Synchronous A novel adaptive minimum frequency control provides up

Synchronous Step-up
DC/DC Converter for White LED Applications

P.Sridevi Ponmalar

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Assistant Professor, Department of Electrical
and Electronics, New Prince Shri Bhavani College of Engineering and Technology,
Chennai, India.

Abstract: A conventional boost converter
has a high power efficient CMOS adaptive controlled boost step-up LED drive
implemented in BCD technology. A novel adaptive minimum frequency control
provides up to 52v from a single battery 4.5v input supply to ten series
connected LEDs at the output. The proposed control scheme provides an accurate
load current while achieving high power efficiency than conventional fixed on
time schemes. TPS40211 and TPS40210are able to switch between PWM (pulse width
modulation) automatically by calculating the feed backs from the inductor and
LEDs current. This controller is functional from light to heavy loading
situations which critical in improvement of power efficiency and battery
life-time for high boost ratio applications in order as provide accurate LED current.

Keywords:
CMOS (complementary metal oxide-semiconductor), BCD technology, PWM (pulse
width modulation control),TPS40211 and TPS40210, LED(light emitting diode).

     Introduction

In
Recent Years, wide use of electrical equipment has forced strict demands for
electrical utilizing energy and this development is constantly growing.
Accordingly, researchers and governments worldwide have prepared on renewable
energy applications for explanatory natural energy consumption and
environmental location. Among different renewable energy sources, the
photovoltaic cell and fuel cell have been considering attractive choice.
However, without additional arrangements, the output voltages generated from
both sources. Thus, a high step-up dc-dc converter is desired in the

 

power
conversion systems corresponding to these two energy sources. In addition to
the mentioned applications, a high step-up dc-dc converter is also required by
many industrial applications, such as high-intensity discharge lamp ballasts
for automobile headlamps and battery backup systems for uninterruptible power
supplies. The conventional boost converter can be advantageous for Step-up
applications that do not demand very high voltage gain, mainly due to the
resulting low conduction loss and design simplicity. Theoretically, the boost
converter static gain tends to be infinite when duty cycle also tends to unity.
However, in practical terms, such gain is limited by the I2R loss
in the boost inductor due to its intrinsic resistance, leading to the necessity
of accurate and high-cost drive circuitry for the active switch, mainly because
great variations in the duty cycle will affect the output voltage directly.

To
overcome this disadvantage the TPS40210 and TPS40211 are used. They are the
wide-input voltage (4.5V to 52V), non-synchronous boost controllers. They are
suitable for topologies which require a grounded source N-channel FET including
boost, fly back, SEPIC and various LED driver applications. The device features
include programmable soft start, over current protection with automatic retry
and programmable oscillator frequency. Current mode control provides improved
transient response and simplified loop compensation. The main difference
between the two parts is the reference voltage to which the error amplifier
regulates the FB pin.

Methodology

To
achieve more efficiency when compare to the existing system nearer to 95%. To
reduce switching loses and power dissipations. To reduce the complex design of
the circuit for the external processing units like error amplifier, current and
voltage sensing unit, PWM controller unit, current and voltage regulator,
oscillator unit and soft switching unit. To produce the high voltage gain with
low input voltage. To maintain the proper duty cycle. To reduce the power
losses in the circuit. The boost converter system consist of one inductor,
capacitor, resistor, controller IC and switch for its operation. The one side
of the inductor is connected to the input terminal and the  another side is connected between switch and
diode meting point. The other side of the diode is connected to the capacitor.
The resistor is connected across the output terminal. The controller IC unit is
connected with the MOSFET switch for PWM operation and also connected with the
another ends of the capacitor, resistor and positive region of the output
terminal to perform the current and voltage limiting, controlling, regulating
operations. The over all control of the circuit is carried out by the TPS40211
OR TPS40210 ICs. The control of the input and output over voltages and over
current, error amplification, voltage regulation, fault clearance and duty
cycle maintenance all are can be done using a single IC. So that the design
complexity is reduced. The heat losses due to the single IC is low when compare
to the conventional method. So that we can able to achieve the 95% efficiency.

Figure 1. functional block diagram of boost
converter

 

 

 

Detailed Description Of Functional Block Diagram

The TPS40210 and
TPS40211 are high-efficiency LED drivers each featuring an integrated DC-DC
inductive boost converter and six high-precision current sinks. TPS40210 is
intended for applications that exclusively use a pulse width modulated (PWM)
signal for controlling the brightness while TPS40211 is intended for
applications that can utilize an I2C master as well.

The boost
converter has adaptive output voltage control. This feature minimizes the power
consumption by adjusting the voltage to the lowest sufficient level under all
conditions.

The adaptive
current sink headroom voltage control scales the headroom voltage with the LED
current for optimal system efficiency.

The LED string
auto-detect function enables use of the same device in systems with 1 to 10 LED
strings for the maximum design flexibility.

Proprietary
hybrid PWM plus current mode dimming enables additional system power savings.
Phase shift PWM allows reduced audible noise and smaller boost output
capacitors.

Flexible CABC
support combines brightness level selections based on the PWM input and I2C
commands.

The TPS40210 and
TPS40211 feature a full set of features that ensure robust operation of the
device and external components. The set consists of input under voltage
lockout, thermal shutdown, overcurrent protection, overvoltage protection, and
LED open and short detection.

Boost Converter

The boost
converter is defined as the output voltage is always greater than the input
voltage. Switched mode supplies can be used for many purposes including DC to
DC converters. Often, although a DC supply, such as a battery may be available,
its available voltage is not suitable for the system being supplied. For
example, the motors used in driving electric automobiles require much higher
voltages, in the region of 500V, than could be supplied by a battery alone.
Even if banks of batteries were used, the extra weight and space taken up would
be too great to be practical. The answer to this problem is to use fewer
batteries and to boost the available DC voltage to the required level by using
a boost converter. Another problem with batteries, large or small, is that
1their output voltage varies as the available charge is used up, and at some
point the battery voltage becomes too low to power the circuit being supplied.
However, if this low output level can be boosted back up to a useful level
again, by using a boost converter, the life of the battery can be extended. The DC input to a boost converter can
be from many sources as well as batteries, such as rectified AC from the mains
supply, or DC from solar panels, fuel cells, dynamos and DC generators. The
boost converter is different to the Buck Converter in that it’s output voltage
is equal to, or greater than its input voltage. However it is important to
remember that, as power (P) = voltage (V) x current (I), if the output voltage
is increased, the available output current must decrease.     MOSFET, both Bipolar power transistors and
MOSFETs are used in power switching, the choice being determined by the
current, voltage, switching speed and cost considerations. The rest of the
components are the same as those used in the buck converter

 TPS40211 AND TPS40210

The TPS40210 and TPS40211 are
used. They are the wide-input voltage (4.5V to 52V), non-synchronous boost
controllers. They are suitable for topologies which require a grounded source
N-channel FET including boost, fly back, SEPIC and various LED driver
applications. The device features include programmable soft start, over current
protection with automatic retry and programmable oscillator frequency. Current
mode control provides improved transient response and simplified loop
compensation. The main difference between the two parts is the reference
voltage to which the error amplifier regulates the FB pin.

Capacitor

Boost Input And Vdd Capacitor Selection

The VDD pin is
typically tied to the same supply as the input of the boost power stage (VIN
node). A 10µF input capacitor is recommended on that node. The voltage

rating of the
capacitor must be at least 10 V. If a supply powering the VDD pin is different
from a supply powering the boost power stage, then 10-µF input capacitors are
required on both VDD and VIN nodes.

Boost Output Capacitor Selection

The inductive
boost converter typically requires two 4.7-µF output capacitors. The voltage
rating of the capacitor must be 35 V or higher as the OVP threshold is at 29.6
V (typ). Pay careful attention to the capacitor tolerance and DC bias response.
For proper operation of the degradation in capacitance

due to
tolerance, DC bias, and temperature should stay above 2 µF. This might require
placing more than two devices in parallel in order to maintain the required
output capacitance over the device operating temperature and output voltage
range.

Inductor

Inductor Selection

The
chosen inductor must be from 10 to 22 µH (for 500-kHz operation) or 4.7 to 10
µH (for 1-MHz operation) and must have a saturation rating equal to, or greater
than, the circuit’s peak operating current.

Performance Analysis

The main
intension of this paper is to design a high efficient boost converter. Hardware
consists of three main constituent which are the input, adaptive boost
converter and the output. The input voltage is from the solar panel, the
adaptive boost converter function is to get high output voltage and to increase
the efficiency these can be achieved by using TPS40211, TPS40210, LP8557,
LP85571 type ICs. These types of ICs are multitasking devices so that they can
act like a regulator for the output voltages and currents, error amplifier,
disable and enable operator, soft switcher, switching frequency manager,
current and voltage sensor, high output gain producer and duty cycle
maintenance operator. These all controlling processes can be done in a single
IC. So that the circuit complex can be reduced, losses also reduced, efficiency
can be obtained is high and the out put voltage is used to glow the LEDs.The boost DC-DC converter generates a 50V to 52V boost
output voltage from a 4.2V to 4.5-V boost input voltage.The converter is a
magnetic switching PWM mode DC-DC inductive boost converter with a current
limit. It uses current programmed mode control, where the inductor current is
measured and controlled with the feedback. During start-up, the soft-start
function reduces the peak inductor current.

Simulation Results

The fully integrated
LED driver circuit is functional for LED currents up to 50 mA at low input
supply voltages (3.0 V to 5.5 V). The LED driver with PWM & PFM controllers
is fully functional in the 40 V process of 0.25 ?m BCD technology, as shown by
the simulated gate-drive, inductor current, LED current and output voltage
waveforms presented in Fig. 2 and Fig. 3.  

Fig.2
Simulated gate-drive, inductor current, led current (50 mA) and output voltage
waveforms of the proposed PWM mode

 

Fig.3 Simulated gate-drive,
inductor current, led current (16 mA)and output voltage waveforms of the
proposed PFM mode

V(gate) is the gate drive signal
of power MOSFET M1. I(L) and I(LED) are the inductor current and the LED
current, respectively. V(boost) is the boost converter output voltage. In Fig.
2, the converter is operating at constant 1 MHz PWM mode. Ripple pk-pk of the
output LED current is 1.34%. In Fig. 3, the controller operating frequency is
not constant and is around 250 kHz. Ripplepk-pk of the output LED current in
PFM mode is 2.75%.

Output Voltage Vs Load Current

                           ILOAD –
Load Current – A

Fig.4 The Graph Between Vout And Iload

Fig.6 Efficiency of 10 LED string

The efficiency
of the proposed PWM/PFM controller has been measured when the LED current is
changing from 3mA to 50 mA. The controller switches between PWM and PFM modes
automatically with the changes of the LED current. The averaged efficiency of
the converter is 86%. This boost LED driver provides up to 32 V from a single
battery (3.6 V to 5.5 V) input supply to 10 series-connected LEDs at the
output, 30mA is the switchover point between PFM mode and PWM mode. PFM
acquires high efficiency when the LED current is less than 30mA. PWM acquires
high efficiency when the LED current is larger than 30mA. The combination
modulation of PWM and PFM realizes constant high power efficiency in a wide
range of LED currents.

 Conclusions

  A novel combination of PWM and PFM controlled
boost converter is proposed, designed, and simulated in 0.25 ?m BCD technology.
The converter provides up to 32 V from a 3.6 V to 5.5 V input supply for 10
serial LEDs at the output. To obtain the best power management efficiency, the
controller switches between PWM mode and PFM mode automatically as the LED
current changes. The averaged efficiency of the converter is 86% when the LED
current is on the range of 3

References 

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Richardson.”Driving high-power LEDs in series-parallel arrays”,National
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 5.  C.H.
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