An analysis of current accuracies in peak and hysteretic current controlled power LED drivers

This paper provides an analysis result of current control accuracy in driving power LEDs from widely varied DC input voltage. The detail analysis results show that the RMS LED current with Buck converter by using Peak Current Control (PCC) decreases according to increasing input voltage. Since the LED driver needs to be simple and low cost, the Buck converter is popular because it can allow continuous flowing current operation without an output bulky capacitor. Based on the simulation and experimental result, it is discussed how to improve current accuracy by using large a inductor size with PCC in Buck converter over wide input voltage variations. The result of PCC in Buck converter is also compared with Hysteretic Current Control (HCC) LED driver. Experimental results with PCC and HCC show that the RMS current accuracy with HCC is much better than that of PCC in Buck converter. In the experiment, the peak current level is set to 800[mA] both in PCC and HCC with the varied input voltage from 14V to 28V DC. 262 [KHz] fixed switching frequency is used in PCC and 1.2 [MHz] switching frequency is obtained with 33 [muH] inductor in HCC. The PCC and HCC are tested to drive two HB-LEDs rated of 750 [mA]. Finally, the current accuracies of 1% with HCC and 10% with PCC are obtained in the test range.