Verifying a circuit design with voltage regulators

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Discussion Overview

The discussion revolves around verifying a circuit design intended to run a 3V motor using voltage regulators. Participants explore the appropriateness of the circuit elements, including capacitors, diodes, and the choice of voltage regulation methods.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions whether the motor truly only draws 8mA and challenges the use of two 10F capacitors in series.
  • Concerns are raised about the choice of diode, suggesting a Schottky diode for a lower voltage drop, with caution regarding its performance at higher temperatures and currents.
  • Another participant proposes using a linear voltage regulator, like the 78L33, for better performance with fewer components.
  • A suggestion is made to consider a buck regulator for higher efficiency, citing a specific product link.
  • One participant expresses skepticism about the circuit's design, suggesting that the capacitors should be treated as short circuits due to charging time and questioning the practicality of the setup.
  • A question is posed regarding the destination of the current after passing through a 1 kOhm resistor, indicating a need for further analysis of the circuit's behavior.
  • Another participant reiterates concerns about the circuit's design, emphasizing its impracticality.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the circuit's design and its practicality, with multiple competing views on the components and methods used. The discussion remains unresolved, with no consensus reached on the validity of the circuit.

Contextual Notes

Limitations include potential missing assumptions about the circuit's operation, dependence on specific definitions of component behavior, and unresolved calculations regarding power ratings and current flow.

Vossi
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Need help verifying if this circuit design and use of elements is correct. The goal here is to run a 3v motor, hence I need to make the use of voltage regulators for a constant 3v energy to transfer.
 
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I guess it's ok, sort of. Does your motor really only draw 8mA?

Why do you have 2 caps in series? and why are they 10F!

The diode must be a schottky for only 0.3V drop. This is ok if you choose a big one like 1N5817 et. al. But, only at room temperature and at low current (like 8mA). If it gets hot it will drop more voltage.

Why not just use a linear voltage regulator, where most of the details have been done for you. You'll get better performance with fewer parts. For example 78L33, they cost about $0.50.
 
Or get a buck regulator for 90% efficiency.
https://www.ebay.com.au/itm/203108764061
 
nMADZfd.jpg


Please help calculate the voltage, current and power of all circuit elements. What is the minimum power rating required for R1 and the voltage regulator?
 
Sorry, but this circuit is just insane.

For the power rating, as it is now you should just take those caps as short circuit since to charge them to 3V will take quite a time. 12V through 1kOhm => you should be able to calculate the power and the current through the (serial) diode too.

Is this some kind of homework? For a real life problem this is just too ... special.
 
Last edited:
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One question to ask yourself is, where does that 8.7mA go after flowing through the 1 kOhm resistor?
 
Rive said:
Sorry, but this circuit is just insane.
+1
@Vossi -- Your thread (well, actually your 2 threads, since you multiple posted it) is locked for Moderation. Please send me a Personal Message (PM -- click on my avatar and "Start a conversation") to let me know if this is for schoolwork or not. Thank you.
 

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