Long Life Incandescent Lamps Using SIDACs

AND8015/D
Long Life Incandescent
Lamps using SIDACs
Prepared by: Alfredo Ochoa, Alex Lara & Gabriel Gonzalez
Thyristor Application Engineers
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APPLICATION NOTE
Abstract
conducting state when the applied voltage of either polarity
exceeds the breakover voltage. As in other trigger devices,
the SIDAC switches through a negative resistance region to
the low voltage on–state and will remain on until the main
terminal current is interrupted or drops below the holding
current.
SIDAC’s are available in the large MKP3V series and the
economical, easy to insert, small MKP1V series axial lead
packages. Breakdown voltages ranging from 110 to 250V
are available. The MKP3V devices feature bigger chips and
provide much greater surge capability along with somewhat
higher RMS current ratings.
The high voltage and current ratings of SIDACs make
them ideal for high energy applications where other trigger
devices are unable to function alone without the aid of
additional power boosting components.
The following figure shows the idealized SIDAC
characteristics:
Since the invention of the incandescent lamp bulb by the
genius Thomas A. Edison in 1878, there has been little
changes in the concept. Nowadays we are currently use them
in our houses, and they are part of our comfort but, since we
are more environmentally conscious and more demanding
on energy cost saving products, along with their durability,
we present here an application concept involved this simple
incandescent lamp bulb in conjunction with the Bilateral
Trigger semiconductor device called SIDAC, offering an
alternative way to save money in energy consumption and
also giving a longer life time to the lamp bulbs.
Theory of the SIDAC
The SIDAC is a high voltage bilateral trigger device that
extends the trigger capabilities to significantly higher
voltages and currents than have been previously obtainable,
thus permitting new, cost effective applications. Being a
bilateral device, it will switch from a blocking state to a
ITM
VTM
Slope = Rs
IH
IS
IDRM VS
I(BO)
V(BO)
VDRM
Rs = (V(BO) – VS)
(IS – I(BO))
SIDACs can be used in many applications as transient
protectors, Over Voltage Protectors, Xeon flasher,
relaxation oscillators, sodium vapor lamp starters, etc.
Once the input voltage exceeds V(BO), the device will
switch on to the forward on–voltage VTM of typically 1.1
V and can conduct as much as the specified repetitive peak
on state current ITSM of 20A (10µs pulse, 1KHz repetition
frequency).
 Semiconductor Components Industries, LLC, 1999
January, 2000 – Rev. 0
1
Publication Order Number:
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through a fixed phase for the most typical levels of ac line
voltages:
This paper explains one of the most typical applications
for SIDACs which is a long life circuit for incandescent
lamps.
The below schematic diagrams show the configurations
of a SIDAC used in series with an incandescent lamp bulb
Option 1: ac line voltage 110V, 60Hz or 50Hz
SIDAC
MKP1V120RL
100 WATTS
110V
AC Line
110V, 60 Hz
Option 2: ac line voltage 220V, 60Hz or 50 Hz
SIDAC
MKP1V120RL
100 WATTS
220V
AC Line
220V, 60 Hz
possible energy reduction is 50% if the lamp wattage is not
increased. The minimum conduction angle is 90° because
the SIDAC must switch on before the peak of the line
voltage. Line regulation and breakover voltage tolerances
will require that a conduction angle longer than 90° be used,
in order to prevent lamp turn–off under low line voltage
conditions. Consequently, practical conduction angles will
run between 110° and 130° with corresponding power
reductions of 10% to 30%.
The following plots show the basic voltage and current
waveforms in the SIDAC and load:
This is done in order to lower the RMS voltage to the
filament, and prolong the life of the bulb. This is particularly
useful when lamps are used in hard to reach locations such
as outdoor lighting in signs where replacement costs are
high. Bulb life span can be extended by 1.5 to 5 times
depending on the type of lamp, the amount of power
reduction to the filament, and the number of times the lamp
is switched on from a cold filament condition.
The operating cost of the lamp is also reduced because of
the lower power to the lamp; however, a higher wattage bulb
is required for the same lumen output. The maximum
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Incandescent Lamp of 100W, 110V, 60Hz
Ch1 Voltage
Vpk = 123V
V(BO)
Ch2 Current
Ipk = 0.96A
–V(BO)
Conduction
Angle
Incandescent Lamp of 50W, 220V, 60Hz
Ch1 Voltage
Vpk = 121V
V(BO)
Ch2 Current
Ipk = 0.33A
–V(BO)
Conduction
Angle
harmonic attenuation. In addition, it is important that the
filter inductor be non–saturating to prevent di/dt damage to
the SIDAC.
The sizing of the SIDAC must take into account the RMS
current of the lamp, thermal properties of the SIDAC, and
the cold start surge current of the lamp which is often 10 to
20 times the steady state load current. When lamps burn out,
at the end of their operating life, very high surge currents
which could damage the SIDAC are possible because of
arcing within the bulb. The large MKP3V device is
recommended if the SIDAC is not to be replaced along with
the bulb.
In order to establish what will be the average power that
an incandescent lamp is going to offer if a SIDAC
(MKP1V120RL) is connected in series within the circuit,
some ideal calculations could be made for these purposes
In both previous cases, once the ac line voltage reaches the
V(BO) of the SIDAC (MKP1V120RL), it allows current
flow to the incandescent lamp causing the turn–on of this at
some specific phase–angle which is determined by the
SIDAC because of its V(BO).
The fast turn–on time of the SIDAC will result in the
generation of RFI which may be noticeable on AM radios
operated in the vicinity of the lamp. This can be prevented
by the use of an RFI filter. A possible filter can be the
following: connect an inductor (100µH) in series with the
SIDAC and a capacitor (0.1µF) in parallel with the SIDAC
and inductor. This filter causes a ring wave of current
through the SIDAC at turn on time. The filter inductor must
be selected for resonance at a frequency above the upper
frequency limit of human hearing and as low below the start
of the AM broadcast band as possible for maximum
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Example: Incandescent lamp of 100W (120V, 60Hz).
200
v(t):
i(t) x 100:
VL(t):
Voltage / Current
100
v(t): Voltage waveform in the SIDAC
l(t): Portion of current waveform applied to the load
(Multiplied by a factor of 100 to make it more graphically
visible)
VL(t): Voltage waveform in the Load
0
–100
–200
0
0.002
Ǹŕ
Ǹŕ
0.004
0.006
0.008
time in seconds
Based on this, it is possible to observe that the average
power output is a little bit lower than the original power of
the lamp (100W), even though the conduction angle is being
reduced because of the SIDAC.
In conclusion, when a SIDAC is used to phase control an
incandescent lamp, the operation life of the bulb is going to
be extended by 1.5 to 5 times which represents a big
economical advantage when compared to the total cost of the
lamp if it is changed. In addition, the original power of the
lamp is not going to be reduced considerably which assures
the proper level of illumination for the area in which the
incandescent lamp is being used for. Finally, since the
SIDACs are provided in a very small axial lead package,
they can be mounted within the same place that the
incandescent lamp is placed.
In this case, the conduction angle is around 130° (6 msecs)
in each half cycle of the sinusoidal current waveform,
therefore, the average power of the lamp can be obtained by
calculating the following operations:
i
eff
+
8.33
10
*3
2
T
2
i(t) dt
0
v
eff
+
8.33
2
T
10
*3
2
v(t) dt
0
Pav = ieffVLeff
Pav = 91.357
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