Nowadays, the dimming driver circuit of the conventional lighting device can be used to adjust the brightness of the lighting device, such as a light emitting diode. A conventional dimming driver circuit comprises a power converting unit, a control unit, a current sensing resistor and a driving unit. Due to that the circuit topologies of the power converting units are different, the conventional dimming driver circuits are classified into two types.
In the first type dimming driver circuit, the power converting unit includes a switch which is connected in series with a positive terminal of the power converting unit. Under this circumstance, a high-side driving unit has to be employed as the driving unit of the dimming driver circuit so as to convert a high voltage into a low voltage required for the switch. In the second type dimming driver circuit, the switch of the power converting unit is electrically connected with the negative terminal of the power converting unit and electrically connected with a reference voltage. Under this circumstance, the current sensing resistor cannot be electrically connected with the reference voltage, and therefore a high-side current detection unit has to be additionally equipped to the dimming driver circuit.
The high-side driving unit and the high-side current detection unit have to be employed in the two types of the dimming driver circuits, respectively. Consequently, the circuitry of the dimming driver circuit is complicated and the fabricating cost is high. In addition, the signal received by the control unit is actually the superposed signal of the error signal and the detecting signal issued from the current sensing resistor. If the dimming signal is lower, the detecting signal issued from the current sensing resistor is lower. Meanwhile, the proportion of the error signal received by the control unit is relatively higher. Consequently, the control unit cannot accurately output the corresponding pulse signal according to the dimming signal, and the output current from the power converting unit cannot be well adjusted according to the dimming signal. The accuracy of dimming by using the conventional dimming driver circuit is unsatisfied because of the current sensing resistor.
Therefore, there is a need of providing dimming driver circuit so as to overcome the drawbacks of the conventional technologies.