Pre-charging inductor in switching converter to achieve high PWM dimming ratio in LED drivers

A regulator system for dimming a light emitting diode (LED) load comprising:

• a first terminal for receiving a dimming signal having a duty cycle, the dimming signal controlling an LED ON-time and an LED OFF time, the dimming signal being at a first frequency;
• a current regulator controlled to supply a regulated current, under a steady-state condition, to the LED load during the LED ON-time and to supply no current to the LED load during the OFF-time, the regulator having an inductor;
• a current detection circuit for detecting an inductor current during a steady-state condition of the regulator to generate a first value corresponding to the inductor current;
• a storing circuit coupled to the current detection circuit for storing the first value during the OFF-time;
• a pre-charger circuit connected to pre-charge the inductor, during the OFF-time, to a current level related to the stored first value wherein, at a start of the next ON-time, the inductor has been pre-charged with a current approximately equal to the inductor current during the steady-state condition of the regulator so that the current supplied to the LED load at the beginning of the next ON-time is approximately equal to the current supplied to the LED load at the end of the previous ON-time;
• a first isolation circuit connected to maintain a control signal in a feedback loop of the regulator substantially constant during the OFF-time;
• and
• an enablement circuit for enabling the regulator to supply the current to the LED load during the LED ON-time wherein, at the start of the LED ON-time, the inductor conducts the pre-charged current.