Microchip logo
  • All
  • Products
  • Documents
  • Applications Notes

PIC16F1508 DALI Dimmable Fluorescent Ballast (Proof of Concept)

Design Highlights:

Rapid Start Intelligent Fluorescent Ballast

  • Universal input 1st stage peak current mode boost supply
  • Resonant LCC inverter for lamp drive
  • 120 VAC – 240 VAC Input
    • Single hardware platform
    • Firmware based configuration
  • Active Power Factor Correction (PFC)
    • 0.95 or better (0.98 at full load)
  • PIC16F1508 Controlled Topology
    • Core Independent Peripheral Integration
    • 5-bit DAC
    • Configurable Logic Cell (CLC)
    • PWM
    • Numerically Controlled Oscillator (NCO) Comparators

DALI Communications

  • Smooth digital dimming control via NCO linear frequency control
  • Analog input or serial e.g. DALI communications
  • MCP1416 FET Driver

Theory of Operation

This proof of concept design is a rapid start resonant fluorescent power supply with active PFC.

Controller Topology

  • Peak current mode DCM boost converter at 150kHz+ switching frequency
  • Internal 5-bit DAC used for voltage envelope reference
  • High Performance Comparators used for peak current mode limits
  • CLC for overall integration and SR-Latch
  • NCO for accurate resonant frequency generation
  1. A boost-strapping power supply consisting of 2 Zener diodes is used to supply power to the FET driver and the microcontroller at startup.
  2. The onboard DAC is used as a voltage divider from the external rectified AC supply voltage to supply a line voltage envelope reference for the power factor correcting peak current mode boost converter. Since the DAC has a selectable tap point the amplitude of the reference is controllable from software.
  3. A small shunt resistor is used to measure the inductor current and the high performance comparator is used to detect when the inductor current reaches the reference current supplied.
  4. The CLC is used as the heart of the controller set up as an SR-Latch. The latch is set by a PWM control signal which turns on the switching FET and starts a near-linear increase in inductor current.
  5. When the inductor current reaches the reference envelope the comparator trips and resets the output SR-Latch in the CLC. The next pulse starts when the PWM starts its next switching cycle.
  6. An ADC is used to roughly regulate the output of this boost converter to above the line voltage (typically 200V or 400V depending on input voltage).
  7. A resonant half-bridge LCC drive circuit is then used to apply this signal to the lamp.
  8. At startup a high frequency signal is generated to heat the lamp filaments.
  9. Once the filaments are on temperature the frequency is quickly reduced to the point where a striking potential is generated by the resonant circuit and the lamp arc is established.

Contact your local sales representative to see a working demonstration of the DALI Dimmable Fluorescent Ballast.

For comments or suggestions on Microchip's Lighting Solutions - please email us at lighting@microchip.com