There are variety of LED power supplies that are equipped with dimming function and numerous dimmers are available. However, different LED lights require different dimming technology and dimmers. Now let’s discuss the three basic dimming technologies for LED in details:
(1) Dimming of Constant Voltage (CV) LEDs
A typical CV LED product is LED strip lights. Each strip consists of an array of LED chips in series with a current limiting component such as a small resistor. The most common configurations are 3 chips with 1 resistor (12V) or 6 chips with 1 resistor (24V) for each segment of the array. Thus, the current for each segment is restricted by the resistor. This can be calculated by Ohms Law: Each LED chip has a voltage drop, by subtracting the total voltage drop you get the voltage across the resistor. Current is equal to voltage divided by resistance, therefore you get the current value for this circuit. By understanding this principle , we can easily know that the current for each string is only dependent on the voltage across it, changing the current out of power supply would not have any effects. However, as we mentioned before, each LED needs a voltage drop to activate, if there’s not enough voltage across them, they will not turn on. Thus alter the voltage for the circuit is not a good approach either. The only option we have left is by switching the circuit ON/OFF at a very fast rate that human eyes cannot see (normally 100kHz). This is called PWM or “Pulse Width Modulation”. Lets look at a typical set-up below:
Tip: Pros and Cons
Easy to set up
High flexibility on driver selection
Long run is tricky
PWM generates noise signal
Hard to integrate to existing system
(2) Dimming of Constant Current (CC) LEDs directly driven by power supply
LEDs running under constant current mode is much easier to control. The system normally doesn’t include any inefficient components like resistor and is directly powered. The circuit is also very flexible, you can have series and parallel wiring in combination, such as the figure shown below:
Design Tip: When design your circuit, it is best to make sure the forward voltage for each paralleled string is the same (i.e. each string needs to be identical), the life time will be much longer this way. Otherwise keep at one single string if possible. If parallel operation cannot be avoid, please refer to our article on how to use LDD driver to achieve multiple string dimming.
Since the LEDs are driven directly by constant current power supply, the voltage will be automatically set at the combined forward voltage drop of LEDs in series. Therefore, if we can change the current supplied to LEDs while maintain the forward voltage, dimming can be achieved. This is actually the basic working principle of Mean Well 3-in-1 dimmable drivers. It uses any of the signals: 1-10V, PWM or resistance to change the output current of Power Supply.
As shown on the diagram above, each driver has 4 wires on the secondary side, 2 of them are for driving the LEDs and the blue and white wires are for dimming signals. This set-up has the maximum flexibility and works on most lighting designs, however the power supply must be carefully matched during design stage. We are able to provide you this service for free.
(3) AC Phase-cut dimming.
This method is very straight forward and similar to what we are using for halogen or incandescent bulbs. The power supply needs to support AC dimmer, our PCD series is designed for this purpose. The working principle similar to a CC system, except it has the dimming control on the AC side, as shown below:
Tip: Pros and Cons
Easily integrated to existing circuit
Dimmer compatibility needs to be verified before installation (We can do this)
Small range of models to choose from
If you need any assistance on choosing the right products, please feel free to contact our friendly support team 09 4770177.