Power chopper dimming controls boost LED driver efficiency and maintains minimum inrush current

introduction

The main advantage of LED lighting is that the output of LED light sources can be accurately controlled using a variety of different dimming techniques. Since LED is an efficient light source, power consumption can also be saved through dimming. Controlling lighting intensity also helps adjust different environmental moods.

Due to many reasons, PWM dimming is preferred for analog dimming. In many applications, PWM dimming helps maintain the color of the light output, regardless of brightness level. For circuit design, PWM control is more conducive to noise suppression; the control signal needs to have precise voltage and dimming frequency, and the driver circuit design cannot be too complicated. In addition to two power lines, PWM dimming usually requires a control line carrying the PWM dimming signal. However, this standard configuration is a disadvantage for a large number of lighting systems that use a shared dimmer, and it is difficult to replace incandescent lamps with 2-wire power supplies for dimming control based on power chopping.

There are many problems with traditional LED drive circuits using power dimming. These drivers will gradually turn off the LED power as the input filter capacitor discharges to the minimum operating voltage. This process causes the input and output filter capacitors to discharge to minimum levels. When the power is turned on again, the surge current replenishes the capacitor charge, causing EMI problems and damage to the dimmer. To avoid these problems, the circuit has to use a large inductance filter, which increases the cost.

The LED driver reference design discussed in this article uses PWM dimming to solve these basic problems. This LED driver uses chopper PWM dimming without causing any supply current overshoot. The design features up to 90% efficiency and operates at 24V. One-way power input is allowed, with a MOSFET half-bridge at the input. Figure 1 shows the top layer of the design board.