Current controlling circuit for a light-emitting diode driver and producing method therefor

摘要

The present disclosure proposes a fully integrated accurate LED output current controlling circuit and method, which can be seamlessly combined with true PWM dimming. The current controlling circuit has an auto zero function in the light-emitting diode driver to eliminate offsets caused by the system, process variations, parasitic effects, dimming and so on in an LED driver application, and thus is capable of controlling the LED current with high accuracy. Moreover, the driver of the present disclosure does not require the use of external components such as an external resistor to regulate current accuracy.

主权项

1. A current controlling circuit, comprising:
a reference current source unit configured to generate a reference current; a current sensing circuit comprising a reference resistor whose first terminal is connected to said reference current source unit, a sensing resistor whose resistance is in a first proportion to the resistance of said reference resistor, a first transistor whose source is connected to a first terminal of said sensing resistor, and an error amplifier; and a first switched capacitor circuit configured to sample a reference voltage at the first terminal of said reference resistor when a switching signal is at a first level and to transfer the sampled reference voltage to the first terminal of said sensing resistor when the switching signal is at a second level, such that a voltage at the first terminal of said sensing resistor is equal to a voltage at the first terminal of said reference resistor, wherein an output of said error amplifier is operable to be coupled to the gate of said first transistor through said first switched capacitor circuit, and said current controlling circuit controls a current flowing through said sensing resistor such that the current is in a second proportion to said reference current, said second proportion being a reciprocal of said first proportion.