DC/DC Converter with Transparent Electronics for application on Photovoltaic Panels

Romano Torres19th July 2013 1

Supervisor: Vitor Grade TavaresSecond Supervisor: Pedro Miguel Cândido BarquinhaSecond Supervisor: Pydi Ganga Bahubalindruni

Master of Electrical and Computers Engineering

Outline

• Motivation• Objectives• a-IGZO TFTs• DC/DC Converter• Amplifier• Regulator• Fabrication• Conclusions• Future Work

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Motivation

• To construct circuits on flexible substracts, such as plastic, glass:– Possible to embody in photovoltaic panels.

• Low cost fabrication at room temperature.

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Objectives

• Design of a boost DC/DC converter using transparent electronics in order to have an increased and stable voltage level with direct current.– Vout > 1.5*Vin;– Efficiency >= 40%

• Fabrication of the circuit in CENIMAT/UNL.

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a-IGZO TFTs

• High parasitic resistance;

• P-type transistors with low performance;

• Threshold voltage shift.

5Staggered bottom-gate TFT structure

Problems:

Voltage Boosting Stage – DC/DC converter

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• Indutors are avoided due to their low performance in transparent technology;

• Capacitor is used to save charge in electric field;

• Vdd < Vout < 2*Vdd

Voltage Boosting Stage - out of phase clock signals

7Lower variation of Vout level.

2 Voltage Boosting Stages in Cascade

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• To increase the voltage level twice;

• Parasitic effects reduce the efficiency;

• 4 TFTs of 320 μm in parallel for each diode-connection are used;

• Vdd < Vout << 3*Vdd

Separation between Boosting Stages

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• Allow a stable voltage level at node E;

• Avoid clock feedthrough in TFT1 and TFT2.

3 Boosting Stages in Cascade

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• Proposed DC/DC converter includes 3 Voltage Boosting Stages;

• Settling time is increased.

Bootstrapping Stage – Proposed DC/DC converter

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• Bootstrapping stage is used to reduce the settling time of the circuit;

• Power consumption is negligble;

• Small capacitors and transistors can be used.

Comparison with previous DC/DC converters in the same technology

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DC/DC converter from other authors Proposed DC/DC converter

DC/DC Converter - Simulation

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Output voltage

With Load

I_load = 162 μAVout=16.37 V

Without Load

Vout=35.5 V

Bootstrapping

Cross-connected

Efficiency

• The supplied current of each voltage source is measured (I_in=167 μA);

• The currents multiplied by the supplied voltage (Vin=10V) are added, resulting in the input power;

• With the same current for each voltage source, efficiency is:

• The current supplied in bootstrapping stage is very low (I_bs=0.12μA);

• The efficiency is: 39.93%

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3 Voltage Boosting Stages - Simulation

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Voltage levels for each stage

DC/DC converter - Layout

165793.55 μm

3068.55 μm

10 DC/DC converters in parallel

- The equivalent resistance of 10 converters in parallel is lower than with only one converter.

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Output voltage

Final circuit with regulation

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Circuit specifications:• Vdd = 10 V• R1 and R2 >> RL

Objectives:• Vout 20 V≃• 50% lower ΔV

Advantage:• More stable voltage leveleven with load variation.

Proposed Amplifier – Block diagram

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Amplifier

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Differential Stage

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Positive Feedback Stage

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Source-Follower Stages

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Common-Source Stages

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Phase Compensation

-In order to have higher phase margin.

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Gain and Phase Response

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Gain: 36.7dB

Phase Margin: 83.79°

Proposed Amplifier - Layout

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2383.8 μm

2450 μm

Regulator

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Voltage levels

Vout = 17.65 VThe voltage variation with the load decreased 80%.

Final Circuit - Layout

2918709.55 μm

14557.1 μm

Fabrication

30DC/DC converter with bootstrapping and 2 boosting stages

Conclusions

• DC/DC converter:– Wide transistors reduce parasitic resistance;– Bootstrapping stage decreases settling time;– 10 converters in parallel reduce the parasitic resistance and

allow more voltage boosting stages, increasing the output voltage level.

• Amplifier:– Good phase margin was achieved;– Voltage gain is enough for the regulation;

• Regulator:– 80% lower fluctuation of the voltage level with load

variations. 31

• Improve the design of the amplifier to increase the gain;

• PWM regulation with duty-cycle variation.

Future Work

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The End

Thank you!

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