Making an IR lighting for Raspberry Pi(RaspPi) NOIR (no infrared filter) camera. This IR will assist the camera to see better in the dark. Below is the circuit diagram for the prototype.
In theory each IR LED draws 20mA, indicator LED draws 20mA. Estimated, I need 30 IR LEDs. The below prototype uses 2 NPN transistors (2N2222), arranged to Darlington pair combination. Darlington pair give the current gain as hfe = hfe1 * hfe2 .
Base on the 2 pics above, we can calculate the hfe. hfe = 0.38/0.00002 = 19000 times. This is Darlington pair combination. So taking square root, 190000.5 = 137.84 times.
Hence without the power of Darlington pair the current gain in 137.84 times.
The below video points out that the NPN transistor 2n2222 is not suitable to switch and transport current to the LEDs as it gets pretty hot , imo using a relay together with transistor is better.
Just bought a Darlington pair NPN power transistor, TIP120. Instead of using a relay with transistor, I have decided to try using this power transistor which have a rating of 60V, 5A. According to TIP120 datasheet, the VBE is 2.5v(max.). So I think should be ok.
Using Eagle PCB software to design the circuit board for all 20pcs IR LEDs.