1
\$\begingroup\$

I am using 3 halogen lights with 5V/0.5A each controlled by a constant current source (or basically "LED driver") because of light accuracy. Right now I am using the PT4115 (step down led driver) for each light bulb, but this one is also getting really hot. Input voltage is 12V. For another revision, I was planing to run all light bulbs (those 7.5W total) with only one IC because of limited PCB space. I was looking around the whole last day but couldn't really find what I was looking for. There are many step up led drivers, but those are really made to drive led's at true colour with PWM dimming instead of analog diming.

Functional schematic:

Text

For example, the Analog Devices led driver can be run on PWM (or frequency set) mode with additional analog diming, but not on analog diming alone, example: https://www.analog.com/media/en/technical-documentation/data-sheets/80421fb.pdf The RT-pin doesnt go down to 0 Hz, but can be only minimised to 250 kHz, which is not suitable, since I need constant lighting without PWM flimmering.

Does some IC series I am looking for even exist or is there any possible solution for turning an PWM input into a constant analog control input with an additional circuit, so that the light is always on without any switching?

\$\endgroup\$
8
  • \$\begingroup\$ "Analog dimming" just means changing the drive current, which any Buck or Boost LED driver can do. The RT pin on that driver is the switching frequency of the Buck/Boost converter. It has nothing do with PWM or dimming. To change the current ("dimming") you would use the CTL pin to set a different drive current. \$\endgroup\$ Aug 14 at 22:08
  • \$\begingroup\$ Ah I mistook the switching frequency of the regulator itself with the frequency of dimming. But still, am I right that although on the datasheet linked in the question on page 6 "LED Current vs CTL Voltage" there is a linear correlation , analog dimming is still limited to 10 steps (or 10:1) or is it linear with non-discrete steps and I am wrong on that one? \$\endgroup\$
    – Dakalaom
    Aug 14 at 22:45
  • \$\begingroup\$ You're limited to current in that range, which is approximately a 10-fold difference. That is an expensive converter designed for high dynamic range PWM dimming. If you don't want that consider a different converter. \$\endgroup\$ Aug 14 at 22:51
  • \$\begingroup\$ Thank you for the help. I know, this is not the website for discussions, but could you point out to a step up converter with up to ~0.7-1A output current and analog dimming functionality? Everything I found was really the same with special PWM dimming or has a bad thermal resistance for those 7.5W output \$\endgroup\$
    – Dakalaom
    Aug 14 at 23:32
  • \$\begingroup\$ @Dakalaom +1 just because I learned a new word -- flimmering! \$\endgroup\$
    – jonk
    Aug 14 at 23:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.