Principle and Operation of DC-DC Boost converter

This PPT explains the operation of 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. DC-DC Boost Converter Step up converter Output voltage is equal 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 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

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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 The load voltage is sum of Vs and VL L dissipates its energy v s v o + _ D S L C Load v s v o + _ D S L C Load

4. Waveforms Imin Imax PWM signal I L I S I D I C v c T ON T Mode-I Mode-II Mode-I Mode-I Mode-II -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