I am building a sunrise alarm clock. The LED is supposed to get brighter over the course of 30 minutes, then remain fully lit for another 30 minutes, then switch off. I am using a digital pin on an Arduino Pro Mini 3,3V to feed a transistor. The Arduino board will sleep for the rest of the time, saving energy. The device is going to be powered by a single 18650 Li-ion battery, with an additional solar panel to charge the battery during the day (using a TP4056 with additional protection circuit).
This is the rest of the circuit. To protect the LED, I am using an MCP1825 LDO to regulate voltage input. I reason that with this small difference between Vin and Vout, it is efficient enough. I chose the MCP1825 for its low quiescent current and fairly low dropout voltage. (If I am lucky, I might obtain the version with shutdown mode). I might have to replace R1 which I have chosen based on an hfe of 30.
So far I have only tested this circuit without the LDO and battery with a stable 3,3V source (I don't have the other parts yet). It works.
I have these questions:
- Given I am using a battery, I figured there is no input capacitor necessary for the LDO. Is that correct?
- If I understand it correctly, an LDO fundamentally acts like a kind of resistor. Does this mean it does not produce any noise and can I therefore do without an output capacitor?
- Would the TP4056 (and/or solar panel) introduce noise anyway, which I would have to filter out with capacitors (input AND output)?
- Will the caps leak current all the time, wasting energy?
- Do you see a way of forgoing voltage regulation or to save energy in any other way in this circuit?
I am trying to understand every single piece of this circuit, but I am still only a beginner. Please let me know of any major flaws in my design and also in the posting of this problem. Thank you.
(I did read the datasheet of the MCP1825 recommending usage of an input capacitor. That does not sound like a necessity though.)