Homework DC-DC

# Homework DC-DC - Buck converter(Step down Converter Example...

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Buck converter (Step down Converter) Example 1. A semiconductor switching element in a power circuit has minimum effective on time of 42 μ s. The dc supply is rated at 1000 V. (1) If the chopper output voltage must be adjustable down to 20 V, what is the highest chopper frequency? (2) If the chopping frequency increases to 500 Hz, what will then be the minimum output voltage? Example 2 The semiconductor switch in a dc step-down converter has a minimum effective off time of 28.5 s. If the constant dc supply is rated at 1250 V and the chopping frequency is 2000 Hz, calculate the maximum duty cycle and the maximum output voltage that can be obtained. Example 3 The dc chopper converter in Example 15.1 is connected to resistive load R=1.85 . What is the average input current when it operates at a frequency of 500 Hz? Example 4 A step-down dc converter is used to convert a 100-V dc supply to 75-V output. The inductor is 200 H with a resistive load 2.2 .If the transistor power switch has an on time of 50 s and conduction is continuous, calculate 1. The switching frequency and switch off time 2. The average input and output currents 3. The minimum and maximum values of the output current 4. The rms values of the diode, switch, and load currents Example 5 A dc–dc step-up converter requires to operate at a fixed output voltage level of 50 V. The input voltage varies between the limits of 22V and 45 V. Assuming continuous conduction, what must be the range of duty ratios? Example 6 A step-up dc converter is used to convert a 75-V battery supply to 100-V output. As in Example 4, the inductor is 200 H and the load resistor is 2.2 . The power transistor switch has an on time of 50 s, and the output is in the continuous current mode. 1. Calculate the switching frequency and switch off-time. 2. Calculate the average values of the input and output current. 3. Calculate the maximum and minimum values of the input current. 4. What would be the required capacitance of the output capacitor Cout in order to limit the output voltage ripple Vo to 10% of Vo? Example 7 A buck–boost converter is driven from a battery Vs =100V and operates in the continuous current mode, supplying a load resistor R=70 . Calculate the load voltage and current and the input current for values of duty cycle D (1) 0.25, (2) 0.5, and (3) 0.75.

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Example 8 A buck–boost converter operates in the continuous current mode at a switching frequency fs =20 kHz. Vs=24 V, Cout=250 μ F, L=200 H, and the load resistance R=1.5 . For a duty cycle D=0.33 calculate (1) the average load voltage and
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## This note was uploaded on 11/02/2009 for the course ECE ece464 taught by Professor Abc during the Spring '09 term at Jacksonville College.

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Homework DC-DC - Buck converter(Step down Converter Example...

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