With so many options available, choosing the right LED transformer can sometimes seem overwhelming. In this article we will go through the question of constant current or DC voltage. In English, constant current is Constant Current (CC) and constant voltage is Constant Voltage (CV). We answer questions about why and when they are needed, and go through their features.
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What is a led driver?A led driver is a device that regulates the amount of current flowing to the led circuits. All driverare either constant voltage (CV) or constant current (CC) or both. The question arises, which of the drivers do you need? The simple answer is that it depends mainly on your LED luminaire. We&#;ve written about Led transformers on the blog before, so there&#;s more information on the subject.
How does LED work?LEDs are the most widely used light source today. LEDs are semiconductor diodes formed by bringing together two slightly different materials to create a PN junction (positive and negative).
P-type holes have an extra positive charge, and N-type electrons have an extra negative charge. By combining these into a PN junction, it produces light by applying a direct current to it.
The colour of the light depends on the materials used in the semiconductor. You can read more about LED as a technology in our article What is LED?
Like any other semiconductor, LEDs allow current to flow forward, but prevent current from flowing backwards. A Led produces light when an electric current passes through it from the anode (+) to the cathode (-).
Current characteristics of LEDsLike traditional PN junction diodes, LEDs are also dependent on the amount of current flowing through the forward voltage. Small changes in voltage cause large changes in current.
Typically, the forward voltage (volts) of LEDs is 2-3.5 V at a forward current of 10-200 mA. In other words, the amount of current increases dramatically with even a small change in voltage.
Temperature coefficient of LEDsOne might think that when the voltage of an LED is fixed, the current is fixed. In other words, the constant voltage or constant current would be same.
In fact, the voltage to current ratio of LEDs is not fixed, but changes with temperature. So although the voltage is fixed, the current is not fixed, but changes with temperature. This is because the LED is a diode, and has a negative temperature coefficient.
The figure below shows 3 curves representing LEDs at different temperatures. At the same voltage of 3.3 volts, the currents are 8 mA, 20 mA and 37 mA.
Temperature coefficient, usually -2 mV/degree (-1.5 &#; 2.5 mV/°C), meaning that as the temperature rises, the current consumption of the LED increases proportionally more steeply.
In other words, in the design of an LED luminaire, the cooling element affects the current consumption of the LED, and to select the right transformer, the current consumption of the LED must be measured at its operating and running temperature.
We have discussed the issue in more detail in our article Why can&#;t leather stand the heat?
What is a constant current LED driver?The constant current driver transformer changes the voltage across the entire lightto maintain a constant current. LEDs designed to work with a constant current transformer therefore need a certain amount of current to work properly.
Led light is brighter at higher current, but if the current is not the amount of current designed for the led, the led will burn brighter and hotter, which will cause the led to burn out quickly. In addition, burning too hot led to a loss of light properties such as colour rendering. This is why constant current transformers are so important for LEDs.
From the LED temperature coefficient graph earlier, we could see that it is better to use a fixed current LED driverto prevent temperature rise.
When do you need a constant current LED driver?Standard current transformers are primarily used in LED luminaires, where the current output of the LED transformer directly supplies power to the LED circuit. This method provides high efficiency and low complexity.
Constant current LED transformers are the best choice if, for example, you are building the luminaire yourself. These drivers can be used with a single bulb or in a LED chain in series. The choice of a Led driverdepends crucially on the purpose for which you intend to use it. The manufacturer of the LED circuit or luminaire always states the amount of current required to operate the LED.
For lighting control, constant current transformers are the best choice because they allow continuous control of brightness and light quality when the amount of current is known.
What is the constant voltage led transformer?However, the most common LED transformers are constant voltage transformers, 12 VDC or 24 VDC. These transformers are designed for DC voltage. The amount of current, in turn, varies. A constant voltage LED light requires a certain amount of voltage to function properly.
These LED lamps have a built-in current limiter or regulator to keep the voltage constant. The current produced by the driver voltage may vary, as the number of LED lights may vary. For example, two metres of conductive tape requires twice as much power as one metre.
Can I use constant voltage led driver for any led directly?We already know that as the operating temperature rises, the current consumption of the LED increases. If the voltage (V) is constant, the current (A) will naturally increase. If we use a constant voltage transformer for a constant current controlled LED, the temperature rise is very fast. When the power is switched on, the LED temperature can easily rise to over +80 or +90 degrees. So the led doesn&#;t last long, and goes out.
According to the graph shown earlier, as the current rises, the temperature rises, e.g. An LED designed for 20 mA current will draw 35 mA and the temperature will reach 85 degrees and keep it there, without increasing the brightness of the LED.
How then can a constant voltage transformer be used for a constant current transformer?An additional current limiter can be added to the circuit. This way, the constant voltage becomes the constant current for the LED. This prevents the LED from over-currenting and overheating, which increases the lifetime of the LED.
When do I need a constant voltage led transformer?Contact us to discuss your requirements of High Efficiency Constant Current LED Strips. Our experienced sales team can help you identify the options that best suit your needs.
You can use a constant voltage (V) led transformer with multiple LEDs connected in parallel, such as led strips. What these LED lights and LED strips have in common is that the manufacturer has installed current limiters into the light.
The picture shows LED strip with a current limiting resistor installed. The resistor limits the current to a series of 3 LEDs with a 470 Ohm resistor. It is a white led circuit that uses a 3.2 V supply voltage. With a 24V led strip in this case, each led circuit receives 30 mA (24V-3×3.2V)/470 = 30 mA current.
This type of construction is suitable for DC to DC led transformers. Led strips always have a limit of 3-6 LEDs per series, which allows the strip to be cut between series.
Let&#;s take the example of an LED strip with 5 sets of 3 LEDs.
Each set of 3 LEDs requires 90 mA (30 mA per LED). So the LEDs work perfectly with 450 mA current.
If we run the strip at 450 mA, but cut off one piece, we are left with four series, and the current in each series increases to 112.5 mA (37.5 mA per LED).
Increased current will start to damage the led circuits, so it is better to use constant voltage led driver with led strips. Led strips are always manufactured for a specific DC voltage. 12 or 24 V. So use them with a DC voltage transformer.
Constant current or DC voltageA short summary of the standard voltage CV and standard current CC transformers:
Constant currentConstant voltagePowerThe amount of current is fixedThe amount of current changesVoltageThe voltage value is variableThe voltage is fixedThe pros and cons of DC voltage
To choose the best LED transformer for your needs, you need to consider the following criteria:
LEDs are inherently constant current controlled. But for many solutions, DC voltage is the best solution. So there is a place for both and they should not be mixed.
If you are interested in the development of (transformer) technology, here is a link to the American Institute of Physics website. After all, technology is constantly evolving.
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When it comes to LEDs, LED Strips or LED modules it is a good idea to use a LED Driver to keep the brightness the same.
There are two types of drivers.
Constant Voltage - This type of driver will have a Fixed Voltage Output. This will depend on the LED voltage rating. It will be a fixed output. The current output for the driver will have a max rating. If the circuit does not draw more that what is required it will work.
Constant Current - This type of Driver will have a Fixed Current Output. This is determined by the current for the LEDs. The Voltage output will be variable. The Voltage can change due to the number of LEDs that are used. Make sure the voltage range will be for the voltage that is required.
The LED Drivers can be either a Board Mount style or External/Internal - Off Board style.
In some cases, depending on the LEDs being used, a AC/DC power supply can also work.
Just check on the Data sheet for the LEDs to see the Voltage needed as well as how much current is needed.
If you are looking for more details, kindly visit Custom LED Light Strip.