I use this lipo charger : https://www.sparkfun.com/products/10161
with an Lipo battery of 400mAh/3.7V.
This lipo charger can be configured in 2 ways : one with 500mA the other with 100mA.
To drive it, I don't use the usb connector to charge the lipo but an 7805 with 2 capacitors because it takes power from an professional battery camera which is 12V.
So from, the lipo charger is in 500mA confiuration. I did some test with an external 9v power supply and the 7805 is very hot, around 90° !!!!
If I understand well, from my dc power with the 7805 : 9V - 5V = 4V and with 0.5A means 2 Watt of thermal dissipation. This is a reson why the 7805 is very hot !
I would like to know if I can use the lipo cherger with these lipo battery with 100mA instead of 500mA, so from it will give only : 0.4 Watts so I hope the 7805 will not be to hot.
If someone can help me or suggest another way of doing it. The system is in small closed box that is only :
The complete system is :
Arduino ProMini 3.3V/8Mhz / Nrf2401 HF transmitter, 1 push Button, 1 small Led, 1 lipo charger and 1 Lipo battery.