DC-DC Converter

1. DC-DC Converter Aashiv Shah Peng Xu Sheesh Nanda

2. Why DC-DC Converter? • Parts of Maharashtra, India have unreliable power supply • Pedal Power used to charge batteries and run gadgets • Batteries are 12 Volts and cannot be used to run radios, lamps etc as they need 3V/6 V • Our design, which converts 12V to 3V/6V will be used to overcome this problem

3. OVERVIEW • Open Loop Used a potentiometer to verify working of circuit without feedback • Closed Loop Added feedback to the circuit and checked working of circuit for outputs of 6V/3V • PCB Implementation Implemented our circuit using Easytrax

4. Picture Of Circuit

5. Component used in circuit • TL494 • IR2117 • MTP50N60V • 1N5820-T

6. TL 494 • Pulse Width Modulation Chip • Used to set Duty Ratio Duty Ratio is set to 0.25 to obtain an output of 3V and 0.5 to obtain an output of 6V

7. IR2117 • High Side Gate Drive • Output of TL 494 not large enough to drive the transistor. • IR 2117 increases the output of the TL 494 so that it can be used to drive the transistor

8. Selection of Diode and Transistor • Diode requires blocking voltage of 12V, forward current of 0.5A and fast switching • Selected 1N5820 Schottky with following parameters Blocking Voltage of 20V Forward current of 3A • Transistor requires same parameters as diode MTP50N06V with blocking voltage of 60V and forward current of 42A used

9. TL494 • 1IN+,1IN- input to amplifier • CTTiming Capacitor • RT Timing Resistor • REF  Reference Voltage • C1  Output

11. TESTING OF TL494 • Voltage waveform across CT (3V peak to peak) (Timing Capacitor) • Voltage across C1 •  PWM comparator combines the saw-tooth waveform from the timing capacitor and DC voltage from potentiometer to give square waveform •  Obtain duty ratio from on-time of TL494

12. OPEN LOOP CIRCUIT • Connect the REF and FEEDBACK with the potentiometer • Manually changed the duty ratio by using the potentiometer as a voltage divider • Used to test the circuit to get 3V/6V output

13. Schematic Of Open Loop Circuit

14. Close Loop Circuit • Compare the value of the output with the reference value from the TL494 use the error amplifier in TL494 • The gain of the amplifier is 1/RC • Through the testing found out R=10KOhms, C=2.2microF • It will provide the duty ratio we need

15. Schematic Of Closed Loop Circuit

16. TESTING OF CIRCUIT • Input  12 V Multimeter Reading • Output  3.12 V (when switch is turned to one side) • Current drawn =0.13 A • Output  5.7V (when switch is turned to other side) Oscilloscope Reading • Output 3.2V (when switch is turned to one side) • Current drawn = 0.13 A • Output  6.25 V (when switch is turned to other side)

17. CIRCUIT EFFICIENCY • Case 1: Load resistance = 56 ohms Vout = 6V Vin = 12V Iin = 0.1A Pin = 1.2W Pout = Vout^2/R = 6^2/56 = 0.642W Efficiency = Pout/Pin *100 = 54% • Case 2: Load resistance = 40 ohms Vout = 3.1V Vin =12V Iin = 0.1A Pin=1.2W Pout = 3.1^2/40 = 0.171W Efficiency = 15% • Case 3 : Load resistance = 56 ohms Vout = 6.23V Vin = 12V Iin=0.139A Pin=1.66W Pout=6.23^2/56 = 0.97W Efficiency = 60% • Case 4: Load resistance = 40 ohms Vout=3.06V Vin = 12V Iin=0.106A Pin=1.2W Pout=3.06^2/40 = 0.23W Efficiency = 20% • Low Efficiency due to low cost components used and low level of power used so small fluctuations cause large drop in efficiency

18. CIRCUIT NOISE • Noise for output of 3.12 V Peak-to-peak voltage of noise= 510 mV Frequency of noise = 35 MHz • Noise for output of 5.7V Peak-to-peak voltage of noise = 531.3mV Frequency of noise = 32 MHz

19. CAPACITIVE LOW-PASS FILTER • Capacitor’s impedance decreases with increasing frequency • The low impedance in parallel with load resistance tends to short out high frequency • Generally preferred over inductive filters as capacitors are much more predictable in their behavior than inductors

20. SOLUTION • Increase load capacitance to 470 microfarad (at 6.17V)  Peak-to-peak ripple voltage changes to 319 mV • Increase load capacitance to 1000 microfarad  Peak-to-peak ripple voltage changes to 134 mV • Finally increase load capacitance to 1500 microfarad  Peak-to-peak ripple voltage changes to 98mV • Concept is same as capacitive low-pass filter where we connect a capacitor parallel to the load capacitance which in effect is same as increasing the load capacitance

21. COMPARISON OF NOISE • Noise at 6.1V for load capacitance = 47 microfarad • Noise at 6.1V for load capacitance = 1500 microfarad

22. COST ANALYSIS

23. SUCCESSES • Got our open loop circuit working for the demo • Got closed loop working • PCB Implementation • Eliminated AC ripple in DC output • Simple and cost-efficient circuit

24. RECOMMENDATIONS • Use a current fuse of 0.5 A  Sets the maximum current limit to 0.5A according to our specifications  Prevents damage to the circuit components from high current  Increases reliability of our circuit • Better feedback circuit  Output voltage will be less responsive to changes in input voltage  More robustness • Better low-pass filter  More protection against noise  Output is DC 3V/6V according to specifications and fluctuates less

25. SPECIAL THANKS • Chad Carlson : for help in debugging • Joe Mossoba : for help in the design of the circuit • Jim Wehmer : Printed Circuit Board Implementation (parts shop) • Scott McDonald : providing components from the parts shop (parts shop)

26. QUESTIONS