IRPLDIM5E
4 Level Switch Dim Fluorescent Ballast using the
IRS2530D
DIM8
TM
Table of Contents
Page
1. Features ...........................................................................................2
2. Overview ..........................................................................................2
3. Circuit Schematics ...........................................................................3
4. Functional Description......................................................................4
5. Fault Conditions .............................................................................10
6. Bill of Materials...............................................................................14
7. IRPLDIM5E PCB Layout ................................................................15
8. Inductor Specifications ...................................................................17
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1. Features
Drives 25W CFL Lamp
Input Voltage: 220VAC
High Frequency Operation
Lamp Filament Preheating
Lamp Fault Protection with Auto-Restart
Low AC Line/Brownout Protection
Microcontroller driven 4 level power pulse dimming
IRS2530D
DIM8
TM
HVIC Ballast Controller
2. Overview
The IRPLDIM5E reference design kit consists of a dimming fluorescent ballast, with a
microcontroller driven dimming control system providing four fixed levels and actuated
by power re-cycle pulses of less than one second, driving a single 25W CFL lamp. The
design contains an EMI filter and a dimming ballast control circuit using the
IRS2530D.
This demo board is intended to help with the evaluation of the IRS2530D (DIM8
TM
)
dimming ballast control IC, demonstrate PCB layout techniques and serve as an aid in
the development of production ballasts using the IRS2530D.
DIM8 Ballast Control
Half-Bridge Driver
EMI Filter
Rectifier
Output Stage
Lamp
Line
Microcontroller
Pulse Detect
Dimming Feedback
Lamp Fault
Figure 2.1:
IRPLDIM5E Block Diagram
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4. Functional Description
The IRPLDIM5E reference design is built on the IRS2530D (DIM8
TM
) dimming platform.
The lamp arc current is detected through RCS after ignition and added to a DC control
voltage to provide an AC signal with a positive offset at the DIM pin of IC1. During DIM
mode the IRS2530D adjusts the oscillator frequency in order to maintain the amplitude of
this feedback signal such that the negative going peak is regulated at the 0V reference. In
this way the peak to peak AC feedback signal amplitude is regulated to twice the DC
control voltage level.
The IRS2530D incorporates a voltage controlled oscillator, whereby the voltage at the
VCO pin determines the frequency. This is also used to realize the preheat and ignition
ramp required to start the lamp. At switch on the voltage at the VCO pin will steadily rise
from 0V. At 0V the frequency will be at its maximum level, which is considerably above the
open circuit resonant point. As the voltage increases, the frequency gradually falls and the
voltage at the lamp increases as well as the current in the cathodes. This configuration
utilizes
voltage mode heating,
which is provided by means of two auxiliary windings on the
resonant output inductor of the ballast circuit. This method is the simplest and cheapest,
however
current mode heating
could be used if an additional transformer were to be
added to sense the arc current.
As the frequency continues to fall, the voltage at the ballast output to the lamp increases
until it reaches a point where it is sufficient to ignite the lamp. At this point arc current
begins to flow in the lamp and a feedback signal is produced at the current sense resistor
RCS. If ignition fails then the IRS2530D will shut down, going into a low VCC current fault
mode.
The dimming control reference voltage is provided at the DIM pin of IC1 and generated by
the micro controller IC2 at output GP2. GP pins refer to
general purpose
I/O pins of the
micro controller, which can be configured by software as high impedance inputs or CMOS
outputs. The DC dimming control voltage is produced by means of an RC integrating filter
supplied by a square wave signal. The square wave signal is generated by the micro
controller, which generates a fixed frequency signal with four separate duty cycle modes.
The higher the duty cycle, the higher the resulting filtered DC dimming control voltage
(Figure 4.1).
The GP1 input of the micro controller IC2 is also connected to the AC line input voltage
through a filter circuit with a very short delay. This allows IC2 to detect very rapidly when
AC power has been removed and restored. The 5V VDD supply storage capacitor C1 is
sufficiently large to allow IC2 to continue to run for more than one second after AC power
has been removed from the ballast. When the AC line is switched off, IC2 detects this
rapidly and starts a timer from this point. If power is restored within one second, the
dimming level is reduced by one level, thus reducing the output square wave duty cycle
and reducing the dimming level by one step. If the dimming level was already at minimum
then it will cycle back to maximum. In the case of AC power being removed for more than
one second the dimming level will not be changed. After C1 has discharged below the
minimum VDD operating voltage of IC2 the micro controller will shut off.
The micro controller that has been used here is a
PIC12F629,
which contains some
EEPROM non-volatile memory. The EEPROM allows the micro to store the last dim level
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