Boost_Converter[1]

Boost_Converter[1] - Page 1 of 10 ELCT 301 Lab Report #8...

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Page 1 of 10 ELCT 301 Lab Report #8 Boost Converter Due: 4/16/2008 ___________________ Jared Tucker Department of Electrical Engineering University of South Carolina Columbia, SC 29208
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Page 2 of 10 Laboratory Grade: Pre-lab computation ____ of 10 Technical Content ____ of 60 Format/Presentation Clarity ____ of 20 Other ____ of 10 Late Deductions ____ ____ of 100 Student Comments: Grader Comments:
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Page 3 of 10 Boost Converter I. Introduction The purpose of this lab was to test my previously constructed inductor by implementation in a boost converter design. There were specifications that the design was required to meet. Based on these specifications, the circuit was designed, constructed and tested. II. Background The boost converter is a switching converter that takes a low level input and produces a high voltage output. The magnitude of the DC output is determined by the duty cycle of the switching input. For the sake of simplicity let us consider the most basic rendition of the circuit, Figure (1). (a) inductor charge (b) inductor discharge Figure 1. Two main states of the circuit: Switch closed (a) and Switch open (b) Lets first consider the case of closed switch Figure (1,a). At the instant the switch is closed, its as if there is a short circuit thus no voltage will flow through the diode. We know that current seeks the path of least resistance. This makes good sense. Now, while the switch is closed, all the current passes through the inductor as it begins to store a charge in its magnetic field. At the instant the switch is open, the short disappears. The stored charge on the inductor then must take the only path left, through the diode. This massive amount of stored charge is then felt at the output R2. You may ask, what is the capacitor doing? Well, the resistor and inductor create an RC circuit. We know that the RC circuit time constant depends on the values of R and C. The RC time constant is perhaps the most important part of the circuit. We stated earlier that the boost converter should have a DC output. Therefore, the time constant of the RC circuit must be much longer than the switching period of the circuit. If the time constant were too short then the huge charge released from the inductor would be dissipated in one big pulse at the output. The RC network absorbs the charge pulse from the inductor acting as a giant well. The time constant is much like a leak in the well. While its magnitude determines how much is able to flow out. I will now proceed to analyze the circuit under ideal conditions. This is done because simulations used do not completely account for all possible non-ideal
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Page 4 of 10 possibilities. By ideal I make the following assumptions: The responses of the system are uniform (the charge of state variables are equivalent at the beginning and end of each period). I will assume that the duty cycle D is fixed at a fixed frequency T where the switch is on for DT and the switch is off for (1-D)T. I will assume that the inductor
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Boost_Converter[1] - Page 1 of 10 ELCT 301 Lab Report #8...

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