Verifying a circuit design with voltage regulators

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SUMMARY

This discussion focuses on verifying a circuit design intended to power a 3V motor using voltage regulators. Key components mentioned include the 78L33 linear voltage regulator and the 1N5817 Schottky diode, which is recommended for its low forward voltage drop. The circuit's design raises concerns regarding the use of two 10F capacitors in series and the overall power rating calculations for the resistor and voltage regulator. Participants emphasize the need for accurate voltage, current, and power calculations to ensure proper functionality.

PREREQUISITES
  • Understanding of voltage regulator types, specifically linear and buck regulators.
  • Knowledge of Schottky diodes and their characteristics, particularly the 1N5817 model.
  • Basic circuit analysis skills, including voltage, current, and power calculations.
  • Familiarity with capacitor behavior in circuits, especially in series configurations.
NEXT STEPS
  • Research the specifications and applications of the 78L33 linear voltage regulator.
  • Learn about the efficiency and use cases of buck regulators in low-power applications.
  • Study the characteristics and selection criteria for Schottky diodes, focusing on the 1N5817.
  • Explore circuit analysis techniques for calculating power ratings and current flow in resistor-capacitor networks.
USEFUL FOR

Electronics engineers, hobbyists designing low-power circuits, and students studying circuit design and analysis will benefit from this discussion.

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.
 
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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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