Lessons In Electric Circuits Volume VI – Experiments Book
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Lessons In Electric Circuits Volume VI – Experiments Book

  • 392CHAPTER 8. 555 TIMER CIRCUITSsmall capacitor for C2. This high frequency square wave is used to turn Q2 on and off as asimple switch.Figure 400,8.13 shows what happens when the Q2 is conducting, and the coil starts to charge.If Q2 were to stay on then an effective short across the batteries would result, but since thisis part of an oscillator this won’t happen. Before the coil can reach it’s maximum current Q2switches, and the switch is open.Figure 8.13:Figure 400,8.14 shows Q2 when it opens, and the coil is charged. The coil tries to maintain thecurrent, but if there is no discharge path it can not do this. If there were no discharge pathis the coil would create a high voltage pulse, seeking to maintain the current that was flowingthrough it, and this voltage would be quite high. However, we have a couple of LEDs in thedischarge path, so the coils pulse quickly goes to the voltage drop of the combined LEDs, thendumps the rest of its charge as current. As a result there is no high voltage generated, butthere is a conversion to the voltage required to light the LEDs.Figure 8.14:The LEDs are pulsed, and the light curve follows the discharge curve of the coil fairlyclosely. However, the human eye averages this light output to something we perceive as con-tinuous light.8.8HOW TO MAKE AN INDUCTORPARTS AND MATERIALS