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Abstract:Solar Cell Knowledge; Characteristic Equation:

I = IL − ID − ISH Vj = V + IRS Shockely Diode Equation:

•Variation in internal R cause o/p voltage variation.•Intensity is inversely proportional to current, which limits at constant voltage.

I-V characteristic Of Solar cell:

•Direct connection to battery is not possible due to variation in battery voltage.•Varying sunlight affects current, hence electronics to optimize power is needed.

BOOST TOPOLOGY:

IC No:MAX856-MAX859Features:0.8V to 6.0V Input Supply Voltage85% Efficiency at 100mAPin-selectable output voltage of 3.3V or 5VCircuit extracts the maximum power from a

solar array to charge a battery stackUp to 500kHz Switching Frequency

Circuit For MAX856

This circuit enables a seven-cell solar panel to charge a three-cell NiCd battery

Operation:High Efficiency C-MOS switching regulator:The MOSFET used has very low threshold voltage to

ensure start-up at low voltages.Unique minimum turn-off time PFM control

scheme is unique feature of the device.No oscillator; switching is accomplished by a pair of

one shots that set a maximum LX on-time (4.5μs type) and a minimum LX off-time(1μs). LX on-time will be terminated early if the inductor current reaches 0.5A before 4.5μs elapses.

Device has a low battery detection facility.Bootstrapped device , hence can turn on at very low

voltage.

Usage:2-Cell and 3-Cell Battery-Operated

Equipment3.3V to 5V Step-Up ConversionGlucose MetersMedical InstrumentationPalmtop ComputersPersonal Data Communicators/ComputersPortable Data-Collection EquipmentSolar Powered Applications

IC No:MAX866-MAX867(Using MAX1771 boost controller)

Features:0.8V to 6.0V Input Supply Voltage 80% Efficiency Over Wide Load Range0.9V Guaranteed Start-Up Supply VoltageProvide 5V rail under full load and as low as 0.8V

input voltageUp to 250khz Switching FrequencyA two-step approach (Figure ) enables the system

to start up and produce the 5V rail under full load.

Typical Operating Circuit:

This two-stage step-up converter derives 0.5A at 5V from a typical solar-cell array, and guarantees start-up under full load.

Usage:1-Cell Battery-Operated EquipmentBackup SuppliesDetectorsPagersRemote ControlsSolar Powered Applications

IC No:TPS61200 TPS61201 TPS61202Features:Operating Input Voltage Range from 0.3 to 5.5 More than 90% Efficiency at

300 mA Output Current at 3.3 V (VIN ≥ 2.4 V)600 mA Output Current at 5 V (VIN ≥ 3 V)

Start-up into Full Load at 0.5 V Input VoltageFixed and Adjustable Output Voltage Options

from 1.8 V to 5.5 V

•Solar cell current depends on area and light intensity. As an effect its important to control current in an application.•This can be done either by limiting current to a certain value or controlling power circuit to operate in most efficient manner.•This is accomplished by keeping I/p voltage to a Certain value where power delivered to supply is maximum , called as maximum power point regulation(MPP).•This circuit also helps in start-up by avoiding access current to flow.

Operation:Average Current Mode topology:Fixed frequency PWM with synchronous rectification.Average inductor current is regulated by a fast current

regulator which is controlled by a voltage control loop.Changes in i/p and o/p voltages is monitored through feed-

forward , and can immediately change the o/p to achieve fast response to these errors.

Controller also sense the maximum peak current for stable and safe operation.

3 N-MOSFETs to maintain synchronous power conversion.Down regulation circuit is turned on when i/p exceeds o/p

voltage, in this mode controller changes the behavior of 2 MOSFET switches to ensure proper and stable regulation of o/p voltage.

Usage:All Single-Cell, Two-Cell and Three-Cell

Alkaline, NiCd or NiMH or Single-Cell Li Battery

Powered ProductsFuel Cell And Solar Cell Powered ProductsPortable Audio PlayersPDAs

IC No:TPS61097-33Features:Operating Input Voltage Range From 0.9 V to 5.5

VUp to 95% Efficiency at Typical Operating

ConditionsFixed Output Voltage Options From 1.8 V to 5.0 VPower-Save Mode for Improved Efficiency at

Low Output PowerOver temperature Protection

Typical Operating Circuit:

OPERATION:Synchronous boost topology. For power switching two actively controlled low R MOSFETs are used.

Controller Circuit• Hysteretic Current Mode controller. • VOUT is monitored through FB n o/p is reflected in current

offset which regulates the o/p voltage.

• Bypass switch turns off when EN is high to make IC as standard Boost Converter , when EN is low it turns on n

bypasses I/p to O/p.

• For low i/p start up circuit turns on to build up sufficient voltage. And as soon as voltage reaches 1.8V it turns of and

i/p voltage controls the circuit.• Circuit provides under voltage lockout, overvoltage

protection, over temperature protection.

Inductor Selection: 4.7μH show good performance over wide range of i/p and o/p.

Usage:All Single-Cell, Two-Cell, and Three-Cell

Alkaline, NiCd, NiMH, or Single-Cell Li-Battery Powered Products

Personal Medical Products Fuel Cell and Solar Cell Powered Products

PDAs Mobile Applications White LEDs

IC No:TPS61220,TPS61221,TPS61222

Features:Operating Input Voltage Range From 0.7 V to 5.5

VUp to 95% Efficiency at Typical Operating

ConditionsFixed Output Voltage Options From 1.8 V to 5.0

V(also available in fixed voltage)Power-Save Mode for Improved Efficiency at

Low Output PowerOver temperature Protection

Typical Operating Circuit:

Working is same as TPS61097-33:

Usage:All Single-Cell, Two-Cell, and Three-Cell

Alkaline, NiCd, NiMH, or Single-Cell Li-Battery Powered Products

Fuel Cell and Solar Cell Powered ProductsPDAs Mobile Applications White LEDs

IC No:TPS61020,TPS61024,TPS61025,TPS61026,TPS61027, TPS61028, TPS61029

Features:Input Voltage Range: 0.9 V to 6.5 V96% Efficient Synchronous Boost ConverterFixed and Adjustable Output Voltage Options Up to

5.5 V Output Voltage Remains Regulated When Input

Voltage Exceeds Nominal Output VoltageLow EMI-Converter (Integrated Anti ringing Switch)

Operation:Fixed Frequency PWM using Multiple feed forward topology : I/p , o/p and voltage drop on N MOSFET is monitored and

forwarded to regulator.(It avoids a slow way through control circuit and error amplifier, and hence increased o/p response).

So control circuit has to handle only small error signal through FB to create more stable o/p.

Peak current on N-MOSFET is sensed to limit current to 1.5A.Device integrates 2 N and P MOSFETS, due to use of low R P

channel MOSFET instead of Schottky rectifier increases efficiency.

Special circuit is deployed using back-gate diode of P-MOSFET to disconnect the o/p load from battery when EN is low. IT hence avoids depletion of battery during shutdown.

Two grounds(GND & PGND) to avoid ground shift.Down regulation mode is turned on when i/p voltage

exceeds o/p voltage, in this mode behavior of P-MOSFET changes accordingly to regulate the voltage.

Circuit enters into a PRECHARGE phase during startup to avoid large current. In this phase it charges the different capacitor till o/p reaches to a certain value.

Circuit provides short circuit protection, under voltage lockout, thermal protection, overvoltage protection.

Device integrates a circuit to avoid ringing when device enters into discontinuous mode.

Usage:All One-Cell, Two-Cell and Three-Cell

Alkaline, NiCd or NiMH or Single-Cell Li Battery, Solar Powered Products

Portable Audio PlayersPDAsCellular PhonesPersonal Medical ProductsCamera White LED Flash Light

IC No:ZXSC100Features:Efficiency maintained over a wide range of input

voltages and load currents82% efficiency @ Vin=1V

Start up under full loadMinimum operating input voltage Vin=0.926VAdjustable output voltage down to Vin to 20 vQuiescent current typically 150μA referred to input

voltage

Operation:Non-Synchronous PFM DC-DC controller IC:Shutdown circuits turns on/off when VCC=1v.At start up COMP1 turns on, hence driver circuit and switching

transistor. This circuit will remain active until voltage at FB exceeds 730mV.

An external resistive network at FB sets the o/p voltage level .COMP 2 forces switching transistor to turn off when Isense

(voltage at emitter of switching transistor) voltage exceeds 25mV.

A mono-stable following the COMP2 extends turn off time of drive to minimum of 2 µS ensuring sufficient time for discharge of inductor.

AND gate ensures switching transistor is always on until Isense

threshold is reached and minimum discharge period is always asserted.

Usage:Cordless telephones

• MP3 players• PDA• Pagers• Battery backup supplies• Electronic toothbrush• GPS receivers• Digital camera• Palmtop computers• Hand held instruments• Portable medical equipment• Solar powered equipment

Other Important IC`sMAX1678(Efficient 1-Cell Step-Up

Converter)0.87V Guaranteed Start-UpUp to 90% EfficiencyEfficient 1-Cell Step-Up ConverterOutput voltage is preset to 3.3V or can be

adjusted from +2V to +5.5VVin=.7v to 5.5 v45mA Output Current at 3.3V for 1-Cell Input90mA Output Current at 3.3V for 2-Cell Input

Circuit For MAX1678

IC No:TPS63000,TPS63001,TPS63002

Features:Input Voltage Range: 1.8V to 5.5VUp to 96% EfficiencyFixed and Adjustable Output Voltage Options from

1.2V to 5.5VAutomatic Transition between Step Down and

Boost ModeUp to 800-mA Output Current at 3.3V in Boost

Mode (VIN > 2.4V)

Operation:Device is based on average current topology:

Almost same as that of TPS61200 with some minor differences in voltage levels .

Usage:All Two-Cell and Three-Cell Alkaline, NiCd or

NiMH or Single-Cell Li Battery Powered Products

Portable Audio PlayersPDAsCellular PhonesPersonal Medical ProductsWhite LEDs

IC No:AP6714Features:Input Voltage Range: .9V to 5.5V94% Efficient Step-Up DC to DC ConverterFixed and Adjustable Output Voltage Options

from 1.8V to 5VCurrent Mode Operation for faster transient

response and better loop stability1.8MHz Operating Frequency

Usage:All One-cell, Two-cell, Three cell, Alkaline,

NiCd or NiMh or Single-cell Li+ Battery Powered Devices.

Cell PhonesDigital CamerasMP3 PlayersPDAs

IC No: NCP1400A: 100 mA, Fixed Frequency PWM Step-Up Micro-power Switching Regulator

Features:Extremely Low Start-Up Voltage of 0.8 VOperation Down to Less than 0.2 VOnly Four External Components for Simple Highly

Efficient ConvertersUp to 100 mA Output Current CapabilityFixed Frequency Pulse Width Modulation OperationOutput voltage can be vary from 1.8 to 5.5v(in fixed

mode)

Operation:Micro-power Step Up DC-DC Converter:Power switching regulators optimized for applications

where power drain must be minimized.Designed to operate in discontinuous mode as fixed

frequency voltage mode boost converter.Soft-start circuit initially pumps up the voltage up to 1.5 v

at a fixed D, the level at which it can operate normally.Device is designed to operate in discontinuous mode . An

internal circuit is employed to insure stability at all i/p and o/p voltage levels.

Over voltage protection, excessive current limit, thermal shutdown is provided.

Usage:Cellular TelephonesPagersPersonal Digital AssistantsElectronic GamesCamcordersHandheld Instruments

Other Similar Products:NCP1450A, NCP1402A

IC No:S-882Z(A charge Pump IC for low power DC-DC conversion)

Features:Operating input voltage: 0.3 to 3.0 VCurrent consumption: During operation 0.5 mA max. (at

VIN = 0.3 V), During shutdown 0.6 µA max. (at VIN = 0.3 V)

Discharge start voltage: 1.8 to 2.4 V (selectable in 0.2 V steps)

Shutdown voltage: Discharge start voltage + 0.1 V (fixed)Oscillation frequency: 350 kHz typ. (at VIN = 0.3 V)

Usage:Stepping up from low-voltage power supply

such as solar cell and fuel cellStepping up internal power supply voltage of

RF tagIntermittent power supply to intermittently

operating system