JPS6118427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter circuit whose frequency increases as the input voltage increases, which is less affected by load and which is easy to start.

Figure 1 shows a conventional so-called current source type self-oscillating inverter, which includes a main transformer 1, switching transistors 2 and 3, a current transformer 4 for continuing oscillation, a capacitor 5, a diode 6, a mag-amp 7, and a rectifying and smoothing circuit. 8, an output detection circuit 9, etc. This has important features such as simple structure, reliable operation, and high efficiency.

As shown in Figure 2a, this inverter oscillates at a nearly constant period regardless of the input voltage, and when the load becomes light, the period becomes longer, or the frequency becomes slower, depending on the oscillation frequency in response to changes in input voltage and load. This is the relationship. However, this relationship is an unfavorable characteristic when the secondary output side of the main transformer 1 is controlled to a constant voltage by a mag-amp or the like 7.

The reason for this will be explained with reference to FIGS. 3a and 3b. FIG. 3a shows a case where the frequency used is slow, and FIG. 3b shows a case where the frequency used is fast.

In the figure, T _D is the dead zone area of the mag amplifier 7,
The output limit is proportional to (a): T _L - T _D /T _L (b): T _H - T _D /T _H. As is clear from the figure, in the same mag-amp 7, the dead zone time width T _D is the same in absolute value, so the higher the frequency, the lower the power that can be taken out.

Referring to FIG. 2b, this means that the higher the frequency, the higher the lower limit of the input voltage with respect to the constant full-load voltage, leading to a decline in the overall function of the stabilized power supply.

In addition, the frequency becomes slower when there is no load (Fig. 2 a)
(the oscillation period becomes longer in 7 had no choice but to gain momentum.

In order to eliminate the above drawbacks, it is necessary that the frequency be low when the input voltage is low, and that the frequency should not become slow even when the load is light, as shown in FIG. 5a. This is a particularly necessary consideration when attempting to construct a mag-amp in a compact and effective manner with a relatively high magnetic flux density by using a material with a low saturation magnetic flux density, such as supermalloy, as the material for the mag-amp.

Furthermore, as the number of diodes 6 inserted in parallel with the capacitor 5 increases, the cutoff characteristics of the transistors 2 and 3 are improved, but the conventional self-excited inverter has the disadvantage that the starting characteristics deteriorate. It is of course also necessary that the starting characteristics be good.

In order to achieve the above object, the present invention connects a transistor to both ends of a capacitor inserted between the base of a current transformer for continuing oscillation and the base of a switching transistor, and A resistor is inserted between the collector and the collector.

With such a configuration, Fig. 4a,
As is clear from the characteristic b, startup starts from a low input voltage, which indicates that oscillation startup is easy. The lower input limit for constant voltage at full load is the same as in FIG. 2b.

In addition, Figure 7 shows the basic circuit in Figure 6 with a circuit that corrects changes in input voltage and load, and the dotted and chain lines in Figure 5a that show its characteristics indicate only changes in input voltage. The dotted line and the solid line show the oscillation period with respect to the input voltage at no load and full load, with the addition of the load change correction.

FIG. 5b shows the characteristics of the output voltage with respect to the input voltage, and the dotted line, solid line, and chain line correspond to those in FIG. 5a, respectively. In this case, it is important that the output is improved to a constant voltage when the input voltage is considerably lower than that in FIGS. 2b and 4b.

Hereinafter, a detailed explanation will be given based on FIG. 6, which is a basic circuit of the present invention.

In Fig. 6, 10 and 11 are DC input terminals, 12 is a power switch, 1 is an unsaturated main transformer, 2 and 3 are switching transistors, and 13 is a power supply switch.
is the starting resistance. Further, 4 is a saturation current transformer for oscillation, 14 is a current supply winding, 15 is a resistor, 6 is a diode, and 5 is a capacitor, and an oscillation continuation circuit 16 is constituted by each of these elements. In the present invention, the emitter and collector of a transistor 17 are further connected in parallel with the capacitor 5 and the diode 6, and a resistor 18 of an appropriate value is connected between the base and collector of the transistor 17.
has been inserted.

Note that although the diode 6 is inserted for safety, it is not necessary for operation. This also applies to FIG. 7, which will be described later.

On the secondary side of the main transformer 1, as in FIG.
Mag amplifier 7, rectifier smoothing circuit 8, output detection circuit 9
It is coupled to output terminals 19 and 20 via.

Next, the operation of the circuit shown in FIG. 6 at startup will be explained. First, when the power switch 12 is closed and a voltage is applied to this inverter, the base currents of the transistors 2 and 3 are supplied via the starting resistor 13. In this case, a reverse voltage is applied between the emitter and the base of the transistor 17, but the transistor 17 is non-conductive in this direction, and the current from the resistor 13 is entirely transferred to the transistor 2.
Supplied on the base of 3. This is an essential condition for starting the self-excited inverter, and in this operation it has the same effect as the diode 6 in FIG.

Next, when oscillation is about to be induced due to the slight unbalance existing between the transistors 2 and 3, these base-emitter currents flow as shown by the arrows in the figure. At this time, the transistor 17 is connected to the resistor 18.
Due to the presence of , the impedance in the direction of the arrow is extremely low, and is less than the value of one diode 6 in FIG. As mentioned above, the lower the voltage consumed in the direction of the arrow, the easier it is to start oscillation, and as shown in FIG. 4a, it is easier to start oscillation even under extremely adverse conditions. The base current of transistors 2 and 3 at startup, that is, transistor 17
Although the passing current is small, it becomes large during operation, so once the start-up is started and operation is started, the impedance of the transistor 17 will be higher than the impedance of an appropriate number of diodes 6 as long as the resistor 18 is appropriately selected.

In this way, it is possible to apply an ideal reverse bias voltage to the transistors 2 and 3 when they are cut off, making it easier to start up.
This alone makes the present invention very effective.

Next, Figure 2 shows the most important application example.
A voltage (V ₁ ) obtained from a separate winding 21 wound around the main transformer 1 is rectified by a diode 22, appropriately smoothed by a capacitor 23, and is connected to a resistor 18 between the base and collector of the transistor 17. A voltage (V ₂ ) appropriately divided by 24 is applied. With such a configuration, it becomes possible to perform an operation to correct the change in the input voltage. In other words, input voltage (Vin), separate winding 21
Since the voltage (V ₁ ) and the voltage (V ₂ ) obtained by converting it into DC and dividing it are proportional to each other, as a result, the voltage between the collector and emitter of the transistor 17 becomes approximately proportional to the input voltage. At this time, the current transformer 4 is configured to be saturated with a constant time product, and is expressed as V _CT ×T≒fixed time product (V·S) ……(1). Therefore, V _CT ≒ V _Q1BE + V _Q3CE …………(2). Here, V _CT is the applied voltage of current transformer 4, V
_Q1BE is the base and emitter voltage of transistor 2,
_VQ3CE represents the collector and emitter voltages of the transistor 17, V.S represents volts, second (voltage time product), and T represents time.

Looking at equation (2), V _Q1BE is approximately constant under most conditions, but V _Q3CE increases as the input voltage increases, as described above. Here, since the saturation period T of the current transformer 4 is T=V·S/V _CT (3), as is clear from this equation (3), it becomes shorter as the input voltage increases. Furthermore, since the basic characteristic of a self-excited inverter is that it reverses when the current transformer 4 is saturated, as the input voltage increases,
This means that the oscillation frequency becomes higher.

According to the above, the first important objective of the present invention is to
The objective of increasing the oscillation frequency in accordance with the input voltage has been achieved.

Next, as a second purpose, in order to reduce the influence of the load, as shown in Figure 7, a voltage proportional to the input current of the inverter is taken out as Vp by a transformer 25 etc. inserted in the input line. is rectified and smoothed by a diode 26 and a capacitor 27, divided by a resistor 28, and supplied to both ends of the resistor 24 in the direction shown in the figure. Then, the change in load, that is, the input current of the inverter, is corrected and the fifth
The characteristics shown in Figure a can be obtained. To explain this operation, the voltage (Vp) increases in proportion to the increase in input current, and the voltage drop across the resistor 24 to which this voltage is applied increases. Therefore, the voltage (V ₂ ) decreases. If this voltage (V ₂ ) decreases, the voltage (V _Q3C
E ) decreases, which means that the period T becomes longer.

In FIG. 5a, when there is no correction corresponding to load changes, the characteristic shown by the chain line becomes the characteristic shown by the solid line, and it becomes possible to almost completely correct changes in the period due to load. In this way, as shown in Figure 5b, the output voltage becomes constant from the point where the input voltage is much lower than in Figures 2 and 4, making it possible to increase the function of the stabilized power supply as a whole. This is the result.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram showing a conventional inverter circuit, Figures 2a and b are oscillation period and output constant voltage characteristic diagrams of the circuit shown in Figure 1, respectively, and Figure 3a is the same diagram for a low frequency case. b is a secondary side output characteristic diagram of the main transformer in the case of high voltage, Figures 4a and b are oscillation period and output constant voltage characteristic diagrams respectively according to the basic circuit of the present invention, and Figures 5a and b are respectively diagrams according to the present invention. FIG. 6 is a basic electric circuit diagram of an inverter circuit according to the present invention, and FIG. 7 is a diagram showing the most important applied circuit diagram of the present invention. 1... Main transformer, 2, 3... Switching transistor, 4... Current transformer for continuing oscillation, 5... Capacitor, 6... Diode, 7... Mag amplifier,
8... Rectifier smoothing circuit, 9... Output detection circuit, 1
0, 11... DC input terminal, 12... Power switch, 13... Starting resistor, 14... Current supply winding, 15... Resistor, 16... Oscillation continuation circuit, 17
...Transistor, 18...Resistor, 19,20...
... Output terminal, 21 ... Separate winding, 22 ... Diode, 23 ... Capacitor, 24 ... Resistor, 25 ...
...Transformer, 26...Diode, 27...Capacitor, 28...Resistor.

Claims (1)

[Scope of Claims] 1. In a self-excited inverter circuit whose main components include a main transformer, a switching transistor, and a current transformer that controls the connection between the base and emitter of the switching transistor, the midpoint of the current transformer and the A transistor is coupled to both ends of a capacitor provided between the emitters of the switching transistor, a resistor is inserted between the collector and the base of the transistor, an additional winding is provided on the main transformer, and this additional winding is An inverter circuit characterized in that the inverter circuit is connected to the resistor between the collector and base of the transistor via a rectifier, a capacitor, and a resistor. 2 A separate current transformer inserted in the input line detects the input current of the inverter, converts this current into a proportional voltage, and converts this voltage across the resistor between the separate winding of the main transformer and the transistor. 2. The inverter circuit according to claim 1, wherein a voltage is applied to the inverter circuit according to claim 1.