JPH06188084A - Inverter drive circuit - Google Patents

Abstract

PURPOSE:To provide stable start-up in a simple constitution at the time of starting. CONSTITUTION:In an oscillation circuit 22 a second terminal and a third terminal are internally connected with an oscillation stop condition to set an output at a low level. The second terminal is connected to resistances 35, 36 through a diode 43. A capacitor 23 is charged, while half a voltage is charged to a capacitor 25. When an oscillation circuit 22 is started to output high levels and low levels alternately, and an SCR 39 is put on through a diode 41 to get a transistor 45 on. By a positive output of the oscillation circuit, a current flows from the second terminal to a pulse transformer 24, and by a negative output, the current flows from the pulse transformer 24 to the second terminal. Since the capacitor 25 is at a stationary condition voltage at the time of starting, a trigger signal of a correct amplitude is given from the pulse transformer to a switching element of an inverter to get on and off alternately necessarily, thereby possibility of deflected magnatization of the pulse transformer is eliminated.

Description

Detailed Description of the Invention

[0001]

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

[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 supply input terminals 11 and 12, and a series circuit of capacitors 14 and 15 is connected between the outputs of the rectifier circuit 13 and a series circuit of FETs 16 and 17 as switching elements. To be done. Connection points of capacitors 14 and 15 and FETs 16 and 1
The primary coil of the output transformer 18 is connected to the connection point with 7. A parallel circuit of a capacitor 19 and a resistor 21 is connected across 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. The capacitor 23 and the Zener diode 20 are connected in parallel between the power supply terminal and the ground terminal of the IC 22. The switching output of the IC 22 is passed through the capacitor 25 to the pulse transformer 2
4 is connected to the primary side. Pulse transformer 24-2
Both ends of the next coils 26 and 27 are connected to the gates and sources of the 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 terminal grounds of the switching regulator IC 22 becomes a voltage determined by the Zener diode 20, and the IC 22 oscillates to cause a pulse transformer. The FET 26 is turned on by the rising pulse of the input rectangular wave signal from 24, the FET 27 is turned on by the falling pulse, and the FETs 26 and 27 are alternately turned on, so that the capacitors 14 and 15 alternately pass through the output transformer 18. After discharging, 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 IC
22 to supply power to the IC 22.

[0004]

In this conventional inverter drive circuit, the pulse transformer 24 may be saturated at the time of start-up, and as a result, the drive signal output amplitude becomes unstable for several cycles at the time of start-up. It is necessary to turn on the main power supply until the transmission is stable or to gradually raise the main power supply voltage without turning on the main power supply until 10 or more cycles after the startup. In the latter case, the control unit is simple. However, there was a problem that an auxiliary circuit was required for the main circuit.

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

In this way, charging / discharging of the capacitor 25 is alternately repeated. In the steady state, the operation is performed in this way, and pulses of the same amplitude are alternately applied to the pulse transformer 24 in the positive and negative directions. However, at startup, the capacitor 25
Since there is no electric 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 the connection point of the transistors 31 and 32, but a pulse is generated because the charging current for the capacitor 25 flows in a superimposed manner. The voltages V ₁ and V ₂ respectively 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 as shown in FIG. 3C. That is, the charging current for the capacitor 25 flows, and at this time, the voltage Vc across the capacitor 25 fluctuates as shown in FIG. 3E, and the oscillation output is superimposed on this. In this way, the amplitude of the rectangular wave pulse applied to the pulse transformer 24 is small, and the average level of the rectangular wave pulse fluctuates. Therefore, driving of the FETs 16 and 17 as switching elements is performed by, for example, the threshold voltage. In the state shown by the dotted line in FIG. 3C, the FETs 16 and 17 do not turn on alternately, and
The part marked with a cross with a two-dot diagonal line is not turned on. For this reason, positive and negative currents do not flow alternately to the pulse transformer 24, the iron core of the pulse transformer 24 is demagnetized and saturated, an excessive current flows, and the F
There was a risk of destroying ET16 and ET17.

Therefore, in the past, the main power supply was turned on once.
Some troublesome things have been done after a few cycles or gradually raising the main power supply voltage.

[0008]

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

[0009]

FIG. 1 shows an embodiment of the present invention, and FIGS.
The same symbols are attached to the portions corresponding to. In the present invention, the oscillation circuit, that is, the switching regulator IC
A voltage dividing circuit including resistors 35 and 36 is connected between both ends of the power supply terminal 22 of the capacitor 22, that is, both ends of the capacitor 23, and the voltage dividing point is connected to the opposite side of the pulse transformer 24 of the capacitor 25. If necessary, a current limiting resistor 37 is connected in series between the voltage dividing resistors 35 and 36 and the capacitor 25. Further, in this embodiment, the output side of the oscillation circuit 22 is short-circuited to the ground in the oscillation stopped state, that is, the oscillation circuit 22 is provided with, for example, the switch 8 between its 4th terminal and the ground terminal. When turned on, the operation is stopped, and in this state, the output side terminals of the oscillation circuit 22 are short-circuited with the second and third terminals, that is, the output terminal of the oscillation circuit 22 is in the low level state. When the switch 38 is turned off, the oscillating circuit 22 starts oscillating operation.
The output of will be output from the high level.

Since the oscillator circuit 22 has such a relationship, 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 inside of the oscillator circuit 22. It will flow and you will not be able to charge it. Therefore, in this example, the SCR 39 is connected across the capacitor 23 via the resistor 45, and the SCR 39 is
A parallel circuit of a resistor and a capacitor is connected between the gate and the cathode of 39, and the output terminal of the oscillation circuit 22 and S
Diode 41 and resistor 42 between the gate of CR39
Are connected in series, 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 oscillator 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 oscillator circuit 22. A transistor 44 is connected between the anode and the cathode of the diode 43, the collector of the transistor 44 is on the cathode side of the diode 43, that is, the polarities of the diode 43 and the transistor 44 are opposite to each other, and the base of the transistor 44 is SCR39. Is connected to the cathode side and is also connected to the emitter.

Thus, when the power supply is off, SCR 39 is off and therefore transistor 44 is
Is off, and when charging of the capacitor 23 is started, the capacitor 25 is charged through the resistor 35 in accordance with the voltage of the capacitor 23. In this way, the capacitor 25 is charged with half the voltage across the capacitor 23. When the oscillator circuit 22 is activated in this state, its output terminal outputs a rectangular oscillation from a high level, and therefore, when the oscillation output becomes positive, the SCR 39 is turned on, which causes the transistor 44 to operate.
Is also turned on. When the output of the oscillating circuit 22 is positive, a current flows to the ground side through the diode 43, the capacitor 25, and the pulse transformer 24. When the output of the oscillating circuit 22 becomes negative, from the ground side through the pulse transformer, the capacitor 25, and the transistor 44. A current flows through the output terminal side of the oscillation circuit 22 through the.

In this case, when the charging of the capacitor 25 rises as shown in FIG. 1B and oscillation starts, a positive voltage is alternately applied to the gates of the FETs 16 and 17 as shown in FIGS. 1C and 1D. Then, the width is wide by one pulse from the start up to reach the specified voltage, but thereafter, the FETs 16 and 17 are alternately turned on and off with a predetermined width. Therefore, the pulse transformer 24 is not likely to be demagnetized.

If the output of the oscillation circuit 22 is a tri-state output and the impedance seen from the output side of the oscillation circuit is infinite when the oscillation is stopped, the SCR 39, the diode 43, and the transistor 45 are provided. Etc. can be omitted.

[0014]

As described above, according to the present invention, since the capacitor connected in series with the pulse transformer is automatically charged in advance, the signal is turned on or off while the main circuit voltage is applied. That is, the oscillation circuit can be started and stopped, the main circuit can be simplified, and the oscillation circuit can be started and stopped from the outside by controlling only the drive signal circuit. In other words, conventionally, it is not necessary to delay the power-on of the main circuit by ten or more cycles or to gradually increase the power supply voltage of the main circuit.

[Brief description of drawings]

FIG. 1A is a connection diagram showing an embodiment of the present invention, and FIGS.
FIG. 4 is a diagram showing the voltage of the capacitor 25 and the output voltage waveform of the pulse transformer.

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

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

Claims (1)

[Claims] 1. A positive current and a negative current are alternately flowed to the primary side of a pulse transformer through a capacitor by the output of the oscillation circuit, and the switching element of the bridge type inverter is turned on and off by the output pulse of the pulse transformer. In the controlled inverter drive circuit, a voltage divider resistor is connected between the positive and negative power supply terminals of the oscillator circuit, and the connection point of the voltage divider resistor is connected to the opposite side of the capacitor from the pulse transformer. Characteristic inverter drive circuit.