JPH0715351Y2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a switching power supply device such as a chopper device and an inverter device, which converts a DC power supply into an AC power supply by switching and supplies the AC power to an inductive load. Is.

[Conventional technology]

FIG. 5 shows a circuit diagram of a conventional chopper device. The chopper device, for example, as shown in FIG. 5, the voltage E ₁
, One end of the switching element 2 is connected to the positive electrode of the DC power supply 1 via the inductive load 4, the other end of the switching element 2 is connected to the negative electrode of the DC power supply 1, and the polarity is opposite to that of the DC power supply 1. The diode 3 is connected in parallel to the load 4.

In this chopper device, the load current I _L flowing through the load 4 can be adjusted by turning on and off the switching element 2.

The operation will be described with reference to FIG. Switching element 2
In the ON state (period T _{O in} FIG. 6), the load current I _L flows through the path of DC power supply 1 → load 4 → switching element 2 → DC power supply 1. At this time, the load current I _L flows through the switching element 2 as the current I _S. The current _ID passing through the diode 3 is zero, the voltage V _S across the switching element 2 is zero, and the voltage V _D across the diode 3 is equal to the voltage E ₁ of the DC power supply 1.

During the transition period when the switching element 2 changes from on to off (time period T _{1 in} FIG. 6), the load current I _L flowing through the switching element 2 gradually changes to the diode 3 in an attempt to continue flowing thereafter. As it flows, the current I _S decreases from the load current I _L to zero. At this time, the current I _D increases from zero and reaches the load current I _L.

The voltage V _D drops from the voltage E ₁ of the DC power supply ₁ to zero. At this time, the voltage V _S changes from zero to the voltage E _{1 of the} DC power supply _1.
Rise to.

When the switching element 2 is off (time period T _{2 in} FIG. 6), the load current I _L flows as the current I _D through the diode 3. At this time, the current I _S flowing through the switching element 2 is zero, the voltage V _S across the switching element 2 is equal to the voltage E ₁ of the DC power supply 1, and the voltage V _D across the diode 3 is zero. .

During the transitional period when the switching element 2 changes from off to on (period T _{3 in} FIG. 6), the load current I _L flowing through the diode 3 gradually commutates toward the switching element 2, so that the current I _D decreases from the load current I _L to zero,
I _S increases from zero to the load current I _L. When the current I _D of the diode 3 becomes zero, the reverse recovery current of the diode 3 starts to flow in the reverse direction as a characteristic of the diode 3, and at this time, the current I _S is equal to the load current of the reverse recovery current of the diode 3.
It is added to I _L and flows. After that, when the peak of the reverse recovery current of the diode 3 passes, the current I _S starts to decrease and becomes the load current I _L. Further, the voltage V _D rises from zero to the voltage E _{1 of the} DC power supply 1 after the peak of the reverse recovery current. At this time, the voltage V _S drops from the voltage E ₁ of the DC power supply ₁ to zero.

FIG. 7 shows a circuit diagram of a conventional inverter device.
In FIG. 7, 11 is a DC power supply, 12 to 15 are switching elements, 16 to 19 are diodes,
20 is the load.

This inverter device includes, for example, switching elements 12, 13
Are alternately turned on at a low frequency with a pause period, and the load 20 is supplied with power by turning on and off the switching elements 15 and 14 at high frequencies during the on periods of the switching elements 12 and 13, respectively. This is equivalent to a combination of two chopper devices shown in FIG.

[Problems to be solved by the device]

In the chopper device of FIG. 5, as described above, when the switching element 2 is turned off, the load current I _L flowing in the load 4 until then is connected to the DC power source 1 in the opposite polarity. It flows as a current I _D through the diode 3.
When the switching element 2 is turned on again before the current _ID flowing through the diode 3 becomes zero, a reverse voltage is applied to the diode 3. At this time, a reverse recovery current flows in the reverse direction (a negative polarity portion of the current I _D in the period T ₃ in FIG. 6). The reverse recovery current changes depending on the value of the current flowing in the diode 3 in the forward direction and the reduction rate (di / dt) of the current. During the period when the reverse recovery current is flowing, the DC power supply 1 is short-circuited. In this state, an excessive current flows in the path of the diode 3 and the switching element 2. The peak of this reverse recovery current increases as the current capacity and breakdown voltage of the diode 3 increase, and the flowing time also increases.

Thus, when a large reverse recovery current flows for a long time, not only the switching element 2 is adversely affected, but also the diode 3 itself is adversely affected.

Further, there is a problem that the switching loss of the switching element 2 is large because the reverse recovery current flows through the switching element 2.

The inverter device shown in FIG. 7 has the same problem as the above chopper device.

Therefore, an object of the present invention is to provide a switching power supply device capable of reducing the switching loss of the switching element without adversely affecting the switching element and the diode.

[Means for Solving the Problems]

In the switching power supply device of the present invention, a switching element is connected between both ends of a first DC power supply via an inductive load, and a diode is connected to the load in a state of reverse polarity with respect to the first DC power supply. The primary winding of the saturable current transformer is inserted in the power feeding path from the first DC power source to the circuit composed of the load, the diode and the switching element, and the secondary winding of the saturable current transformer is connected. A series circuit of a second DC power supply and a current limiting resistor is connected between both ends.

The direction of the magnetic flux generated in the magnetic core of the saturable current transformer by the current flowing through the primary winding of the saturable current transformer by the voltage of the first DC power source is saturated by the voltage of the second DC power source. The direction of the magnetic flux generated in the magnetic core of the saturable current transformer by the current flowing in the secondary winding of the current transformer is set to be the opposite direction.

In addition, the voltages of the first and second DC power supplies are set to E ₁ and E, respectively.
₂ , the resistance value of the resistor is R, the primary / secondary turns ratio of the saturable current transformer is 1: n, and the maximum load current flowing to the load is I _LM
Then, it is set so that E ₂ + nE ₁ ≧ (I _LM / n) R (1) is satisfied.

[Action]

In the configuration of the present invention, the saturable current transformer having the primary winding interposed in the power supply path from the first DC power supply to the load is such that the switching element is off from the second DC power supply. Due to the current flowing through the switching element, the switching element is saturated in the opposite direction from when it is on.

When the switching element changes from off to on, a reverse recovery current flows in the diode due to the voltage of the first DC power supply, and the reverse recovery current causes the saturable current transformer to shift to an unsaturated state. As a result, a voltage appears across the primary winding of the saturable current transformer, and this voltage reduces the voltage applied to the diode from the first DC power supply, and as a result, flows to the diode. The reverse recovery current will be suppressed.

After this, after the reverse recovery current of the diode has subsided, the first
The magnetic flux of the saturable current transformer generated by the current flowing through the primary winding due to the voltage of the DC power supply exceeds the magnetic flux generated by the current flowing through the secondary winding due to the voltage of the second DC power supply, and the saturable current transformer is saturated Then, the voltage across the primary winding of the saturable current transformer becomes zero, and current is supplied from the first DC power supply to the load without limitation.

After that, when the switching element is turned off after that, the load current flowing in the load flows through the diode and the current in the primary winding of the saturable current transformer disappears.At this time, the secondary winding of the saturable current transformer is lost. In addition, the saturable current transformer is saturated in the opposite direction to that when the switching element is on by the current flowing from the second DC power supply through the resistor.

In the above operation, by satisfying the condition of the expression (1), the load current flowing in the load when the switching element is off is completely commutated from the diode to the switching element, and This is possible only when the reverse recovery current flows in the. If the above conditions are not satisfied, the load current does not completely commutate to the switching element, and the forward current flows through the diode even a little, the current limiting function by the saturable current transformer is effective. Does not work and the saturable current transformer becomes saturated, an excessive reverse recovery current flows from the first DC power supply through the diode.

〔Example〕

A first embodiment of the present invention will be described with reference to FIGS. In this chopper device, as shown in FIG. 1, one end of a switching element 2 is connected to a positive electrode of a DC power supply 1 via an inductive load 4, and the other end of the switching element 2 is connected to a negative electrode of the DC power supply 1. And load 3 with diode 3
Are connected in parallel to the DC power source 1 in reverse polarity. The configuration so far is the same as that of the conventional example shown in FIG.

In addition, a saturable current transformer 7 is provided between the positive electrode of the DC power source 1 and the circuit including the load 4, the diode 3 and the switching element 2.
The primary winding is inserted, and the DC power supply 5 is connected between both ends of the secondary winding of the saturable current transformer 7 via the resistor 6.

Then, with respect to the direction of magnetic flux generated in the saturable current transformer 7 of the magnetic core by the current flowing through the primary winding of the saturable current transformer 7 by the voltage E ₁ of the DC power source 1, the voltage E ₂ of the DC power source 5 For example, the polarity of the DC power supply 5 is set such that the direction of the magnetic flux generated in the magnetic core of the saturable current transformer 7 by the current flowing through the secondary winding of the saturable current transformer 7 is opposite.

Further, the voltage E ₂ of the DC power supply 5 and the resistance value R of the resistor 6 are set so as to satisfy the condition of the above-mentioned formula (1).

Further, as the magnetic core of the saturable current transformer 7, one having good high frequency characteristics such as ferrite is used. Further, the capacity of the magnetic core may be a voltage-time product represented by the product of the voltage E ₁ of the DC power supply 1 and the diode reverse recovery time, and after the reverse recovery current of the diode 3 disappears, a saturable current change occurs. Since it is better that the container 7 is completely saturated, it is better not to set it larger than necessary.

The saturable current transformer 7 is configured such that, for example, a secondary winding is wound around a ring-shaped magnetic core in a toroidal shape, and the DC power source 1 and the load are connected.
4, a conductor connecting the circuit including the diode 3 and the switching element 2 is penetrated through the magnetic core.

The operation of this embodiment will be described with reference to FIGS. The state where the switching element 2 is on (the period of FIG. 2
At T ₀ ), the load current I _L flows in the route of the DC power supply 1 → the primary winding of the saturable current transformer 7 → the load 4 → the switching element 2 → the DC power supply 1. At this time, the load current I _L flows through the switching element 2 as the current I _S. The current I _D passing through the diode 3 is zero, the voltage V _S between the two poles of the switching element 2 is zero, and the voltage V _D between the two poles of the diode 3 is equal to the voltage E ₁ of the DC power supply 1. Further, the magnetic core of the saturable current transformer 7 is
The voltage E ₁ of the DC power source 1 is saturated by current flowing through the primary winding, in a position of over B-H curve of FIG. 3, voltages V ₁ across the primary winding is zero, The saturable current transformer 7 does not limit the load current I _L flowing to the load 4.

During the transitional period when the switching element 2 changes from on to off (period T _{1 in} FIG. 2), the load current I _L flowing through the switching element 2 gradually changes to the diode 3 in order to continue flowing thereafter. As it flows, the current I _S decreases from the load current I _L to zero. At this time, the current I _D increases from zero and reaches the load current I _L.

Further, the voltage V _D drops from the voltage E ₁ of the DC power supply ₁ to zero. At this time, the voltage V _S changes from zero to the voltage E _{1 of the} DC power supply _1.
Rise to.

When the switching element 2 is off (period T 2 in FIG. ₂ ), the load current I _L flows as the current I _D through the diode 3. At this time, the current I _S flowing through the switching element 2 is zero, the voltage V _S across the switching element 2 is equal to the voltage E ₁ of the DC power supply 1, and the voltage V _D across the diode 3 is zero. . The magnetic core of the saturable current transformer 7 shifts from the position on the B-H curve of FIG. 3 to the position from the position of the switching element 2 as time passes from the beginning of the period T ₂ . It will be saturated in the opposite direction.

During the transition period when the switching element 2 changes from OFF to ON (period T _{3 in} FIG. 2), the load current I _L flowing through the diode 3 gradually commutates toward the switching element 2, so that the current I _D decreases from load current I _L to zero and current I _S increases from zero to load current I _L. When the current I _D of the diode 3 becomes zero, the reverse recovery current of the diode 3 starts to flow in the reverse direction. At this time, the current I _S is the diode 3
The reverse recovery current of is added to the load current I _L and flows.
After that, when the peak of the reverse recovery current of the diode 3 passes, the current I _S starts to decrease and becomes the load current I _L. In addition, the voltage V _D rises from zero to the voltage E _{1 of the} DC power supply 1 after the peak of the reverse recovery current. At this time, the voltage V _S is the DC power supply 1
The voltage E ₁ drops from zero to zero.

Further, the magnetic core of the saturable current transformer 7 shifts from the position on the BH curve of FIG. 3 to the position with the passage of time from the beginning of the period T ₃ .

During the period T ₃ during which the magnetic core of the saturable current transformer 7 shifts from the position on the BH curve in FIG. 3 to the position, the magnetic core is in the unsaturated state, and the voltage across the primary winding is V ₁ occurs. This voltage
V ₁ acts to reduce the voltage V _D of the diode 3 and the voltage V _S of the switching element 2, and the current flowing in the diode 3
The reverse recovery current of I _D will be suppressed. When the reverse recovery current is suppressed in this way, the time during which the reverse recovery current is flowing becomes slightly longer than in the conventional example.

After a period T ₃ is the same as the period T _0, the magnetic core of the saturable current transformer 7 is to maintain the saturation state.

Voltage generated across the primary winding of the saturable current transformer 7 described above
V ₁ is generated in response to the generation of a voltage across the resistor 6 by the secondary current flowing in the secondary winding based on the primary current flowing in the primary winding of the saturable current transformer 7. Become.

In addition, the diode 3 using the saturable current transformer 7 described above
The limiting operation of the reverse recovery current of (4) satisfies the condition of the expression (1), and when the switching element 2 is off, the load 4
This is possible only when the load current I _L flowing through the diode 3 is completely commutated from the diode 3 toward the switching element 2 and the reverse recovery current flows through the diode 3.

If equation (1) condition is not satisfied, if the load current I _L is not allowed to flow rolling towards the fully switching element 2, and a forward current flows through the diode 3 even slightly, saturable current transformer When the saturable current transformer 7 saturates because the current limiting function of the transformer 7 does not work effectively, an excessive reverse recovery current flows from the DC power supply 1 through the diode 3. Therefore,
When designing a circuit, it is necessary to satisfy the condition of expression (1) without fail.

The above equation (1) is derived from the following idea. That is, a voltage is applied to the primary winding of the saturable current transformer 7.
When E ₁ is applied, the current flowing in the secondary winding is I _LM / n
The secondary current of the saturable current transformer 7 becomes
When this is expressed by a mathematical expression, it becomes like the expression (2), and by modifying the expression (2), the expression (1) is obtained.

E ₂ + nE ₁ ) / R−I _LM / n ≧ 0 (2) This chopper device has a saturable current transformer 7 in the power supply path from the DC power supply 1 to the circuit composed of the load 4, the diode 3 and the switching element 2. The primary winding of the saturable current transformer 7
The DC power supply 5 is connected to the secondary winding of the saturable current transformer 7 via the resistor 6, and the magnetic core of the saturable current transformer 7 is driven by the current flowing in the primary winding of the saturable current transformer 7 by the voltage E ₁ of the DC power supply 1. The direction of the magnetic flux generated in the magnetic core of the saturable current transformer 7 by the voltage E ₂ of the DC power source 5 flowing in the secondary winding of the saturable current transformer 7 is opposite to the direction of the magnetic flux generated in The reverse recovery current flowing in the diode 3 can be suppressed and the adverse effect on the switching element 2 and the diode 3 can be reduced because the condition of the equation (1) is satisfied. it can.

In the transitional period when the switching element 2 changes from off to on, the saturable current transformer 7 shares a part of the voltage to reduce the voltage applied to the switching element 2 and suppress the current flowing through the switching element 2. Therefore, the switching loss in the switching element 2 can be reduced.

Further, since the peak of the reverse recovery current of the diode 3 can be suppressed to a low level, the peak of the current flowing out from the DC power supply 1 in a normal state can be suppressed. Therefore,
When an overcurrent detection circuit is provided on the output side of the DC power supply 1 to protect the circuit, the threshold value for overcurrent detection can be brought close to the steady load current, and overcurrent detection can be performed with high accuracy. It is possible to reliably protect the switching element 2 and the like due to overcurrent.

The primary winding of the saturable current transformer 7 may be inserted between the negative electrode of the DC power supply 1 and the other end of the switching element 2.

FIG. 4 is a circuit diagram showing the construction of the inverter device of the second embodiment of the present invention. Also in this inverter device, the primary winding of the saturable current transformer 23 similar to that of the chopper device of FIG. 1 is used as a power supply path from the DC power supply 11 to the switching elements 12 to 15, the diodes 16 to 19 and the load 20. The DC power supply 21 is connected via a resistor 22 to the secondary winding of the saturable current transformer 23. The operations of the saturable current transformer 23, the DC power supply 21, and the resistor 22 in this embodiment are the same as those in the case of FIG. 1, and the conditions satisfied by this circuit are also the same as in the equation (1).

The effect of this embodiment is similar to that of the first embodiment.

[Effect of device]

According to the switching power supply device of the present invention, the primary winding of the saturable current transformer is inserted in the power feeding path from the first DC power source to the parallel circuit of the load and the diode, and the secondary winding of the saturable current transformer is inserted. Since the second DC power source is connected to the via a resistor to satisfy the predetermined condition, the reverse recovery current flowing in the diode can be suppressed and the adverse effect on the switching element and the diode can be reduced. it can.

Further, in the transition period when the switching element changes from off to on, the saturable current transformer shares a part of the voltage to reduce the voltage applied to the switching element and suppress the current flowing through the switching element. It is possible to reduce the switching loss at.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention,
FIG. 2 is a voltage / current waveform diagram of each part in FIG. 1, FIG. 3 is a BH characteristic diagram showing a BH characteristic of a saturable current transformer, and FIG. 4 is a second embodiment of the present invention. FIG. 5 is a circuit diagram showing the configuration of an example of the prior art, FIG. 5 is a circuit diagram showing the configuration of the conventional example, FIG. 6 is a waveform diagram of each part of FIG. 5, and FIG. 7 is a circuit diagram showing the configuration of another conventional example. . 1 ... DC power supply, 2 ... switching element, 3 ... diode, 4 ... load, 5 ... DC power supply, 6 ... resistor,
7: Saturable current transformer

Claims (1)

[Scope of utility model registration request] 1. A first DC power supply, a switching element connected between both ends of the first DC power supply via an inductive load, and a switching element having a polarity opposite to that of the first DC power supply. A diode connected in parallel with a load, a saturable current transformer having a primary winding interposed in a power feeding path from the first DC power source to a circuit including the load, the diode and a switching element, and the saturable current transformer A second DC power supply connected across the secondary winding of the transformer and a series circuit of a current limiting resistor, the primary winding of the saturable current transformer depending on the voltage of the first DC power supply. To the direction of the magnetic flux generated in the magnetic core of the saturable current transformer by the current flowing through the saturable transformer by the current flowing in the secondary winding of the saturable current transformer by the voltage of the second DC power supply. The direction of the magnetic flux generated in the magnetic core of the sink becomes the opposite direction. And set the voltages of the first and second DC power supplies to E ₁ and E ₂ respectively.
When the resistance value of the resistor is R, the primary-secondary winding ratio of the saturable current transformer is 1: n, and the maximum load current flowing through the load is I _LM , E ₂ + nE ₁ ≧ A switching power supply device set to satisfy (I _LM / n) R.