Compact Fluorescent Lamps (CFLs)
• Advantages over incandescent lamps
– Energy savings
– Longer lifetime
• Disadvantages over incandescent lamps
– Higher initial cost
– Not as easy to have 3-way control (dimming)
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Fluorescent vs. Incandescent
• Convert UV light to
visible light
• Two-stage conversion
– Electrons collide with
mercury atoms,
causing photons of uv
light to be released
– UV light converts to
visible as it passes
through the phosphor
coating inside the
glass tube
• Convert heat to light
– Burn a filament (wire)
at very high
temperature
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Fluorescent vs. Incandescent (cont.)
• More efficient
• Less efficient
– 25% of energy
consumed generates
light
– Lower lamp
temperature
– Longer life
– 5% of energy
consumed generates
light
– High filament
temperature (350°F)
– 2,000 hour lifetime
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Components and Assembly
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CFL Operation
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Electronic Ballast Block Diagram
Blocks circuitgenerated noise
AC-to-DC
Conversion
DC-to-AC
Conversion
Ignite and Run
the Lamp
Feedback circuit to control lamp current
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Lamp Requirements
• Current to pre-heat the filaments
– Low-Frequency AC to DC Conversion (input)
• High Voltage for Ignition
• High-Frequency AC current during running
– High-Frequency DC to AC conversion (output)
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Generate High-Frequency
50% duty-cycle AC Square
Wave
Resonant tank circuit
filters square wave to
a sinusoid and drives
lamp
AC-toDC Conversion
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At turn-on
• During pre-ignition, the resonant tank is a
series LC circuit with a high Q factor
• Control IC sweeps the half-bridge
frequency from maximum down towards
the resonant frequency of the LC circuit
• Lamp filaments are pre-heated as the
frequency decreases and the lamp voltage
and load current increase
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Lower the frequency until the lamp ignites
Filaments are pre-heating
To dim the lamp,
increase the frequency
of the half-bridge
The gain of the
resonant tank
decreases and the
lamp current increases
The feedback circuit
adjusts the half-bridge
operating frequency
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IRS2530D Dimming Control IC
Supply Voltage
High-side gate driver supply
Half-bridge high-side gate
driver output
Power and signal ground
Dimming reference
and AC lamp
current feedback
input
High voltage supply return
and half-bridge sensing input
Half-bridge low-side gate
driver output
VCO input
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IRS2530D Dimming Control Method
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Combine AC Lamp Current measurement with a
DC reference voltage at a single node
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3-Way Incandescent Lamp Dimming
Filament #1
4-Position Switch
Filament #2
Common
0 – OFF,
1 – Filament #1 –LOW,
2 – Filament #2 – MED,
3 – Filaments in Parallel -- HIGH
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3-Way Dimming for CFL
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3-Way Socket
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EMI Filter
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Rectifier and Voltage Doubler
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Control Circuit and Half-Bridge Inverter
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Resonant Tank
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Lamp-Current Sensing and Feedback
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Three-Way Interface Circuit
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Lamp Voltage and Current (Maximum)
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Lamp Voltage and Current (Medium)
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Lamp Voltage and Current (Minimum)
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Maximum: 43kHz, 240mA
Medium: 62kHz, 94mA
Minimum: 67kHz, 31mA
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