# Constant current source (aka "LED driver"): Behaviour with halogen light bulb

I wanted to ask a quick question. When running (power) LEDs, they mostly require an adequate constant current source / LED-driver IC. Most of the time you connect multiple LEDs in series, so that the forward voltage adds up and the forward current remains the same as with only 1 LED: I can easily calculate the forward voltage of LEDs as this one is described in nearly every datasheet given the forward current and thus calculate the output power and the power loss on the driver IC:

$$\P_{loss} = \frac{P_{out}}{Efficiency_{operating.point}}-P_{out}\$$

I want to exactly control the light intensity of halogen lights and therefore also use a LED driver.

I want to use 3 halogen lights @5V/0.5A, each 2,5W, total 7,5W. Input voltage is 12V (lets consider dropout voltage as theoretically 0V).

My question: Can I apply the LED configuration for halogen lights like that: Or does the light bulbs need to be all in series or parallel (like on a constant voltage source).

• Is the second schematic using 2 LEDs and 1 halogen, or is it using 3 halogens? Aug 11, 2021 at 11:29
• Note that incandescent lights are designed to use constant voltage, so they can draw a lot higher power after turn-on and heat up fast. running them at constant current will make thier turn-on very slow. Aug 11, 2021 at 12:10
• @Oskar Skoy First schematic is just for clarification of the typical application layout of LED driver ICs. Second one is the one applied for this special use case with 3 halogen light bulbs, none LEDs. But this one shouldn't work, because for all of them to be on the same light intensity, they need to be strictly on one string. But I still couldn't find a boost mode constant current converter 12V in to 15V/0.5A out with analog dimming function (strictly no PWM) Aug 12, 2021 at 13:40