# Flicker-free LED driver at low DC: how to select driver

I tried several LED drivers and some of them have an undesirable behavior: at low duty-cycle levels you can notice flickering. This is not due to the actual PWM of course, but due to the driver itself.

When selecting a driver, what should I check to be sure it's flicker-free?

Unfortunately, only few of datasheets report this feature. For example ILD8150 says:

Flicker free operation

Let's say I want to select TPS92830: how to be sure the LED won't flicker?

• This is a linear driver. Linear drivers shouldn't flicker unless your power supply flickers. Jul 9 '21 at 15:16
• @user253751, ss far as I understand ILD8150 is a DC/DC buck (not linear) and it states it does not flicker.
– Mark
Jul 9 '21 at 15:21
• You may be interested in my article on dimmable mains PSU control which shows how one input can accept voltage, resistance and PWM control and convert it to an analog current control. Jul 9 '21 at 18:26
• @Mark The TPS92830 is a linear driver. Jul 12 '21 at 9:05

The TPS92830 is a linear driver (it says so in the datasheet). Linear drivers don't flicker, assuming that your power supply doesn't flicker. However, they are less efficient.

The ILD8150's "flicker-free" claim applies to its "hybrid mode", used at low brightness values:

Hybrid dimming is an Infineon unique one-pin dimming method that combines analog dimming and PWM dimming of the LEDs current in one hybrid dimming curve.

12.5 percent to 0.5 percent in hybrid mode with flicker-free modulation frequency of 3.4 kHz

They are simply saying that the PWM frequency is high enough that humans won't notice the flicker. So to see if another driver is "flicker-free" you can check the PWM frequency it uses.

• Got it. Also the expression "fixed frequency step-down DC/DC converter designed to operate as a constant-current source" may do the trick? It's from LT3592 (mouser.it/datasheet/2/609/3592fc-1269757.pdf)
– Mark
Jul 9 '21 at 15:42
• @Mark Usually switched converters do not use PWM output at all (they may take it as a control input but will not pass it to the output). They will have some current ripple at the switching frequency, but you can control that and anyway it is usually at MHz so invisible. Jul 9 '21 at 16:00

You are talking about two fundamentally different technologies for controlling LED brightness. They are not compatible, and it looks like a design contradiction-in-terms.

• On one hand, you link us to LED drivers which are constant-current. That is exactly what it says on the tin. Since the current is constant, the light is constant. If due to internal workings it is irregular, you could certainly smooth it by adding capacitance.

• On the other hand, you talk about PWM and duty cycles. Those imply an "on/off" cycle repeating frequently. They can be a hot-bed of flickering if the cycle frequency (not duty cycle) is too low.

These two contradict each other. A driver can't be both.

So methinks you are doing something out-of-spec here, like trying to input PWM into a constant-current driver to try to achieve dimming. Forget it. Use one technology soup to nuts.

Constant-current dimming is possible, by changing the constant current to a different value. That needs to be done at or by the CC driver.