- #1
Sketching Waveforms in Circuits w/ Diodes
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Homework Help Overview
The original poster is tasked with sketching the output waveforms of a 5Vp sine wave at 100 Hz applied to circuits involving normal and Zener diodes. The discussion revolves around understanding the behavior of these diodes under varying input conditions.
Discussion Character
- Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants explore the behavior of normal and Zener diodes when subjected to a sine wave input, questioning how the diodes will react during different phases of the waveform. The original poster expresses confusion about the output when the Zener diode's threshold is not reached.
Discussion Status
Some participants have provided insights into diode behavior, particularly regarding the Zener diode's threshold and its implications for the output waveform. The conversation includes considerations of how multiple diodes in parallel might affect the output, with some participants suggesting that the output would resemble that of a single diode.
Contextual Notes
The discussion includes assumptions about the input signal characteristics and the specific configurations of the diodes in the circuits, as well as the implications of the Zener diode's threshold voltage relative to the input signal.
- #2
dancergirlie
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I am only still stuck on the first one!
- #3
gneill
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Normal diodes conduct (ideally becoming short circuits) when they are forward biased, and are open circuits when reverse biased. Zener diodes act like regular diodes in the forward direction, but they "fail" in the reverse direction after some specified voltage -- they too ideally become short circuits after the "zener voltage" threshold is reached in the reverse direction.
So your task is to imagine this 5V peak-to-peak input signal being connected to these circuits and how the diodes are going to react as the input varies. In your first circuit, for example, both the normal diode and the zener diode are going to short out all the positive half of the voltage cycle, since they'll both be forward biased. In the negative half of the cycle the normal diode will be reverse biased, so it can't conduct (so just ignore it). The zener will also stay cut off until its zener voltage threshold is reached. Then it'll clamp the signal at that value until it drops below the threshold again.
So your task is to imagine this 5V peak-to-peak input signal being connected to these circuits and how the diodes are going to react as the input varies. In your first circuit, for example, both the normal diode and the zener diode are going to short out all the positive half of the voltage cycle, since they'll both be forward biased. In the negative half of the cycle the normal diode will be reverse biased, so it can't conduct (so just ignore it). The zener will also stay cut off until its zener voltage threshold is reached. Then it'll clamp the signal at that value until it drops below the threshold again.
- #4
dancergirlie
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since my zener diode has a threshold of 6.3V, and since my voltage is 5V peak to peak, it will never reach that threshold, so won't it always just be zero output?
- #5
gneill
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dancergirlie said:
A 6.3V threshold means that it'll never conduct in the reverse direction, yes. So it'll behave like a normal diode in this case. Note how it's wired in the same direction as the normal diode beside it; they'll both just behave as normal diodes as long as the input signal is never more than 6.3V negative (which it won't do here).
- #6
dancergirlie
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so would the fact that I have two "normal" diodes in the same biased in the same direction in parallel change what my output waveform would look like, or would it just resemble what it would look like if I had one diode in the circuit?
- #7
gneill
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You can't make a short circuit shorter! 
Yup, It'll behave just like a single diode.
Yup, It'll behave just like a single diode.- #8
dancergirlie
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thanks so much for the help :D