Dimmable mains PSU control

Mean Well HLG-80H-15A dimmable PSU.
Mean Well HLG-80H-15A dimmable PSU.

Many of the LED power supplies such as those by Mean Well, etc., offer three modes of control: output constant current level can be adjusted through the control input

  • by connecting a variable or fixed resistance to the control terminals,
  • using a 0 ~ 10 V DC control signal,
  • using a 10 V PWM signal between.

To do this the controller input is something similar to the circuit below.

Adjustable constant current PSU input circuit.
Adjustable constant current PSU input circuit.
  1. For DC voltage control we just apply the voltage, it gets to the controller with a slight lag depending on the R1/C1 delay and output power is set.
  2. For PWM a pulse train would be used as shown in Figure 2. This time R1 and C1 filter the PWM to obtain the average DC value in the 0 to 10 V range. Output power is set as before.

    A PWM control signal.
    PWM signal transitioning from high pulse width (75%) to low (25%) and back again. Note amplitude remains constant. This will result in a control input of 7.5 V and 2.5 V respectively giving 75% and 25% of rated current.
  3. To sense a resistance connected to the input the PSU  supplies a small current to the input terminals as shown by the constant current source. On the units I am familiar with 100 kΩ gives full brightness so that means the voltage drop across the 100 kΩ is 10 V and I = V/R = 10/100k = 0.1 mA.
    This theory is supported by the fact that if you use one pot to control multiple power-supplies that the required pot value is 100/n where n is the number of power-supplies. This makes sense as each PSU will drive 0.1 mA into the pot. So for five lamps in parallel on the one pot R = V/I = 10/0.5m = 2 kΩ.
  4. Finally, if nothing is connected to the control input the 0.1 mA will charge C1 to 10 V and give 100% brightness.

It’s simple and flexible and rather ingenious.


Link: Mean Well HLG-80H series. Note that these PSUs use a 1 – 10 V control signal rather than 0 – 10 V as discussed above. This will make little practical difference.


Datasheet extract

Mean Well HLG-80H dimmable PUS wiring and output vs control graphs.
Mean Well HLG-80H dimmable PUS wiring and output vs control graphs.