I want to control several SMD-LEDs (0603) 3.5V - 25mA, using a voltage source of 4V. Each LED needs a resistor of ~20 Ω to work fine, like shown in the circuit below:
But I would like to switch and control the LEDs pairwise. So in this example LED1 & LED2 should light together and in a next step LED1, LED2, LED3 & LED4 should all light together. In my real project I have 16 LEDs in total. I got to know that the 74HC595 must not exceed 70mA, but each LED needs 25, so I need to have a separate source for all LEDs and an NPN-transistor for each state to be able to switch my LEDs using the 74HC595.
- Is that correct?
- Will the following circuit work? (Note: I simplified the 74HC595 in this circuit)
Please be fair, I'm a beginner in electrical engineering.