JPS61224874A - Inverter - Google Patents

Abstract

PURPOSE:To improve the reliability by setting the drive width (t) for driving a switching transistor to become t<1/4f with respect to an operating frequency (f), thereby increasing the circuit efficiency. CONSTITUTION:An inverter 2 formed of four switching transistors (Tr) Q1-Q4 is connected with a power source 1, and an inductive load 4 such as a discharge lamp is provided through a transformer 3. A switching improving capacitor C is connected between the primary windings N1 of the transformer 3. In this case, when TrQ1-Q4 are driven by a drive circuit 5, the drive width (t) is selected to become t<1/4f where (t) is the drive width, and (f) is the operating frequency of the inverter. Thus, the TrQ maintains ON state while causing a current to flow reversely, and even if a forward drive current is slightly delayed, it is normally turned ON to shorten the driving period.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inverter device that outputs a rectangular wave voltage using a switching inverter circuit using switching transistors.

2. Description of the Related Art Conventionally, this type of inverter device has generally been constructed of a switching inverter circuit using switching transistors and an inverter transformer. here,
The switching inverter circuit has a configuration in which, for example, four transistors are bridge-connected, and each pair of transistors is controlled to be ON10FF every half cycle by a drive circuit. In such a switching circuit,
It is normal to design an overdrive in consideration of variations in each element. That is, when the output voltage to the load 1, for example, an inductive load, is a rectangular wave as shown in FIG. 10(a), the collector current of the switching transistor becomes a triangular wave as shown in FIG. 10(b). The width of this triangular wave is 1/4 f of the operating frequency f if the load is purely inductive (L type), but becomes wider if a resistance component is included. Therefore, the drive width t' for driving the switching transistor is t'>1 as shown in FIG.
/4f.

Problems to be Solved by the Invention With such a conventional overdrive method, excessive charge is injected into the switching transistor, resulting in poor switching performance in response to the fall of the triangular collector current. arise. As a result, disadvantages such as poor circuit efficiency and increased heat generation from the switching transistors occur.

Accordingly, one aspect of the present invention is to improve circuit efficiency by improving switching at turn-off of a switching transistor;
An object of the present invention is to obtain an inverter device that can reduce heat generation and improve reliability.

Means for Solving Problems The present invention provides an inverter device that outputs a rectangular wave voltage using a switching inverter circuit 2 including switching transistors Q1 to Q4, in which the drive width for driving the switching transistors Q□ to Q is set to t. , where f is the operating frequency, a configuration is adopted in which t<1/4f is set.

This is based on the discovery that when the active load is an inductive load 4, the switching transistor Q can operate even if the drive width t is narrower than the conduction time of the collector current of the switching transistor Q. By doing so, the excess charge injected into the switching transistor Q can be reduced, the switching characteristics at the time of turn-off can be improved, and the heat generation of the switching transistor Q can also be reduced. , drive loss in the drive circuit can also be reduced.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 7. First, FIG. 2 shows the basic circuit configuration. Power supply 1 has four switching transistors Q connected in a bridge.
1 to Q4 are connected to each other, and diodes D1 to D4 connected in opposite directions are provided in parallel to each transistor Q1 to Q, and a switching inverter circuit 2 is configured by these transistors.

An inverter transformer 3 is provided on the output terminal side of the switching inverter circuit 2, and an inductive load 4 including an inductance component, such as a discharge lamp, is connected to its secondary winding N2. Socite.

A capacitor C for improving switching is connected between the output terminals of the switching inverter circuit 2, that is, between the primary windings N of the inverter transformer 3. Further, the switching transistors Q□ to Q4 are driven by the drive circuit 5, and the transistors Q, , Q, and the transistors Q,, Q, form a pair, and the switching transistors Q□ to Q4 are driven by the driving circuit 5, and the transistors Q, , Q, and the transistors Q, , Q, are connected to each other in pairs, and the switching transistors
It is to be used as FF. The circuit configuration itself is similar to the conventional one, and its basic operation will be explained with reference to FIG.

First, the output voltage Vo for the inductive load 4 is shown in the same figure (a).
As shown in FIG. 2, a rectangular wave is generated by the action of the switching inverter circuit 2. On the other hand, since the output current 0 lags behind the voltage Vo due to the inductive nature of the load, it becomes as shown in FIG. 3(b). Considering this for example, a pair of Q□ and Q4 in the switching inverter circuit 2, its collector current I
c has a triangular wave shape as shown in FIG. This (c
), the portion indicated by the broken line is the diode D1. A current flows through D4 (therefore, the diode is reversely connected to the switching transistor). Now, if we consider the case where there is no capacitor C, the fall of the triangular wave-shaped collector current is shown as a diagonal line because it lags behind the voltage as shown in the enlarged view of Fig. 4(a). An overlapping portion of the voltage and current occurs, and a turn-off loss occurs in the switching transistors Q, , Q, (or Q2 and Q3). In this regard, by providing a capacitor C, as shown in Fig. 4 (
By delaying the rise of the voltage as shown in b),
This reduces overlap with current and improves turn-off switching.

Here, an example of the configuration of the drive circuit 5 for the switching transistors Q1 to Q4 will be outlined with reference to FIG. 5. Basically, ICTL494 for switching regulator manufactured by Tl (Texas Instruments)
6, and the outputs of the output terminals 11 and 8 of the switching part included in this IC 6 are alternately set to 0N.
Transformer 7 with 10FF and connected to output terminal 11 pin
The secondary winding 7a+7b of the switching transistor Q
The secondary winding 8a of the transformer 8 is connected between the base B and emitter E of , , Q, and similarly connected to the output terminal 8 pin.
8b is the base B of the switching transistor Q, ,Q,
- emitter E. The drive width t for the switching transistor Q is determined in IC6.

Regarding the operation in this point, the IC 6 can be equivalently shown as shown in FIG. That is, a triangular wave voltage Va with a frequency f from an oscillator 9 whose operating frequency f is determined by a capacitor Ca and a resistor Ra connected to pins 5 and 6, and a divided voltage is given by a voltage dividing resistor R and R2, and a dead time is generated. The comparator 10 compares the voltage vb input to pin 4, which is a control terminal, and determines the drive width t during the period in which the triangular wave voltage Va from the oscillator 9 exceeds the voltage vb from pin 4 (7th Diagram (a)
, (b)). The output Vc from the comparator 10 is alternately distributed and output as Vd and Ve from the output terminals 11 and 8 pins by the distribution circuit 11 (see FIGS. 7(c) and 7(d)).

Therefore, this embodiment is characterized by the drive of the switching transistors Q to Q4 by the drive circuit 5. That is, the drive width for driving Q1 to Q4 is t.
, when the operating frequency of this inverter device is f, the first
As shown in Figure (c), the drive width t is set to satisfy the relationship t<1/4f. This is because it has been found that when the load is an inductive load 4, it is possible to operate even if the drive width t of the switching transistor Q is narrower than the conduction time of the collector current Ic. To further explain this point, the current indicated by the broken line in FIG. It also flows slightly in the opposite direction (emitter → collector). As a result, the switching transistor Q can maintain an ON state while current flows in the opposite direction.
Compared to turning on from a completely OFF state,
Even if the forward drive current is slightly delayed, it will turn on normally. By thus shortening the period during which the switching transistor Q is driven, the excess charge injected into the switching transistor Q is reduced, and the switching at the time of turn-off is improved.

As a result, the efficiency of the main circuit is improved, and the heat generated by the switching transistor Q is also reduced, resulting in improved reliability of the inverter device.

Furthermore, by shortening the drive period of the switching transistor Q, the drive loss in the drive circuit 5 is also reduced, making it possible to downsize the circuit components.

It will be more efficient overall. In this way.

In particular, an inverter device suitable for inductive loads can be provided.

In this embodiment, the switching inverter circuit 2 has a bridge circuit configuration with four switching transistors Q1 to Q4, but as shown in FIG. , a double-end type as shown in FIG. 9 can be similarly applied.

Effects of the Invention As described above, the present invention provides the drive width t for driving the switching transistor such that t<1 with respect to the operating frequency f.
/4f, it is possible to shorten the drive period, reduce excess charge injected into the switching transistor, improve switching at turn-off, and reduce heat generation in the switching transistor. Further, the drive loss of the drive circuit can be reduced, and the efficiency and reliability of the circuit can be improved.

[Brief explanation of drawings]

FIG. 1 is a timing chart showing the features of an embodiment of the present invention, FIG. 2 is a circuit diagram, FIG. 3 is a timing chart showing basic operation, FIG. 4 is a timing chart showing the action of a capacitor, and FIG. The figure is a circuit diagram of the drive circuit, Figure 6 is a circuit diagram showing its general operation, Figure 7 is a timing chart, Figures 8 and 9 are circuit diagrams showing modified examples, and Figure 10 is a conventional example. This is a timing chart. 2... Switching inverter circuit, Q engineering ~ Q4...
・Switching transistor applicant: Toshiba Electric Materials Corporation 3” Figure 3z Figure 7゜

Claims (1)

[Claims] In an inverter device that outputs a rectangular wave voltage using a switching inverter circuit using switching transistors, when the drive width for driving the switching transistor is t, and the operating frequency is f, t<1/4.
An inverter device characterized in that it is set to f.