We claim:1. A circuit comprising:a photovoltaic cell;an integrator having a first input coupled to the photovoltaic cell, a second input coupled to a reference voltage, and an output; anda regulator having a conducting terminal coupled to the output of the integrator and a voltage regulated output regulated by the reference voltage;wherein the integrator is configured to adjust the reference voltage provided to the regulator in response to a voltage drop in the photovoltaic cell.2. The circuit of claim 1 further comprising:a first resistor having a first lead coupled to the photovoltaic cell and a second lead coupled to the first input;a second resistor having a first lead coupled to the first resistor and a second lead coupled to ground; anda third resistor having a first lead coupled to the first resistor and the second resistor.3. The circuit of claim 1 further comprises:a capacitor having a first lead coupled to the first input of the integrator and a second lead coupled to the output of the integrator; anda first transistor having a control terminal coupled to the output of the integrator, a first conducting terminal coupled to a current source and a second conducting terminal coupled to a fourth resistor.4. The circuit of claim 2 wherein the regulator further comprises:a second transistor having a control terminal and the first conducting terminal coupled to the first conducting terminal of the first transistor and a second conducting terminal coupled to ground;a third transistor having a control terminal coupled to the control terminal of the second transistor, a first conducting terminal coupled to ground and a second conducting terminal coupled to an operational amplifier;a fourth transistor having a first conducting terminal coupled to the current source and a second conducting terminal coupled to the operational amplifier;a fifth transistor having a first conducting terminal coupled to the current source, a second conducting terminal coupled to the operational amplifier and a control terminal coupled to a control terminal of the fourth transistor; anda diode coupled to the operational amplifier and the fifth transistor.5. The circuit of claim 1 wherein the reference voltage comprises a temperature coefficient that is essentially equal to a temperature coefficient of the photovoltaic cell.6. The circuit of claim 1 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a pulse wave modulator.7. The circuit of claim 1 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a battery.8. A circuit comprising:a photovoltaic cell;an integrator having a first input coupled to the photovoltaic cell, a second input coupled to a reference voltage, and an output;a first transistor having a control terminal and a first conducting terminal coupled to the output of the integrator and a second conducting terminal coupled to ground;a second transistor having a control terminal coupled to the control terminal of the second transistor, a first conducting terminal coupled to ground and a second conducting terminal coupled to an operational amplifier;a third transistor having a first conducting terminal coupled to the current source and a second conducting terminal coupled to the operational amplifier;a fourth transistor having a first conducting terminal coupled to a current source, a second conducting terminal coupled to the operational amplifier and a control terminal coupled to a control terminal of the third transistor; anda diode coupled to the operational amplifier and the fourth transistor;wherein the integrator is configured to adjust the reference voltage provided to the first conducting terminal of the first transistor in response to a voltage drop in the photovoltaic cell.9. The circuit of claim 8 further comprising:a first resistor having a first lead coupled to the photovoltaic cell and a second lead coupled to the first input;a second resistor having a first lead coupled to the first resistor and a second lead coupled to ground; anda third resistor having a first lead coupled to the first resistor and the second resistor.10. The circuit of claim 8 further comprises:a capacitor having a first lead coupled to the first input of the integrator and a second lead coupled to the current limiting output of the integrator; anda fifth transistor having a control terminal coupled to an output of the integrator, a first conducting terminal coupled to a current source and a second conducting terminal coupled to a fourth resistor.11. The circuit of claim 8 wherein the reference voltage comprises a temperature coefficient that is essentially equal to a temperature coefficient of the photovoltaic cell.12. The circuit of claim 8 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a pulse wave modulator.13. The circuit of claim 8 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a battery.14. A circuit comprising:a photovoltaic cell;an integrator having a first input coupled to the photovoltaic cell, a second input coupled to a reference voltage, and an output;a capacitor having a first lead coupled to the first input of the integrator and a second lead coupled to the output of the integrator;a first transistor having a control terminal coupled to the output of the integrator, a first conducting terminal coupled to a current source and a second conducting terminal coupled to a fourth resistor;a regulator having a control terminal coupled to the current source and a voltage regulated output regulated by the reference voltage;wherein the first transistor is configured to adjust the reference voltage provided by the integrator to the regulator in response to a voltage change in the photovoltaic cell.15. The circuit of claim 14 further comprising:a first resistor having a first lead coupled to the photovoltaic cell and a second lead coupled to the first input;a second resistor having a first lead coupled to the first resistor and a second lead coupled to ground; anda third resistor having a first lead coupled to the first resistor and the second resistor.16. The circuit of claim 14 wherein the regulator further comprises:a third transistor having a control terminal coupled to the control terminal of the second transistor, a first conducting terminal coupled to ground and a second conducting terminal coupled to an operational amplifier;a fourth transistor having a first conducting terminal coupled to the current source and a second conducting terminal coupled to the operational amplifier;a fifth transistor having a first conducting terminal coupled to the current source, a second conducting terminal coupled to the operational amplifier and a control terminal coupled to a control terminal of the fourth transistor; anda diode coupled to the operational amplifier and the fifth transistor.17. The circuit of claim 14 wherein the reference voltage comprises a temperature coefficient that is essentially equal to a temperature coefficient of the photovoltaic cell.18. The circuit of claim 14 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a pulse wave modulator.19. The circuit of claim 14 further comprising an inductor having a first terminal coupled to the diode and a second terminal coupled to a battery.