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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
Constant Power SMD LED Tube light with Variable Input
Voltage
Saurabh Gandhe#1 ,Pooja Bora#2, Avinash K. Dwivedi#3
#1 Dept. of Electronic & Tele Communication,Pimpri chinchwad college of engineering
Pune, India .
#2 Dept. of Electronic & Tele Communication,Pimpri chinchwad college of engineering
Pune, India,
#2 Dept. of Electronic & Tele Communication,Pimpri chinchwad college of engineering
Pune, India.
ABSTRACT
A transit vehicle lighting system has a plurality of LED-based lighting fixtures for providing
interior illumination. A control network comprises a plurality of slave nodes for controlling the
LED-based lighting fixtures, and a master node for controlling the slave nodes Many of today’s
portable electronics require backlight LED-driver solutions with the following features: direct
control of current, high efficiency, PWM dimming, overvoltage protection, load disconnect,
small size, and ease of use. Intensity of SMD LED are controlled by a controller which is based
on IC TPS926920/9001Q.
Key words: PWM dimming; overvoltage protection; TPS926920/9001Q
Corresponding Author: Saurabh Gandhe
INTRODUCTION
A. SMD LED
It consists of a lead frame which is embedded in a white thermo. The reflector inside this
package is filled with a mixture of epoxy and TAG phosphor. The TAG phosphor converts the
blue emission partially to yellow, which mixes with the remaining blue to give white. This is a
fine 3 W Pure white LED, it is very painfully bright; It is recommended not looking directly at
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
these LEDs when they are lit up. This SMD LED should be contacted to a larger heat sink to
prevent overheating of the LED element. appears in the
Figure 1
B. About Boost Integrated Circuit
IC TPS9260 is buck-boost IC. The TPS92690/90Q1 is a high voltage, low-side NFET controller
with an adjustable output current sense resistor voltage. Ideal for LED drivers, it contains all of
the features needed to implement current regulators based on boost, SEPIC, flyback, and buck
topologies. Output current regulation is based on peak current mode control supervised by a
control loop. This methodology eases the design of loop compensation while providing inherent
input voltage feed-forward compensation. The TPS92690/90Q1 includes a high voltage start-up
regulator that operates over a wide input range of 4.5V to 75V. The PWM controller is designed
for high speed capability including an oscillator frequency range up to 2.0 MHz. The
TPS92690/90Q1 includes an error amplifier, precision reference, cycle-by-cycle current limit,
and thermal shutdown.
C. About PWM Wave
The NE555 is a highly stable device for generating accurate time delays or oscillation.
Additional terminals are provided for triggering or resetting if desired. In the time delay mode of
operation, the time is precisely controlled by one external resistor and capacitor. For astable
operation as an oscillator, the free running frequency and duty cycle are accurately controlled
with two external resistors and one capacitor. The circuit may be triggered and reset on falling
waveforms, and the output circuit can source x°C or sink up to 200mA or drive TTL circuits.
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
BLOCK DIAGRAM
A. Description
Fig. 2 Block Diagram
The Intensity Control Block gives voltage input to the PWM Controller Circuit. PWM controller
circuit triggers the constant current boost IC (TPS926920) then it is given to the constant current
IC via Mosfet Circuit. Mosfet is a voltage controlled device. Finally, the output of the constant
current IC is used to control the intensity and power of SMD LED Tube light.
B. Working and calculation
Forward voltage of SMD led is 3.3V approximately. Lumens range is from 180 to 200 so
average lumens is 190 and we want 8 SMD led to mount on strip SMD led PCB so total lumens
is 190*8=1520 lumens of the circuit should be near to 1600 and total wattage used is 4 watt-12
watt. The current flow through the SMD led is 840mA so 12 watt is power consumption. Using
working principle of LDR circuit , control the value of the resistance .
Pulse width modulation of timer IC 555 increased the life time of the tube light. Cost of the
circuit is expensive due to use of SMD led but its long life time and its efficiency is more so its
better to use than simple tube light and the arrangement of SMD leds as shown in diagram, it is
seen that if one led damages there is no effect to other leds, they are not damage due to short
circuit.
For maximum forward voltage buck-boost IC is used. Here we can also use LM317 but its
forward voltage rating is maximum 2 V, and we have 3.7 V. Maximum voltage range of the
circuit is 24-30V.And current flowing through the SMD led is 1A,power consumption of the
circuit by using ohms law is 1A*12 ohm=12 watt.
The current range is approximately 280mA so power consumption of the circuit is
280mA*12ohm=3.36 watt. It is near to forward cut off voltage .The efficiency of the tube light
having more lumens and less power rating of the led tube .
B. PCB design of constant power SMD LED tubelight using TPS92690 IC.
It is a multilayer PCB designed in Diptrace.
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
Fig. 3a Front View and Fig.3b Rear View
COMPARISON BASED ON CURRENT CONTROLLED CIRCUITS
There are many ways available to control or limit the current rather to use current boost IC.
Comparison is given below with advantages and disadvantages.
A. Resistor For LED Current Limitations
The only advantage of using this circuit is it provides simplest solution to current control. But it
has high power loss across the RLED. Resistor needs to be defined for maximum supply voltage
conditions. For typical supply voltage conditions the LED current is much lower, which leads to
a visible decrease of brightness e.g. during start stop operation. LED nominal current range
cannot be used for nominal operation conditions, because current has to be fixed for maximum
supply voltage. No intrinsic overvoltage protection (during supply voltage spikes the LEDs are
stressed significantly, because of exceeding the LEDs maximum ratings) ,degradation of LEDs
No simple temperature protection of the LEDs possible. Reduced LED lifetime. Any diagnosis
functions needs to be realized by additional circuits. Only limited LED chain length, dependent
on the LED forward voltage VF and minimum supply voltage.
Fig.4.1 Resistor For LED Current Limitations
Fig. 4.2 Constant Current IC
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
B. Constant Current IC
In the constant current IC circuit LED can be used in the nominal operation condition at full
brightness. Stable brightness during start and stop. This circuit also provides intrinsic
overvoltage protection and thus no LED degradation, high temperature protection of LEDs is
also possible. It has an additional feature of integrated diagnosis functions (optional). However it
has high power loss across the constant current source and increased components count.
Only limited LED chain length, dependent on the LED forward voltage VF and minimum supply
voltage to increase the efficiency of the total system a so called Matrix setup could be used
asdescribed later in this application note.
C.DC/DC convertor in constant current mode
Fig.4.3. DC/DC convertor in constant current mode
This circuit has the highest efficiency. LED can be used in the nominal operation condition at
full brightness. Stable brightness even during start stop. This converter is capable of handling
high brightness LEDs. Various topologies are possible. It also provides intrinsic overvoltage
protection and no LED degradation. High temperature protection of LEDs is also possible.
Integrated diagnosis functions is optional. But the drawback is increased components count and
PCB layout needs to be optimized regarding EMC performance.
D. Current Boost IC
The TPS92690 is an N-channel MOSFET (NFET) controller for boost, SEPIC, buck, and flyback
current regulators which are ideal for driving LED loads. The controller has wide input voltage
range allowing for regulation of a variety of LED loads. The low-side current sense, with low
adjustable threshold voltage, provides an excellent method for regulating output current while
maintaining high system efficiency. The TPS92690 uses peak current mode control providing
good noise immunity and an inherent cycle-by-cycle current limit. The adjustable current sense
threshold provides a way to analog dim the LED current, which can also be used to implement
thermal foldback. The dual function n DIM pin provides a PWM dimming input that controls the
main GATE output for PWM dimming the LED current also. When designing, the maximum
attainable LED current is not internally limited because the TPS92690 is a controller. Instead it is
a function of the system operating point, component choices, and switching frequency allowing
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
the TPS92690 to easily provide constant currents up to 5A. This simple controller contains all
the features necessary to implement a high efficiency versatile LED driver.
CIRCUIT SIMULATED DESIGNED IN MULTISIM
A. PWM wave generation circuit
Timer IC 555 is used to generate
the PWM wave. This PWM
circuit is used to trigger the
TPS926920 IC which is used to
control the intensity and maintain
constant power of SMD LED
Tubelight. When the circuit
powers up, the trigger pin is
LOW as capacitor C1 is
discharged. This begins
Figure 5.1 The output is seen on the CRO.
the oscillator cycle, causing the output to go HIGH. When the output goes HIGH, capacitor C1
begins to charge through the right side of R4 and diode D2. When the voltage on C1 reaches 2/3
of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge
(pin 7) to go LOW. When the output (pin 3) goes LOW, capacitor C1 starts to discharge through
the left side of R4 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and
discharge (pin 7) pins go HIGH, and the cycle repeats. Note the configuration of R4, D1, and D2.
Capacitor C1 charges through one side of R4 and discharges through the other side. The sum of
the charge and discharge resistance is always the same, therefore the wavelength of the output
signal is constant. Only the duty cycle varies with R4. The overall frequency of the PWM signal
in this circuit is determined by the values of R4 and C1. In the schematic above, this has been set
to 144 Hz. To compute the component values for other frequencies, use the formula:
Frequency = 1.44 / (R4 * C1)
In this circuit, the output pin is used to charge and discharge C1, rather than the discharge pin.
This is done because the output pin has a "totem pole" configuration. It can source and sink
current, while the discharge pin only sinks current. Note that the output and discharge pins go
HIGH and LOW at the same time in the oscillator cycle.
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
B. Output of PWM wave
As you can see from the diagram, a 90%
duty cycle signal is on for 90% and off for
10%. These signals are sent to the
TPS926920 ICat a high enough frequency
that the pulsing has no effect on the motor.
The end result of the PWM process is that
the overall power sent to the motor can be
adjusted from off (0% duty cycle) to full on
(100% duty cycle) with good efficiency and
stable control.
Figure 5.2
Table 1 Output
Frequency
Cahnnel A
166.6Hz
221.180mv
C. Hardware implementation
Channel B
3.749V
Fig 5.3
RESULT AND DISCUSSION
The arrangement of SMD led circuits is as shown in figure. If one of the led are short circuited
due to some over flow of current and voltage then also the circuit works properly, there is no
effect to other SMD leds’.They are more efficient so high lumens power exists. The efficiency of
SMD led is more because of less power rating and less power consumption. Only. Limited LED
chain length is allowed, depending on the LED forward voltage Vf and minimum supply voltage
to increase efficiency.There is a requirement to work our circuit between the range of 3V to 24V
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International Journal of Computer Application
(Special issue- Issue 5, Volume 2 (January 2015)
Available online on http://www.rspublication.com/ijca/ijca_index.htm
ISSN: 2250-1797
and using this IC TPS92690 we achieve the target upto 27V.We get upto 90% efficiency at linear
constant source. Also life time of LED is increased.
The arrangement of SMD led circuits is as shown in figure. If one of the led are short circuited
due to some over flow of current and voltage then also the circuit works properly, there is no
effect to other SMD leds.
REFERENCES
[1] Diego Gonzalez Lamar, Javier Sebastian Zuniga, Alberto Rodriguez Alonso, Miguel
RodriguezGonzalez, Marta Maria Hernando Alvarez. A Very Simple Control Strategy for Power
Factor Correctors Driving High-Brightness LEDs. IEEE Transactions on Power Electronics,
2009; 24(8):2032-2042.
[2] Dongsheng Ma, Janet Wang, Minkyu Song. Adaptive On-Chip Power Supply With Robust
One-CycleControl Technique. IEEE Transactions on Very Large Scale Integration (VLSI)
Systems. 2008; 16(9): 1240-1243.
[3] Huang-Jen Chiu, Yu-Kang Lo, Jun-Ting Chen, Shih-Jen Cheng, Chung-Yi Lin, Shann-Chyi
Mou, AHigh-Efficiency Dimmable LED Driver for
[4] Low-Power Lighting Applications. IEEE Transactions on Industrial Electronics. 2010;
57(2): 735-743.
[5] Hongbo Ma, Jih-Sheng Lai, Quanyuan Feng, Wensong Yu, Cong Zheng, Zheng Zhao. A
Novel Valley-Fill SEPIC-derived Power Supply without Electrolytic Capacitors for LED
Lighting Application. IEEE Transactions On Power Electronics. 2012; 27(6): 3057-3071.
[6] KV Hari Prasad, CH Uma Maheswar Rao, A Sri Hari. Design and Simulation of A Fuzzy
LogicController for Buck & Boost Converters. International Journal Advanced Technology&
Engineering Research. 2012; 2(3): 218-224.
[7] Hari S, Balamurugan R. A valley-fill SEPIC-derived power factor correction topology for
LED lightingapplications using one cycle control technique, International Conference on
Computer Communication and Informatics (ICCCI). 2013: 1-4.
[8] E.S.Kim,C.J.Kim, "A Constant Current Controller Design for Power
Transactions on KIEE, Vol.59, No.3, 2010.
LED Drive",
[9] Baixiong Kuang, Jerry Lin, Yongchang Wang, Chin Seong Khor Control network for LEDbased lighting system in a transit vehicle,US8786191B2
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On 6-8 Jan 2015 organized by
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