What is the output of this UJT relaxation oscillator circuit?

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Discussion Overview

The discussion revolves around the output of a UJT (Uni-Junction Transistor) relaxation oscillator circuit, including its characteristics and calculations related to its operation. Participants explore assumptions needed for calculations, the role of various components, and the implications of circuit design choices.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes the need for specific values like VEB or VBB to determine the output, suggesting that without these, assumptions must be made.
  • Another participant agrees that the lack of specifications limits the analysis but suggests that the shape and frequency of the output signal can still be discussed.
  • There is a discussion about the assumptions made regarding VEB, with one participant questioning whether assuming it to be 0.7 volts is reasonable.
  • Participants discuss the role of a Zener diode in the circuit and its effect on the NPN transistor's base voltage.
  • Confusion arises regarding the identification of transistors in the circuit, with participants clarifying the distinction between NPN and PNP types, and the specific role of the UJT.
  • One participant expresses uncertainty about how to calculate the frequency of the circuit pulses and seeks clarification on formulas related to capacitor charging.
  • Another participant mentions that the current through the PNP transistor affects the overall circuit behavior, particularly in relation to the UJT and capacitor.

Areas of Agreement / Disagreement

Participants express a mix of agreement and confusion regarding the assumptions and calculations needed for the circuit analysis. There is no consensus on the specific output characteristics or the implications of the circuit design choices, indicating multiple competing views and unresolved questions.

Contextual Notes

Participants highlight limitations due to missing specifications and the need for assumptions in calculations. There is also mention of the potential variability in component specifications affecting design outcomes.

Who May Find This Useful

Readers interested in UJT circuits, relaxation oscillators, and the implications of component specifications in circuit design may find this discussion relevant.

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  • #32
Hmmm... no flowers or anything!

190/100 :rolleyes:
 
  • #33
Femme_physics said:
I assume as in before Vout = Vp + Veb ?
Was this established somewhere before? If you mark "voltage arrows" on your schematic, using KVL, you'll be able to demonstrate whether this should be a + or a minus Veb.

You are deciding here how to sketch the Vout pulse, and you need Vout's maximum value in order to sketch it. We know Vp (from Vcc and the manufacturer's data), so what value are you going to use for VEB in the above equation?
 
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  • #34
NascentOxygen said:
Was this established somewhere before? If you mark "voltage arrows" on your schematic, using KVL, you'll be able to demonstrate whether this should be a + or a minus Veb.

You are deciding here how to sketch the Vout pulse, and you need Vout's maximum value in order to sketch it. We know Vp (from Vcc and the manufacturer's data), so what value are you going to use for VEB in the above equation?

You're right, I confused the signs

http://img825.imageshack.us/img825/336/signsz.jpg
 
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  • #35
Can you check that last line ...
 
  • #36
Oh, sorry

Vout = Vp - Veb
 
  • #37
Confirmation?
 
  • #38
Femme_physics said:
Confirmation?
Ah, that's looking better. :smile:

Though I'm still wondering what value you'll use for that unijunction transistor's VEB?
 
  • #39
We don't know its value so we can't actually solve it, just leave it as an unknown

We can make the assumption it's 0.7 volts of course...but maybe it's best to stay on the safe side and leave it as an unknown?
 
  • #40
Femme_physics said:
We don't know its value so we can't actually solve it, just leave it as an unknown

We can make the assumption it's 0.7 volts of course...
If you need a value, it's going to be the value of VEB when in the breakdown region, viz. VV. For your problem, VV is given as 2.1V (or maybe 1.1V depending on which question is considered).
 
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