An LED lamp may have advantages of low power consumption and long lifetime compared to a fluorescent lamp, an incandescent lamp, a three-wave fluorescent lamp, or similar devices. In order to drive LED illumination devices, input power supplied to the home may be alternating current, and/or a converter which converts alternating current to direct current may be needed.
When being driven with alternating-current (AC) power, the LED illumination devices may be broadly classified into an isolation type and a non-isolation type devices. In the case of an isolation type, there may be no risk of an electric shock because an LED load ground and an AC power supply ground may be electrically separated from each other, however there may be a problems with relatively high manufacturing costs.
FIG. 1 shows an isolation-type LED lamp driver circuit based on a flyback converter, in accordance with the related art. The flyback converter may be used because the flyback converter may require only one high-voltage switching element, and therefore the flyback converter may have a relatively simple structure and/or may be implemented at relatively lower cost.
AC power may be a full-wave rectified through a rectifier. A full-wave rectified signal may be converted to DC through a filter and used. In this case, however, a separated circuit may be needed to maximize power factor.
A flyback converter structure may be used to transmit energy to the LED load insulated from the rectified power. In the flyback converter structure, energy may be stored in a magnetizing inductance on the primary side of a transformer while a switch is turned on, and/or energy in the magnetizing inductance may be transmitted to an LED load on the secondary side of the transformer when the switch may be turned off.
A controller may serve to control the on/off operation of the switch such that the secondary-side LED current may have a desired value. To control the secondary-side current, it may be necessary to detect the secondary-side current and/or to feed back the detected secondary-side current to the controller. Since the primary side and the secondary side may be needed insulated from each other, it may necessary to use an element, such as an opto-coupler, which may transmit a signal through light to feed back the current. In FIG. 1, a snubber may serve to suppress high-voltage spark due to resonance caused by parasitic inductance when the switch is turned off.
With this structure, it may be possible to control the LED current constant regardless of a fluctuation in the LED load, a fluctuation in the power supply voltage, or the like. A dimmer control leakage pull down using main power device in a flyback converter may be a configuration in which a secondary-side current may be predicted from a switching duty signal and a peak current transmitted from the primary side to the secondary side, and the peak of the secondary-side current may be compared with a power supply voltage to be supplied, thereby controlling an LED current regardless of a fluctuation in an LED load or a fluctuation in power.
However, in an isolation-type LED lamp driver circuit based on a flyback converter of the related art, it may be necessary to provide an additional secondary-side current sensor circuit and an isolation element, such as an opto-coupler. For this reason, there may be a problem in that the whole system increases in volume, and manufacturing costs may be difficult to minimize. From cost reduction viewpoint of the system, it may be necessary to control the secondary-side current with no additional circuit in the isolated flyback converter.
There may be a demand for a technique for controlling a current with no secondary-side additional circuit and a function of shaping the secondary-side current in tune with an input voltage to minimize a phase difference and to maximize a power factor. There may also be demand for a function of controlling illuminance to correspond to a firing angle control-type dimmer.