Power management IC for single solar cell

A single solar cell provides close to 0.5 V output at its maximum power point, which is very

low for any electronic circuit to operate. To get rid of this problem, traditionally multiple

solar cells are connected in series to get higher voltage. The disadvantage of this approach

is the efficiency loss for partial shading or mismatch. Even as low as 6-7% of shading can

result in more than 90% power loss. Therefore, Maximum Power Point Tracking (MPPT)

at single solar cell level is the most efficient way to extract power from solar cell.

Power Management IC (MPIC) used to extract power from single solar cell, needs to

start at 0.3 V input. MPPT circuitry should be implemented with minimal power and area

overhead. To start the PMIC at 0.3 V, a switch capacitor charge pump is utilized as an

auxiliary start up circuit for generating a regulated 1.8 V auxiliary supply from 0.3 V input.

The auxiliary supply powers up a MPPT converter followed by a regulated converter. At

the start up both the converters operate at 100 kHz clock with 80% duty cycle and system

output voltage starts rising. When the system output crosses 2.7 V, the auxiliary start up

circuit is turned off and the supply voltage for both the converters is derived from the system

output itself. In steady-state condition the system output is regulated to 3.0 V.

A fully integrated analog MPPT technique is proposed to extract maximum power from

the solar cell. This technique does not require Analog to Digital Converter (ADC) and

Digital Signal Processor (DSP), thus reduces area and power overhead. The proposed

MPPT techniques includes a switch capacitor based power sensor which senses current of

boost converter without using any sense resistor. A complete system is designed which

starts from 0.3 V solar cell voltage and provides regulated 3.0 V system output.