JPH0365061A - Power supply circuit - Google Patents

Abstract

PURPOSE:To improve a power utilization efficiency and obtain a compact apparatus by a method wherein a low voltage DC source and a commercial AC source can be applied with one inverter circuit. CONSTITUTION:An inverter circuit is a push-pull current type inverter circuit which is connected to the primary side of a transformer 8 and has two switching devices 6a and 6b and a control means 13 which drives the switching devices 6a and 6b alternately while providing a period during which both the switching devices 6a and 6b are driven when a DC source 1 is used as an electric source and which drives the switching devices 6a and 6b alternately while providing a period during which both the switching devices 6a and 6b are not driven when a commercial AC source is used as an electric source. With this constitution, both the AC source 2 and the DC source 1 can be applied with one converter, so that a compact apparatus can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power supply circuit, and more particularly to a power supply circuit for electrical and electronic equipment used with both commercial AC power supply and low voltage DC power supply.

(Prior Art) In recent years, various electrical and electronic devices that are normally used with commercial AC power sources and can be used outdoors have been developed. When used outdoors, it is necessary to drive electric/electronic equipment with a low voltage DC power source of about 12V to 24V, such as a storage battery for an automobile.

Attempts have also been made to use inverter microwave ovens, which are currently widely used, outdoors.

The configuration of a typical conventional inverter microwave oven is shown in FIG. In the inverter microwave oven 60, the commercial AC power supply 6
6 (100V, 50/60Hz) is converted into DC power by a rectifier circuit 61. This DC power is made to have a high frequency by a single-stone resonant inverter circuit 62, and is boosted by a step-up transformer 63. The output of the transformer 63 is rectified by a voltage doubler full-wave rectifier circuit 64 and used to drive a magnetron 65.

When operating the inverter microwave oven 60 having the configuration shown in FIG. 6 with a low voltage DC power supply, as shown in FIG.
A C/A C inverter 71 is provided, and a low voltage DC power supply 7
The output of 2 is converted to the same 100V, 50/60 Hz as the commercial AC '1#66 by the DC/AC inverter 71.
This AC power is used to operate the inverter microwave oven 60.

(AH to be Solved by the Invention) In the method described above in which a DC/AC inverter is used to convert the output of a low voltage DC power source into AC and input it to an inverter microwave oven, a DC/AC inverter is Since power conversion is performed twice between the microwave oven and the inverter circuit of the inverter microwave oven, there is a problem in that the efficiency of power use is extremely low.

Also, since two inverters are required, ii!
The cost of the source circuit also increases. Furthermore, when a DC power source such as an automobile storage battery has a small capacity, an expensive inverter circuit with low power loss, that is, high power utilization efficiency, is required.

Although it is theoretically possible to change the specifications of a conventional non-inverter microwave oven so that a low-voltage DC power supply is directly connected to the inverter circuit, this would require an inverter switching element with a large current capacity. Such a solution is not realistic.

In order to efficiently drive an inverter microwave oven with a low-voltage DC power supply, the inverter microwave oven is equipped with a push-pull voltage type inverter circuit that can reduce the current capacity of the switching elements, and this inverter circuit is equipped with a DC II
It is also conceivable to connect the source directly. However, with this method, especially when the output voltage of the DC power supply is low,
Since the current flowing through the inverter circuit is large, there is a problem that switching loss becomes large. In addition, although a push-pull voltage inverter circuit is used that can reduce the current capacity of switching elements, the inverter circuit current is large, so expensive circuit components such as switching elements with large current capacity and transformer windings are used. The problem of increased costs arises due to the need to do so. Furthermore, when operating an inverter microwave oven equipped with a push-pull voltage type inverter circuit on a commercial AC power supply, the voltage of the commercial AC power supply must be stepped down and rectified to the voltage of a low-voltage DC power supply. In addition to the above power conversion, two power conversions are required: AC-AC and AC-DC, resulting in low power utilization efficiency. In addition, the transformer connected to the commercial AC power source for step-down must be compatible with the low frequency of the commercial AC power source, which increases its weight and size.

The present invention was made in view of the current situation, and
The purpose is to use one inverter circuit for AC and DC power! The object of the present invention is to provide an inexpensive and compact power supply circuit that can handle the power source.

(Means for Solving the Problems) The i-source circuit of the present invention is a power supply circuit that uses both an AC power source and a DC power source as a power source, and includes an inverter circuit and a transformer that boosts the output of the inverter circuit. The inverter circuit is a push-pull current type inverter circuit connected to the primary side of the transformer, and when two switching elements and a DC power source are used as the power source,
The two switching elements are driven alternately while providing a time during which both switching elements are driven together, and when a commercial AC power source is used as a power source, the two switching elements are driven together. and a control means for driving alternately while providing periods when the vehicle is not in use, thereby achieving the above object.

Further, the power supply circuit of the present invention is a power supply circuit that uses both an AC power source and a DC power source as a power source, and includes an inverter circuit and a transformer that boosts the output of the inverter circuit,
The inverter circuit is a push-pull current type inverter circuit connected to the primary side of the transformer, and includes a first switching element having a first terminal connected to one end of the primary winding of the transformer; A second switching element having a first terminal connected to the other end of the primary winding and a second terminal connected to a second terminal of the first switching element, and a DC power source are used as a power source. In this case, the first and second switching elements are driven alternately while providing a time during which both switching elements are driven, and when a commercial AC power source is used as a power source, the first and second switching elements are comprising a control means for driving the elements alternately while providing a time during which both switching elements are not driven, and a reactor having one end connected to a tap on the primary side of the transformer,
The power supply circuit selectively connects a rectifier circuit for rectifying the output of the AC power source, the other end of the reactor, one output terminal of the DC II source, and one output terminal of the rectifier circuit. The other output terminal of the DC power supply and the other output terminal of the rectifier circuit are both connected to the second terminal of the first switching element and the second output terminal of the second switching element. 2, thereby achieving the above object.

(Example) The invention will now be described with reference to examples.

FIG. 1 shows a circuit diagram of an embodiment of the present invention. Of the control circuit 13, rectifier circuit 3, and reactor current detection circuit 12 shown as blocks in FIG. 1, the rectifier circuit 3 and the reactor current detection circuit 12 have known configurations. The control circuit 13 will be explained in detail later. Further, although this embodiment is a power supply circuit for an inverter microwave oven, the power supply circuit of the present invention is a commercial AC mil! It can be used as a power supply circuit for various electrical and electronic devices used both in low-voltage DC power supply and in low-voltage DC power supply.

The power supply circuit in FIG. 1 is a push-pull current type inverter that converts DC power obtained from a low-voltage DC power source (for example, an automobile storage battery) 1 or a commercial AC power source 2 via a rectifier circuit 3 into AC power. circuit, a step-up transformer 8 for boosting the output voltage of the inverter circuit, a step-up transformer 8
The inverter circuit includes a voltage doubler full-wave rectifier circuit for rectifying the output of the inverter, and a power supply switch 4 for connecting either the DC power source 1 or the rectifier circuit 3 to the inverter circuit. The voltage doubler full wave rectification [1t
The magnetron 14 of the microwave oven is driven by the output. From the secondary side of the step-up transformer 8, a power supply for the filament of the magnetron 14 and a power supply for the control circuit 13 of the inverter circuit are also taken.

The above-mentioned voltage doubler full-wave rectifier circuit has a known configuration, and has two
diodes 10a, 10b and two capacitors 9
a, 9b.

The inverter circuit includes two power transistors 6a.
, 6b, a reactor 5 having a secondary winding 15, a diode 7, a current transducer 11, a reactor current detection circuit 12, and a control circuit 13 for driving transistors 6a and 6b.

The collectors of the transistors 6a and 6b are connected to one end 8a and the other end 8b of the primary winding of the transformer 8, respectively. The emitters of transistors 6a and 6b are connected to each other. By driving the bases of the transistors 6a and 6b by the control circuit 13, the current flowing through the primary side of the transformer 8 is switched at high speed. Power MO8FET, IGB in place of transistors 6a and 6b
A switching element such as T may also be used.

Direct current? 4[1 has one end connected to the connection point between the emitter of the transistor 6a and the emitter of the transistor 6b, and the other end connected to one end of the first switch 4a of the power supply switch 4. The other end of the first switch 4a is connected to a tap 8c of the primary winding of the transformer 8 via the reactor 5. The rectifier circuit 3 has one output terminal connected to the connection point between the emitter of the transistor 6a and the emitter of the transistor 6b, and the other output terminal connected to the second output terminal of the power switch 4.
The first switch 4a and the reactor 5 are connected via the switch 4b.
connected to the connection point.

The power supply switch 4 is operated manually or automatically, and when the DC power supply 1 is used, the first switch 4a is closed, and when the commercial AC power supply 2 is used, the second switch 4b is closed.

The secondary winding 15 and diode 7 of the reactor 5 are transistors 6a which are switching elements.

6b.

The reactor current detection circuit 12 detects the magnitude of the current flowing through the reactor 5 based on the output of the current transducer 11. The output of the reactor current detection circuit 12 is given to the control circuit 13.

The configuration of the control circuit 13 is shown in FIG. The positive edge trigger one-shot circuit 21 and the negative edge trigger one-shot circuit 22 output pulses at the rise and fall of the rectangular wave output from the oscillation circuit 20, respectively. The triangular wave generation circuit 23a outputs a triangular wave every time a pulse from the positive edge trigger one-shot circuit 21 is input. The triangular wave generating circuit 23b generates a triangular wave every time a pulse from the negative edge trigger one-shot circuit 22 is input.

The comparison circuit 24a receives the triangular wave from the triangular wave generation circuit 23a and the voltage reference value on the next side of the transformer, and the output of the comparison circuit 24a goes to a high level during a period in which the voltage level of the triangular wave is higher than the voltage reference value. Become. Comparison circuit 24b
The output of the triangular wave generating circuit 23b becomes high level during a period in which the voltage level of the triangular wave from the triangular wave generating circuit 23b is higher than the voltage reference value.

The output of the comparison circuit 24a is connected to two inverters 27a and 28a, two AND gates 29a and 30a, and O
An XOR (eXclusi
ve OR) circuit 26a.

The other input of the XOR circuit 26a is the output of the power supply selection circuit 25. The power supply selection circuit 25 operates in conjunction with the power supply switch 4 shown in FIG. 1, and its output is at a high level when the commercial AC power supply 2 is selected, and when the DC power supply 1 is selected. is at a low level. Therefore, when the DC power supply 1 is selected, the XOR circuit 26a
The output of the XOR circuit 26a becomes high level while the output of the comparison circuit 24a is high level, and when the commercial AC l1192 is selected, the output of the XOR circuit 26a becomes high level while the output of the comparison circuit 24a is low level. become the level. XOR
The output of circuit 26a is applied to the gate of transistor 6a. When the output of the XOR circuit 26a is at a high level, the transistor 6a is turned on.

The output of the comparison circuit 24b is output from two inverters 27b and 28b, two AND gates 29b and 30b, and O
The signal is applied to an XOR circuit 26b composed of an R gate 31b. The XOR circuit 26b also includes a power supply selection circuit 2.
5 outputs are given. The relationship among the outputs of the comparison circuit 24b, power supply selection circuit 25, and XOR circuit 26b is
This is the same as described regarding circuit 26a. The output of the XOR circuit 26b is applied to the gate of the transistor 6b. When the output of the XOR circuit 26b is at a high level, the transistor 6b is turned on.

Note that the control circuit 13 shown in FIG. 2 does not utilize the detection output of the reactor current detection circuit 12.

Control circuit 13 when DC current [1 is selected]
The operation timing of is shown in FIG. 3A. Triangular wave generation circuit 2
Since the circuits 3a and 23b alternately output triangular waves, the outputs of the comparison circuits 24a and 24b alternately become high level.

Therefore, the outputs of the XOR circuits 26a and 26b also become high level alternately, and the transistors 6a and 6b are alternately turned on. What is important here is that the comparison circuit 24a
The transformer-next-side voltage reference value is set such that there is a period in which the output of the comparator circuit 24b and the output of the comparator circuit 24b are simultaneously at a high level. By this, XOR
A period (a=b and C to Cd) occurs in which both the outputs of the circuits 26a and 26b are at a high level, and during this period, both transistors 6a and 6b are in an on state.

FIG. 3B shows the operation timing of the control circuit 13 when the commercial AC power source is selected. In this case, when the outputs of the comparison circuits 24a and 24b are at a low level, the outputs of the XOR circuits 26a and 26b are at a high level, respectively. Therefore, the XOR circuit 2
The outputs of 6a and 26b are both at a low level, and during that period, both transistors 6a and 6b are in an off state.

The operation of this embodiment will be explained.

(1) When the low-voltage DC power supply 1 is used, the primary winding of the step-up transformer 8 is short-circuited and energy is stored in the reactor 5 during the period (a-b) when both transistors 6a and 6b are on. . When the transistor 6a is turned off, the energy stored in the reactor 5 is released via the transformer 8 during periods b to C.
Capacitor 9a is charged. Next, the transistor 6a is turned on, and energy is stored in the reactor 5 again during periods C to d. Subsequently, when the transistor 6a is turned off, the energy stored in the reactor 5 is released via the transformer 8 during the period d-e.
Capacitor 9b is charged. The primary voltage of the transformer 8 when the energy of the reactor 5 is released is the sum of the voltage of the DC power supply 1 and the voltage of the reactor 5. In this way, boosting is performed when a DC power source is used. The degree to which the reactor 5 boosts the voltage depends on the period during which both the two transistors 6a and 6b are on (
a − b , c − d ).

(2) When commercial AC 111iX2 is used When the transistor 6a is first turned on, energy is stored in the reactor 5 during periods 1 to g, and at the same time, current flows through the transformer 8.

Therefore, energy is released to the secondary side of the transformer 8,
Capacitor 9b is charged. When the transistor 6a is turned off, the energy stored in the reactor 5 returns to the power source during the period gh through a path including the diode 7, the secondary winding 15 of the reactor, and the second switch 4b. Next, when the transistor 6b is turned on, energy is accumulated in the reactor 5 during a period h to l, and at the same time, energy is released to the secondary side of the transformer 8, charging the capacitor 9a. transistor 6
When b is turned off, the energy stored in the reactor 5 returns to the power source during the period i-J. Period when one transistor is on (1~g1 h~
The primary side voltage of the transformer 8 in 1) is obtained by subtracting the voltage of the reactor 5 from the power supply voltage output from the rectifier circuit 3. In this way, voltage step-down is performed when a commercial AC power source is used.

The role of the protection circuit including the diode 7 and the secondary winding 15 of the reactor 5 will be described. In the case where the DC power supply 1 is used, it is assumed that the transistor 6a is instantaneously switched to the off state while both the transistors 6a and 6b are on. In this case, if the above protection circuit is not provided, the current will not be cut off instantaneously, but the current will be maintained,
A voltage in the same direction as the power supply voltage is generated across the reactor 5 to maintain energy. Therefore, a high voltage obtained by superimposing the voltage of the reactor 5 and the power supply voltage is applied to the transistor 6a, and there is a risk that the transistor 6a will be destroyed.

When the reactor 5 is provided with the secondary winding 15, when the transistor 6a is switched from the on state to the off state, a current of the same ampere-turn as the current flowing through the reactor 5 flows through the secondary winding 15. flows. Since this current is consumed by the DC power supply 1 as a load, the voltage applied to the transistor 6a is only the power supply voltage, and the risk of destruction of the transistor 6a is reduced. Diode 7 is provided to prevent backflow.

The adjustment of the output voltage in this embodiment is performed by the triangular wave generators 23a and 2.
This is done by comparing the output of 3b with the voltage reference value on the next side of the transformer.

The output current is adjusted by the oscillation circuit 2 of the control circuit 13 in FIG.
This is done by using, for example, the circuit shown in FIG. 4 instead of 0, and providing a pause period in the switching of the transistors 6a and 6b. The output of the oscillation circuit 42 is a rectangular wave with a longer period than the rectangular wave output from the oscillation circuit 41, as shown in the timing chart of FIG. The oscillation circuit 41 is the second
This is similar to the oscillation circuit 20 shown in the figure. The output of the oscillation circuit 42 is given to the D input terminal of the D flip-flop 45 via the comparator circuit 44, and the output of the oscillation circuit 41 is given to the clock terminal of the D flip-flop 45, so that the output terminal Q of the D flip-flop 45 is appears in Since the output of the oscillation circuit 41 is ANDed with the output of the D flip-flop 45 by the AND gate 46, during the period when the output of the D flip-flop 45 is at a low level, that is, during the period when the output of the comparator circuit 44 is at a low level, The output of the oscillation circuit 41 does not pass through the AND gate 46, and switching of the transistors 6a and 6b is stopped during this period.

The comparison circuit 44 includes an oscillation circuit 42 and an error amplification amplifier 4.
3 outputs are given. The output of the comparison circuit 44 becomes high level when the output of the oscillation circuit 42 is larger than the output of the error amplification amplifier 43. The error amplification amplifier 43 is supplied with the detection output of the reactor current detection circuit 12 (see FIG. 1) and the reactor current reference value.
Since this subtracts the reference value from the detection output and amplifies it, the output of the oscillation circuit 42 is at a high level and the difference between the detection output of the reactor current detection circuit 12 and the reactor current reference value is within a predetermined range. During a certain period, the output of the comparison circuit 44 becomes high level. Therefore, when the current value of the reactor 5 is large, the period during which the output of the comparator circuit 44 is at a high level is shortened, and the period during which the switching of the transistors 6a and 6b is stopped becomes long, so that the output current is suppressed.

(Effects of the Invention) According to the present invention, a single inverter circuit can support both a low-voltage DC power source and a commercial AC power source, thereby providing an inexpensive and compact power supply circuit with high power utilization efficiency. In the 14-source circuit of the present invention, when a DC power source is used, boosting is performed, so the value of current flowing through the inverter circuit can be suppressed. Therefore, switching loss can be kept low, and there is no need to use expensive circuit components with large current capacities. Further, according to the present invention, the turns ratio of the step-up transformer can be reduced, and therefore, the step-up transformer can be made smaller and lighter.

4.' No. I Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 is a block diagram of a control circuit of the embodiment, and Figures 3A and 3B show the operation of the control circuit. 4 is a block diagram of an example of a circuit for adjusting the output current of the embodiment, FIG. 5 is a timing chart showing the operation of the circuit in FIG. 4, and FIG. 6 is a conventional inverter microwave oven. FIG. 7 is a block diagram showing a conventional method for operating the inverter microwave oven with a low voltage DC power supply.

1...Low voltage DC power supply, 2...Commercial AC power supply, 3.
... Rectifier circuit, 4...' I4 source switch 9 switch, 5...
Reactor, 5 a s 6 b... Power transistor (switching element), 7... Diode, 8
...Step-up transformer, 9a, 9b...Capacitor,
10a, 10b...Diode, 11...Current transducer, 12...Reactor current detection circuit, 13...Control circuit, 14...Magnetron.

that's all

Claims (1)

[Claims] 1. In a power supply circuit that uses both an AC power source and a DC power source as a power source and includes an inverter circuit and a transformer that boosts the output of the inverter circuit, the inverter circuit:
A push-pull current type inverter circuit connected to the primary side of the transformer, comprising two switching elements, and when a DC power source is used as a power source, both switching elements drive the two switching elements. control means for driving the two switching elements alternately while providing a time during which the two switching elements are driven, and when a commercial AC power source is used as a power source, driving the two switching elements alternately while providing a time during which both switching elements are not driven A power supply circuit equipped with 2. In a power supply circuit that uses both an AC power source and a DC power source as a power source and includes an inverter circuit and a transformer that boosts the output of the inverter circuit, the inverter circuit:
A push-pull current type inverter circuit connected to the primary side of the transformer, comprising: a first switching element having a first terminal connected to one end of the primary winding of the transformer; a second switching element having a first terminal connected to its other end and a second terminal connected to a second terminal of the first switching element; The first and second switching elements are driven alternately while providing a time during which both switching elements are driven, and when a commercial AC power source is used as a power source, the first and second switching elements are driven as both switching elements. and a reactor having one end connected to a tap on the primary side of the transformer, and the power supply circuit rectifies the output of the AC power supply. further comprising a rectifier circuit, and power supply switching means for selectively connecting the other end of the reactor to one of the output terminals of the DC power source and one output terminal of the rectifier circuit, the other output terminal and the other output terminal of the rectifier circuit are both connected to a connection point between the second terminal of the first switching element and the second terminal of the second switching element; .