Hi there,
than I used the Instructables KSQ Instructables.com-KSQ with improved temperature stability
I was busy here and noticed that their control behavior is not that great and that the dimensioning also requires individual fine tuning, I happened upon the data sheet for the PAM2804 https://www.diodes.com/assets/Datasheets/PAM2804.pdf
This small, inconspicuous 5-legged friend has a lot behind its ears because it can operate a (power) LED with up to 1 amp from a supply voltage of 2.5V to 6.5V. If the voltage difference is large enough, it works as a switching regulator with a synchronous rectifier to keep voltage losses to a minimum. Below that, it continues to work in the same way in LDO mode. Below 2.5V, it also switches off LEDs with a correspondingly low Uf in order not to deeply discharge LiPo cells.
I made a small circuit board based on the AppNote of the datasheet. Today the circuit boards came from China and I set up and tested a sample right away.
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The board measures a tiny 21 x 31 mm and is 3.5 mm high without terminals, and 12.5 mm with 3.5 mm screw terminals
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The current-determining resistor requires 100 mV.
I fitted 300 milliohms, which corresponds to 333 mA. Lt. Measurement is 324 mA.
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The circuit looks simple, but you shouldn't be blinded by it. The switching frequency is a sporty 1.5 MHz! The layout must be designed accordingly in order not to build a medium wave transmitter
I think I managed to do that quite reasonably.
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A dimming input (PWM) is also available. This board is ideal if you want to operate an LED in the range of 0.1 - 1 ampere from a LiPo, 2 zinc-carbon cells or a USB power supply unit, eg also in connection with a microcontroller.
In case anyone has a need, I still have a few boards left because I created board panels to make the most of the space 
