An LED element has been widely used in a signaling light, an electric bulletin board, a backlight of a display device and a car light as a light source for display or illumination. In addition, an LED light bulb which is replaceable of a traditional filament bulb has been put on the market. The LED light bulb has some advantages. Of the same light amount, the power consumption of an LED light bulb is lower than that of the filament bulb. Also, the LED light bulb can obtain the maximum amount of light at the time of turning it on.
For a fluorescent light, an ultraviolet light is converted into a visible light by a fluorescent material applied on an inside wall of a glass tube. After two filament electrodes of the fluorescent light are preheated before the discharge, an instantaneous high voltage is applied between both electrodes. As a result, thermal electrons are emitted from a cathode filament to an anode filament by the discharge phenomenon, and ultraviolet light is generated by the collisions of the thermal electrons and mercury particles.
A certain type of a fluorescent lighting fixture includes a starter that preheats the filament electrodes to generate an instantaneous high voltage. The fluorescent lighting fixture further includes a ballast that maintains the current to a constant value after the discharge occurs. Three lighting methods, which are called a glow tube starter type, a rapid start type and an inverter type, are known. Various ballasts are used even though the fluorescent lighting fixtures are lit with the same lighting method.
The LED illumination lamp includes a rectifier that converts a commercial alternating current into a direct current in order to supply a direct current to multiple LED elements. In addition, the LED illumination lamp requires a constant current circuit to supply a constant current to the LED elements for stabilizing brightness. A capacitive constant current circuit is well known for smoothing a direct current voltage outputted from the rectifier by a smoothing capacitive. The capacitive constant current circuit can derive a voltage waveform that is close to an ideal direct current voltage while a structure is relatively simple.
The smoothing capacitor of the capacitive constant current circuit consists of electrolytic capacitor since a large current capacity is demanded. An electrolytic capacitor with low durability shortens the lifetime of an LED illumination lamp. Also, a countermeasure for any damage of the electrolytic capacitor is required.
A semiconductor constant current circuit using a diode is safer than the capacitive constant current circuit. However, the semiconductor constant current circuit cannot remove a ripple of the current to a degree of stably lighting the LED elements. In recent years, most of constant current circuits of LED illumination lamps become chopper type constant current circuits. A chopper type constant current circuit can prevent the ripple of the current by repeatedly switching on and off a switching element at a high frequency. As a result, a flickering that can be sensed by human beings can be prevented.
Rewiring work is required when the LED light, replaced with the fluorescent light, is installed in a fluorescent light equipment. This rewiring work includes works for disconnecting an existing ballast from an alternating-current power supply and removing a glow starter. When a straight tube LED illumination lamp equipped with a certain type of direct current power supply is installed in the fluorescent light equipment, it may not be easy to reinstall a fluorescent light therein. It may also not be easy to install therein a straight tube LED illumination lamp equipped with another type of direct current power supply.
The patent document 1 discloses a straight tube LED illumination lamp which can be installed in a fluorescent light equipment. According to the invention of the patent document 1, a rewiring work is not required, and anyone with no technical knowledge can install the straight tube LED illumination lamp to the existing fluorescent light equipment. Since a structure of the straight tube LED illumination lamp is simple, a manufacturing cost can remain low.