JPH04295281A - Inverter control circuit - Google Patents

Abstract

PURPOSE:To suppress the ripple of the lamp current of a discharge lamp by the dispersion of the property of the switching element in the analog control circuit of a discharge lamp triggering circuit. CONSTITUTION:The switch control signal between a gate and a source is controlled by feeding the signal T2 between a drain and a source back to a PWM circuit 1, and counting data in the period of the signal T2, which becomes high during ON because of the variation of the characteristics of bipolar transistors, with slow clock, and also, counting data in the OFF period of the signal T2 with quick clock.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control circuit mainly used in a discharge lamp lighting circuit.

0002

[Prior Art] A conventional inverter control circuit for controlling a load circuit, particularly a discharge lamp lighting circuit, has at least one series circuit of a pair of switching elements connected between both ends of a DC power supply. A circuit is known that includes a control circuit that alternately turns on and off to supply an alternating current to a load circuit connected to a connection point between the pair of switching elements. A digital control circuit for the inverter is composed of a microcomputer that stores a control program configured to turn one switching element in each series circuit off and then turn on the other switching element, and a digital PWM circuit. A control signal is generated from

As shown in FIG. 3, the digital PWM circuit includes a data latch circuit 4 that holds control data from a microcomputer, and generates a switch control signal that controls the on/off frequency of a switching element based on the control data. It is configured mainly around counter circuits 5. A high frequency voltage generated by alternately turning on and off the switching elements of the load main circuit 2 in response to a switch control signal from the digital PWM circuit 7 side is applied to the discharge lamp to light the discharge lamp. In the digital PWM circuit 7 of FIG. 3, when the drain-source voltage increases, the gate-source voltage is reduced by that amount, and the on time becomes shorter.

In contrast to the digital PWM circuit 7 shown in FIG. 3, there is a monostable multi-circuit PWM circuit 8 shown in FIG. It detects and outputs an on-pulse with a constant width.In order to keep the on-time constant, variations in the off-time, that is, when the signal between the drain and source is high, directly affect the oscillation period, resulting in frequency variations. becomes larger.

Due to variations in the storage time of the bipolar transistor used as one of the switching elements on the load main circuit 2 side in FIG. 3, the switch control signal fluctuates, resulting in large fluctuations in the lamp current. That is, when the on period of the bipolar transistor becomes longer due to variations in the characteristics of the bipolar transistor, as shown in (a) of FIG. Since the period T3 where the gate-source signal voltage is high does not change, in the conventional circuit diagram 3, the on-state of the bipolar transistor changes significantly and the lamp current fluctuates. In other words, as the on period of the bipolar transistor of the switching element increases, the lamp current of the discharge lamp decreases.

[0006]

[Problems to be Solved by the Invention] As a countermeasure to this problem, the conventional analog control circuit shown in FIG. 7 detects the drain-source signal that becomes high when the bipolar transistor Q1 is turned on and uses it as the ON correction signal S1, as shown in FIG. , the switch control signal is controlled by slowly charging the capacitor C of the oscillation circuit during the period in which the ON correction signal S1 is high, and charging and discharging at a high speed in the period when the ON correction signal S1 is low. The width of this ON correction signal S1 is designed to increase as the ON period of the bipolar transistor Q1 becomes longer, so that the period where the gate-source voltage is high becomes longer and the ramp current is controlled in the direction of increasing. become. Therefore, the lamp current is held constant even if there are variations in the characteristics of the parts. However, analog circuits have a large number of parts, so there is a problem that the characteristics of the circuit parts vary, making it necessary to carefully select parts with high precision. An inverter control circuit according to the present invention aims to eliminate the problems of the analog control circuit of a discharge lamp lighting circuit as described above and to suppress fluctuations in lamp current due to variations in characteristics of switching elements.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the inverter control circuit according to the present invention feeds back the drain-source signal voltage to the PWM circuit to reduce the drain voltage which increases when turned on due to variations in the characteristics of the bipolar transistor. - The switch control signal of the gate-source voltage is set to be controlled by counting the source voltage section with a slow clock and counting the off section of the drain-source voltage with a fast clock.

[0008]

[Operation] In the inverter control circuit according to the present invention, the gate-source signal voltage for controlling the lamp current for lighting the discharge lamp is determined by the drain-source signal voltage from the switching element side. However, in order to suppress fluctuations in the lamp current due to variations in the characteristics of the bipolar transistors used as switching elements, the control data from the microcontroller is counted using a slow clock for the drain-source signal. At the same time, the off period of the drain-source signal is counted using a fast clock. The remaining portion counted using the slow clock is then counted using the fast clock, thereby sending out the corrected portion and controlling the gate-source signal. In addition, during the period in which counting is performed using a slow clock, in order to prevent the switching elements from turning on at the same time, the signal is output through the drain-source voltage and the AND circuit, so the gate-source signal is in the off state, and the bipolar transistor's signal is turned off. To maintain a constant lamp current of a discharge lamp regardless of variations in characteristics.

[0009]

[Embodiment] An embodiment of the inverter control circuit according to the present invention is shown in FIG. 1. In contrast to the conventional PWM circuit 7 shown in FIG. The circuit configuration is different, and the other circuit configurations are similar to the conventional circuit configuration. The ON correction section 6 outputs the drain-source voltage T2 of the feedback signal shown in FIG. A signal is obtained.

The gate-source signal that controls the lamp current for lighting a discharge lamp is controlled by feeding back the drain-source signal from the switching element side to the control circuit. In order to suppress fluctuations in the lamp current due to variations in the characteristics of the bipolar transistors in use, the control data from the microcomputer 3 is counted using the slow clock as the drain-source signal T2 of the feedback signal, and the drain-source signal T2 is T2
The gate-source signal is controlled by counting with a fast clock during the off-period. By counting the remaining portion counted using the slow clock using the fast clock, the correction portion T4 shown in FIG. 2 is sent out to control the gate-source signal. Note that during the period in which counting is performed using a slow clock, the gate-source signal is in an OFF state because it is output through the AND circuit with the drain-source signal in order to prevent the switching elements from being turned on simultaneously. Therefore, the lamp current of the discharge lamp can be held constant regardless of variations in the characteristics of the bipolar transistors.

[0011]

Effects of the Invention The inverter control circuit according to the present invention can be used in an inverter device that lights a discharge lamp at high frequency by alternately turning on and off both switching elements inserted between both ends of a DC power source. One of the switching elements is driven in synchronization with the current flowing in the load main circuit or the generated voltage, and the other switching element is turned on for a predetermined period of time after the one switching element turns off. It is equipped with a digital PWM circuit that is driven to operate, and the digital PWM circuit controls fluctuations in the output current flowing through the load main circuit in response to fluctuations in the ON period of the switching element based on variations in the one switching element. Since the present invention is equipped with a correction means for controlling the on period of the one switching element in such a manner as to suppress can be suppressed. Furthermore, unlike conventional analog circuits, there is no need to increase the number of parts or use high-precision parts, making it possible to obtain an extremely economical inverter control circuit. .

[Brief explanation of drawings]

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

FIG. 2 is an explanatory diagram of the operating state same as above.

FIG. 3 is a circuit diagram in which a digital control section is added to a conventional inverter control circuit.

FIG. 4 is a diagram illustrating the operating state of the same as above.

FIG. 5 is a monostable multi-type PWM circuit diagram.

FIG. 6 is a diagram illustrating the operating state of the same as above.

FIG. 7 is a circuit diagram in which an analog control section is added to a conventional inverter control circuit.

FIG. 8 is a diagram illustrating the operating state of the same as above.

[Explanation of symbols]

1 PWM circuit 2 Load main circuit 3. Microcomputer 4 Data latch circuit 5 Counter circuit 6 On-correction circuit

Claims (1)

[Claims] 1. At least one circuit is provided with a series circuit of a pair of switching elements inserted between both ends of a DC power source and repeating an on-off operation alternately, and a connection point between both of the pair of switching elements and the In an inverter control circuit that supplies high-frequency power to a load main circuit connected between one end of a DC power supply, one switching element of the pair of switching elements is synchronized with the current flowing in the load main circuit or the generated voltage. The other switching element includes a digital PWM circuit that is driven to turn on for a predetermined period of time after the one switching element turns off. It is characterized by comprising a correction means for controlling the on-period so as to suppress the fluctuation of the output current flowing through the load main circuit with respect to the fluctuation of the on-period due to the variation in the characteristics of the one switching element. Inverter control circuit.