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.
IC No:MAX856-MAX859 Features: • 0.8V to 6.0V Input Supply Voltage • 85% Efficiency at 100mA • Pin-selectable output voltage of 3.3V or 5V • Circuit extracts the maximum power from a solar array to charge a battery stack • Up to 500kHz Switching Frequency Relevant Link: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1207 http://www.maxim-ic.com/appnotes.cfm/an_pk/484
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 Equipment • 3.3V to 5V Step-Up Conversion • Glucose Meters • Medical Instrumentation • Palmtop Computers • Personal Data Communicators/Computers • Portable Data-Collection Equipment • Solar Powered Applications
IC No:MAX866-MAX867(Using MAX1771 boost controller) Features: • 0.8V to 6.0V Input Supply Voltage • 80% Efficiency Over Wide Load Range • 0.9V Guaranteed Start-Up Supply Voltage • Provide 5V rail under full load and as low as 0.8V input voltage • Up to 250khz Switching Frequency • A two-step approach (Figure ) enables the system to start up and produce the 5V rail under full load. Relevant Link: http://www.maxim-ic.com/appnotes.cfm/an_pk/1029
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 Equipment • Backup Supplies • Detectors • Pagers • Remote Controls • Solar Powered Applications
IC No:TPS61200 TPS61201 TPS61202 Features: • 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 Voltage • Fixed and Adjustable Output Voltage Options from 1.8 V to 5.5 V Relevant Link: http://focus.ti.com/docs/prod/folders/print/tps61200.html
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.
Power saving mode facility is available to improve efficiency at light loading conditions and low frequency. • Under-voltage lock out, over temperature protection, over voltage protection, soft start , short circuit protection is provided. • Due to efficiency constraints i/p current can sometimes be more than 10-20 times that of o/p current at some of operating states and during start-up as impedance is low high current flow can occur.
Usage: • All Single-Cell, Two-Cell and Three-Cell Alkaline, • NiCd or NiMH or Single-Cell Li Battery Powered Products • Fuel Cell And Solar Cell Powered Products • Portable Audio Players • PDAs
IC No:TPS61097-33 Features: • Operating Input Voltage Range From 0.9 V to 5.5 V • Up to 95% Efficiency at Typical Operating Conditions • Fixed Output Voltage Options From 1.8 V to 5.0 V • Power-Save Mode for Improved Efficiency at Low Output Power • Over temperature Protection Relevant Link: http://focus.ti.com/docs/prod/folders/print/tps61097-33.html
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 offsetwhich 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 V • Up to 95% Efficiency at Typical Operating Conditions • Fixed 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 Power • Over temperature Protection Relevant Link: http://focus.ti.com/docs/prod/folders/print/tps61220.html
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 Products • PDAs • Mobile Applications • White LEDs
IC No:TPS61020,TPS61024,TPS61025,TPS61026,TPS61027, TPS61028, TPS61029 Features: • Input Voltage Range: 0.9 V to 6.5 V • 96% Efficient Synchronous Boost Converter • Fixed and Adjustable Output Voltage Options Up to 5.5 V • Output Voltage Remains Regulated When Input Voltage Exceeds Nominal Output Voltage • Low EMI-Converter (Integrated Anti ringing Switch) Relevant Link: http://focus.ti.com/docs/prod/folders/print/tps61020.html
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 Players • PDAs • Cellular Phones • Personal Medical Products • Camera White LED Flash Light
IC No:ZXSC100 Features: • Efficiency maintained over a wide range of input voltages and load currents82% efficiency @ Vin=1V • Start up under full load • Minimum operating input voltage Vin=0.926V • Adjustable output voltage down to Vin to 20 v • Quiescent current typically 150μA referred to input voltage Relevant Link: http://diodes.com/products/catalog/detail.php?item-id=1624&popup=datasheet
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 reachedand 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`s MAX1678(Efficient 1-Cell Step-Up Converter) • 0.87V Guaranteed Start-Up • Up to 90% Efficiency • Efficient 1-Cell Step-Up Converter • Output voltage is preset to 3.3V or can be adjusted from +2V to +5.5V • Vin=.7v to 5.5 v • 45mA Output Current at 3.3V for 1-Cell Input • 90mA Output Current at 3.3V for 2-Cell Input
IC No:TPS63000,TPS63001,TPS63002 Features: • Input Voltage Range: 1.8V to 5.5V • Up to 96% Efficiency • Fixed and Adjustable Output Voltage Options from 1.2V to 5.5V • Automatic Transition between Step Down and Boost Mode • Up to 800-mA Output Current at 3.3V in Boost Mode (VIN > 2.4V) Relevant Link: http://focus.ti.com/docs/prod/folders/print/tps63000.html
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 Players • PDAs • Cellular Phones • Personal Medical Products • White LEDs