How to choose the right power supply
Introduction
Choosing the Right LED Power Supply: It’s Not Rocket Science!
Selecting an LED power supply is straightforward when you consider some important points. However, making the wrong choice can have serious consequences. In this article, our CEO, Dr. Michael Heidinger, guides you through the basics. Dr. Heidinger earned his Ph.D. in Lighting Technology at the Karlsruhe Institute of Technology and conducted research on durable LED power supplies.Power Supply:
Constant Current or Constant Voltage?
Or Both?
Types of LED Power Supplies
- Constant Current power supplies are used when the LED is directly driven, and no external resistor is present. In this case, the LEDs must be connected in series. Wiring the LEDs in series significantly reduces their lifespan.
- Constant Voltage power supplies are used when there is an external current limitation, meaning there is a resistor present. Constant voltage systems are generally less efficient but more flexible in design, as LEDs with resistors can be wired in parallel.
- Universal power supplies or CCCV (Constant Current Constant Voltage) power supplies, also known as Constant Current–Constant Voltage power supplies, provide both functions. While this function was traditionally found in laboratory power supplies, innovative manufacturers now offer it as well.
Types of LED Power Supplies
Identifying the Right Type of LED Power Supply
Constant Current Power Supplies provide a fixed current. An output voltage range is also specified, within which the output voltage should lie. The output voltage is the sum of all forward voltages of the LEDs.Example LL-10W: The power supply is labeled as a constant current power supply. The label indicates 5-30V 350mA. (See image on the side). Accordingly, the power supply delivers 350mA in the voltage range from 5V to 30V. Therefore, it is a constant current power supply.
Constant Voltage Power Supplies provide a fixed voltage. Often, a maximum current is also specified within which the output voltage should lie. The output voltage is the sum of all forward voltages of the LEDs.Example DCC4812: The power supply is labeled as a constant voltage power supply. An output voltage and a maximum output current are specified.
CCCV Power Supplies specify both flexible ranges: voltage and current.Example DIG-CCCV-15W: The power supply is titled as a constant voltage and constant current power supply. Both current and voltage are indicated.
Remember:
The value of the constant indicates the type of power supply.The Power
Calculating the Power Requirement of the LED Power Supply
The power (P) of a power supply in watts is determined by the current (I), measured in amperes, and the voltage (U):P = U * I
Many power supply manufacturers recommend multiplying the calculated power by a factor of 1.5 to 2. This derating is suggested because the stated power ratings cannot be sustained permanently. Often, such recommendations indicate poor product quality, and power supplies with such suggestions should not be used.Lifetime
The LED Power Supply Determines the Lifespan
LEDs offer lifespans ranging from 50,000 to 300,000 hours. However, some LED lights fail well before reaching these numbers. Typical failures of LED lights (see image) manifest as flickering or the power supply not starting. Some power supplies, due to their design, have a shorter lifespan than an incandescent bulb. In many cases, the power supply is responsible for these issues. Almost all power supplies use electrolytic capacitors that limit the lifespan. Power supplies without electrolytic capacitors, using film capacitors instead, have demonstrated a lifespan of up to 70 years in tests conducted in collaboration with the Karlsruhe Institute of Technology (source). Digital Power Systems, therefore, recommends: Pay attention to power supplies that omit electrolytic capacitors.Mortal danger
due to non-isolated power supplies
Isolation from the Mains – A Lifesaver
When power supplies have a mains input, isolation is strongly recommended. Without this isolation, the user may experience an electric shock even by touching a single contact. Therefore, it is crucial to ensure that this isolation is present. Often, this is referred to as “galvanic isolation.” Example: The LL-10W is a galvanically isolated constant current LED driver.
