JP3268672B2 - Inverter drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter driving circuit used for driving a half bridge or a full bridge for generating a high frequency signal for lighting a neon tube, for example.

[0002]

2. Description of the Related Art A small-capacity half-bridge inverter is shown in FIG.
Shown in A full-wave rectifier circuit 13 is connected between the AC power input terminals 11 and 12, a series circuit of capacitors 14 and 15 is connected between outputs of the rectifier circuit 13, and a series circuit of FETs 16 and 17 as switching elements is connected. Is done. The connection point of the capacitors 14 and 15 and the FETs 16 and 1
The primary coil of the output transformer 18 is connected to a connection point between the output transformer 18 and the power supply 7. A parallel circuit of a capacitor 19 and a resistor 21 is connected between both ends on the output side of the full-wave rectifier circuit 13. Further, the positive side of the capacitor 19 is connected to the power supply terminal of the IC 22 of the switching regulator, and the negative side is connected to the ground terminal. A capacitor 23 and a Zener diode 20 are connected in parallel between a power supply terminal and an earth terminal of the IC 22. The switching output of the IC 22 is supplied to the pulse transformer 2 through the capacitor 25.
4 is connected to the primary side. 2 of the pulse transformer 24
Both ends of the secondary coils 26 and 27 are connected to the gates and sources of FETs 16 and 17 as switching elements, respectively.

When AC power is applied between the terminals 11 and 12 and the voltage of the capacitor 19 reaches a predetermined voltage, the voltage between the power supply terminals of the switching regulator IC 22 becomes a voltage determined by the Zener diode 20 and the IC 22 oscillates, and the pulse transformer From 24, the FET 26 is turned on by the rising pulse of the input rectangular wave signal, the FET 27 is turned on by the falling pulse, and the FETs 26 and 27 are turned on alternately. Discharge occurs, and AC power is output from the output transformer 18. This output transformer 1
8 is provided with a third winding 28, the output of which is
22 to supply power to the IC 22.

[0004]

In the conventional inverter driving circuit, the pulse transformer 24 may be saturated at the time of starting, and as a result, the output amplitude of the driving signal becomes unstable for several cycles at the time of starting, and the driving circuit Do not turn on the main power supply until 10 or more cycles after start-up. It is necessary to turn on the main power supply after the transmission is stabilized, or to gradually raise the main power supply voltage. However, there is a problem that an auxiliary circuit is required for the main circuit.

[0005] As a result of pursuing the reason for the problem that the amplitude of the drive signal becomes unstable at the start of transmission, it has been found that the cause is as follows. That is, FIG. 3A shows a connection relationship between a part of the internal configuration of the switching regulator IC 22 and the pulse transformer 24. The capacitor 23 is charged by the constant current I by the switching oscillation operation, and the capacitor 23 is discharged by twice I,
Accordingly, the output transistor 31 is connected to the capacitor 2
5. A current flows in one direction of the pulse transformer through the primary side of the pulse transformer 24, and then the output transistor 32 is turned on, and a current flows from the pulse transformer 24 through the capacitor 25 through the transistor 32.

The charging and discharging of the capacitor 25 are alternately repeated as described above. In the steady state, the operation is performed in this manner, and pulses having the same amplitude are applied to the pulse transformer 24 alternately in the positive and negative directions. However, at startup, the capacitor 25
Since there is no charge in the capacitor 25, a charging current for the capacitor 25 also flows. That is, as shown in FIG. 3B, a rectangular wave output having the same amplitude is generated on the positive and negative sides from the oscillation output terminal of the IC 22, which is a connection point of the transistors 31 and 32, but the charging current for the capacitor 25 is superimposed and flows. As shown in FIG. 3C, the voltages V ₁ and V ₂ induced in the secondary coils 26 and 27 of the transformer 24 have positive and negative amplitudes smaller than the amplitude of the oscillation output and are biased. That is, a charging current flows to the capacitor 25, and at this time, the voltage Vc between both ends of the capacitor 25 fluctuates as shown in FIG. 3E, and the oscillation output is superimposed thereon. As described above, the amplitude of the rectangular wave pulse applied to the pulse transformer 24 is small and the average level thereof is fluctuated. However, in the state shown by the dotted line in FIG. 3C, the FETs 16 and 17 are not turned on alternately, respectively.
Are not turned on at the places marked with a cross in two-point diagonal lines. For this reason, positive and negative currents do not flow alternately through the pulse transformer 24, the core of the pulse transformer 24 is demagnetized and saturated, an excessive current flows, and F
ET16 and 17 could be destroyed.

Therefore, conventionally, the main power supply is turned on for one
It has been troublesome to do this after several cycles or to gradually raise the main power supply voltage.

[0008]

According to the present invention, a voltage dividing resistor is connected between the positive and negative power supply terminals of the oscillation circuit, and the voltage dividing point is inserted between the oscillation circuit and the pulse transformer. The capacitor is connected to the opposite side of the pulse transformer, that is, to the oscillation circuit side. Therefore, when the voltage is started to be supplied to the oscillation circuit, the capacitor 25 is also charged through the voltage dividing circuit at the same time. Therefore, when the oscillation circuit becomes normal and operates, the charging current to the capacitor 25 stops flowing and the capacitor 25 stably operates. It works.

[0009]

FIG. 1 shows an embodiment of the present invention, and FIGS.
The same reference numerals are given to portions corresponding to. In the present invention, an oscillation circuit, that is, a switching regulator IC
A voltage dividing circuit composed of resistors 35 and 36 is connected between both ends of the power supply terminal 22, that is, both ends of the capacitor 23, and the voltage dividing point is connected to the side of the capacitor 25 opposite to the pulse transformer 24. A current limiting resistor 37 is connected in series between the voltage dividing resistors 35 and 36 and the capacitor 25 as necessary. Further, in this embodiment, the output side of the oscillation circuit 22 is short-circuited to the ground while the oscillation is stopped, that is, the oscillation circuit 22 is connected between the fourth terminal and the ground terminal by, for example, the switch 8. When turned on, the operation is stopped. In this state, the second and third terminals on the output side of the oscillation circuit 22 are short-circuited, that is, the output terminal of the oscillation circuit 22 is in a low level state. When the switch 38 is turned off, the oscillation circuit 22 starts oscillating. In this state, the oscillation circuit 22
Is output from a high level.

In the case of the oscillation circuit 22, such a relationship is established. Therefore, even if the capacitor 25 is charged before the oscillation starts, a current flows from the voltage dividing point of the voltage dividing circuit through the oscillation circuit 22. It flows and cannot be charged. Therefore, in this example, the SCR 39 is connected between both ends of the capacitor 23 via the resistor 45,
A parallel circuit of a resistor and a capacitor is connected between the gate and the cathode of the oscillator 39.
A diode 41 and a resistor 42 between the gate of the CR 39
, And the anode side of the diode 41 is the output side of the oscillation circuit 22. A diode 43 is connected between the output side of the oscillation circuit 22 and the connection point of the resistors 35 and 36, and the anode side of the diode 43 is the output side of the oscillation circuit 22. A transistor 44 is connected between the anode and the cathode of the diode 43, and the collector of the transistor 44 is connected to the cathode of the diode 43. That is, the diode 43 and the transistor 44 have polarities opposite to each other. And to the emitter.

In this manner, when the power supply is off, the SCR 39 is off, so that the transistor 44
Is also off, and when charging of the capacitor 23 is started, the capacitor 25 is charged through the resistor 35 according to the voltage of the capacitor 23. In this manner, the capacitor 25 is charged with half the voltage between both ends of the capacitor 23. When the oscillation circuit 22 is started in this state, its output terminal outputs a rectangular oscillation from a high level. Therefore, when the oscillation output becomes positive, the SCR 39 is turned on, whereby the transistor 44 is turned on.
Is also turned on. When the output of the oscillation circuit 22 is positive, a current flows to the ground through the diode 43, the capacitor 25, and the pulse transformer 24. When the output of the oscillation circuit 22 becomes negative, the current flows from the ground through the pulse transformer, the capacitor 25, and the transistor 44. A current flows to the output terminal side of the oscillation circuit 22 through the output terminal.

In this case, when the charge to the capacitor 25 rises as shown in FIG. 1B and oscillation starts, for example, a positive voltage is applied to the gates of the FETs 16 and 17 alternately as shown in FIGS. That is, although the width is wide by one pulse from the start to the reaching of the specified voltage, the FETs 16 and 17 are alternately turned on and off with a predetermined width thereafter. Therefore, there is no fear that the pulse transformer 24 is demagnetized.

If the output of the oscillation circuit 22 is a tri-state output and the impedance viewed from the output side in the oscillation circuit becomes infinite in the oscillation stop state, the SCR 39, the diode 43, the transistor 45 Etc. can be omitted.

[0014]

As described above, according to the present invention, a capacitor connected in series with a pulse transformer is automatically charged in advance, so that a signal is turned on or off while a main circuit voltage is applied. That is, the oscillation circuit can be started and stopped, so that the main circuit can be simplified. In addition, the start and stop of the oscillation circuit from the outside need only be controlled by the drive signal circuit. That is, it is not necessary to delay the power supply to the main circuit by more than ten cycles or to perform the trouble of gradually raising the power supply voltage of the main circuit in the related art.

[Brief description of the drawings]

FIG. 1A is a connection diagram showing an embodiment of the present invention, and FIGS.
FIG. 5 is a diagram showing the voltage of the capacitor 25 and the output voltage waveform of the pulse transformer.

FIG. 2 is a diagram illustrating a simplified configuration example of a half-bridge inverter.

3A is a diagram showing a connection state between a part of the inside of an oscillation circuit 22 and a pulse transformer 24, and FIGS. 3B to 3E are a transmission output at the time of rising of the oscillation circuit, a pulse transformer output, and a voltage between both ends of a capacitor 25. FIG.

Claims (1)

(57) [Claims] A positive current and a negative current alternately flow to the primary side of a pulse transformer via a capacitor by an output of an oscillation circuit, and an output pulse of the pulse transformer turns on and off a switching element of a bridge type inverter. In the inverter driving circuit to be controlled, a voltage dividing resistor is connected between the positive and negative power supply terminals of the oscillation circuit, and a connection point of the voltage dividing resistor is connected to a side of the capacitor opposite to the pulse transformer. Characteristic inverter drive circuit.