chapter+1 - Ch 1 Regulators and DC-DC Converters 1 Goals...

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Unformatted text preview: Ch. 1. Regulators and DC-DC Converters 1. Goals Understand the usage and operating method of regulators and DC-DC converters and implement a circuit that produces a desired voltage 2. Objectives 1. Understand the characteristics and operating method of the regulators 2. Understand the characteristics and operating method of the DC-DC converters 3. Understand the characteristics and operating method of sensors 3. Theory 3.1. Regulator A voltage regulator is a device that maintains an output of a certain voltage level regardless of the change in input voltage and / or environmental variables. Since using the power supply as the supply voltage directly onto the circuit can introduce various noise and distortions, most circuits receive the voltage from regulators. There are mainly two types of voltage regulators : a linear type and a switching type. A linear type have simple circuit structures, utilizes cheap components and has an excellent output voltage characteristics, but it tends to have bad efficiency that introduces much heat, requiring, in some cases, heat insulating boards. Some of the most utilized linear type ICs are the 78XX series, where XX refers to the output voltage. For example, 7805 is a voltage regulator IC with the output voltage level of 5Vs. Switching type utilizes the pulse width modulation (PWM) and controls the on/off duty of the pulse to control the average voltage level. While this type introduces few heating, it is more expensive and has a more complicated circuit structure. Some of the most utilized switching type ICs are 2575-XX series, where XX again regers to the output voltage. In general, linear type regulators require at least 2V+supply voltage. In other words, to produce the output voltage level of 5V, the input voltage must be at least 7V. On the other hand, LDOs require the input voltage to be only 0.2~0.5V higher than the output voltage. LDO is a kind of linear type regulators and is an acronnym for Low Drop Output. Another kind of linear type regulators is the regulated constant voltage source. Regulated constant voltage source like figure 1.1 detects the output voltage, compares it with the difference between an appropriate ratio of the measurement value of Vm and the reference voltage(Vref), and changes the output current to change the measurement value to equal the reference voltage, which in turn keeps the output voltage constant. Comparator R L R 1 R 2 V S V ref I E I B V m V o Figure 1-1 Structure of the regulated constant voltage source From figure 1-1, when V ref = V m , the base current of the BJT I BQ and the desired output voltage V OQ , if the output voltage becomes lower than V OQ , V m also decreases which in turn produces a negative difference between V ref and V m . If the current of BJT I B is increased to be larger than I BQ , the BJT emitter current I E increases and thus the current through the load resistors. This effectively increases the output voltage. On the other hand, if the output voltage is larger than Vthe output voltage....
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chapter+1 - Ch 1 Regulators and DC-DC Converters 1 Goals...

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