JPS5918869Y2 - inverter circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to an inverter circuit that reduces overshoot when power is applied, and also suppresses the voltage applied to switching elements even when excessive power supply voltage is applied for a short period of time, such as due to lightning surges. It has been made possible to do so.

A conventional inverter circuit is configured as shown in FIG. 1, and as is well known, at startup, one of the pair of transistors 1 and 2 is turned on via bias resistor 3 or bias resistor 4, and after startup, The driving force induced in the base winding 5 turns on the pair of transistors 1 and 2 alternately to induce alternating current power of a predetermined frequency in the secondary winding 7 of the oscillating lance 6.

The oscillation frequency in a stable state is determined by parallel resonance between the inductance components of the primary windings 8 and 9 and the capacitance component of the capacitor 10.

However, in such an inverter circuit, the power switch 1
When the DC power supply 12 is turned on, the inductor 13 provided in the input line enters in series with the parallel resonance system.

Therefore, in a transient state when power is applied, a series vibration system exists between the inductance of the inductor 13 and the capacitance of the capacitor 10, and overshoot occurs.

That is, as is well known, when power is applied to a series oscillation system, the terminal voltage of the capacitor initially oscillates beyond a predetermined final value, and converges to the final value over time.

The overshoot refers to a value exceeding the final value in the above phenomenon, and in the circuit of FIG. 1, this is directly applied to the transistors 1 and 2, so there is a risk of destroying them.

In addition, when a rectified commercial power source is used as the DC power source 12, if an excessive voltage is applied to the power source compared to a steady state such as a lightning surge, an excessive voltage may be applied to the transistors 1 and 2. may be added and destroy it.

Therefore, as shown in FIG.
, the capacitor 16 is connected in series, and the capacitor 1
6 and a discharge resistor 17 connected in parallel are connected between the primary windings 8 and 9, the center tap, and the emitters of the transistors 1 and 2.

That is, with this configuration, the resistor 15
A time resistor 15 determined by the time constants of the capacitor 16 and the capacitor 16 is added to the series vibration system to put the system in a slow braking state and reduce overshoot.

When a predetermined period of time has passed and a stable oscillation state has been reached, the capacitor 16 is charged with the entire voltage between the center taps of the primary windings 8 and 9 and the emitters of the transistors 1 and 2, so the resistor 15 Almost no power loss occurs.

Further, since the resistor 17 is a discharge resistor of the capacitor 16 after the power supply is removed, there is almost no power loss.

Furthermore, even if an excessive power supply voltage is applied for a short period of time due to a lightning surge, this voltage is absorbed by the inductor 13 and capacitor 16, and has the function of preventing the voltage applied to the transistors 1 and 2 from increasing. , the larger the capacitance of the capacitor 16, the greater the effect of suppressing the voltage applied to the transistors 1 and 2.

However, in this case, if the capacitance of the capacitor 16 is made too large, the charging current of the capacitor 16 via the inductor 13 becomes large until the power switch 11 is turned on and the state shifts to a stable oscillation state. saturation occurs, and at this time transistors 1 and 2
When the transistors become conductive at the same time, the current flowing through the transistors 1 and 2 becomes excessive, and the current may be destroyed.

In addition, as shown in FIG. 3, there is a device in which a Zener diode 18, which is a voltage suppressing element, is connected between the terminals 450. In this case, when the power is turned on or when there is an excessive input, the voltage between the terminals 490 is suppressed to that Zener voltage, and the transistor 1 , 2 can be prevented from being applied with excessive voltage.

However, if the Zener voltage is not made larger than the peak value of the voltage applied between the terminals 450 in a stable oscillation state, current will flow through the Zener diode 18, causing power loss. At the time of power-on and excessive input, the voltage applied to transistors 1 and 2 cannot be suppressed.

That is, the Zener voltage needs to be set within a narrow range, making it difficult to manufacture or manually manufacture such a Zener diode 18.

The present invention solves the above problems, and its feature is that the DC power source on the primary winding side of the oscillation transformer is connected to the secondary winding side via a pair of switch elements that conduct alternately. In an inverter circuit configured to be supplied as a power source, a series circuit of a capacitor and a voltage suppressing element is connected between terminals of the DC power source via a forward diode, and a discharge resistance of the capacitor is provided. .

Hereinafter, the present invention will be explained according to the illustrated embodiment.
As shown in the figure, a series circuit of a capacitor 19 and a Zener diode 20 which is a voltage suppressing element is connected between the terminals of the DC power supply 12, that is, between the terminals 450 via a forward diode 21, and a discharge resistor 22 is connected to the capacitor 19. are connected in parallel, and the Zener voltage of the Zener diode 20 is set lower than the peak value of the voltage applied between the terminals 450 in a stable oscillation state.

Next, the operation will be explained.

In steady state, capacitor 19 is charged to the peak value of the voltage across terminals 490 minus the zener voltage of zener diode 20.

However, this Zener voltage is the terminal I. If the voltage is higher than the daily voltage, the capacitor 19 will not be charged.

When an excessive voltage is applied for a short time, the voltage between the terminals 450 is suppressed to the sum of the voltage across the capacitor 19 and the Zener voltage, and the magnitude of the Zener voltage has no relation to the voltage to be suppressed.

Moreover, the voltage charged in the capacitor 19 is lower than that in the conventional case (FIG. 2) because of the presence of the Zener diode 20, and as a result, the charging current through the inductor 13 when the power is turned on is reduced, and therefore the voltage charged in the capacitor Even if the capacitance of the inductor 19 is increased, the core of the inductor 13 will not be saturated and no inconvenience will occur.

Further, the Zener voltage only needs to be lower than the peak value of the voltage between the terminals 450, and its setting range is widened, making it easier to manufacture or obtain the Zener diode 20.

Although the Zener diode 20 is used as the voltage suppressing element in the above embodiment, an avalanche diode, a variass, etc. may be used instead.

□Also, as shown in Fig. 5, the discharge resistor 20 is a diode 2.
1 may be connected in parallel, and in this case, when the voltage between the terminals 170 becomes low, discharge occurs in a loop shown by arrow a.

Furthermore, in the embodiment, a transistor 1 is used as a switch element.
, 2 are used, but a semiconductor switch such as a GTO thyristor may also be used.

According to the present invention, a series circuit of a capacitor and a voltage suppressing element is connected between the terminals of a DC power supply via a forward diode, and a discharge resistance of the capacitor is provided.
This capacitor and voltage suppression element can suppress the output voltage of the DC power supply, reduce overshoot when power is applied, and prevent excessive power supply voltage from being applied to the switch element even if it is applied for a short period of time due to lightning surges, etc. Voltage can be suppressed.

Furthermore, since the charging current of the capacitor can be suppressed by the voltage suppressing element, for example, even if the capacitance is increased, there will be no problem such as excessive current flowing through the switching element and damaging it.

In addition, since the operating voltage of the voltage suppressing element is set lower than the peak value between the power supply terminals in a stable oscillation state, the capacitor is normally adjusted to the difference in the operating voltage of the voltage suppressing element from the peak value between the power supply terminals. It is possible to maintain the voltage across the series circuit of the capacitor and the voltage suppression element at the voltage between the power supply terminals by keeping the capacitor and the voltage suppressing element in a charged state. By reacting extremely sensitively, the above-mentioned excessive voltage can be suppressed very effectively.

Furthermore, the voltage between the power supply terminals is pulsating due to circuit oscillation, with alternating current being superimposed on direct current. With the direction diode and discharge resistance,
It is possible to suppress as much as possible an increase in power loss due to current flowing through the voltage suppressing element by suppressing the voltage with a large time constant and making it gentle.

Moreover, since the operating voltage of the voltage suppressing element can be made lower than the voltage between the power supply terminals as described above, there is no problem such as difficulty in manufacturing or obtaining the voltage suppressing element.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams showing conventional examples, FIG. 4 is a circuit diagram showing one embodiment of the present invention, and FIG. 5 is a circuit diagram showing another embodiment. 1.2...Transistor, 6...Oscillating transformer, 7...Secondary winding, 8,9...
・Primary winding, 12...DC power supply, 19...
... Condenser, 20 ... Zener diode, 21 ... Diode.

Claims (1)

[Scope of utility model registration request] In an inverter circuit configured to supply DC power on the primary winding side of an oscillation transformer as AC power to the secondary winding side via a pair of switch elements that are alternately conductive, between the terminals of the DC power supply, A series circuit of a capacitor and a voltage suppression element is connected through a forward diode, and the operating voltage of the voltage suppression element is set lower than the peak value between the power supply terminals in a stable oscillation state, and the capacitor is discharged. An inverter circuit characterized by being equipped with a resistor.