Auto-excitation type electronic ballast with over-temperature protection function

Abstract

The invention relates to a self-excited type electronic ballast with overtemperature protection, which comprises rectifying filter circuits in series, a half-bridge drive circuit and an output circuit. An overtemperature protection circuit is connected between the output circuit and the half-bridge drive circuit. In the overtemperature protection circuit, the collecting electrode and the emitting electrode of a triode are connected with the collecting electrode and the emitting electrode of a triode in the half-bridge drive circuit in parallel while the base electrode of the triode is connected with a unidirectional controllable silicon cathode which is connected with a starting capacitor. The triggering terminal of the unidirectional controllable silicon is connected with the output terminal of an overtemperature detecting circuit by a bilateral diode. An inductance secondary winding, a diode, a thermal resistor and a voltage divider resistance are connected in series to form the overtemperature detecting circuit. The common terminal of the thermal resistor and the voltage divider resistance is connected with the input terminal of the bilateral diode in the overtemperature detecting circuit. The voltage divider resistance is connected with an electrolytic capacitor in parallel and an inductor is connected between the half-bridge drive circuit and the output circuit in series while the thermal resistor is arranged between the radiating ribs of the collecting electrode of the two triodes in the half-bridge drive circuit. The self- excited type electronic ballast with overtemperature protection of the invention can avoid the high-temperature operation of the triodes in the half-bridge drive circuit.

Description

technical field [0001] The invention relates to electronic lighting technology, in particular to a self-excited electronic ballast which prevents the triode in the half-bridge drive circuit from overheating. Background technique [0002] Fluorescent lamps are energy-saving and efficient lighting sources, and have been widely used in various fields. Such as figure 1 Shown is the working principle diagram of the existing typical self-excited electronic ballast. The DC power terminal output by the rectification and filtering circuit is connected to the base of the triode G2 through the resistor R1 and the bidirectional diode D2 in the half-bridge drive circuit, and the common terminal of the resistor R1 and the bidirectional diode D2 has a charging capacitor C indirectly connected to the ground, and the base of the triode G2 The pole passes through the second secondary winding L22 of the magnetic ring transformer L2 and is grounded together with the emitter of the triode G2, ...

AI Technical Summary

Problems solved by technology

However, self-excited electronic ballasts also have shortcomings: to implement effective protection functions when high temperature conditions (above 100°C) occur, it is necessary to add many additional protection circuits, making the structure complex and difficult to complete the protection functions

In particular, due to the aging of the lamp tube, the tube voltage of the lamp tube increases, the tube current decreases, and the oscillation frequency increases, which eventually leads to a rapid increase in the tube temperature of the power transistor in the half-bridge drive circuit, causing the circuit board (PCB) to lose power in the high-power transistor The solder joints of the pins are scorched and carbonized, and even smoke, etc.

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