Switching Voltage Regulator
- 1. Switching Voltage Regulator Group 17 Jeffrey Little Taylor Caggiano Ivan Bercovich
- 2. Progress Report Block Diagram Description Individual Responsibilities Functionality Specifications Power Issues Summary
- 3. 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. Error Amp : 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.
- 4. 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
- 5. Error Amplifier From Feedback From Reference To 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
- 6. From Analog Devices Application Note
- 7. Oscillator 741 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.
- 8. Switch “ Sziklai Pair” BJT Configuration Uses a NPN and PNP to supply more current Current supplied is the product gain of the two transistors
- 9. ƒ ripple ≈ ƒ triangle_wave. Therefore, we can pick C so that most of the AC noise is forwarded to ground. Description (Switching)
- 10. Duty Cycle = T HIGH /T≈ Vo Functionality
- 11. Ripple Ripple at the Output with .56 µF Capacitor at Output Ripple at the Output with 680µF Capacitor at Output
- 13. 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)
- 14. Progress Report
- 15. 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.