JPH06204746A - Self-oscillation circuit - Google Patents

Abstract

PURPOSE:To make oscillating frequency stable and to attain inexpensive circuit configuration with less number of components. CONSTITUTION:An OFF pulse is outputted from an oscillator and oscillated at a stable frequency (f). The frequency (f) of the OFF pulse is higher than an oscillated frequency f0 of the self excited oscillator circuit. When a capacitive component is fluctuated due to dispersion in the capacitive load, the oscillating frequency is fluctuated. However, the OFF pulse whose frequency is (f) is fed to the base of a transistor (TR)Q1 via a TRQ4 when the TRQ1 is turned on to synchronizingly turn off the TRQ1. Thus, the TRQ1 is forcibly turned off through synchronization with the OFF pulse. Then the oscillation is stably continued at the frequency (f) by synchronizing the TRQ1 with the OFF pulse whose frequency is (f).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited oscillating circuit which outputs an alternating current such as a sine wave output and a rectangular wave output and is used as a switching power supply.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional self-excited oscillation circuit that outputs a sine wave. It includes a transistor Q ₁ , which is a switching element, an output transformer T, a starting resistor R ₁ , and a base resistor R ₁ .
₂ , capacitors C ₁ , C _{2 and the} like. The output transformer T is composed of a primary winding n ₁ , a base winding n ₂ , a secondary winding n _3, etc., and a load 2 is connected to the secondary winding n ₃ . The load 2 may be connected to an electronic circuit and may include a rectifier circuit. DC power supply 1
Therefore, the voltage Vin is applied to the self-excited oscillation circuit.

Now, when the voltage Vin is applied from the DC power source 1, the resistors R ₁ and R ₂ and the base winding n of the output transformer T are applied.
_A voltage is applied to the base of the transistor Q ₁ via ₂ . Then, the transistor Q ₁ is turned on, and a current flows through the primary winding n ₁ of the output transformer T. Then, the collector current of the transistor Q ₁ increases, and the linear increase of the collector current is limited by the restriction of the base current and the like, whereby the voltage generated in the base winding n ₂ becomes small, and the transistor Q ₁ becomes Suddenly turning off.

Here, FIG. 2A shows the base voltage V _B of the transistor Q ₁ at this time, and FIG. 2B shows the collector voltage V _C of the transistor Q ₁ . Figure 2 (b)
As shown in, the transistor Q ₁ has a linear operation,
The output of the secondary winding n ₃ of the output transformer T becomes a sine wave output, and this sine wave output is supplied to the capacitive load 2. Further, in FIG. 2A, f ₀ is the oscillation frequency of the self-excited oscillation circuit shown in FIG. 5, and toff is the transistor Q ₁
Shows the off period. Here, the oscillation frequency f ₀
If load 2 is accompanied by a capacitive load C, is given by Incidentally, L is the inductance of the output transformer T. f ₀ = 1 / 2π (LC _T ) ^1/2 ... where C _T is the combined capacitance of the capacitive load C and the capacitor C ₂ .

FIG. 6 shows another conventional self-excited oscillation circuit, which is a so-called Royer circuit. This circuit has two transistors Q ₁ and Q _{2 that} are turned on and off alternately.
And the output transformer T self-oscillate to output a rectangular wave. In this circuit, the DC power supply 1 is connected to the midpoint of the primary winding n ₁ of the output transformer T, and the other ends of the primary winding n ₁ are connected to the collectors of the transistors Q ₁ and Q ₂ , respectively. Further, the starting resistance R ₁ is the base resistance R ₂
It is connected to the midpoint of the base winding n ₂ of the output transformer T via the respective other ends of the base winding n ₂ transistor Q
It is connected to the bases of ₁ and Q ₂ .

When the voltage Vin is applied from the DC power supply 1, the variation of h _FE of the transistors Q ₁ and Q ₂ causes h _FE
The larger one turns on first to start the oscillation operation. That is, when the voltage Vin is applied, it is applied to the bases of the transistors Q ₁ and Q ₂ through the resistors R ₁ and R ₂ , but if the h _{FE of the} transistor Q ₁ is large, this transistor Q ₁ comes first. Turn on. When the transistor Q ₁ is turned on, the transistor Q ₁ is connected to the primary winding n _{1 1} of the output transformer T.
₁ the collector current flows, is induced a voltage in the base winding n _{2 1} of the output transformer T, by applying a current to the base of the transistor Q _1, to maintain the on-state transistor Q _1.

Then, the magnetic flux density of the output transformer T rises, magnetic saturation occurs, and the transistor Q ₁ is rapidly turned off. At the same time, the voltage on the base winding n _{2 2} is turn on the transistor Q ₂ occurring. In this manner, the transistors Q ₁ and Q ₂ are alternately turned on and off repeatedly to generate a rectangular wave output AC voltage at the secondary winding n ₃ of the output transformer T. Incidentally, FIG. 4 (a) shows the transistor Q ₁
The base voltage V _B1 of the transistor Q is shown in FIG.
Shows _one of the collector-emitter voltage V _CE.

[0008]

The conventional example has the following problems. That is, in the self-excited oscillation circuit that outputs the sine wave shown in FIG. 5, the oscillation frequency f ₀ is represented by the above equation, and the capacitance component C fluctuates due to the variation in the capacitive load. Therefore, there is a problem in that the oscillation frequency changes due to load variation (variation of C in the formula) and the oscillation frequency cannot be stabilized.

Further, in the self-excited oscillation circuit which outputs the rectangular wave shown in FIG. 6, the oscillation frequency f ₀ is expressed by the following equation. f ₀ ∝Vin / Bm · N · S ···, where Vin is the input voltage, Bm is the saturation magnetic flux density of the output transformer T, N is the number of turns of the primary winding n ₁ of the output transformer T,
S is the cross-sectional area of the core of the output transformer T. Such FIG.
Although the oscillating frequency f ₀ of the self-excited oscillating circuit shown in is expressed by the above equation, there is a problem that the oscillating frequency is changed by the variation of parts due to the influence of h _{FE of} the transistor used and the like, and it cannot be stabilized. is there.

Therefore, in the case of sine wave output and rectangular wave output as well, there is a method of separately exciting control as a means for stabilizing the oscillation frequency. FIG. 7 shows the case of the separately excited control, in which the bases of the transistors Q ₁ and Q _{2 which} perform switching operation
Pulse signals V _A and V _B as shown in FIGS.
Enter a, by turning on and off the transistors Q _1, Q ₂ alternately, it is intended to forcibly control the oscillation frequency of the transistor Q _1, Q _2. Incidentally, 3 is a drive circuit for controlling the ON state of the transistor Q ₃ .

However, in the case of the separately excited control as shown in FIG. 7, there is a problem that the number of parts is increased and the cost is increased.

The present invention has been provided in view of the above points, and provides a self-excited oscillation circuit for stabilizing the oscillation frequency, and having a small number of components and an inexpensive circuit configuration. It is provided.

[0013]

SUMMARY OF THE INVENTION The present invention is a self-excited oscillating circuit which is composed of a switching element and an output transformer and which oscillates self-excited at a predetermined frequency set separately, and oscillates at the preset frequency, An off pulse for turning off the switching element in synchronization is applied to a control terminal of the switching element.

[0014]

According to the present invention, by applying the off pulse to the control terminal of the switching element, the switching element oscillates stably at the frequency of the off pulse applied from the other, while continuing the self-excited oscillation. In this way, since the frequency is stably synchronized with others, the oscillation frequency does not change and the oscillation frequency can be stabilized. Moreover, unlike the separately excited control, since it is a self-oscillation circuit, the number of parts is small, and a small and inexpensive circuit configuration can be obtained. Even if a short circuit occurs on the load side, the self-excited oscillation does not lead to the destruction mode.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Since the configurations of the self-excited oscillation circuit that outputs a sine wave and the self-excited oscillation circuit that outputs a rectangular wave are the same as those of the conventional one, the gist of the present invention will be described in detail. FIG. 1 shows a specific circuit diagram of a self-oscillation circuit that outputs a sine wave. The transistor Q ₁ is connected between the base and emitter of the transistor Q ₁ .
₄ are connected in parallel, and an off pulse is applied to the base of this transistor Q ₄ .

As shown in FIGS. 1 and 2C, the off pulse is output from an oscillator (not shown),
It oscillates at a stable frequency f. The frequency f of this off-pulse is set to a frequency higher than the oscillation frequency f ₀ of the self-excited oscillation circuit.

Here, when the self-excited oscillation circuit is oscillated at the oscillation frequency f, if the C component changes due to the variation of the capacitive load, the oscillation frequency changes as described above. However, in this embodiment, when the transistor Q ₁ is on, an off pulse having a frequency f is applied to the base of the transistor Q ₁ via the transistor Q ₄ so that the transistor Q ₁ is turned off. Therefore, as shown in FIG. 2D, the transistor Q ₁ is forcibly turned off in synchronization with the off pulse. And to
After a period of ff, the transistor Q ₁ is turned on, also, synchronization is bought by the off-pulse, transistor Q ₁
Is forcibly turned off, and oscillation is stably maintained at the frequency f.

(Embodiment 2) FIG. 3 shows Embodiment 2 and shows a specific circuit diagram of a self-excited oscillation circuit that outputs a rectangular wave.
In the present embodiment, since the two transistors Q ₁ and Q ₂ are alternately turned on and off to oscillate, the frequency of the off pulse is set to 2f. That is, as shown in FIG.
Transistor Q ₅ is connected in parallel between the base and emitter of transistor Q ₁ , and transistor Q ₆ is connected in parallel between the base and emitter of transistor Q ₂ . Then, the bases of the transistors Q ₁ and Q ₂ are connected in common, and the bases of the transistors Q ₁ and Q ₂ have a frequency of 2
An off pulse of f is applied.

[0019] FIG. 4 (c) shows the off pulse, FIG. (D) shows shows the base voltage V _B1 of the transistor Q _1, FIG. (E) show no collector-emitter voltage _CE1 of the transistor Q ₁ There is. Even if the oscillation frequency f ₀ fluctuates due to variations in parts, etc., when the transistor Q ₁ is on,
The off pulse synchronizes the transistor Q ₁ forcibly, and the next off pulse synchronizes the other transistor Q ₂ with the other transistor Q ₂ forcibly turns off, which is repeated to stabilize the frequency f. Will continue to oscillate.

1 and 3, the driving transistor Q ₄ , and the transistors Q ₅ and Q ₆ are used as the transistor Q ₁ and the transistors Q ₁ and Q ₂ , but an FET or the like is used instead of the transistor. You may use. Also, FIG.
Then, the off pulse is applied to the transistor Q ₁ via the transistor Q _4, and in the case of FIG. 3, the off pulse is applied to the transistors Q ₁ and Q ₂ via the transistors Q ₅ and Q _6. An off pulse may be directly applied to the bases of Q ₁ and the transistors Q ₁ and Q _{2 so} that the oscillation is synchronized and the oscillation is stably maintained at the frequency f.

The width of the off pulse depends on the transistor Q.
₁ , as long as it is enough to turn off the transistors Q ₁ and Q ₂ , there is no particular limitation. Further, as shown in FIG. 2 and FIG. 4, the rising edge of the off pulse may be during the period during which the transistor Q ₁ and the transistors Q ₁ and Q ₂ are on, not only at the end portion but also during the off pulse. Regardless of the timing, after the synchronization by the off pulse, the oscillation is stably maintained at the frequency f of the off pulse.

[0022]

According to the present invention, a switching element,
In a self-excited oscillation circuit configured by an output transformer and self-oscillating at a predetermined frequency set separately, an off pulse that oscillates at the preset frequency and turns off in synchronization with the switching element is controlled. Since the off-pulse is applied to the terminal, the off-pulse is applied to the switching element, so that the switching element continuously oscillates at the frequency of the off-pulse applied from the other while sustaining self-excited oscillation. In this way, since the frequency is stably synchronized with others, the oscillation frequency does not change and the oscillation frequency can be stabilized. Moreover,
Unlike the separately excited control, since it is a self-oscillation circuit, the number of parts is small, and the circuit configuration can be small and inexpensive. In addition, even if a short circuit occurs on the load side, the self-excited oscillation does not result in the destruction mode.

[Brief description of drawings]

FIG. 1 is a specific circuit diagram of a self-oscillation circuit for outputting a sine wave according to an embodiment of the present invention.

FIG. 2 is an operation waveform diagram according to FIG. 1 of the present invention.

FIG. 3 is a specific circuit diagram of a self-excited oscillation circuit when outputting a rectangular wave according to a second embodiment of the present invention.

FIG. 4 is an operation waveform diagram according to FIG. 3 of the second embodiment of the present invention.

FIG. 5 is a specific circuit diagram of a self-excited oscillation circuit in the case of outputting a sine wave of a conventional example.

FIG. 6 is a specific circuit diagram of a self-excited oscillation circuit when outputting a rectangular wave of a conventional example.

FIG. 7 is a circuit diagram of a main part in the case of another excitation control of another conventional example.

FIG. 8 is an operation waveform diagram according to FIG. 7 of a conventional example.

[Explanation of symbols]

1 DC power supply 2 Load Q ₁ transistor Q ₄ transistor T Output transformer

Claims (1)

[Claims] 1. A self-excited oscillating circuit comprising a switching element and an output transformer, which self-oscillates at a predetermined frequency set separately, oscillates at the preset frequency, and synchronizes with the switching element. A self-excited oscillation circuit characterized in that an off pulse for turning off is applied to a control terminal of the switching element.