Lab_4 - EE 101A / Winter 10 Lab #4 (Week of 2/1) Lab 4:...

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EE 101A / Winter 10 Lab #4 (Week of 2/1) Page 1 of 6 Lab 4: Voltage Regulation Sedra & Smith, Chapter 3.5 1. Motivation: How can we get rid of those ripples? dr As you measured in the previous lab, the rectifier output is single polarity, but still half a sine wave. In this lab, we'll use two new circuit components – a capacitor and a Zener diode – to smooth out the voltage signal. By the end of this lab, our converter will output a respectable DC voltage. The remaining labs will add extra features and make our converter more robust. Fig. 1 shows where we are as of Lab 3. Figure 1. Circuit schematic as of Lab 3 2. Capacitors Capacitors appear in most undergraduate physics courses, but often remain a mysterious circuit element to most students. Among its many applications, in this course we will focus on its charge storage properties. As you probably know from physics, placing a voltage V across a capacitor causes charge C V to accumulate on the plates, where C is the capacitance. Question 1: We place a capacitor across the output nodes of the full wave rectifier and send in our usual 60 Hz, 18 V rms sine wave. Sketch the expected voltage across the capacitor for time 0 ~ 25 ms. Hint: A diode only allows current to flow in one direction. I = dQ/dt, so that means charge can only flow in one direction as well.
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EE 101A / Winter 10 Lab #4 (Week of 2/1) Page 2 of 6 Looking at the waveform, we may think that our job is done. But we need to realize that this circuit has no load. The concept of a load is an important one, so we’ll discuss this a bit before moving on. In the circuit above, the voltage just sits across the capacitor and does no useful work. Now imagine that we connected some device across the output, and for a 25 V supply voltage, it draws 25 mA of current. This device could be a lamp, toaster, computer, etc., but we’ll represent it with our generic resistor pill
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This note was uploaded on 03/30/2010 for the course EE 101A taught by Professor Wong during the Winter '08 term at Stanford.

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Lab_4 - EE 101A / Winter 10 Lab #4 (Week of 2/1) Lab 4:...

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