Summary of ELEKTOR ARTICLE: LED BOOSTER FOR MICROCONTROLLERS
Summary: A 3 V microcontroller cannot properly drive white LEDs because their forward voltage (~3.2 V) exceeds the supply. Instead of using a full boost-converter plus transistor, the article shows a simpler solution: use a single inductor as a boost element. By switching the inductor to ground, energy is stored in its magnetic field; when the switch opens, the collapsing field generates a higher voltage that can light the white LED, acting like a minimal boost converter.
Parts used in the LED Booster for Microcontrollers:
- White LED
- Inductor (coil) L
- Switch S (transistor or MOSFET acting as switch)
- Input voltage source UIN (3 V supply from microcontroller)
There’s many a time when you want to connect a white LED to a microcontroller operating from a 3 V supply voltage. Unfortunately, this doesn’t work and your nice white LED only lights up feebly or not at all.
Why does it work perfectly with red and green LEDs, but not with white? A bit of data sheet research reveals the reason: white LEDs have a forward voltage of 3.2 V, so a 3 V supply is simply not enough to let them light up properly. The advice you often see in online forums is to use a boost converter to generate a higher voltage, along with a transistor switch to control the LED. For just a single LED, this seems like a lot of overhead.
The good news is that there’s an easier way. And it only needs one inexpensive component: an inductor, which costs next to nothing.
Operating principle of a boost converter
Take an inductor L (a coil) and connect one end to the input voltage UIN and the other end to a switch S tied to ground. When the switch S is closed, a gradually rising current flows through the inductor L, creating a magnetic field. When the switch S is opened a bit later the magnetic field collapses, generating an inductive voltage over the coil (Figure 2), the same as an ignition coil in a car.
Read more: ELEKTOR ARTICLE: LED BOOSTER FOR MICROCONTROLLERS
- Why does a white LED not light properly from a 3 V supply?
Because white LEDs have a forward voltage of about 3.2 V, which is higher than a 3 V supply. - Why do red and green LEDs work fine on 3 V but white does not?
Because red and green LEDs have lower forward voltages than white LEDs, so 3 V is sufficient for them. - What common solution is suggested online to drive white LEDs from 3 V?
The common advice is to use a boost converter to generate a higher voltage and a transistor switch to control the LED. - What simpler alternative does the article propose?
Use a single inductor as a boost element together with a switch to create a higher voltage pulse to drive the LED. - How does the inductor method generate a higher voltage?
When the switch to ground opens after current flowed through the inductor, the collapsing magnetic field generates an inductive voltage higher than the input. - What role does the switch play in the inductor-based booster?
The switch grounds the inductor to allow current to build, and opening the switch causes the inductor to produce the boost voltage. - Is an inductor a more economical option for a single white LED?
Yes, the article states an inductor is inexpensive and simpler than a full boost converter for a single LED.
