JPH05316740A - Inverter - Google Patents

Abstract

PURPOSE:To improve the efficiency of an inverter, by driving in a constant- current manner the emitters of the switching transistors of a Royer oscillation circuit with the collector output of the output transistor of an IC for controlling a DC-DC converter. CONSTITUTION:Constant-current control of the discharge current of a cold- cathode discharge tube 31, which is the load of an inverter, is performed by making the average value of the switching currents of switching transistors 11, 12 of a Royer oscillation circuit variable depending on the value of the discharge current. That is, the emitters of the switching transistors 11, 12 of the Royer oscillation circuit are driven via a choke coil 23 by the collector of an output transistor 113 of an IC 20 for controlling a DC-DC converter. Therefore, the average current of the Royer oscillation circuit is made low, and the discharge current is controlled in a constant-current manner. Thereby, the efficiency of the inverter is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device suitable as a power source for a load requiring current control in a wide range,
In particular, the present invention relates to an inverter device suitable as a power source for a cold cathode discharge tube capable of dimming.

[0002]

2. Description of the Related Art An inverter device is a device for converting DC power into AC power and is used in various electrical equipment as a so-called inverse conversion device. FIG. 3 is a circuit diagram showing a conventional inverter device used for a discharge tube. In FIG. 3, reference numeral 10 is a step-up transformer for a Royer oscillator circuit including a primary coil 10P, a secondary coil 10S, and a feedback coil 10F. Reference numerals 11 and 12 denote NPN-type switching operation transistors which together with the step-up transformer 10 constitute a Royer oscillation circuit. Reference numeral 13 is a capacitor for voltage resonance, and 14 is the choke coil. As a result, the collector-emitter voltage when the transistors 11 and 12 are off becomes sinusoidal, and the primary coil 1 of the transformer 10
The voltage waveform of 0P and the secondary coil 10S becomes a sine wave. The choke coil 14 is connected to the DC-DC converter described later, and the cold cathode discharge tube 31 is connected to the output side. Due to the self-oscillation of this inverter, a sinusoidal high voltage appears at the output side at a frequency of several tens of KHz,
The cold cathode discharge tube lights up. 20 is a PNP transistor 2 for switching operation which constitutes a DC-DC converter
It is an integrated circuit (IC) that controls the base circuit of No. 1 and operates as a step-down chopper circuit. This IC includes an oscillator OSC that generates a triangular wave and two operational amplifiers A for comparison.
1 and operational amplifier A2, oscillator OSC and operational amplifier A1
A PWM comparator COMP for comparing the output voltage of either A2 or A2, and an output transistor driven by this PWM comparator for driving the base of the PNP transistor 21 for switching operation. In this IC, two operational amplifiers A1 and A2 are connected to the other PWM comparator input circuit for comparison with the oscillator OSC by the PWM comparator as described above, but the output voltage of these two operational amplifiers is high. The other voltage is compared with the output of the oscillator OSC. It should be noted that the IC having the above configuration is defined as a DC-DC converter control IC here, and even if it is used for other purposes, it is called a DC-DC converter control IC as long as the internal configuration does not change. I will decide. 22 is a flywheel diode, and 23 is a choke coil. Reference numeral 24 is a capacitor, and the choke coil 23 and the capacitor 24 form an LC filter. Reference numerals 25 and 26 are capacitors and resistors for determining the oscillation frequency, and 27 to 30 are phase correction C and R elements of the operational amplifiers A1 and A2 of the DC-DC converter control IC 20. The diodes 15 and 16 are for rectifying the positive component of the discharge current flowing through the cold cathode discharge tube 31. Reference numerals 18 and 19 are resistors and capacitors which form a low-pass filter for converting the current waveform into a direct current. This filter output is the DC-DC converter control IC2.
0 is connected to the + input terminal of the operational amplifier A2. That is, a voltage proportional to the average value of the positive cycle of the discharge current is obtained across the capacitor 19, and this voltage is compared with the reference voltage inside the DC-DC converter control IC 20 by the operational amplifier A2, and the difference between the two is obtained. An output voltage proportional to the voltage is obtained. As shown in FIG. 2, this output voltage and DC-DC
A PWM comparator compares the triangular wave output of the oscillator OSC of the converter control IC 20. That is, when the discharge current increases for some reason, the output voltage of the operational amplifier A2, which serves as an error amplifier, shifts from the B line to the A line. As a result, the output of the PWM comparator changes from the C line to the D line. That is, the on-time of the PNP transistor 21 for switching operation, which is an output transistor, becomes short, the output voltage of the DC-DC converter decreases, and the power supply voltage of the Royer oscillator circuit decreases, so the discharge current decreases. Therefore, constant current control of the discharge current is possible. 32 and 33 are DC-D
This is a resistor for making the output voltage of the C converter a constant voltage. This is the secondary coil 10 of the step-up transformer 10 when the cold cathode discharge tube 31 is not connected or before discharge is started.
A resistor for detecting the output voltage of the DC-DC converter for making the voltage of S a constant voltage. The connection point of the resistors 32 and 33 is the operational amplifier A1 of the DC-DC converter control IC 20.
Is connected to the + input terminal of the negative feedback loop, and DC-D
The output voltage of the C converter is made constant. Since the outputs of the operational amplifiers A1 and A2 are OR-connected, the higher output voltage of the operational amplifiers A1 and A2 is given priority and the PWM is performed.
Input to the comparator.

[0003]

It is known that there is a limit to the power conversion efficiency of the above-mentioned conventionally used inverter device. Because efficiency = (DC
-DC converter efficiency) * (Lower circuit efficiency), and it was necessary to increase each efficiency in order to increase the efficiency. For example, the biggest cause of deterioration in the efficiency of the DC-DC converter is the PNP transistor 2 for switching operation.
1, switching loss of the diode 22, copper loss and iron loss of the choke coil 23. Therefore, these losses cannot be zero.

Therefore, the present invention is intended to eliminate the above-mentioned conventional inconveniences, and an object thereof is to improve the efficiency as much as possible and to control the current in a wide range. To provide a simple inverter device.

[0005]

In order to achieve the above-mentioned object of the present invention, the present invention alternates the direction in which a direct current supplied from a direct current power source flows by the operation of a switching element that turns on and off. In an inverter device that is converted by a conversion means to be converted into an alternating current, a negative current is fed back to a current detection means for detecting a load current flowing at an output end, and an output of the current detection means to a conversion means for turning on / off the switching element. Negative feedback means, control means for detecting an increase / decrease in the input DC power supply voltage to control the current control operation of the conversion means in the decreasing / increasing direction, and the detection value of the detecting means for detecting the load current is a predetermined value. Switching means for inputting the output of the negative feedback means to the conversion means in a larger state and operating the control means in a state where the detection value of the detection means is less than or equal to a predetermined value. To provide an inverter apparatus according to claim Rukoto.

[0006]

The chopper circuit (DC-DC converter) can be omitted by driving the emitter of the switching operation transistor of the Royer oscillator circuit with a constant current by the collector output of the output transistor of the DC-DC converter control IC, and the efficiency can be improved. Can be improved. Also,
When there is no load, input DC voltage is DC-DC by switching circuit
It is input to the converter control IC, and the action of the IC stabilizes the AC output voltage.

[0007]

An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of an inverter device when a cold cathode discharge tube is used as a load. In FIG. 1, the same parts as those shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the conventional method shown in FIG. 3, the constant current control of the discharge current of the cold cathode discharge tube is performed by varying the power supply voltage of the Royer oscillator circuit, that is, the output voltage of the DC-DC converter according to the value of the discharge current. It was done by
In the present invention, the average value of the switching currents of the switching operation transistors 11 and 12 of the Royer oscillator circuit is varied according to the value of the discharge current.
That is, the collector of the output transistor 113 of the DC-DC converter control IC 20 is connected to the switching operation transistor 1 of the Royer circuit via the inductor 23.
It is connected to 1 and 12 emitters. Diode 1
A positive cycle of the lamp current is detected by 5 and 16, and the output is converted into a direct current by a low-pass filter including a resistor 18 and a capacitor 19, and then the output is I- for DC-DC converter control.
It is input to the + input terminal of the operational amplifier A2 of C20. That is, a voltage proportional to the average value of the positive cycle of the discharge current is obtained across the capacitor 19, and this voltage and DC-
The reference voltage inside the DC converter control IC 20 is compared by the operational amplifier A2, and an output voltage proportional to the voltage difference between the two is obtained. As shown in FIG. 2, this output voltage and the oscillator OSC of the DC-DC converter control IC 20
The triangular wave output of is compared with the PWM comparator. That is, when the discharge current increases for some reason, the output voltage of the operational amplifier A2 shifts from the B line to the A line. As a result, the output of the PWM comparator changes from the C line to the D line. That is, the output transistor 11
On-time of 3 becomes narrow. The collector of the output transistor 113 drives the emitters of the switching operation transistors 11 and 12 of the Royer oscillator circuit via the choke coil 23. That is, the average current of the Royer oscillator circuit is reduced, and the discharge current is controlled by constant current control. The diode 22 is for returning the magnetic energy when the current of the inductor 23 is off to the input power source side.

A resistor 132 connected to the DC input terminal,
133 is provided to detect the input DC voltage in order to make the voltage of the primary coil 10P of the step-up transformer 10 constant when the cold cathode discharge tube 31 is not connected or before the discharge tube starts discharging. Has been. Resistors 132 and 133
Is connected to the + input terminal of the operational amplifier A1 of the DC-DC converter control IC 20, and the voltage of the secondary coil 10S of the step-up transformer 10 is constant regardless of the value of the input DC voltage. Turn into. The collector of the switching transistor 124 is a DC-DC converter control I
It is connected to the + input terminal of the operational amplifier A1 of C20.

When the cold cathode discharge tube 31 is not connected or before the discharge is started, the switching transistor 124 is off because the voltage across the capacitor 19 is 0 volt. Therefore, the resistors 132 and 133, the operational amplifier A1
DC-DC converter control IC2 by negative feedback by
The ON time of the output transistor 113 of 0 is constant regardless of the input DC voltage. When the cold cathode discharge tube 31 is connected and the discharge current is flowing, the switching transistor 124 is turned on by setting the voltage of the capacitor 19 to 0.7 V or more, and the constant voltage operation by the resistors 132 and 133 is performed. Only the constant current control by the operational amplifier A2 is performed. The voltage for this switching is the variable resistor 17
Can be adjusted freely.

[0011]

As described in detail above, in the inverter device according to the present invention, the DC-DC converter can be omitted from the conventional device, and the inverter device is provided in the DC-DC converter control IC. Since the output transistor drives the emitter of the switching operation transistor of the Royer oscillator circuit, the switching loss can be suppressed low, and the loss of the entire Royer oscillator circuit can be reduced. Since the choke coil is also connected to the emitter of the Royer oscillator circuit, the voltage applied to the inductor is reduced, and as a result, the core loss is reduced. Therefore, the overall efficiency can be improved as compared with the conventional circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter device according to the present invention.

FIG. 2 is a characteristic diagram showing operating characteristics of the inverter device.

FIG. 3 is a circuit diagram of a conventional inverter device.

[Explanation of symbols]

10 ... Step-up transformer 10P ... Primary coil 10S ... Secondary coil 10F ... Feedback coil 11 ... NPN type switching operation transistor 12 ... NPN Type switching actuating transistor 13-Capacitor 14-Choke coil 15-Diode 16-Diode 17-Variable resistor 18- Resistor 19 ... Capacitor 20 ... DC-DC converter control IC A1 ... Operational amplifier A2 ... Operational amplifier COMP ... PWM comparator 21 ... Switching PNP transistor for operation 22. Flywheel diode 23. Choke coil 24. Capacitor 25. Capacitor 26 ... resistor 31 ... cold cathode discharge tube 32 ... resistor 33 ... resistor 113 ... output transistor 124 ... switching transistor 132 ... resistor 133 ... resistor

Claims (3)

[Claims] 1. A load flowing to an output terminal in an inverter device for converting a direct current supplied from a direct current power source into an alternating current by converting the flowing direction by an operation of a switching element which is turned on and off alternately. Current detecting means for detecting a current, negative feedback means for negatively feeding back the output of the current detecting means to a converting means for turning on / off the switching element, and the converting means for detecting an increase / decrease in an input DC power supply voltage. Control means for controlling the current control operation in the decreasing / increasing direction, and the output of the negative feedback means is input to the converting means in a state where the detection value of the detecting means for detecting the load current is larger than a predetermined value, and the detecting means An inverter device comprising: a switching unit that operates the control unit when a detected value is equal to or less than a predetermined value. 2. The switching means for alternately switching the direction of the direct current flowing by the operation of the switching element which is turned on and off is a Royer oscillator circuit.
The described inverter device. 3. The inverter device according to claim 1, wherein the load of the inverter device is a cold cathode discharge tube.