1. M2-3 Buck Converter Objective is to answer the following questions: 1.How does a buck converter operate?

2. Buck Converter The input voltage is always greater than the output voltage

3. Buck Configuration The input voltage is always greater than the output voltage V OUT V IN VMVM V GATE L C I SW ILIL V IN time 20V 15V 10V 5V 0V V OUT time 7.5V 5V 2.5V 0V 10V

4. Switching Regulator Components Switching Power Supply Block Diagram V IN V OUT Switching Power Supply Switch Error Amplifier Bandgap Reference PWM Controller Network

5. External Network An external network (consisting of an inductor, capacitor, and diode) transforms the energy from the PWM controlled power switch into a desired output voltage Network Switch V IN V OUT V IN = 12 V V OUT = 5 V

6. Recirculation Diode V OUT V IN V OUT V IN S IN S GND VMVM VMVM

7. How a Switching Regulator Works V IN Switching Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage OK 50% Filter Network V OUT

8. How a Switching Regulator Works V IN Voltage Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage OK 50% Filter Network V OUT

9. How a Switching Regulator Works V IN Voltage Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage OK 50% Filter Network V OUT

10. How a Switching Regulator Works V IN – 1V Voltage Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage Low 60% Filter Network V OUT

11. How a Switching Regulator Works V IN – 1V Voltage Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage Low 60% Filter Network V OUT

12. How a Switching Regulator Works V IN Switching Regulator Duty Cycle Controller Output Monitor V OUT time 5V Voltage Ok 50% Filter Network V OUT

13. Step Down Switching Regulator Steady State Operation V OUT V IN VMVM V GATE + V L - C OUT I SW ILIL V GATE goes high V M ~ V IN V L = V M – V OUT t VMVM t V GATE t ILIL V OUT t I SW t R LOAD -V F -VF+-VF+

14. Step Down Switching Regulator Steady State Operation V OUT V IN VMVM V GATE C OUT I SW ILIL V L Constant t VMVM t V GATE t ILIL V OUT t I SW I L and I SW increase t R LOAD C OUT is charged by I L and V OUT increases -V F -VF+-VF+ + V L -

15. Step Down Switching Regulator Steady State Operation V OUT V IN VMVM V GATE C OUT I SW ILIL V GATE = 0V The pass transistor is turned off I SW = 0A t VMVM t V GATE t ILIL V OUT t I SW t R LOAD I L cannot go to 0A instantly: V M goes negative V L = V M – V OUT -V F -VF+-VF+ + V L -

16. Step Down Switching Regulator Steady State Operation V OUT V IN V GATE C OUT I SW ILIL But, V M is clamped to -V F and I L decays through the diode t VMVM t V GATE t ILIL V OUT t I SW t R LOAD C OUT stabilizes the output voltage so V OUT will only slowly decay -V F V M = -V F -VF+-VF+ + V L -

17. Step Down Switching Regulator Steady State Operation V OUT V IN V GATE C OUT I SW ILIL The MOSFET is turned on and off to repeat the sequence R LOAD t VMVM t V GATE t ILIL V OUT t I SW t -V F V M = -V F -VF+-VF+ + V L -

18. Volt-Second Balance V OUT V IN VMVM V GATE C OUT I SW R LOAD ILIL t V GATE t + V L - ILIL

19. Volt-Second Balance In steady state, the inductor current ripples about an average, I L,AVG : Therefore, the total area (or volt- seconds) under the inductor voltage waveform is zero. VLVL t V IN - V OUT -V OUT T DT (1-D)T

20. Voltage-Second Principle and the DC Transfer Function From: we can calculate the transfer function of the step down switching voltage regulator

21. V IN vs. V OUT and Duty Cycle, D V OUT V IN L C OUT I SW ILIL R LOAD S IN S GND During steady state: V L,AVG = 0V + V L - VLVL time V IN - V OUT -V OUT T DT (1-D)T

22. V OUT Increases with D V OUT = DV IN V OUT V IN VMVM V GATE C OUT I SW ILIL V OUT R LOAD t VLVL t V GATE V IN - V OUT t + V L - -V OUT S IN S GND

23. V OUT Decreases with D V OUT = DV IN V OUT t VLVL t V GATE V IN - V OUT t -V OUT V OUT V IN VMVM V GATE C OUT ILIL R LOAD + V L - S IN S GND I SW

24. Ripple Current Recall, I L is the sum of the current flowing through S IN and S GND V OUT V IN C OUT ILIL R LOAD S IN S GND I GND time I SW I GND ILIL I L,AVG I SW

25. Memo