21-Watt Universal AC LED Driver with Accurate Average-Mode Constant Current Control

The project presented here is an average current mode control LED driver operating in a constant off-time mode. The project consists of a bridge rectifier followed by a buck converter operating with a fixed off-time of 20µs. The circuit provides accuracy, and line and load regulation of the LED current. The output LED current accuracy is +/-4%. The project is built using HV9961 chip which is equipped with a current limit comparator for hiccup-mode output short circuit protection. A PWM dimming input is provided that accepts an external control of a TTL-compatible signal. Connect the PWMD terminal to the VDD terminal using the jumper provided to enable the LED driver.

Features

• Supply 90V to 265V AC 50Hz/60Hz
• Output 20 to 60V, 350mA
• Full Load Efficiency Up to 92%
• Switching Frequency 38Khz
• Fast Average Current Control
• PWM Dimming Input (Jumper J1)
• Output Short-Circuit Protection with Skip Mode
• PCB Dimensions 74.93 x 40.64mm
• 4 x 4MM Mounting Holes

Connections and Other Details

• CN1: Pin 1 = AC Live Input, Pin 2 = AC Neutral Input (90V to 265V AC Input)
• CN2: Pin 1 = DC 20V to 60V DC @ 350mA Output (+LED), Pin 2 = -LED
• Jumper J1: Pin 1 = VDD, Pin 2 = PWM In/Enable, Pin 3 = GND, Connect to VDD = Enable, Use as PWM input for Dimmer Function

PWM Dimming

The circuit is capable of being PWM dimmed by applying a square wave TTL compatible signal between PWMD and GND terminals of Jumper J1. However, since there is no galvanic isolation on the board, care must be taken to prevent damage to the PWM dimming source and/or the circuit.

The LED driver features tight regulation of the LED current within a few milliamps over the entire range of the input AC line and the output LED string voltage. The LED current accuracy is almost insensitive to the passive component tolerances, such as the output filter inductance or the timing resistor. The accuracy of the LED current is mainly determined by the internal 275mV ± 3% reference voltage of the HV9961 control IC and by the external current sense resistor R4 and R5 tolerance. The output current can be adjusted down to 60mA using the onboard resistor R3. However, accurate current control is only achieved with continuous conduction of the filter inductor, i.e., when the LED current is greater than the inductor ripples current amplitude.

Schematic

Parts List

Connections

Gerber View

Photos

Video

HV9961 Datasheet

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