I’m trying to calculate the max current pulled from my 15V and -15V supplies. My OPAMPS also use the supplies for current.
All of my numbers seem really whack.
The part I am most confused about is the part with the transistors…
I have struggled with transistor circuits a lot and am hoping someone could help walk me through what I need to do.
Assumptions:
- Caps are shorted because that is when we have max current
- Both the speaker and mic do not draw current (?)
Questions:
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What equations will I need for the PNP and NPN transistors? How do I implement them
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Do I need to worry about the mic or speaker in this situation?
- Should my voltages seriously be that large? I feel like they are too large but I cannot justify why since my gain is so large.
Photos:
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Circuit
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Work
Best Answer
I'm not going to finish the problem for you, but i can point out a couple of places you went wrong.
Why did you assume that the capacitor is shorted for max current draw? Instead, assume that max draw happens when you are saturating the amplifier - id assume a waveform that is 50% saturated high and 50% saturated low.
Your gain of 101 only applies to small signal waveforms. In reality, if the output voltage of the op amp is greater than it's max output swing (typically +/- 13V or so for a +/- 15V op amp, it will rail high or low.
The current through the base of the transistors will be probably 2 orders of magnitude lower than the current thorough the collector, so unless you're trying to be really precise, you can likely ignore it.
The most current you could ever get through the transistor is what you'd get if one or the other transistor (Not both at the same time) was assumed to be fully on, and is limited by the 100 ohm resistor - as well as any resistance of the speaker.