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Ways of Powering RGB LED Lamp
As you can see from the photos above, This is a Nationstar RGB SMD3535 Lamp (which is a normal pixel of the led screen), There has three led lamps in it. Red lamp, Green lamp, and Blue lamp. While for different lamps, it has different volt-ampere characteristic features. For the red lamp, Its powering voltage is around 1.6V, and for the Green and Blue lamps, their powering voltage is around 2.8V. You can see the volt-ampere characteristic chart below:
LED screen are made up of pixels (RGB lamp), According to the volt-ampere characteristic curve. It has two main powering ways: Constant current powering, and Constant voltage powering, Which has the cooresponding drive IC: Constant current IC, and Constant voltage IC.
- Constant Voltage Drive IC: Powering the LED lamp with constant Voltage in the circuit.
- Constant Current Drive IC: Powering the LED lamp with constant current in the circuit.
As it is difficult to control the lamp’s brightness through voltage. Constant voltage powering is normally used single color led screen which does not have a high greyscale requirement. Constant Current powering become the mainstream in full color led screen applications.
Common Cathode LED Screen And Common Anode LED Screen
Though the constant current is the mainstream of powering the led screen. Due to different drive IC and circuits, It still has two different powering technology. Common Annode powering, and Common Cathode powering.
- Common Anode powering: The RGB lamp’s anode are connected in the same line as the common terminal, and the cathode are used as the driving terminal.
- Common Cathoder powering: The RGB lamp’s Cathode are connected in the same line as the common terminal, and the Common anode are used as the driving terminal.
What is Common Anode LED Screen
For common anode LED Screen, Usually the red, green and blue lamp in the RGB lamp would use the same power supplies (the same power supply voltage). According to the optoelectronic characteristics of LEDs, the driving voltage of the red LED light is lower than that of the green LED light and the blue LED light. In order to ensure the balance of IC heat generation and the long-term stable operation of the screen, the driving circuit must be adjusted with a peripheral bias circuit.
For example, if the input voltage is 4V, the red lamp’s voltage drop is around 1.8V, blue and green lamp’s voltage drop is around 3V. The constant current IC driver also have around 0.7V voltage drop. Hence the red lamp circuit needs to add a resistor to share the voltage drop of the driver IC, while the blue and green circuit do not need.
After using a resistor in the red lamp circuit, The resistor would also consume energy, which would change into heat. Hence the led screen that uses common anode powering would generate more heat (the design should consider heat dissipation carefully) and also be difficult in circuit layout design.
What is Common Cathode LED Screen?
For common cathode LED Screen, The red lamp is using a different power supplier from blue and green lamp. The red lamp’s input voltage would be around 2.8V-3V, hence we do not need to add an extra resistor like the common anode led screen does to share the voltage drop. Which means that with the common cathode design, the whole circuit would have less heat output than the common anode led screen, and also consume less energy, and more easy in circuit layout design.
Because of the less heat, the common Cathode LED Screen can also give out a better displaying quality. And also a longer life span.
Comparison of Common Anode LED Screen and Common Cathode LED Screen
| Common Anode | Common cathode | |
| Theory | Anode are connected in the same terminal | Cathode are connected in the same terminal |
| Powering way | Low voltage drive | High Voltage drive |
| Wattage/Heat | High | Low |
| Divider Resistor | Need | No need |
| Circuit Layout Difficulty | Difficult | Easy |
| Power supplier | Single power supplier | Double power supplier |
| Displaying Quality | Low | Better |
| Life Span | Low | High |
