Transcript Dimming Presentation

Dimming Methods
Types of Solid State Dimming
Types of Fluorescent Dimming
HID Dimming
By Jon Limbacher of Spectrum Lighting
Technology Comparison
 Professional dimming has come a long way from the candle snuffers of the
18th century to the gas tables of the 19th century and resistance dimmers of
the early 20th century. Forward phase dimming with SCR technology has
reigned over conventional loads since the early 1960s and is still today the
most cost-effective choice for dimming installations.
 When forward phase technology emerged, electronic components made it
possible to allow only portions of the AC cycle through to the load. The
familiar SCR and Triac devices were used to control the intensity of light,
varying the switch ON point of the lamp current each half cycle (forward
phase). The convergence of improvements in transistor technology, lower
technology costs and more improved processors brought forth reverse
phase dimming, also called trailing edge dimming, which switched OFF the
current flow at a predetermined interval.
 Patented techniques for producing a pure sine wave output with variable
amplitude to control lighting levels use transistors to slice the mains into
pulses, vary the current using pulse width modulation, and average the
result, which produces a continuous, variable amplitude smooth sine wave.
Forward Phase Control
(SCR)
 The basic SCR dimmer will remain the choice for
budget-conscious dimming installations for the
foreseeable future. The simple technique of varying the
switch-on point of the lamp current each half-cycle is
established in tradition and is very cost effective.
 Most forward phase technology is the best in its class
and boasts high quality choke designs on all dimming
products. Advanced options take dimming a stage further
with high-risetime chokes to reduce the filament noise by
slowing the rise time of the curve even more.
Forward Phase Control
Forward Phase Drawbacks
 The disadvantages of the technique include noisy filaments that can buzz
audibly, and the possibility of cross-interference between dimmers and
audio systems.
 SCR dimmers are actually quite efficient, and very little gets lost in the
dimming circuit itself. But when operated at anything less than full output,
the SCR dimmer presents a distinctly non-linear load, creating what is
known as “triplen harmonics.” This means that the phase currents in a
three-phase system do not cancel out as intended, but, rather, add up. In
the worst possible case, the neutral current can be up to 73% higher than
any one-phase current. The harmonics also produce audible noise and
overheating in the distribution wiring and feeder transformers and can lead
to penalties from utility companies.
 With its distorted waveform, SCR dimming is simply unsuitable for many
loads, including most electronic transformers and electronic ballasts for
fluorescent and metal-halide sources. In some cases, the load will perform
badly; in other cases, the load and the dimmer may sustain permanent
damage.
Reverse Phase Control
 . The IGBT is a semiconductor that is fast replacing both regular transistors
and the trusted SCR in many power control applications. IGBT stands for
Insulated Gate Bipolar Transistor. Invented in the late 1970s by Frank
Wheatley at RCA and currently in its fourth or fifth generation of
development, IGBTs are the preferred component for power control
applications. They are significantly more efficient and easier to control than
most other power semiconductors. IGBTs are commonly available with
ratings up to 1200 amps and about 1700V, making them suitable for use in
just about any dimming application imaginable.
 The commercially-practical implementation of reverse phase dimming uses
IGBT transistors. A transistor differs from an SCR in that it can be controlled
to gradually vary the current, not just to switch it on. By gradually turning off
the current rather than turning it on, a reverse phase angle dimmer reduces
the filament noise in a similar fashion as a forward phase SCR dimmer
without the need of a choke.
Reverse Phase Control
Reverse Phase Drawbacks
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RPC dimmers can be very quiet and compact. They work well for filament loads or electronic lowvoltage transformers but are unusable with inductive loads. Neon, ballasted loads, fans, and small
electric motors will generate destructive inductive kickback energy when dimmed by an RPC
dimmer. RPC dimmers either should not be used with these loads or should switch to forwardphase control (FPC) to dim such loads. In both cases, FPC or RPC, the dimmers are producing
triplen harmonics.
Using a transistor as a switch (on or off) produces minimal heat, while using a transistor to directly
control the voltage to a load creates a lot of heat. The more time spent by the transistor in the
analog mode, the more heat it produces. Specifications for 800µS rise or fall time require the
transistor to operate in an analog mode the entire 800µS. This can raise the operating
temperature past the limits set by the transistor manufacturer. Some designs prevent failure of the
IGBT by turning it off early, thereby producing less heat, and importantly, less fall time. Reduced
fall time means increased lamp noise!
The reverse phase dimmer is still chopping the waveform at the line frequency, so harmonic
currents and electrical interference are still present. Acoustic noise for forward and reverse phase
dimmers has been evaluated and is quantitatively the same for equivalent rise and fall times.
More importantly, reverse phase dimmers that modify their behavior to become forward phase
dimmers at will, in order to handle certain loads, are capable of creating harmonic neutral currents
well in excess of the design specifications for either a completely forward phase or reverse phase
system. A sine wave dimmer creates no harmonic currents.
Pulse Width Modulation
(Sine Wave)
 SineWave dimmers offer complete silence and energy efficiency and
represent the state of the art in dimming systems.
 Pulse Width Modulation (PWM) techniques are employed in
SineWave dimmers for controlling the amplitude of the incoming
power supply. In basic terms, the input supply is sliced at high
frequency (40-50 kHz) and the transistors are switched, varying the
ratio of on/off time within the sample period. The 'on' period of the
'mark/space ratio' is proportional to the power needed to match the
amplitude of a sine wave at that point in the mains cycle.
 The output current waveform is smoothed using a passive network
to produce an output waveform that accurately represents the
waveform profile of the incoming supply. The PWM process adds
less than 1% distortion to the mains supply, resulting in a completely
silent dimmer with a remarkable facility for dimming almost any load.
Pulse Width Modulation
Sine Wave Drawbacks
Sine wave dimmers are more expensive
than corresponding SCR dimmers — a lot
more expensive, in some cases. This is
partly due to the complexity of sine wave
technology but also to the relatively small
number of dimmer channels produced
and, perhaps, to a lack of serious
competition in the marketplace. Right now,
the market is dominated by a small
number of specialist manufacturers .
How Fluorescent Lamps Work
Lamp Basics
Unlike an incandescent light source, where atoms
are excited by heat, in a fluorescent tube atoms are
excited by a chemical reaction.
How Fluorescent Lamps Work
 The inside of the lamp is coated with a
phosphor mix that illuminates when UV
radiation comes in contact with the glass.
Since light is not a direct result of filament
glow, fluorescent lamps are inherently more
efficient than incandescent lamps.
Once the tube is excited, the
electrodes continue to remain heated
due to current transfer, but the voltage
required to maintain the gas excitation
drops down significantly from the
strike voltage.
How Fluorescent Lamps Work
When you turn the lamp on, the current
flows through the contact pins to the
electrodes. There is a considerable
voltage across the electrodes, so
electrons will migrate through the gas
from one end of the tube to the other.
This energy changes some of the
mercury in the tube from a liquid to a gas.
As electrons and charged atoms move
through the tube, some of them will
collide with the gaseous mercury atoms.
These collisions excite the atoms,
bumping electrons up to higher energy
levels. When the electrons return to their
original energy level, they release light
photons.
How Ballasts work
 A ballast slows down changes in current
• Electronic ballasts vary the frequency at which they
run the lamps without changing the electrode voltage
and are therefore able to get a much wider range of
dimming.
• Fluorescent fixtures are dimmed using a special
dimmable ballast. This is because standard (AKA
Magnetic) ballasts typically do not have the ability to
maintain electrode heat to the degree required for
proper gas excitation when input voltage is varied.
How Ballasts work
2 Wire
Fluorescent
• These are very common ballasts and the easiest to
install.
• They require a dimmed hot and a neutral (ground is
understood)
How Ballasts work
2 Wire Fluorescent
Recommended Ballasts
Advance Mark X
Lutron Tu-Wire
How Ballasts work
3 Wire Fluorescent
• These ballasts are also common and are usually quite
inexpensive.
• They use two dimmers for control and power,
requiring a dimmed hot, a switched hot, and a neutral
(ground is understood).
• The 2 dimmers associated with this ballast must by
code share a common breaker.
How Ballasts work
3 Wire Fluorescent
Recommended Ballasts
Lutron FDB
Lutron ECO-10
How Ballasts work
4 Wire Fluorescent
• These are not seen as often as the 2-wire and 3-wire
models.
• They use a hot (non-dim), neutral ,plus two lowvoltage conductors for 0-10vdc control (ground is
understood).
• Control current is sourced by the ballast and sinked
by an external device.
How Ballasts work
4 Wire Fluorescent
Recommended Ballasts
Advance Mark 7
Motorola Helios
Ballast Ratings
1%, 5%, 10% what does it mean?
• The percentages are based on light output measured
with a light meter.
•This is essentially a Linear Scale
• The human eye does not perceive light increase linearly
but rather as a close function of “square law”
• When looking at the minimum light level output by a
fluorescent fixture, the eye will see more light than the
percentage touted.
Ballast Ratings
1%, 5%, 10% what does it mean?
HID Dimming
Yes you can do it
Sine wave or Reverse Phase
Special Electronic ballasts with 0-10Vdc control
But, you probably should not
Not useful below 50-60% light output
Poor lamp performance
“Cool” purple or green color shifts