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FAQ

What is the difference between a constant current (CC) application and a constant voltage (CV) driver application?

Constant-current (CC) designs eliminate the need for limiting resistors or any current limiting devices that consume power and reduce overall efficiency. The driver is required to control the current flow to the LED’s, since LED’s are current driven devices. The LED brightness is proportional to the current flow through the LED.

**Examples of CC applications: LED Luminaires such as downlights, spotlights, accent lighting, LED bulb replacements, etc.

Constant-voltage (CV) designs utilize current limiting resistors or other limiting devices/circuits to control the current to the LED’s. The driver is only required to regulate the voltage to the LED system. This is used in linear type lighting, such as LED strip lighting, rope lighting, etc. That is because there are too many LED’s connected in a string over many feet, which makes CC impossible to implement. Each parallel LED in a strip, requires its own limiting resistor to control the current flow through the LED.

How do you use the SLD/XLD series drivers as a constant current driver?

The SLD/XLD series sense the load type and switches to either CC or CV mode, depending on the load. If the LED load does not have limiting resistors, the LED’s will tend to want to sink an unlimited amount of current, as they cannot control current. The SLD/XLD driver senses this and switches to CC mode and controls the current. If the LED circuits contain limiting resistors/devices, the current will be controlled and the driver simply regulates the output voltage.

Can you provide us with a wiring diagram for each one?

See catalog.

What happens if you run an XLA at a voltage under its recommended range?

The output current will lose regulation and will be unstable. It is not recommended to run the XLA series below its compliance voltage range, as damage to the LED or driver may occur.

What is Tc, and what is the Tc for the GRE product families?

There are two types of Tc’s (case temperature ratings):

  1. UL places a maximum Tc on their test reports, from the maximum transformer winding temperature they determine from the testing and the construction materials used. Our XLA series will have a max UL Tc of about 100C-110C.
  2. LED lighting mfg also require drivers to have maximum Tc on their drivers, which indicates the maximum case temperature the driver can sustain from external sources (such as LED and heatsinks) without damage or adversely affecting the driver life/reliability. Our XLA25 and XLA18 series have a max Tc of 90C or more for 3 year warranty and 80-85C for 5 year warranty, using higher grade electrolytic caps.

What is the best way to increase max ambient operating temperature? Is it better to dim or to use the pot(s) to reduce output power? Does it differ based on product family?

Both methods can be used for reducing output power. However, the most straightforward method to determine exactly how much output power is being reduced, is by using the trim pots on the drivers.

Can you tie outputs together on the multiple output versions of SLD/XLD to increase power? i.e. Can you tie 3 strings together of XLD200B-412V-FC to have a 36V output and a 12V output?

Yes, you can tie the outputs together to increase voltage. However, the total load current should be less than the individual driver current ratings, and the drivers should be operated in CV mode only. Also, it is suggested that diodes be connected across each driver output, in reverse bias mode, to prevent damage to the driver, if one driver comes up to voltage ahead of the other drivers, or if one driver output goes into protect mode (OCP, OTP, etc).

What’s the difference between the SLD-DIM and XLD-DIM? How do they dim? PWM? 0-10V? Do you need an external supply voltage?

The XLD-DIM is a smaller, low power version of the SLD-DIM1. Both operate in PWM output mode for dimming. The XLD-DIM only operates with a 3-wire potentiometer input. The SLD-DIM1 operates with a 100K pot or a 0-10V input control signal from dimmer controls such as Lutron low voltage dimmer controls. The XLD-DIM was made for dimming low cost LED table lamps or under cabinet lights, where a low cost pot can be used for dimming. The SLD-DIM is a higher power dimming module for Higher power LED applications, such as signage and luminaires.

What’s the difference between leading edge, trailing edge, 0-10, Triac, etc.?

Leading edge (also known as Forward Phase) dimming refers to the low cost triac type dimmers that phase cut the leading edge of the AC sinewave.
Trailing edge (also known as Reverse Phase) dimming refers to the higher end Mosfet based dimmers, which phase cut the trailing edge of the sinewave.

Our XLA series drivers can operate with either type dimmer.

0-10V dimming is a low voltage, secondary side control method, where a DC voltage level is applied to a driver (or dimmer module) to control the output level, either through PWM or DC voltage/current. This 0-10V signal can come from a commercial low voltage dimmer, such as a Lutron dimmer control, or from an adjustable DC supply, which can be adjusted from 0-10V DC, or even a computer controlled system, which uses a A/D converter output that generates the 0-10V signal level.