JPH06269160A - Power supply - Google Patents

Abstract

PURPOSE:To provide a power supply which can be operated even under a bad environment, e.g. as an onboard power supply, by preventing saturation of an inductor. CONSTITUTION:A main circuit 1 has a constitution wherein a series circuit of a switching element Q1 repeating ON/OFF operation and a part of the main winding (nm) of an inductor L1 is connected with a DC power supply E while a series circuit of the remaining part of the main winding (mn) of the inductor L1, a diode and a capacitor is connected in parallel with the switching element Q1. Output voltage from the main circuit 1 is detected by a detecting circuit 2 and a control circuit 3 controls ON interval of the switching element Q1 to stabilize the output voltage from the main circuit 1. The inductor L1 has a detection winding (nd) coupled electromagnetically with the main winding. When no voltage is induced in the main winding (nd), a protective circuit 4 decides that the inductor L1 is saturated and shortens ON interval of the switching element Q1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a switching element which is repeatedly turned on and off, and an inductor having a winding which is energized when the switching element is turned on and off. The present invention relates to a power supply device used as such.

[0002]

2. Description of the Related Art Conventionally, there has been provided a switching power supply in which an output voltage is controlled by connecting and disconnecting an input voltage by turning on and off a switching element.
This kind of switching power supply has the feature that power loss is small, and if the switching element is turned on and off at high frequency, the volume of the inductor used for transformation and insulation will be small, and it will be small and lightweight. Because it has, it is widely used. For example, when an HID lamp is used as a vehicle headlight, it is used as a power supply device for lighting the HID lamp by boosting the voltage of the vehicle battery using a step-up switching power supply.

By the way, in this type of switching power supply, there are known a circuit type in which the input and output are common ground and a circuit type in which the input and output are insulated via a transformer. In the former, a choke coil or an auto transformer is used as an inductor to perform step-up or step-down, and in the latter, a transformer is provided as an inductor in the output section for both step-up and step-down and insulation. In such an inductor, as shown in FIG. 10, the magnetic flux density determined by the circuit configuration is the saturation magnetic flux density Bm _{2 at the} temperature Ta.
It is designed to be used in a temperature range that is smaller than the above. That is, the upper limit temperature Ta that can be used is regulated by the temperature characteristics of the saturation magnetic flux density of the core and the circuit configuration. On the other hand, in in-vehicle and outdoor applications, the operating temperature range is -50 ° C to + 100 ° C, which is a severe operating condition, and the upper limit temperature Ta must be set extremely high. In the circuit configuration designed under the conditions, the temperature of the inductor core becomes higher than the design condition, the saturation magnetic flux density is reduced, and the inductor is likely to be saturated. If the inductor saturates, the designed output cannot be obtained. Here, if feedback control is performed so as to stabilize the output voltage, when the output voltage drops due to saturation of the inductor, the current flowing through the inductor is increased to increase the output voltage. There is a problem that the switching element is damaged due to a large current flowing through the switching element. That is,
The magnetic flux density Bm ₁ inside the inductor is Bm ₁ = L depending on the peak value Ip of the current, the inductance L of the inductor, the number of turns N of the winding of the inductor, and the cross-sectional area S of the core.
It can be expressed as Ip / NS, and it is required to use the magnetic flux density Bm ₁ so as not to exceed the saturation magnetic flux density Bm ₂ at the operating temperature.

Therefore, in order to prevent the saturation of the inductor even when the usage condition exceeds the allowable range, a circuit configuration in which the protection circuit 4 is provided as shown in FIG. 7 can be considered. Figure 7
The main circuit 1 of this circuit is a step-up type chopper circuit. That is, a capacitor C ₂ connected in parallel to the DC power source E, a capacitor C and a series circuit of a part of the inductor L ₁ and the switching element Q ₁ made of MOSFET
₂ has a main circuit 1 connected between both ends of the switching element Q ₁ and a series circuit of the remaining part of the inductor L ₁ , the diode D ₁ and the capacitor C ₁ .
In the main circuit 1, when the switch element Q ₁ is turned on, a current proportional to the on time flows into the inductor L ₁ (see FIG. 9), and when the switch element Q ₁ is turned off, the inductor L ₁ is turned on.
It operates so that the energy stored in the output side is supplied to the output side through the diode D ₁ . The output voltage, which is the voltage across the capacitor C ₁ , changes depending on the ON period of the switch element Q ₁ .

In order to stabilize the voltage applied to the load 5 such as a vehicle-mounted headlight, the voltage across the capacitor C ₁ is obtained from a series circuit of _two resistors R ₁ and R _{2 connected} in series. The voltage is divided by the detection circuit 2 and input to the control circuit 3. In the control circuit 3, the detection voltage output from the detection circuit 2 is supplied to the sawtooth wave generation circuit 3 by the comparator CP ₁ .
It is compared with the voltage level of a sawtooth wave having a constant cycle and constant amplitude output from a. That is, the sawtooth wave as shown in FIG. 8A is output from the sawtooth wave generation circuit 3a and compared with the detection voltage output from the detection circuit 2 as shown by the broken line in FIG. 8A. Therefore, the comparator CP
_As shown in FIG. 8B, a rectangular wave signal having a wider width is output from _{1 as} the voltage across the capacitor C ₁ decreases. This rectangular wave signal has a constant cycle equal to the cycle of the sawtooth wave, and the ON period becomes longer as the output voltage of the main circuit 1 decreases. Therefore, the switching element Q ₁
If the output voltage of the main circuit 1 is reduced, the ON period of the switch element Q ₁ is extended, the energy stored in the inductor L ₁ is increased, and the output voltage of the main circuit 1 is increased. . In short, the output voltage of the main circuit 1 is feedback-controlled by the detection circuit 2 and the control circuit 3 so as to suppress the fluctuation of the output voltage.

In the circuit configuration of FIG. 7, the protection circuit 4 monitors the current flowing through the inductor L ₁ during the ON period of the switch element Q ₁ so that the inductor L ₁ is not saturated. That is, the current flowing during the ON period of the switching element Q ₁ to the inductor L _1, the switch element Q ₁
Are compared by a comparator CP ₃ is detected as inserted voltage across the resistor R _3, the upper limit voltage Vx which is set by the reference voltage generating unit 4d and the voltage across the resistor R ₃ between the capacitor C ₂ and . Comparator CP ₃
Outputs the H level during the period when the voltage across the resistor R ₃ exceeds the upper limit voltage Vx. In other words, as shown in FIG. 8 (c), the current I ₁ flowing through the inductor L ₁ during the ON period of the switching element Q _1, i.e. the voltage across the resistor R ₃ is elevated in proportion to the ON time of the switching element Q ₁ During the period when this voltage exceeds the upper limit voltage Vx, the output of the comparator CP ₃ becomes H level as shown in FIG. 8D. Therefore, a large current I ₁ as an inductor L ₁ is saturated sets an upper limit voltage Vx as the voltage across the inductor L ₁ and a resistor R ₃ flowing through the switching element Q ₁ is greater than the upper limit voltage Vx, the comparator CP _{If the} switch element Q ₁ is controlled to turn off when the output of ₃ becomes the H level, the resistance R ₃
The saturation of the inductor L ₁ can be prevented by the protection circuit 4 including the comparator CP ₃ and the reference voltage generator 4d.

That is, in the circuit of FIG. 7, the logical product of the output of the control circuit 3 and the negation of the output of the protection circuit 4 is obtained by the logical circuit 3b 'as shown in FIG. By controlling Q ₁ , the output voltage of the main circuit 1 is stabilized and the saturation of the inductor L ₁ is prevented. In order to prevent the saturation of the inductor L ₁ without using the protection circuit 4 described above, it is necessary to use the large-sized inductor L _1, which causes a problem that the size of the inductor L ₁ is increased as a whole. hand,
If the saturation of the inductor L ₁ is prevented by the above circuit configuration, it is possible to prevent the saturation of the inductor L ₁ even though it is small, and it is possible to provide a power supply device suitable for applications such as in-vehicle use.

[0008]

However, in the circuit configuration shown in FIG. 7, the resistor R ₃ is inserted in the circuit for storing energy in the inductor L ₁ , and when the energy is stored in the inductor L _1. In addition, there is a problem that power loss occurs due to energization of the resistor R ₃ .

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and by providing a protection circuit for preventing the saturation of the inductor, it is possible to prevent the inductor from becoming large in size and to be used in a vehicle or an outdoor application. It is an object of the present invention to provide a power supply device that can be used even under such a bad environment and that does not cause a large power loss when detecting saturation of an inductor.

[0010]

In order to achieve the above object, the present invention provides an inductor having a switching element that is repeatedly turned on and off and a winding that is energized as the switching element is turned on and off. A main circuit provided, a control circuit for detecting the output voltage of the main circuit and controlling the ON period of the switch element in the direction of reducing the change in the output voltage, and a period in which a signal for turning ON the switch element is generated from the control circuit. When the inductor saturation is detected, it is equipped with a protection circuit that controls to reduce the ON period of the switch element.The inductor is equipped with a detection winding that is electromagnetically coupled to the above winding. It is characterized in that it is determined that the inductor is saturated if is not induced.

[0011]

According to the above construction, the detection winding is provided in the inductor of the main circuit, and if the voltage is not induced in the detection winding, it is determined that the inductor is saturated, and the control circuit sends a signal for turning on the switch element. If it is determined that the inductor is saturated during the period when it is being generated, the ON period of the switch element is controlled so as to be reduced, so the temperature conditions for automotive use such as a power supply for headlights are severe. Even when the inductor is saturated, the energy stored in the inductor can be reduced by controlling the ON period of the switching element to decrease when the inductor saturates. It is possible to prevent damage to the elements and the like.
Also, because the protection circuit prevents inductor saturation, it does not cause circuit abnormalities even in environments where the temperature exceeds the design specifications.Therefore, it is not necessary to design in consideration of the high temperature environment, and the inductor can be used at room temperature. It is possible to use a small-sized one that does. Moreover, since no resistor is used in the electric path through which the main current flows as a means for detecting the saturation of the inductor, there is no loss due to the resistor and the efficiency is high.

[0012]

(Embodiment 1) This embodiment basically has the configuration shown in FIG. That is, the main circuit 1 for converting the direct-current power supply E into high frequency is provided, and the output voltage of the main circuit 1 is detected by the detection circuit 2 and supplied to the load 5. The output voltage of the main circuit 1 detected by the detection circuit 2 is input to the control circuit 3, and the control circuit 3 adjusts the ON period of the switch element Q ₁ so as to reduce the change in the output voltage of the main circuit 1.

On the other hand, the main circuit 1 is turned on by the control circuit 3.
Switching element Q ₁ and inductor L ₁ controlled to be off
Includes an inductor L ₁ is energized with the on-off, the inductor L ₁ is provided with a detecting winding nd which is electromagnetically coupled to the main winding nm. The induced voltage of the detection winding nd is input to the protection circuit 4 to determine the presence or absence of the induced voltage, and it is determined that the inductor L ₁ is saturated while the induced voltage is not generated, and the control circuit 3 controlling the by, or to stop the on-off action switch element to Q ₁ limits the oN period or switching element Q _1.

This embodiment will be described using a specific circuit. As shown in FIG. 2, the main circuit 1 includes an inductor L ₁ comprises a main winding nm and a detecting winding nd, inductor L ₁
One end of a switch element Q ₁ such as a MOSFET is connected to the tap provided on the main winding nm of the. A series circuit of a part of the main winding nm of the inductor L ₁ and the switch element Q ₁ is connected between both ends of the DC power source E, and the remaining part of the main winding nm is connected in series with the diode D ₁ and the capacitor C _1. Connected,
This series circuit is connected across the switching element Q ₁ . The voltage across the capacitor C ₁ is applied to the load 5 as the output of the main circuit 1. That is, the main circuit 1 constitutes a step-up type chopper circuit.

Detection circuit 2 for detecting the output voltage of the main circuit 1.
Is two resistors R connected across the capacitor C _1.
1, consists series circuit of R _2, the output voltage of the main circuit 1, after being divided by the series circuit is input to the control circuit 3. The control circuit 3 includes a constant period and a sawtooth wave generating circuit 3a for generating a sawtooth wave of constant amplitude, and a voltage level of the detection voltage and the sawtooth wave by the detecting circuit 2 compares by the comparator CP _1. The comparator CP ₁ sets its output to H level while the sawtooth voltage level is higher than the detection voltage. Therefore, the comparator CP ₁
Output becomes a rectangular wave signal having a cycle equal to the cycle of the sawtooth wave, and the lower the detection voltage, the longer the ON period of the rectangular wave signal.

On the other hand, in the protection circuit 4, a resistor R ₇ is connected in parallel to the detection winding nd of the inductor L ₁ to detect the detection winding nd.
Based of the induced voltage of the transistor Q ₃ - is applied to the series circuit of the resistor R ₈ connected to the emitter and the emitter, the voltage across the resistor R ₈ transistor Q ₃ is turned on is forward biased is output by the induced voltage To be configured. That is, an induced voltage whose polarity is alternately inverted is generated in the detection winding nd depending on whether the switch element Q ₁ is turned on or off. However, the transistor Q _{3 has} one polarity (the polarity during the on period of the switch element Q ₁ ). The H level signal is output only during the period in which the induced voltage is generated, and the L level signal is output during the other periods. The signal output through the transistor Q ₃ is inverted in the logic circuit 4a, and then the logical product with the output of the comparator CP ₁ is obtained. Therefore, in the logic circuit 4a, the output of the comparator CP ₁ is at the H level and no induced voltage is generated in the detection winding nd, or the polarity of the induced voltage is inverted from the period when the switch element Q ₁ is on. Then, the output is set to H level to activate the timer circuit 4b.

When the timer circuit 4b is activated, the transistor Q ₂ provided in the reference voltage generator 4c is turned off for a certain period of time during the timed operation of the timer circuit 4b. Reference voltage generator 4
c is three resistors R ₄ connected across the power supply,
A series circuit of R ₅ and R ₆ is provided, and the collector and emitter of the transistor Q ₂ are connected in parallel to the resistor R ₆ .
While the transistor Q ₂ is on, the resistor R ₆ is short-circuited and the reference voltage drops.

The reference voltage output from the reference voltage generator 4c is input to the comparator CP ₂ together with the sawtooth wave output from the sawtooth wave generation circuit 3a, and the voltage level of the sawtooth wave is compared with the reference voltage. In the comparator CP ₂ , the output is set to H level while the voltage level of the sawtooth wave is higher than the reference voltage. Therefore, the output of the comparator CP ₂ becomes a rectangular wave signal having a cycle equal to the cycle of the sawtooth wave and having a constant duty cycle according to the reference voltage set by the reference voltage generator 4c. The output of the comparator CP ₂ is inputted to the AND circuit 3b together with the output of the comparator CP ₁ as the output of the protection circuit 4, switching element Q ₁ is controlled by the logical product of the outputs of the comparators CP _1, CP _2.

That is, both comparators CP ₁ and CP ₂
Switch element Q ₁ while both outputs are at H level
Turns on. Since the duty cycle of the output of the comparator CP ₂ is constant,
The output of ₂ determines the maximum value of the duty cycle of the rectangular wave signal which controls the switching element Q ₁ . Further, since both comparators CP ₁ and CP ₂ generate a rectangular wave signal by comparing the sawtooth wave and the reference voltage, the falling timings of the rectangular wave signals output from both comparators CP ₁ and CP ₂ are almost equal, The rising timing is limited by the rectangular wave signal output from the comparator CP ₂ . On the other hand, when the timer circuit 3c is activated and the transistor Q ₂ is turned off, the switching element Q ₁ is compared with the period when the transistor Q ₂ is on.
The maximum value of the duty cycle of the rectangular wave signal that controls the signal is reduced.

The operation of the above configuration will be described with reference to FIG. A sawtooth wave as shown in FIG. 3A is output from the sawtooth wave generation circuit 3a, and the sawtooth wave is generated by the comparator CP.
_In FIG. ₁ , it is compared with the detection voltage in the detection circuit 2 shown by the broken line in FIG. At this time, since the timer circuit 4b is not activated as shown in FIG. 3 (g), the transistor Q ₂ is on, and the reference voltage generating unit is turned on as indicated by the chain double-dashed line in FIG. 3 (a). In 4c, the reference voltage is set low. That is, the maximum value of the duty cycle of the rectangular wave signal that controls the switch element Q ₁ is set to a large value. AND circuit 3b turns on and off the switching element Q ₁ outputs a logical product of the outputs of the comparator CP _1, CP ₂ as in FIG. 3 (b), the main winding nm of inductor L _1, FIG. 3 A current I ₁ as shown in (c) flows. If the current I ₁ flowing through the main winding nm changes linearly in this way, the detection winding nd becomes a rectangular wave as shown in FIG. Therefore, the voltage across the resistor R ₈ connected to the emitter of the transistor Q ₃ changes as shown in FIG.

If the inductor L ₁ is saturated under the condition that the ambient temperature becomes high, the voltage is not induced in the detection winding nd as shown in FIG. Even though Q ₁ is on, the voltage across the resistor R ₈ connected to the emitter of the transistor Q ₃ becomes L level. Therefore, the output of the logic circuit 4a becomes H level for a short time as shown in FIG.
As shown in (g), the timer circuit 4b is activated, and the transistor Q ₂ is turned off during the timed operation of the timer circuit 4b for a fixed time. As a result, the reference voltage rises as shown by the alternate long and short dash line in FIG. 3A, and the maximum value of the duty cycle of the switching element Q ₁ is limited during this period. In this way, when the inductor L ₁ is saturated, the ON period of the switching element Q ₁ is limited to prevent the saturated state of the inductor L ₁ from continuing, and as a result, the main circuit 1 (particularly the switching element Q ₁ ) It is possible to prevent damage due to overload.

(Embodiment 2) This embodiment shows an example in which the main circuit 1 is a flyback type inverter circuit as shown in FIG. That is, in the main circuit 1 of this embodiment, the inductor L ₁ has the primary winding n ₁ , the secondary winding n _2, and the detection winding nd, and the primary winding n ₁ and the switching element Q ₁ Is connected between both ends of the DC power supply E, and the secondary winding n ₂
It has a configuration in which a series circuit of a diode D ₁ and a capacitor C ₁ is connected between both ends of. Detection circuit 2 for detecting the output voltage of the main circuit 1, which is the voltage across the capacitor C _1.
Is a series circuit of three resistors R ₁₁ , R ₁₂ , and R ₂ ,
The voltage at the connection point between the resistors R ₁₂ and R ₂ is input to the control circuit 3. This in the main circuit 1, is induced voltage in the secondary winding n ₂ to the time of the on-time and off switching elements Q _1, the output voltage corresponding to the ratio between the on period and the off period switching element Q ₁ is output It is supposed to be done. The other configuration is the first embodiment.
The description is omitted because it is similar to the above.

(Embodiment 3) In this embodiment, as shown in FIG. 5, a booster type chopper circuit similar to that of Embodiment 1 is used for the main circuit 1. Further, as in the second embodiment, the detection circuit 2 uses a series circuit of three resistors R ₁₁ , R ₁₂ , and R ₂ . The control circuit 3 uses the comparator CP ₁ as in the first embodiment.
The sawtooth wave generation circuit 3a is provided, and the output of the control circuit 3 and the output of the protection circuit 4 are connected to the AND circuit 3b.
It is also similar to the first embodiment in that the switch element Q ₁ is controlled by a rectangular wave signal which is a logical product of both.

The difference of this embodiment lies in the structure of the protection circuit 4, in which the output of the logic circuit 4a is input to the D flip-flop FF instead of the comparator CP ₂ , the reference voltage generator 4b and the timer circuit 4c. By setting the inverted output of the flip-flop FF as the output of the protection circuit 4, the inductor L
_The difference is that the on / off operation of the switch element Q ₁ is stopped when ₁ is saturated. Since the power supply voltage is input to the data terminal of the D flip-flop FF, the inverted output which is the output to the AND circuit 3b is set to the L level at the rising edge of the input.
The switch element Q ₁ is continuously turned off.

That is, the sawtooth wave generation circuit 3a outputs a sawtooth wave as shown in FIG.
It is assumed that the detection circuit 2 outputs a detection voltage as shown by a broken line in FIG. At this time, the rectangular wave signal as shown in FIG. 6B is output from the comparator CP ₁ . On the other hand, in the protection circuit 4, the voltage across the resistor R ₈ connected to the emitter of the transistor Q ₃ in response to the induced voltage of the detection winding nd of the inductor L ₁ is as shown in FIG. Therefore, the output of the logic circuit 4a is as shown in FIG.
As shown in FIG. 6, the output of the comparator CP ₁ is at the H level and the voltage across the resistor R ₈ is at the L level, and the inverted output of the D flip-flop FF is shown in FIG. It goes to L level as in (f). That is, the output of the comparator CP ₁ is H
During the period in which the switch element Q ₁ is turned on and the switch element Q ₁ is turned on, the inductor L ₁ is saturated and the detection winding n
When the induced voltage is not generated in d, the transistor Q ₃ is turned off and, as a result, the inverted output of the D flip-flop FF becomes L level. After this time,
As shown in (g), the output of the AND circuit 3b continuously becomes the L level, and the switch element Q ₁ is kept in the off state. Other configurations are similar to those of the first embodiment.

[0026]

As described above, according to the present invention, the detection winding is provided in the inductor of the main circuit, and when the voltage is not induced in the detection winding, it is determined that the inductor is saturated, and the switch element is turned on from the control circuit. When it is determined that the inductor is saturated during the period when the signal to be generated is controlled, the ON period of the switch element is controlled to be decreased, so that the temperature that is used as a power source for a headlight, etc. Even in applications where the conditions are severe, when the inductor saturates, the energy stored in the inductor can be reduced by controlling the ON period of the switching element to decrease, and as a result, inductor saturation This has an advantage that it is possible to prevent overheating and damage to the switch element and the like. Also, because the protection circuit prevents inductor saturation, it does not cause circuit abnormalities even in environments where the temperature exceeds the design specifications.Therefore, it is not necessary to design in consideration of the high temperature environment, and the inductor can be used at room temperature. There is an effect that it can be used as small as that of the above. Moreover, since a resistor is not used in the electric path through which the main current flows as a means for detecting the saturation of the inductor,
The effect is high efficiency without loss due to resistance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment.

FIG. 2 is a circuit diagram showing a first embodiment.

FIG. 3 is an operation explanatory diagram of the first embodiment.

FIG. 4 is a circuit diagram showing a second embodiment.

FIG. 5 is a circuit diagram showing a third embodiment.

FIG. 6 is an operation explanatory diagram of the third embodiment.

FIG. 7 is a circuit diagram showing a conventional example.

FIG. 8 is an operation explanatory diagram of a conventional example.

FIG. 9 is a diagram showing a waveform of a current flowing through an inductor.

FIG. 10 is a diagram showing a relationship between an ambient temperature and a saturation magnetic flux density of an inductor.

[Explanation of symbols]

1 main circuit 2 detection circuit 3 control circuit 4 protection circuit 5 load E DC power supply L ₁ inductor nd detection winding Q ₁ switch element

Claims (1)

[Claims] 1. A main circuit having a switching element that alternately turns on and off and an inductor having a winding that is energized when the switching element is turned on and off, and an output voltage detected by detecting the output voltage of the main circuit. The control circuit controls the ON period of the switching element in the direction of decreasing the change of the switching element and the direction in which the ON period of the switching element is decreased when the saturation of the inductor is detected during the period when the signal that turns on the switching element is generated from the control circuit. And a protection circuit for controlling, the inductor includes a detection winding electromagnetically coupled to the winding, and the protection circuit determines that the inductor is saturated unless a voltage is induced in the detection winding. Power supply.