JPH0359668B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to, for example, a primary side circuit of an inverter such as a switching regulator, and particularly relates to overvoltage to a switching element due to a back electromotive force in a primary winding circuit of a transformer. The present invention relates to a primary side circuit of an inverter that reduces the amount of noise.

[Prior Art] The configuration of the primary side circuit of a conventional inverter is shown in FIG. 4A, and its timing diagram is shown in FIG. 4B. Here, 500 is a pulse signal that turns on and off the transistors 501 and 502;
It is input to the base of 01 and 502. When the pulse signal 500 rises now (timing T1 in FIG. 4B), the transistors 501 and 502 are simultaneously turned on, and the primary winding 504 of the transformer 503 is turned on.
A current IC flows through. Next, when the pulse signal 500 falls, the transistors 501 and 502 are simultaneously turned off (timing T2), and the ratio of the number of turns between the primary winding 504 and the secondary winding 505 is A voltage corresponding to the voltage is generated.

When both the transistor 501 and the transistor 502 are off, the induced voltage generated in the primary winding 504 causes the diode 506 and the primary winding 5 to
04 and the diode 507, a current flows from the common side of the power supply V _i toward the positive side. At that time, diodes 506 and 507 are in a conductive state, so the voltage across them is only the forward voltage drop, and the emitter potential of transistor 501 is approximately
At 0V, the collector potential of the transistor 502 becomes approximately equal to the power supply voltage value _Vi .

[Problems to be Solved by the Invention] However, when the transistors 501 and 502 are in the off state, the voltage between the terminals of the transistors 501 and 502 shown at 510 in FIG. 4B is suppressed to below the power supply voltage. This is difficult and requires the use of a switching element having a withstand voltage at least twice the primary power supply voltage.

Therefore, if the primary side circuit of the inverter is constructed using such transistors with high withstand voltage,
In addition to high costs, there were other problems such as increased power loss, reduced power supply efficiency, and decreased switching speed.

The present invention has been made in view of the above conventional example, and provides a high-speed and efficient primary side circuit of an inverter using a switching element having a withstand voltage at least lower than the power supply voltage as a switching element on the primary side of the inverter. The purpose is to

[Means for Solving the Problem] In order to achieve the above object, the primary side circuit of the inverter of the present invention has the following configuration. That is, a primary winding of a transformer connected between a first and a second switching element and energized when both the first and second switching elements are in a conductive state; two inductive elements connected between the primary power source of the transformer and the first and second inductive elements;
an oscillation circuit that switches the switching elements almost simultaneously, and when the first and second switching elements are in a non-conducting state, a back electromotive force generated in the primary winding causes the primary side to switch through the two inductive elements. A circuit that conducts current from the common side of the power supply to the power supply voltage side.

[Operation] In the above configuration, the transformer is connected between the first and second switching means, and when both the first and second switching means are in a conductive state, the primary winding of the transformer is energized, and the first and second switching means are connected. When the second switching means becomes non-conductive, the back electromotive force generated in the primary winding is absorbed by the inductive element connected to both ends of the primary winding, and the voltage applied to the first and second switching elements is reduced. It works to suppress it.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Basic explanation of the configuration of the primary side circuit of the inverter (FIGS. 1 and 2)] FIG. 1 is a simplified basic configuration diagram of the primary side circuit of the inverter according to the embodiment.

In the figure, 100 is the primary power supply of the transformer 102, and its power supply voltage is Vc. Oscillation circuit 10
1 starts oscillating at the same time as the power supply 100 is turned on,
Pulse signals having the same timing are output to transistors 103 and 104. This oscillation circuit 101 may be configured to change the oscillation frequency in response to the output voltage on the secondary side of the transformer 102.

Both 103 and 104 indicate switching elements, which are represented by transistors here.
Other switching elements such as FET may also be used.
When the pulse signal from the oscillation circuit 101 rises, transistors 103 and 104 are simultaneously turned on (conducting), and current flows through the primary winding 105 of the transformer 102. Next, when the pulse signal from the oscillation circuit 101 falls, the transistor 10
3 and 104 are simultaneously turned off (non-conductive). This allows the primary windings 105, 108 and 10
An induced voltage is generated in the transformer 102.
Current flows through the secondary winding of transformer 102, and an output voltage is generated on the secondary side of transformer 102.

On the other hand, on the primary side of the transformer 102, the primary winding 10
5, 108, and 109 causes a current to flow from the common side of the primary power supply 100 through the diode 107, the coil 108, the primary winding 105, the coil 109, and the diode 110.

At this time, if the coil 108 is not present, the emitter of the transistor 104 will be approximately 0V, ignoring the voltage drop in the forward direction of the diode 107.
At this time, the collector-emitter voltage of the transistor 104 is approximately equal to the power supply voltage of the primary power supply 100, and is approximately Vc. However, by providing the coil 108 as in the circuit of the embodiment,
Due to the reverse voltage V1 of the coil 108 that occurs when the transistors 103 and 104 are off, the emitter of the transistor 104 is pushed up by "V1" toward the "+Vc" side, and the collector-emitter voltage when the transistor 104 is off becomes Vc - V1. Become.

Also, if the coil 109 is not present, the transistor 1
The collector voltage of transistor 03 is approximately Vc if the forward voltage effect of diode 110 is ignored, and the voltage between the collector and emitter of transistor 103 when it is off is approximately Vc. However, as in the circuit of the embodiment, the coil 109 is connected to the primary winding 105 and the + of the power supply.
By providing between the sides, the transistor 103
Coil 1 generated by the current flowing from the common side of power supply 100 to the power supply voltage side when 104 and 104 are off.
Due to the reverse voltage V2 of 09, the collector voltage of the transistor 103 is lowered by "V2" from the power supply voltage +Vc, and the transistor 10
The collector-emitter voltage of No. 3 is Vc-V2.

Figure 2 shows the voltage waveforms of each part in Figure 1 and the coil 1.
10 is a diagram showing a voltage waveform between the collector and emitter of the transistor 103 when there are no transistors 08 and 109. FIG.

In FIG. 2, 20 is a pulse signal output from the oscillation circuit 101, and 21 is a coil 108, 10.
9 shows the voltage waveform between the collector and emitter of the transistor 103 when the transistor 9 is not present. 24 indicates the time during which both transistors 103 and 104 are on, and 25 indicates the time during which both diodes 107 and 110 are conductive due to the back electromotive force induced in the primary winding 105. Coil 10 like this
8,109, the collector-emitter voltage Vce of transistor 103 would rise to the power supply voltage. 26 indicates the time during which both transistors 103 and 104 are in the off state.

22 is the transistor 10 in the circuit of FIG.
The voltage waveform between the collector and emitter of No. 3 is shown, and its maximum value is the value obtained by subtracting the reverse voltage V2 of the coil 109 from Vc. Similarly, 23 is the collector of the transistor 104 in the circuit of FIG.
The voltage waveform between emitters is shown. Since the voltage of the transistor 104 is pushed up from the Vc side by V1, this voltage is also below the power supply voltage, similar to the voltage value indicated by 22, and the maximum value is Vc - V1.

[Description of the actual power supply circuit (Figure 3)] Figure 3 is a diagram showing an example of an actual power supply circuit.It is an example of a power supply circuit that inputs an AC voltage of 80 to 250V and outputs +5V6A. The numbers attached to capacitors, coils, etc. indicate their respective resistance values and capacitances of the capacitors.

When AC power is input, a DC voltage obtained by rectifying the AC voltage is input to the DC-DC converter 35, and power is supplied to the switching circuit 33. As a result, the switching circuit 33 starts a switching operation, and the transformer 32 inputs pulse signals of the same phase to the bases of the transistors Q1 and Q2.
In this way, transistors Q1 and Q2 are controlled to turn on and off simultaneously.

When transistors Q1 and Q2 are turned on, current flows through primary winding L1 of transformer 34. Next, when transistors Q1 and Q2 turn off at the same time, a back electromotive force is generated in the primary windings L1, L2, and L3. L1, coil
Current flows through L3 and diode D2, and as shown at 22 and 23 in Figure 2, transistors Q1 and
The voltage between the collector and emitter of Q2 is suppressed below the power supply voltage.

Further, in carrying out this operation, the same effect can be obtained by using another transformer.
That is, the primary winding of another transformer is inserted in series in the path of the current flowing when both transistors are on, and the two secondary windings are the same as windings 108 and 109 of transformer 102. The same effect can be obtained by placing it in the same position.

The switching circuit 33 inputs the output voltage of the secondary side of the transformer 34, and controls the on/off frequency of the transistors Q1 and Q2 in response to fluctuations in the output voltage, thereby stabilizing the output voltage. It is planned.

As described above, according to this embodiment, the maximum voltage between the collector and emitter and between the collector and base of the two transistors on the primary side of the transformer is suppressed to below the power supply voltage value, so the switching speed is fast. Efficient low voltage transistors can be used. Therefore, it is possible to create a low-cost, efficient power supply circuit with less loss during switching.

[Effects of the Invention] As described above, according to the present invention, a switching element having a withstand voltage lower than the power supply voltage can be used as a switching element on the primary side. This has the effect of providing a circuit.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a simplified configuration of the primary side circuit of the inverter of the embodiment, and FIG. 2 is a diagram showing the timing of each part of the circuit in FIG. 1 and the voltage between the collector and emitter of the transistor when there is no coil. Third
The figure is a diagram showing an example of the power supply circuit of the embodiment, Fig. 4A
4B is a diagram showing the configuration of a primary side circuit of a conventional inverter, and FIG. 4B is a diagram showing timing waveforms of various parts of the primary side circuit of a conventional inverter. In the figure, 31, 32... oscillation circuit, 33... switching circuit, 100... power supply, 101... oscillation circuit, 34, 35... DC-DC converter, 10
2...Transformer, 103, 104...Switching element (transistor), 105...Primary winding, 1
06... Secondary winding, 107, 110... Diode, 108, 109... Coil.

Claims (1)

[Scope of Claims] 1. A series circuit in which a DC voltage source and a primary winding connected between a first and a second switching element are connected in series; a first inductive element connected in parallel; a second inductive element connected in parallel to the primary winding and the second switching element; and switching the first and second switching elements almost simultaneously. When the oscillation circuit and the first and second switching elements change from a conductive state to a non-conductive state, a back electromotive voltage generated in the primary winding causes the direct current to flow through the first and second inductive elements. A primary side circuit of an inverter, comprising: a circuit that conducts current from a common side of a voltage source to a power supply voltage side;