Switching Voltage Regulator

ECE 324 Term Project – Little, Caggiano, Bercovich

Switching Voltage RegulatorGroup 17

Jeffrey LittleTaylor CaggianoIvan Bercovich

ECE 324 Term Project – Little, Caggiano, Bercovich

Progress Report

•Block Diagram•Description•Individual Responsibilities•Functionality•Specifications•Power Issues•Summary

3ECE 324 Term Project – Little, Caggiano, Bercovich

Block Diagram

Reference Voltage: Adjustable voltage set by the 13V supply and a 50k potentiometer. Input to the Error Amp and compared with the feedback.

ErrorAmp: Linear amplifier made with a 741 Op Amp with a Gain of 50V/V. Outputs an Error Voltage that determines the duty cycle of the pulse input to the switch.

Comparator: Compares the Error Voltage to a triangle wave (32 kHz oscillator). Produces a pulse train with a duty cycle proportional to the error. Responsible for turning the switch on and off.

Switch: BJT Configuration (Sziklai Pair)- Turned on and off at the rhythm specified by the output pulse from the comparator. Allows current to flow to the output.

Filter: Maintains continuous voltage at output. Inductor assures a constant current flow and capacitor filters 32kHz switching frequency.

Feedback: Feeds the output voltage to the Error Amp to be compared with the reference.

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Individual Responsibilities

Jeffrey Little•Oscillator & Pulse Width Modulation Design •Oscillator & PWM Construction•Debug•Pre-design planning, Division

Taylor Caggiano•Filter & Feedback Design •Filter & Feedback Construction•Debug•Slides for Final Demonstration •Report Ivan Bercovich •Switch Design •Switch Construction•Debug•Integration Analyst•Progress Report Slides

5ECE 324 Term Project – Little, Caggiano, Bercovich

Error Amplifier

From Feedback

From ReferenceTo Comparator

The gain of the linear amplifier is defined by a resistor ratio. In our case, we are using 50K (light) and 1K (dark) resistors in order to get a 50 V/V gain

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From Analog Devices Application Note

7ECE 324 Term Project – Little, Caggiano, Bercovich

Oscillator741 Op Amp used as an integrator.

Comparator used to generate square wave by hitting the negative and positive rails.

Frequency is defined by RC:Where Vs is the amplitude of the wave and Vp is the positive supply.

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Switch

“Sziklai Pair” BJT Configuration•Uses a NPN and PNP to supply more current •Current supplied is the product gain of the two

transistors

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ƒripple ≈ ƒtriangle_wave.

Therefore, we can pick C so that most of the AC noise is forwarded to ground.

Description (Switching)

10ECE 324 Term Project – Little, Caggiano, Bercovich

Duty Cycle = THIGH/T≈ Vo

Functionality

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Ripple

Ripple at the Output with .56 µF Capacitor at Output

Ripple at the Output with 680µF Capacitor at Output

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DEMONSTRATE FUNCTIONALITY

13ECE 324 Term Project – Little, Caggiano, Bercovich

Specifications

Adjustable between 1.85V and 11.5V at full load.

Capable of sourcing 145mA over all range.

Output voltage ripple 30mV

Low dynamic output resistance.

Efficiency 50% @ 2V -> 84% @ 11.5V

Voltages adjustable between 2 and 10 V.

Capable of sourcing 120mA over full voltage range.

Low output voltage ripple (<50mV)

Low dynamic output resistance.

Efficiency 50%, η=(Power Supplied to the load)/(Total Power Consumed)

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Progress Report

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Summary

•Pulse Width Modulation Design•Goal: Creating a pulse train with a duty cycle that depends on the input voltage.

•Filter Circuitry•Goal: Choose appropriate Capacitor value for the specified 1.1mH inductor. Achieving required ripple spec.

•Note: Calculated capacitor value is much smaller than actual.

•Switch•Goal: Ensure total ON and OFF switching in response to pulses. Transistor must be able to handle current and voltage required.

•Note: “Sziklai Pair” Method Implemented to increase current gain.

•Switch Driver & Feedback Loop•Goal: Add protection diode and filter and see output voltage vary respectively with input to

PWM. Connect feedback.

•Efficiency Measures•Goal: Measure in appropriate locations for accurate calculations. Measure ripple.

•Note: Measure after supply filtering and at both ends of the voltage spec.

16ECE 324 Term Project – Little, Caggiano, Bercovich