Principle and Operation of DC-DCBuck-Boost converter

This PPT explains the operation of Buck-Boost converter. It also explains how to draw the waveforms, derive the expressions for output voltage, ripple current, ripple voltage, L,C, critical values of L and C.

1. Introduction to DC-DC Buck-Boost Converter Steps down and up the voltage Output voltage is lesser or greater than the input voltage There are 2 modes, mode 1(switch ON) and mode 2(switch OFF) It consists of a switch, L, C and a diode, the switch is operated with a duty ratio of The output voltage is negative, hence called as Inverting Regulator. v s v o + _ D S L C Load Vs- Input DC voltage S- Switch ( MOSFET/IGBT/GTO/BJT) D-Diode Vo- Output voltage L-Inductor C-Capacitor

2. Applications Source: prodctodc.com Source: roboticsandautomationnewscom Source: prodctodc.com Self regulating power supply Automotive Power amplifier Adaptive control Source: go.gale.com Battery Power System Source: bpsbattery.com DC motor drives Source: myoutube.com

3. Modes of Operation Mode I During this mode, S is closed and D is open L stores energy Mode II During this mode, D is turned ON and S is turned OFF L dissipates its energy v s v o + _ D S L C Load v s v o + _ D S L C Load

4. Waveforms Mode-I Mode-II Mode-I Mode-I Mode-II Imin Imax PWM signal I L I S I D I C v c T ON T -I o PWM- Pulse Width Modulation Signal Imax-Maximum inductor current Imin -Minimum Inductor current T ON -ON time of the switch T OFF -OFF time of the switch

5. Modes of Operation Mode I:(0<t<T ON ) v s v o + _ D S L C Load

6. Modes of Operation Mode I:(0<t<T ON ) (1) (1a) Also k is called duty cycle or duty ratio T is switching period T ON is ON period v s v o + _ D S L C Load

7. Modes of Operation Mode II : (T ON <t<T) (2) Also (2a) v s v o + _ D S L C Load

8. Output voltage Equating volt time equivalents, (1) and (2)

9. Ripple current We know that Using (1a) and (2a) Imin Imax Mode-I Mode-II Mode-I Mode-II I L

10. Ripple voltage Mode-I Mode-II Mode-I

11. Condition for continuous conduction In order to obtain the continuous inductor current, the inductor and capacitor values should be more than a particular value known as critical values ( L cr and C cr ) These values are obtained by equating the ripple current to 2 times the load current and the ripple voltage to 2 times the load voltage.

12. Derivation of L cr and C cr R is load resistance

13. Thank you