Hello guys. Could you please give me some advice for my circuit?
The above circuit was drawn for the purpose of making PCBs, and I wanted the volume of PCBs should be as small as possible.
This circuit must not have any problems after operating thousands of times.
Therefore, circuit stability is more important than anything else, but all of the works I have implemented so far have been made for the purpose of operating only once or twice, so I would like to get feedback on the circuit so that it can operate stably even if I run it tens of thousands of times.
Let me briefly explain the circuit.
Main function
When the switch connected to PB0 is pressed (MCU built-in pull-up resistance is activated), PB1 sends a signal to the MOSFET, current flows, and four LEDs connected in parallel turn on.
The LED is a high-brightness LED that requires about 3.5V and 500mah of current. (It says 3W on the specification, but it's roughly within 2W per each). A total of four LEDs are listed in parallel.
Resistance is placed per LED with 1 ohm and 1/4W to limit the current.
The battery is a 3.7V lithium polymer battery. A high-discharge battery with a discharge rate of 25C is used because sufficient current must be supplied to the LED instantaneously. I don't intend to use 7.4V and 11.1V batteries because I need to reduce the volume of the product.
And finally the famous TP4506 module is used for charging the battery. Personally, I think it should be improved the most at the moment.
Questions
I think I need to install a diode to protect the battery from reverse voltage, where should we put it?
Currently, LEDs are placed in parallel and resistors for current limitation are placed, but I wonder if there will be a better arrangement.
For your information, batteries must be 3.7V, 25C, and 300mah. In addition, it takes up too much volume to configure the boost circuit, so it meets the 3.7V battery specification as much as possible.
TP4056 is not suitable for the above circuit, which requires instantaneous high current to bring and use ready-made products as they are. I think I need to make a new battery charging circuit suitable for the above circuit.
We want to provide stable DC power to the MCU, which circuit should we add?
The maximum amount of dischargeable current of TP4056 is limited, so the LED is directly connected to the battery. But in this case, wouldn't the TP4056 be too much and cause the module to burst?
As for 1. Why would your battery experience reverse voltage? You are using properly keyed connectors? TP4056 handles rest.
2. Having them parallel like drawn is fine, just make sure your pcb uses wide traces on anything where high currents flow.
3. TP4056 docent limit discharge current under normal conditions. As for charger, TP4056 is good for up to 1 A of current.
4. Regulator, preferably something that mentions LDO so you can use most of battery voltage range. Not sure about that microcontroller, but i would use something that works at 3,3V.
5. Like i said TP4056 docent limit discharge current, its only charger chip. Your most likely limitations will come from things in high current discharge path, pcb traces, etc... Charger chip is supposed to be in parallel to battery, juts like your led's.
Question: is this really just TP4056 or is this one of those Chinese modules that has also protection on it?
I'd be looking at some type of LED driver.
Series LED resistors there have to disipate a lot of heat etc.
Even @ 2w per LED, a 1 ohm resistor will have the LED current flowing through it.
Say 3.5v for the LED @ 2w, that's close to 0.6A.
1 ohm with 0.6 A is 0.36W not 1/4w
With your switch, even though you are using pullups, still need some sort of debounce either in the code or hardware.
Leds drawing over 2A total are not going to operate "thousands of times" on a 300mAh battery.
BTW...what turns the LEDs off....??
Indeed, dissipating a significant amount of energy in series resistors on a battery powered device is just...well, not so smart. In general, power leds should IMO never be driven with current limiting resistors. There are excellent (and many!) buck led driver IC's out there that are easy to implement and quite efficient. They generally also have an enable/dim pin, which eliminates the switching mosfet.
I'd add a pullup resistor on PB5/RST on the ATtiny85.
Also observe all the other comments of the posters; I agree with them all.
No, your led does not require 500 'mah' of current....
Be sure to prototype this circuit before ordering PCB's. You can get these little SMD-to-pin header converter boards that you can solder SMD parts onto so you can prototype with them; may be convenient for the TP4056 (or similar device that you'll end up with), led drivers etc.
Note that PCB layout (if/when you get to that stage; it sounds pretty far away still to me...) also has its pitfalls. Read everything you can on how to properly layout a PCB.
All right.
Resistors out, replace them with well made led drivers which can be a substitute for MOSFETs in terms of switching.
What is the reason you recommended me to add a pullup resistor on RST? There is nothing attached there. Does it prevent the MCU from resetting over and over again?
I noticed that I still have a lot of difficulties to overcome until the project's complete.
I think I'll restart my diagram from the beginning
Thanks for all your help sir!
So do you recommend me to use a led driver, hook the leds up in series, and give them a 3.5 * 4 volts in total? Would that be a much stable setup than hooking them up with current limiting resistors and putting them in parallel?
p.s I'll code the MCU to automatically turn the leds off after 2000 microseconds pass.
The below design was copied from an eBay 18650 UPS board. The board design is basically a consolation of three purpose designed IC's.
Looking at the schematic:
The first stage is the battery charging ckt
The second stage is the battery protection ckt
The third state is a 3.7 to 5V boost circuit (not needed for your application)
You should look at the first two stages and see if you feel you need that level of protection.
I worked at an Automotive OEM. My philosophy was..." if you make a million of anything, if something can go wrong (with the design) it will"
