JPH06348350A - Power unit - Google Patents

Abstract

PURPOSE:To protect a DC power supply against its adverse connection, to prevent the deterioration in performance of a main circuit and a protecting circuit, and also to suppress the voltage drop and the power consumption of the protecting circuit. CONSTITUTION:A protecting circuit 3 is provided with a switch element Q1 which is inserted between a DC power supply E and a main circuit 1 so that a parasitic diode D1 which consists of an enhancement type MOSFET and set between the drain and the source is set in the forward direction. When the power supply E has the adverse polarity, the element Q1 is turned off by the output of a comparator CP1 based on the both-terminal potential of the element Q1. Under such conditions, the diode D1 of the element Q1 is set in reverse to the power supply E which is reversely connected. Therefore the currents passing through the element Q1 and the circuit 1 can be surely prevented.

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 mainly for converting a relatively low-voltage DC power supply such as a vehicle battery into AC power and supplying the AC power to a load.

[0002]

2. Description of the Related Art Generally, a power supply device using a direct current power supply such as an on-vehicle battery as an input is equipped with a protection circuit for preventing a failure of the power supply device when the polarity of the direct current power supply is reversely connected by mistake. . As a protection circuit of this type, as shown in FIG. 18, a diode D ₀ inserted in the forward direction between a DC power supply E and a main circuit 1 which converts the DC power supply E into AC power and supplies the AC power to a load 2 is used. The configuration used is considered. The main circuit 1 includes a front power supply circuit 1a for connecting and disconnecting the DC power supply E to step up and down by a transformer or the like, and a front power supply circuit 1a.
And an inverter circuit 1b for converting the output of the above into an alternating electric power.

However, in this type of power supply device, the input current to the main circuit 1 may become a large current of 10 A or more, and when such a large current flows, a voltage drop and power consumption in the diode D ₀ occur. It becomes a problem. That is, even with relatively small Schottky diode voltage drop as the diode D _0, the voltage drop of the diode D ₀ is a 0.6～1.0V, when a large current flows as described above However, since the power consumption of the diode D ₀ is as large as several W to tens of W, there is a problem that the efficiency of the power supply device as a whole is lowered.
Further, when the DC power source E has a relatively low voltage, the ratio of the voltage drop in the diode D ₀ to the voltage of the DC power source E becomes large, and the input voltage of the main circuit 1 (the capacitor C
_{Since the} rate of decrease of the voltage (both ends of ₁ ) becomes large, the efficiency is significantly reduced as compared with the case where the diode D ₀ is not used.

In order to solve such a problem, FIG.
As shown in FIG. 5, the collector-emitter of the low breakdown voltage bipolar transistor Tr is inserted between the DC power source E and the main circuit 1 in place of the diode D ₀ , and the connection polarity of the DC power source E is reversed by the reverse connection detection circuit. A configuration is conceivable in which the bipolar transistor Tr is turned off when the polarity is detected. However, since the bipolar transistor Tr is driven by current, it is necessary to increase the base current when the input current is large, and eventually the power consumption in the bipolar transistor Tr increases and the efficiency of the power supply device as a whole decreases. The problem arises. In addition, since the base current is large, it is necessary to increase the output current of the reverse connection detection circuit that drives the bipolar transistor Tr by applying the base current to the bipolar transistor Tr, which also causes a problem in efficiency reduction.

In order to solve the above-mentioned drawbacks of the diode D ₀ and the bipolar transistor Tr, as shown in FIG. 22, a switch element Q composed of an enhancement type MOSFET which is voltage driven is used in place of the bipolar transistor Tr. It is conceivable that there is a problem
No. 235531). The switch element Q is an n-channel, has a drain connected to the positive electrode of the DC power source E and a source connected to the main circuit 1.

In this configuration, since the ON resistance of the switch element Q is small, the voltage drop is smaller than that of the Schottky diode even when a large current flows (the ON resistance is 20 mΩ, for 10 A). The voltage drop is 0.2 V), and since it is driven by voltage, the power consumption of the drive circuit is small.

[0007]

However, as shown in FIG.
A parasitic diode D exists between the drain and the source of the switch element Q used in the circuit shown in FIG. 1, and the parasitic diode D has a polarity opposite to that of the DC power source E.
Therefore, when the polarity of the DC power supply E is reversed by mistake, the positive electrode of the DC voltage V-the main circuit 1-the parasitic diode D
-Current flows through the path of the negative pole of the DC power supply E, and the main circuit 1
There is a problem that the performance of the capacitor C ₁ having a polarity such as an electrolytic capacitor provided between the input ends of the main circuit 1 in order to suppress the fluctuation of the input voltage to the main circuit ₁ and the switch element Q may be deteriorated. There is.

An object of the present invention is to solve the above-mentioned problems, to prevent deterioration of the performance of the main circuit and the protection circuit against the reverse connection of the DC power supply, and to suppress the voltage drop and power consumption in the protection circuit. The present invention is intended to provide a power supply device that does.

[0009]

In order to achieve the above object, a main circuit for converting a direct current power supply into alternating current power to supply power to a load, and a voltage application to the main circuit of the direct current power supply. In a power supply device including a protection circuit that detects the polarity and stops the power supply to the main circuit when the polarity is reverse, the protection circuit includes an enhancement type MOSFET and a parasitic diode existing between the drain and the source is in the forward direction. A switch element for polarity inserted between the DC power supply and the main circuit so that the polarity of the switch element for polarity is controlled to be off when the voltage application polarity of the DC power supply is reverse polarity. Is characterized by.

According to a second aspect of the present invention, in the first aspect of the present invention, a capacitor for suppressing fluctuation of the input voltage is connected between the connection ends of the main circuit and the DC power source, and the polarity detection circuit includes the DC power source and the capacitor. It is characterized in that the connection polarity of the DC power supply is determined by detecting the direction of the current between the one end and the other end. According to a third aspect of the present invention, in the first aspect of the present invention, a direct current power source is provided between the drain and the source so that the parasitic diode which is formed of the enhancement type MOSFET and exists between the drain and the source is in the opposite direction to the polarity switch element. A voltage switch element connected in series to the polarity switch element between the main circuit and the voltage detection circuit, and a voltage detection circuit that detects the voltage of the DC power supply and controls the voltage switch element to turn off when the voltage is out of the specified range. Is added.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the polarity detection circuit determines the connection polarity of the DC power source by comparing the potentials at both ends of the series circuit of the polarity switching element and the voltage switching element. It is characterized by determining.

[0012]

According to the first aspect of the present invention, as the protection circuit, for the polarity inserted between the DC power source and the main circuit so that the parasitic diode which is composed of the enhancement type MOSFET and exists between the drain and the source is in the forward direction. Since a switch element and a polarity detection circuit that controls the switch element for polarity to be turned off when the voltage application polarity of the DC power source is opposite polarity, the parasitic diode is connected in the opposite direction to the reverse connection of the DC power source. As a result, the performance of the main circuit and the protection circuit can be prevented from deteriorating, and the voltage drop and power consumption in the protection circuit can be suppressed.

The structures of claims 2 to 4 are defined by claim 1.
Is a preferred embodiment of According to the above configuration,

[0014]

【Example】

(Embodiment 1) As shown in FIG. 1, in the main circuit 1, a DC power source E is intermittently connected by a switching element, and the stored energy in an inductor is utilized or a DC voltage boosted higher than the voltage of the DC power source E is used by a transformer. It is configured by a front power supply circuit 1a that outputs a voltage and an inverter circuit 1b that converts the DC voltage output from the front power supply circuit 1a into AC power and supplies the AC power to the load 2. The inverter circuit 1b is configured to output low frequency AC power.

A capacitor C ₁ such as an electrolytic capacitor for suppressing fluctuations in the input voltage to the main circuit 1 is connected between the connection ends of the DC power source E to the main circuit 1. That is, in the main circuit 1, since the input power source is intermittently connected by using the switching element, the capacitor C ₁ is used to reduce the impedance on the power source side and suppress the fluctuation of the input voltage. Also, the negative electrode of the DC power source E and the capacitor C ₁
Is an n-channel enhancement type MOSFET, and the drain and source of the switch element Q ₁ are inserted between the negative electrode and one end thereof. The switch element Q ₁ has a source connected to the negative electrode of the capacitor C ₁ and a drain connected to the negative electrode of the DC power source E. Also, the switching element Q ₁
The drain potential and the source potential of the comparator are compared by the comparator CP ₁ as a reverse connection detection circuit, and the comparator CP ₁ is at the H level and the switch element Q ₁ is turned on while the source potential is higher than the drain potential. Connected. In this way, the switch element Q ₁ and the comparator CP ₁ constitute the protection circuit 3.

In the above structure, when the DC power source E is normally connected, the drain potential of the switch element Q ₁ becomes lower than the source potential, so that the output of the comparator CP ₁ becomes H level and the switch element Q ₁ becomes Turn on. That is, power is supplied to the main circuit 1. At this time, the voltage drop is small at the switching element Q _1, power consumption in the switching element Q ₁ be large current passes to the switching element Q ₁ is reduced. The switch element Q ₁ is a comparator CP.
_{Since the} voltage is driven by ₁ , the comparator CP
₁ requires almost no output current, comparator CP
The power consumption in ₁ is also small. As a result, the power consumption of the protection circuit 3 including the switch element Q ₁ and the comparator CP ₁ can be reduced, and the efficiency as a whole is hardly reduced despite the provision of the protection circuit 3.

On the other hand, when the DC power source E is connected to the opposite polarity to that shown in FIG. 1, the drain potential becomes higher than the source potential between the drain and the source of the switch element Q ₁ , so that the output of the comparator CP ₁ is L. Switch element Q
₁ is turned off, and the main circuit 1 is protected because the DC power supply E is not supplied to the main circuit 1. Further, the parasitic diode D ₁ of the internal switching element Q ₁ is,
Since the negative electrode side of the capacitor C ₁ is the anode,
No current flows to the switch element Q _1, and since there is no a reverse polarity voltage is also applied to the capacitor C _1, the deterioration of the characteristics of the switching element Q ₁ and the capacitor C ₁ does not occur Of.

(Embodiment 2) In this embodiment, as shown in FIG. 2, a resistor R ₁ is inserted between the drain of the switch element Q ₁ and the negative electrode of the DC power source E, and the comparator CP ₁ is connected to the resistor R _1.
The configuration is different from that of the first embodiment in that the potentials at both ends of ₁ are connected so as to be compared, and other configurations are the same as those of the first embodiment. As such a resistor R ₁ , a part of the conductive pattern of the circuit board made of a printed board may be used. Here, in the comparator CP ₁ , the output is set to the H level and the switch element Q ₁ is turned on only when the drain potential of the switch element Q ₁ is higher than the negative potential of the DC power source E.

Therefore, when the DC power source E is normally connected as shown in FIG. 2, the comparator CP ₁
Output goes high, the switch element Q ₁ is turned on, and power is supplied to the main circuit 1. The voltage drop at this time becomes larger by the amount of the resistor R _{1 than in} the first embodiment, but since the resistor R ₁ can be made sufficiently small, there is almost no problem. In addition, DC power supply E
Is connected to the opposite polarity, the output of the comparator CP ₁ becomes L level, the switch element Q ₁ is turned off, and the power supply to the main circuit 1 is stopped. At this time, since the anode of the parasitic diode D ₁ is connected to the negative electrode of the capacitor C ₁ , current does not flow from the DC power source E to the switch element Q ₁ and the main circuit 1, and as a result, It is possible to prevent the deterioration of the characteristics of the circuit 1 and the capacitor C ₁ . Other configurations are similar to those of the first embodiment.

(Embodiment 3) In this embodiment, a power supply device using a protection circuit 3 having a function of protecting the DC power source E from excessive voltage and the like and a protection function of reverse connection is shown. The protection function against the excessive voltage of the DC power supply E is required in the following cases. For example, a car battery has 12
There are V system, 24V system, etc.
If it is erroneously connected to the DC power source for V, it will lead to failure if there is no protection function, but such a problem can be avoided by using the configuration of this embodiment.

That is, as shown in FIG. 3, basically, in addition to the configuration of the first embodiment, the resistors R ₂ and R _{3 for} dividing the voltage of the DC power source E and the resistors R ₂ and R ₃ are connected. resistor R ₂ compares the potential of the point between the reference voltage V _ref, R ₃ of the output to a lower period than the potential reference voltage V _ref at the connection point between the comparator CP ₂ to H level, the switch element Q ₁ and the DC power supply And a switch element Q ₂ which is inserted between the negative electrode of E and is turned on while the output of the comparator CP ₂ is at the H level. The switch element Q ₂ is an n-channel enhancement type MOSFET, and is a switch element Q ₁
And the drains are commonly connected, and the source is connected to the negative electrode of the DC power supply E. The comparator CP ₁ for controlling the switching element Q ₁ is, compares the source potential and the source potential of the switching element Q ₂ of the switch element Q _1, the source potential of the switching element Q ₁ is than the source potential of the switching element Q ₂ Switch element Q
Turn on ₁ .

If the polarity and voltage of the DC power source E are both normal and the potential at the connection point of the resistors R ₂ and R ₃ is lower than the reference voltage V _{ref, the} output of the comparator CP ₂ becomes H level and the switch The element Q ₂ is turned on. At this time since the source potential of the switching element Q ₁ is higher than the source potential of the switching element Q _2, the output of the comparator CP ₁ the switch element Q ₁ becomes the H level is turned on. Eventually, both switching elements Q ₁ and Q ₂ are turned on and power is supplied to the main circuit 1.

On the other hand, although the polarity of the DC power source E is normal, the voltage is high and the potential at the connection point of the resistors R ₂ and R ₃ is the reference voltage V.
_When it becomes higher than _ref, the output of the comparator CP ₂ becomes L
The switch element Q ₂ is turned off and turned off. At this time, the switch element Q ₁ is on, but the switch element Q 1
_{Since the second} parasitic diode D ₂ is connected in the reverse direction, no current flows and the power supply to the main circuit 1 is stopped.

Further, when the voltage of the DC power source E is normal but the polarity is opposite, the output of the comparator CP ₁ becomes L level, and the switch element Q ₁ is turned off. In this state, the switching element Q ₂ is on, but since the parasitic diode D ₁ of the switching element Q ₁ connects the cathode to the positive electrode of the DC power source E, the main circuit 1 is not supplied with power in the end. , The switch element Q ₁ and the main circuit 1 are protected. This operation is similar to that of the first embodiment.

When the polarities of the DC power source E are opposite polarities and the voltage is high, both the switching elements Q ₁ and Q ₂ are turned off. Therefore, the main circuit 1 and the switching elements Q ₁ and Q are naturally turned off. ₂ is protected. As described above, since the protection circuit 3 reversely connects the DC power supply E and also protects against overvoltage, the withstand voltage of the capacitor C ₁ should be set so as to correspond to the reference voltage V _ref set in the protection circuit 3. That is, it is not necessary to set the breakdown voltage higher than necessary, and the power supply device can be downsized.

(Embodiment 4) In Embodiment 3, protection against excessive voltage is performed, but in this embodiment, as shown in FIG. 4, protection is performed for both overvoltage and undervoltage. That is, basically, in place of the comparator CP ₂ of the third embodiment, the switch element Q is used by using the window comparator CP ₂₀ which sets the output to the L level when the voltage of the DC power source E is excessively high or low. ₂₁ , Q
_It controls ₂₂ . Here, instead of the switch element Q ₁ shown in the third embodiment, switch elements Q ₁₁ and Q ₁₂ made of MOSFETs are connected in parallel, and instead of the switch element Q ₂ , a switch element Q _{21 made of} a MOSFET is used. , Q ₂₂ are connected in parallel. Further, a resistor R ₁ is inserted between the negative electrode of the capacitor C ₁ and the sources of the switch elements Q ₁₁ and Q ₁₂ , and the comparator CP ₁ compares the potentials across the resistor R ₁ as in the second embodiment. The direction of the current is detected by the.

The window comparator CP ₂₀ is composed of three comparators CP ₂₁ , CP ₂₂ and CP ₂₃ , of which two comparators CP ₂₁ and CP ₂₂ are resistors R ₂ and R _3.
The potential at the connection point is compared with reference voltages V ₁ and V ₂ (V ₁ <V ₂ ). In one comparator CP ₂₁ , the resistance R ₂ ,
While the potential at the connection point of R ₃ is lower than the reference voltage V ₁ , the output is set to H level, and in the other comparator CP ₂₂ , the potential at the connection point of the resistors R ₂ and R ₃ is higher than the reference voltage V _2. The output is set to H level. In addition, the comparator CP
Reference numeral ₂₃ compares the outputs of both comparators CP ₂₁ and CP ₂₂ with the reference voltage V _3, and sets the outputs to the H level only while both outputs of the comparators CP ₂₁ and CP ₂₂ are at the L level. That is, the comparator CP ₂₃ produces an output corresponding to the negation of the logical product of the two comparators CP _21, CP _22. Therefore, the voltage of the DC power source E becomes excessive or excessively small, and the potential at the connection point of the resistors R ₂ and R ₃ becomes the reference voltage V.
_When it is lower than ₁ or higher than the reference voltage V ₃ , the output of one of the comparators CP ₂₁ and CP ₂₂ becomes H level,
The input to the comparator CP ₂₃ becomes higher than the reference voltage V _{3 and} the output of the comparator CP ₂₃ becomes L level. Therefore, the switch elements Q ₂₁ and Q ₂₂ are turned off, and the power supply to the main circuit 1 is stopped.

In the front power supply circuit 1a according to the present embodiment, the drain and source of the switching element S ₁ composed of a MOSFET are connected in series to the primary winding of the transformer T, and the secondary winding of the transformer T has a diode. the D ₃ are connected in series, and has a configuration connected in parallel with capacitor C ₂ to the series circuit. The switching element S ₁ is switched at a relatively high speed so that the current flowing through the primary winding of the transformer T is interrupted at a high frequency. Further, the diode D ₃ is connected to the polarity that releases the energy stored in the transformer T to the capacitor C ₂ and the subsequent stage during the off period of the switching element S ₁ .

A capacitor C is provided downstream of the front power supply circuit 1a.
_The inverter circuit 1b in which ₂ is connected between the input terminals is connected. The inverter circuit 1b switching element S ₂ to S ₅
Be of four bridge type using a switching element S ₂ to S ₅ connected two by two in series, are connected in parallel the series circuits to the capacitor C _2. In addition, a load 3 is provided between the connection points of the switching elements S _{2 to} S ₅ connected in series.
A series circuit of an inductor L ₁ and an inductor L ₁ is inserted, and a capacitor C ₃ that bypasses a high frequency current is connected in parallel to the load 3. Each switching element S ₂ to S ₅ is across the load 3 has become the positive side and the negative side is a pair of input power is controlled to on and off alternately in each pair. That is, by alternately generating a period in which the switching element S ₂ and the switching element S ₅ are turned on and a period in which the switching element S ₃ and the switching element S ₄ are turned on, the current passing through the load 3 is reduced. Alternating directions are applied to supply AC power to the load 3. Switching frequency of the switching element S ₂ to S ₅ is set sufficiently lower than the switching frequency of the switching element S _1, the capacitor C ₃ has low impedance in the frequency region of the switching frequency of the switching element S _1, the switching element The impedance is set to be high in the frequency range of the switching frequencies S _{2 to} S ₅ . Other configurations are similar to those of the first embodiment.

In each of the above embodiments, the switching element Q ₁ (Q
Comparing ₁₁ , Q ₁₂ ) and Q ₂ (Q ₂₁ , Q ₂₂ ) with comparator C
Although it is directly driven by the outputs of P ₁ and CP ₂ (CP ₂₃ ), the comparators CP ₁ and CP ₂ (C ₂ are connected via a drive circuit in which two transistors are connected in a totem pole form.
The output of P ₂₃ ) is switched to the switching elements Q ₁ (Q ₁₁ , Q ₁₂ ), Q ₂
It may be given to (Q ₂₁ , Q ₂₂ ).

(Embodiment 5) In this embodiment, a structure as shown in FIG. 5 is provided so as to protect against reverse connection. That is, a series circuit of _two resistors R ₂ and R ₃ is connected across the DC power source E, and the comparator CP ₁ compares the potentials across the resistor R ₃ connected to the negative side of the DC power source E. The output is set to the H level while the potential at the connection point between the resistors R ₂ and R ₃ is higher than the potential at the connection point between the resistor R ₃ and the negative electrode of the DC power source E. This comparator CP ₁
Is output to the gate of the switch element Q ₁ via the drive circuit 4. The switch element Q ₁ has a source connected to the negative electrode of the capacitor C ₁ provided in the main circuit 1 and a drain connected to the negative electrode of the DC power source E.

According to the above construction, when the polarity of the DC power source E is normal, the potential at the connection point between the resistors R ₂ and R ₃ is higher than the potential at the connection point between the resistor R ₃ and the negative electrode of the DC power source E. At this time, the output of the comparator CP ₁ becomes H level, and the switch element Q ₁ is turned on.
On the other hand, when the polarities of the DC power source E are opposite, the positive electrode of the DC power source E is connected to one end of the resistor R ₃ , and the potential at this portion is higher than the potential at the connection point of the resistors R ₂ and R _3. Also, the output of the comparator CP ₁ becomes L level, and as a result, the switch element Q ₁ is turned off. At this time, the parasitic diode D ₁ of the switch element Q _{1 has} a polarity opposite to that of the DC power source E, so that no current flows through the capacitor C ₁ and the switch element Q ₁ . Other configurations are similar to those of the first embodiment.

(Embodiment 6) In this embodiment, as shown in FIG. 6, instead of using the comparator CP ₁ and the drive circuit 4 in the embodiment 5, the connection point of the resistors R ₂ and R ₃ is switched to the switch element Q _1. It is directly connected to the gate of. In this configuration, when the DC power source E is connected in reverse polarity, since the gate potential of the switching element Q ₁ is lower than the source potential, the switch element Q ₁ is than turned off. Other configurations and operations are similar to those of the fifth embodiment.

(Embodiment 7) In this embodiment, as shown in FIG. 7, a Zener diode ZD ₁ is connected in parallel to a resistor R ₃ in the structure of Embodiment 6. With this configuration, the same operation as that of the sixth embodiment is performed except that the switch element Q ₁ is turned on when the DC power source E having a voltage equal to or higher than the voltage specified by the Zener diode ZD ₁ is connected with the normal polarity.

(Embodiment 8) This embodiment shows an example in which the power supply to the load 3 can be maintained in the main circuit 1 even if the input voltage drops for a short time. First, a comparative example will be described. Here, the DC power supply E is connected to the main circuit 1 via the power switch SW ₁ . Further, it is assumed that a discharge lamp is used as the load 3 and the main circuit 1 is composed of a discharge lamp lighting circuit 1c and a peripheral circuit that controls the discharge lamp lighting circuit 1c. As shown in FIG. 10, it is assumed that the diode D ₅ protects the DC power source E from being connected in reverse polarity. Further, the main circuit 1 is a discharge lamp lighting circuit, and a discharge lamp is used for the load 3. In order to activate the main circuit 1, a comparator CP ₅ is provided which raises the output to H level and generates an activation signal when the cathode potential of the diode D ₁ is higher than the reference voltage V ₅ . By providing such a comparator CP ₅ , the DC power source E
The operation of the main circuit 1 is prevented from becoming unstable when the voltage is low.

The configuration of FIG. 10 operates as shown in FIG. That is, a period a shown in FIG. 11 is a normal lighting / extinguishing state, and a period c shows a state when the load 3 fails to start. In the normal lighting state during the period a, the output of the comparator CP ₅ is H through the diode D _5.
Since the level is reached, the main circuit 1 is activated and power is supplied to the load 3. When the load 2 is turned off, the capacitor C
The voltage e across ₁ no longer decreases.

When a high-pressure discharge lamp is connected as the load 2 to the main circuit 1 of FIG. 10 and used as a vehicle headlight, it needs to be restarted instantly. Therefore, it is turned on by a start signal generated from the comparator CP _5. The main circuit 1 is sometimes provided with a function of applying a high voltage pulse to the load 2. Further, since it is dangerous to continue to apply the high voltage pulse when the engine is not started at the end of life or the like, a function for stopping the high voltage pulse is provided. In other words, when the power supply voltage rises across a predetermined voltage, a high voltage pulse is generated to start, and when the power supply voltage falls below the predetermined voltage, it is turned off.

The period b in FIG. 11 is the state when the start-up fails and no current flows in the load 2 unless the load 2 is lit. Therefore, even if the power switch SW ₁ is turned off, the capacitor C ₁ is turned off. The terminal voltage e may not drop.
In this state, even if the power switch SW ₁ is turned on again, the terminal voltage of the capacitor C ₁ does not cross the reference voltage V ₅ , so that it is not possible to generate a high voltage pulse for starting, and there is no lighting. Will continue. That is,
In the unlit state, it is impossible to detect the on / off state of the power switch SW ₁ .

On the other hand, if the technique described in Japanese Patent Laid-Open No. 1-117660 is applied, a circuit configuration as shown in FIG. 12 is also possible. That is, n-channel MOSFE
The source of the switching element Q _{1 formed} of T is connected to the negative electrode of the capacitor C ₁ between the drain and the source of the capacitor C ₁
Of the switching element Q ₁ is connected to the positive electrode of the capacitor C ₁ via the resistor R ₂ . In addition, the comparator C
The drain potential and the source potential of the switch element Q ₁ are compared using P ₁ , and the switch element Q ₁ is turned on when the source potential is higher than the drain potential.
In this configuration, since the direction of the current flowing through the switch element Q ₁ is detected and the switch element Q ₁ is turned on / off, it is possible to protect the reverse connection of the DC power source E similarly to the diode D ₁ .

However, the above problem when the load 2 is not lit cannot be solved. Therefore, as shown in FIG. 13, a configuration is conceivable in which an input voltage to the comparator CP ₅ is obtained by using a diode D ₆ having an anode connected to the anode of the diode D ₅ . In this configuration, since it is possible to faithfully detect an input voltage in the comparator CP _5, it is possible to restart in response to the even power cycle switch SW ₁ at the time of non-lighting as described above.

However, in a vehicle headlight, there is a possibility that a voltage drop may occur for a short time due to a wrong connection or a state of a load connected to the same power source (battery). Even in such a case, it is desirable not to turn off the load 2 from the viewpoint of safety. That is, when the voltage drops for a short time, the lighting state is maintained by discharging the charge of the capacitor C ₁ . Therefore, in addition to the configuration shown in FIG. 13, the configuration of FIG. 14 in which the capacitor C ₄ is connected to the positive input terminal of the comparator CP ₅ can be considered. In this configuration, the lighting state is maintained by delaying the detection of the voltage drop by the comparator CP ₅ .

However, with such a configuration, design becomes very difficult. That is, if the capacitance of the capacitor C ₄ is too large, the electric charge of the capacitor C ₁ is discharged and the load 2 disappears. If the capacitance of the capacitor C ₄ is too small, the voltage drop for a short time will occur. Load 2
Will turn off. This embodiment shows a configuration in view of the problems of the various configurations as described above. As shown in FIG. 8, a capacitor C ₁ provided at the input part of the main circuit 1 is connected to a direct current through a diode D ₅ and a direct current. A switch SW ₂ is connected in parallel to the diode D ₁ and connected to the power source E. The switch SW ₂ is turned on / off based on the lamp current of the load 3 detected by the current transformer CT. That is, the output of the current transformer CT is amplified by the amplifier A ₁ and converted into a voltage, and this voltage is compared with the reference voltage V ₄ by the comparator CP ₄ . In the comparator CP ₄ , when the load (discharge lamp) 3 is on and the output voltage of the amplifier A ₁ is higher than the reference voltage V ₄ , the output is set to H level and the switch SW ₂ is turned on. Further, when the load (discharge lamp) 3 is not lit and the lamp current does not flow and the output voltage of the amplifier A ₁ is lower than the reference voltage V ₄ , the switch SW ₂ is turned off.

The anode of the diode D ₅ is connected in common with the anode of another diode D ₆ , and this diode D 5
The cathode of ₆ is input to the comparator CP ₅ . In the comparator CP ₅ , if the voltage of the DC power source E detected via the diode D ₆ is higher than the reference voltage V ₅ , the output is H level.
A start signal is generated as a level to start the discharge lamp lighting circuit 1c.

Next, the operation of the above configuration will be described with reference to FIG. In FIG. 9, a period a shows a state in which the load 3 is normally turned on, a period b shows a state in which power is not supplied from the DC power source E due to a disconnection or the like, and a period c fails in starting the load 3. It shows the state. Here, the voltage v of the DC power supply E shown in FIG. 9A changes in the same manner as the waveform of the cathode potential of the diode D ₆ shown in FIG. It is written so as to clearly show the state where the supply of No. is stopped.

If the normal state of the period a is changed to the state of the period b due to disconnection or the like, the input voltage υ to the main circuit 1 decreases as shown in FIG. 9 (a), but FIG. 9 (b).
As shown in FIG. 9D, the switch SW ₂ is kept on because the load 3 is lighting. Therefore, the cathode potential of the diode D ₆ gradually decreases as shown in FIG. 9C due to the discharge of the capacitor C _{1, and} the restart is not performed while the cathode potential is higher than the reference voltage V ₅ , so that the short-term is not performed. The lighting state of the load 3 is maintained due to disconnection or the like.

On the other hand, as shown by the period c in FIG. 9, the load 3
When the start of the load fails, as shown in FIG.
Is not lit, switch SW as shown in Fig. 9 (d)
₂ is in the off state, the cathode potential of the diode D ₆ is the input voltage v to the main circuit 1 (see FIG. 9C).
Since the same change as in (a) is made, the activation signal is generated in response to the on / off of the power switch SW ₁ , and the load 3 can be reliably turned on.

As described above, the lighting state of the load 3 can be maintained as long as the terminal voltage of the capacitor C ₁ is maintained even if the power supply is interrupted for a short time, and the power supply is stopped when starting fails. Even if the switch SW ₁ is turned on / off in a short time, it can be surely started. (Embodiment 9) In this embodiment, as shown in FIG. 15, a switching element Q ₅ comprising an enhancement type MOSFET in which the diode D ₅ in the embodiment 8 is an n channel is used.
Is replaced with. The switch element Q ₅ is a resistor R ₅
The gate is connected to the positive electrode of the capacitor C ₁ via the, the source is connected to the negative electrode of the capacitor C ₁ , and the drain is connected to the negative electrode of the DC power source E. Further, the drain voltage and source voltage are compared by the comparator CP _7, the output of the comparator CP ₇ is input to the gate of the switching element Q ₅ through the switch SW _2. The comparator CP ₇ sets the output to the H level while the source potential of the switch element Q ₅ is higher than the drain potential. Further, the comparator CP ₆ has the negative electrode of the DC power source E (that is, the drain of the switch element Q ₅ ) without the diode D ₂ interposed.
And the reference voltage V ₆ is higher than the drain potential of the switch element Q ₅ , the comparator CP
The output of ₆ becomes H level and a start signal is output. When the load voltage of the comparator CP ₅ is not lit and the output voltage of the amplifier A ₁ becomes lower than the reference voltage V ₅ , the output of the comparator CP ₅ becomes H level and the switch SW ₂ is turned on.

If the voltage is no longer applied to both ends of the capacitor C _{1 due} to a disconnection or the like during the lighting period of the load 3, the switch SW ₂ is kept off at this time, and therefore the voltage across the capacitor C ₁ becomes a resistance. the gate of the R ₅ and the switching element Q ₅ - is applied between the source is maintained oN state of the switch element Q _5, the discharge lamp lighting circuit 1c by the output of the comparator CP ₇ is maintained in the operating state. This state continues until the discharge of the capacitor C ₁ progresses and the switch element Q ₅ cannot be maintained in the ON state. On the other hand, when the load 3 is not lit, the comparator CP
_Since the output of ₅ is at H level and the switch SW ₂ is on, if the load 3 fails to start and the power switch SW ₁ is turned on / off in a short time at the time of starting, the capacitor C ₁ is electrified. Regardless of the state of the power switch SW
Switch element Q ₅ is turned on / off according to the ON / OFF state of _1.
It can be turned off, and as a result, a reliable start can be performed. Further, when the DC power source E is connected to the opposite polarity, the output of the comparator CP ₇ becomes L level, so that the switch element Q ₁ is kept in the OFF state. At this time, the parasitic diode of the switch element Q ₅ is the DC power source E. The positive electrode side of is the cathode. Therefore, as in the first embodiment, the switch element Q ₅ and the capacitor C ₁ are protected against reverse connection. In addition, in the configuration of the present embodiment, since the switch element Q ₅ composed of the MOSFET is inserted in the power supply path of the discharge lamp lighting circuit 1c, the voltage is compared with the configuration of the embodiment 8 in which the diode D ₅ is inserted. There is less drop and less power loss. The other configuration is similar to that of the eighth embodiment, and therefore the description is omitted.

(Embodiment 10) In this embodiment, as shown in FIG. 16, in the configuration of Embodiment 8, instead of the switch SW ₂ , the input to the comparator CP _{6 is connected} to the capacitor C _1.
Switch SW ₃ for selecting one of the positive electrode of the diode D _{6 and} the cathode of the diode D ₆ , the positive electrode of the capacitor C ₁ is connected to the input of the comparator CP ₆ when the load 3 is lit, and the diode D is not lit when the load 3 is not lit. _The switch SW ₃ is controlled by the output of the comparator CP ₅ so that the cathode of ₆ is connected to the input of the comparator CP ₆ .

The operation is the same as that of the eighth embodiment, the period a shown in FIG. 17 is in a normal state, the period b ₁ is a state where a voltage drop occurs for a short time, and the period b ₂ is a short-time power supply due to disconnection or the like. The state where the interruption occurs, the period c shows the state where the starting fails.
In the period b ₁ and the period b ₂ , as shown in FIG. 17A, the voltage drops or the voltage is cut off from the lighting state.
As described above, the lighting state of the load 3 is maintained, and the output of the comparator CP ₅ causes the switch SW ₃ to connect the positive electrode of the capacitor C ₁ to the comparator CP _{6 as shown} in FIG. Therefore, the comparator CP ₆ has the configuration shown in FIG.
The voltage as shown in (c) is applied, the output of the comparator CP ₆ is at H level, the operation of the discharge lamp lighting circuit 1c is maintained, and the load 3 is continuously lit. This state continues until the discharge of the capacitor C ₁ progresses and the lighting state of the load 3 can no longer be maintained.

[0051] Moreover, when attempting to start the load 3, since the output of the comparator CP ₅ is the cathode of the diode D ₆ a L level is applied to the comparator CP _6, the state of charge of the capacitor C ₁ is The comparator CP ₆ outputs a start signal corresponding to the ON / OFF of the power switch SW ₁ regardless of the power switch SW ₁
The discharge lamp lighting circuit 1c can be surely started even if the lamp is turned on and off in a short time.

Here, instead of the diode D ₆ , Example 9 is used.
Similarly to the above, a switch element composed of a MOSFET may be used. By using such a switch element, power loss can be reduced.

[0053]

As described above, according to the present invention, as a protection circuit, an enhancement type MOSFET, which is a parasitic diode existing between the drain and the source, is inserted between the DC power source and the main circuit so as to be in the forward direction. Since a polarity switch element and a polarity detection circuit that controls the polarity switch element to be turned off when the voltage application polarity of the DC power supply is the opposite polarity, the parasitic diode reverses to the reverse connection of the DC power supply. Therefore, it is possible to prevent the deterioration of the performance of the main circuit and the protection circuit, and to suppress the voltage drop and the power consumption in the protection circuit. .

[Brief description of drawings]

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

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

FIG. 3 is a circuit diagram showing a third embodiment.

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

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

FIG. 6 is a circuit diagram showing a sixth embodiment.

FIG. 7 is a main part circuit diagram showing a seventh embodiment.

FIG. 8 is a circuit diagram showing an eighth embodiment.

FIG. 9 is an operation explanatory diagram of the eighth embodiment.

FIG. 10 is a circuit diagram showing a comparative example.

FIG. 11 is an operation explanatory diagram of a comparative example.

FIG. 12 is a circuit diagram showing another comparative example.

FIG. 13 is a circuit diagram showing still another comparative example.

FIG. 14 is a circuit diagram showing another comparative example.

FIG. 15 is a circuit diagram showing a ninth embodiment.

FIG. 16 is a circuit diagram showing a tenth embodiment.

FIG. 17 is an operation explanatory diagram of the tenth embodiment.

FIG. 18 is a circuit diagram showing a conventional example.

FIG. 19 is a circuit diagram showing another conventional example.

FIG. 20 is a circuit diagram showing still another conventional example.

[Explanation of symbols]

1 Main circuit 2 Load 3 Protection circuit C ₁ Capacitor CP ₁ Comparator D ₁ Parasitic diode E DC power supply Q ₁ Switch element

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Shinbori 1048, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Toshiro Nakamura, 1048, Kadoma, Kadoma City, Osaka Matsushita Electric Co., Ltd. (72) Inventor Takashi Kambara 1048, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (4)

[Claims] 1. A main circuit for converting a direct current power supply into alternating current power to supply power to a load, and a polarity of a voltage applied to the main circuit of the direct current power supply is detected, and when the polarity is opposite, power supply to the main circuit is stopped. In a power supply device including a protection circuit, the protection circuit is composed of an enhancement type MOSFET, and a polarity switch inserted between the DC power supply and the main circuit so that a parasitic diode existing between the drain and the source is in the forward direction. A power supply device comprising: an element; and a polarity detection circuit that controls a switch element for polarity to be off when the voltage application polarity of a DC power supply has opposite polarities. 2. A capacitor for suppressing fluctuations in input voltage is connected between the connection ends of the main circuit and the DC power supply, and the polarity detection circuit detects the direction of current between the DC power supply and one end of the capacitor. The power supply device according to claim 1, wherein the connection polarity of the DC power supply is determined by the. 3. A polarity diode between the DC power source and the main circuit is provided between the drain and the source so that a parasitic diode which is formed of an enhancement type MOSFET and exists between the drain and the source is in a direction opposite to the polarity switching element. A switch element for voltage connected in series to the switch element, and a voltage detection circuit for detecting the voltage of the DC power supply and controlling the switch element for voltage to turn off when the voltage is out of a specified range are added. The power supply device according to claim 1. 4. The polarity detection circuit determines the connection polarity of a DC power source by comparing the potentials at both ends of a series circuit of a polarity switching element and a voltage switching element. Power supply.