What You Need to Know About a Push Led Driver
As the name suggests a push led driver uses the mains supply to power its output circuit. This allows it to act as a dimmer.
The current to the LEDs is pumped through the driver in one of two ways; pulse width modulation (PWM) or amplitude modulation (AM).
Both methods do their job well but PWM has a few disadvantages. This is why some drivers are combined with AM to offer an even better solution to dimming.
Current
The LED driver is a complex beast and you have to be pretty serious about your craft to get it right. One of the more difficult parts is selecting the best octave band suited to your needs. A good quality supplier should be able to help you find the most cost effective solution for your specific application. They are also able to offer you the best possible support. Whether you are a design or manufacturing professional, a knowledgeable partner can save you time, money and stress. The best way to go about identifying and contacting the right provider is to give them a call. You can also ask them to make a list of the most suitable suppliers for your project and provide you with a tailored proposal based on your requirements. We will be more than happy to help you out in any way we can. Our phone number is 1300 242 832 and we look forward to hearing from you.
Voltage
The maximum output voltage of a push led driver is determined by the forward voltage (Vf) of the LEDs that are being driven. Generally, the output voltage of a push led driver will vary with temperature. This is called thermal runaway and can cause serious damage to LEDs if not corrected. The push led driver compensates for the change in Vf by delivering constant current to the LED(s).
A low-wattage LED can be driven from a higher input voltage. This is known as ‘dual-output’ and uses two resistors (R1 and R2) to control the LEDs current. This helps to balance the load between the two outputs, and allows the current to be controlled by a momentary contact switch or logic level signal.
High-wattage LEDs require more current to light up, and the higher their power, the greater the variation in Vf across the circuit. This variation is due to the change in push led driver voltage across the LED when it is warm. If the LED is allowed to get too hot, this will cause it to draw too much current until it burns out.
To prevent this, the voltage in a push led driver should be set to a lower value than the input voltage. The voltage of the port expander supply is usually higher than that of the input, and the VEXT supply is lower. This ensures that the VEXT supply can supply the port expander outputs without overheating.
Some push led drivers are able to drive multiple LEDs in parallel, which reduces the drive voltage needed and the drive current available for each LED. This is possible because the ‘ballast’ resistors in the driver are designed to help to ‘balance’ the current between the LEDs. The ‘ballast’ resistors can be omitted when all the LEDs have identical forward voltages, or are of the same type and manufacturer.
The ‘ballast’ resistors are a safety feature that helps to avoid the LEDs overheating and thermal runaway. This is particularly important when using high-power LEDs with a lower output voltage than the input voltage, as their temperature can increase significantly and they can overheat. The ‘ballast’ resistors also help to avoid short-circuiting or open circuits on the secondary of the driver.
Temperature
The temperature in a push led driver can make all the difference to its performance, as it affects not only its output, but also its lifespan. For this reason, the case temperature of a LED driver is one of its most important features and should never go above 45@ Celsius (150F) as this could result in damage to the internal electronics or shorten the life of the product.
This is usually achieved by placing the hottest component in the device near to an over-temperature protection resistor, which can detect when the temperature is too hot and react accordingly. This protects the LED driver from overheating by reducing its output until the temperature is back within the recommended range. This feature is not available on all push led drivers, however. For example, the LM386 series of constant current drivers from Mean Well does not have a thermal sensor and so would require external over-temperature protection in order to achieve this functionality. The LM386 is an extremely low profile LED driver that is designed as a fanless unit suitable for both indoor and outdoor environments, with a protection rating of IP67 despite not having a cooling fan inside. It is also the world’s first fully programmable DALI and push-button LED driver in a single module.
Safety
There are a number of safety measures that should be taken to ensure the safe operation of a push led driver. These include EMC (electromagnetic compatibility) testing, UL (Underwriters Laboratories) compliance and safety extra-low voltage (SELV) design rules. In addition, it is push led driver advisable to select a high-quality LED driver that has a long lifespan and does not require frequent replacements.
UL Class 2 drivers comply with the standard UL1310, which means that the output is considered safe to touch and does not require primary safety protection at the LED or luminaire level. These drives operate at power levels of less than 60 volts in dry applications, 30 volts in wet applications, less than 5 amps and 100 watts. While safer than a class 1 driver, these restrictions limit the number of LEDs that can be run by a class 2 drive.
UL class 1 drivers are a bit more expensive than a class 2 driver, but they can operate more LEDs and are typically more efficient. Besides, the UL class 1 driver is more dependable and has a longer lifetime than a class 2 LED driver. It also does not require frequent replacements and can withstand repeated failures. If you need to purchase an LED driver, make sure that it has a UL or cUL label and complies with the standards published by UL, NFPA, ANSI and CSA.