IALB-Institute of Electrical Drives, Power Electronics and Components 1 One-Quadrant Converter As an example of a one-quadrant converter a buck converter(also known as step-down converter)is presented in the picture below. The name of the step-down converter results from the arithmetic mean at the output side which is less than the arithmetic mean at the input de Figure 1-1 shows a typical step-down converter with an idealized freewheeling diode and idealized switch as a replacement for real power-semiconductor devices Is R L Figure 1-1: One-quadrant converter UL: Voltage at the load-side UD: Direct voltage of the sourc S closed u Destination:0≤ul≤U t+0 f (To= Period of oscillation) Note 0 u Figure 1-2 Current and voltage at an idealized switch Pvs=is·us Pvs: Power losses at the switch, at a real switch (IGBT, MOSFET, etc. )the power losses are Pvs>0. This means less efficiency and the need of bigger heat sinks Requirement: Power losses Pvs at the switches have to be as low as possibleIALB – Institute of Electrical Drives, Power Electronics and Components - 1 - 1 One–Quadrant Converter As an example of a one-quadrant converter a buck converter (also known as step-down converter) is presented in the picture below. The name of the step-down converter results from the arithmetic mean at the output side which is less than the arithmetic mean at the input side. Figure 1-1 shows a typical step-down converter with an idealized freewheeling diode and an idealized switch as a replacement for real power-semiconductor devices. UD Figure 1-1: One–quadrant converter UL: Voltage at the load-side UD: Direct voltage of the source S closed: L UD u = : ton S opened: uL = 0: toff Destination: 0 ≤ u L ≤UD 14243 0 0 1 0 f T t t t U t t U t t u on off on D on off D on off L = + = + ⋅ + ⋅ = (T0 = Period of oscillation) Note: Figure 1-2: Current and voltage at an idealized switch PVS = iS ⋅ uS PVS: Power losses at the switch; at a real switch (IGBT, MOSFET, etc.) the power losses are PVS > 0. This means less efficiency and the need of bigger heat sinks. Requirement: Power losses PVS at the switches have to be as low as possible!