage generated by the inductance element when the first switching element is off is not large. Since the absorption power is not set unnecessarily high, the snubber circuit power There is an effect that the loss can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is an operation waveform diagram of the second embodiment of the present invention.

FIG. 5 is a circuit diagram of a third embodiment of the present invention.

FIG. 6 is an operation waveform diagram of the third embodiment of the present invention.

FIG. 7 is a circuit diagram of a fourth embodiment of the present invention.

FIG. 8 is an operation waveform diagram of the fourth embodiment of the present invention.

FIG. 9 is a block circuit diagram of a conventional HID lamp lighting device.

FIG. 10 is an output characteristic diagram of a conventional general HID lamp.

FIG. 11 is a luminous flux characteristic diagram of a conventional general HID lamp.

FIG. 12 is an output characteristic diagram of a conventional instantaneous lighting HID lamp.

FIG. 13 is a luminous flux characteristic diagram of a conventional instantaneous lighting HID lamp.

FIG. 14 is a circuit diagram of a conventional general boost chopper circuit.

FIG. 15 is a circuit diagram of a boost chopper circuit using a conventional auto transformer.

FIG. 16 is an equivalent circuit diagram of a boost chopper circuit using a conventional auto transformer.

FIG. 17 is an operation waveform diagram of a boost chopper circuit using a conventional auto transformer.

[Explanation of symbols]

 1 Control Circuit 2 Snubber Circuit 3 Comparison Circuit 4 Duty Detection Circuit T1 Autotransformer D1 Diode C2 Smoothing Capacitor Q1 First Switching Element Q2 Second Switching Element

Claims (1)

[Claims] 1. A series circuit of an inductance element and a first switching element is connected between input terminals, energy is stored in the inductance element when the switching element is on, and energy of the inductance element is released when the switching element is off. In a power supply device that obtains an output voltage different from an input voltage in a smoothing capacitor between output terminals, a snubber circuit connected in parallel with the first switching element includes a second switching element for constant switching, and the first switching A means for controlling the second switching element for constant switching of the snubber circuit is provided so that the surge voltage absorbing power of the snubber circuit increases when the induced electromotive voltage generated by the inductance element when the element is off is large. And power supply.