Frequently Asked Questions

Welcome to our Frequently Asked Questions page where you can find answers to some of the common questions we are asked about LED Lighting Drivers and Power Supplies. If you do not find the answer for you question, please contact us to ask us.

Questions about LEDs

Light Emitting Diodes (LEDs) are miniature lights produced by moving electrons in a semiconductor. The light is emitted when power (current/voltage) is applied to it. LEDs contain no burning gas or filaments so they are long lasting and generate little heat. Lack of a filament makes them more durable and they contain no toxic mercury to pollute the environment.

An LED doesn’t burn out like a standard lamp so individual LEDs do not need to be ordinarily replaced. Instead the LED gradually produces lower output levels over a very long period of time.

LEDs from reputable manufacturers have an average rated life of 50000+ hours. When compared with Incandescents and CFLs under same usage and conditions an LED lamp could last for 15years before replacing.

LEDs bring a number of advantages to the lighting industry including high efficiency; superior durability and a greater usage lifetime when compared to other lamp sources which can result in reduced maintenance. These benefits can translate into significant energy savings (up to 80%) and reduced maintenance costs leading to an overall reduction in the Total Cost of Ownership over the products lifetime and a very quick ROI.

Yes, LEDs love to be dimmed and unlike conventional lighting will actually extend the life of the LED.

FRIWO′s range of LED drivers can provide precise and tightly controlled dimming.

Yes. LEDs achieve full brightness almost instantly and this isn’t affected by low temperatures.

Different chipsets have different characteristics and most quality manufacturers and suppliers will select a specific chip that best suits the application. Each manufacturer has different strengths and may use different technologies and different packaging techniques in what is still technology wise a very dynamic and competitive market with new developments and benchmarks being announced quarterly.

It is therefore important when selecting LED modules that you are dealing with a proven technology and quality driven company with evidence to support their technical claims. This will help you ensure that you can develop a solution which will supply a quality light output; competitive priced and long lasting product.

Questions about LED Drivers

LEDs tend to operate from relatively low voltages and require a PSU to reduce the mains voltage supply down to the voltage or current that is required by the LED product. The AC voltage needs to be converted, rectified and smoothed. PSUs can be either constant voltage or constant current.

FRIWO offer a range of LED drivers from 10W – 100W.

CC LED drivers are designed to maintain a Constant Current during operation. A CC LED driver balances the output current from each channel to ensure reduced EMI interference and maintain the long lifetime of LEDs. The CC LED driver circuit allows the driver to operate in the ‘constant current region’ also ensuring there is no variation in the brightness of the LEDs. This means you do not have to use resistors or control the current being fed to the LEDs so they can be used in series as long as the forward voltage is within the specified output range of the LED power driver.

CC devices must be wired in series.

CC Led drivers are suitable for a wide range of applications including architectural lighting; task lighting; medical lighting; transportation lighting; lit signage; safety and security lighting and outdoor area lighting.

FRIWO’s range of LED drivers can be used in both CC and CV mode.

CV LED drivers are designed to maintain a Constant Voltage during operation regardless of the current variations between 0-100%. A CV LED driver is ideal for paralleled LED lighting arrays because they generically have an in built resistor to control the current, therefore a CV driver would be required to convert the AC power to the required DC voltage.

CV devices must be wired in parallel.

CV Led drivers are suitable for a wide range of applications including architectural lighting; task lighting; medical lighting; transportation lighting; lit signage; safety and security lighting and outdoor area lighting.

FRIWOS’ range of LED drivers can be used in both CC and CV mode.

With Constant Voltage the LED module only requires a fixed voltage often 12VDC or 24VDC. The current is usually regulated by either resistors that have been wired in series with the LEDs or by an on board/built in regulator that the LED module may have.

CV loads may be added in parallel across the output of the driver until the maximum output current is reached.

This arrangement is often used in installations where the number of LED modules being connected is unknown however may provide inconsistent Led performance and reduced life.

With Constant Current the reverse is true. The current is fixed by the driver whilst the voltage will vary depending on the load. The more LEDs that are attached the higher the output voltage will be up to a maximum set by the driver. This can provide uniform brightness and colour behaviour of the LEDs with no negative impact on LED Lifetime.

This methodology is usually used when the load/number of LEDs is known and you want to achieve optimal efficiency.

FRIWO′s range of LED drivers can be used in both CC and CV mode. (Link)

Usually the manufacturer of the LED module will specify whether it is for use with either a Constant Voltage or Constant Current driver. You cannot run an LED module designed for CC from a CV supply without damaging it. However a CV LED load will run (albeit inefficiently) from a CC driver. Another indication is if the LED module is rated in milliamps (mA) or volts (V). Milliamps indicates a CC driver and Volts means a CV driver is required.

FRIWO’s range of LED drivers can be used in both CC and CV mode.

PWM (pulse width modulation) LED drivers change the switching frequency from 100 modulations (Hz) per second to make the LED appear to be continuously lit, with no flicker. PWM dimming enables minimal colour shift when adjusting the LED brightness. However one must be aware that PWM dimming requires a higher inrush current and resulting potential noise.

FRIWO′s DIMMBox uses a frequency of 600 Hz to be absolute flicker free

1-10V dimming LED drivers utilise analogue dimming to set the light levels between 10%-100% of the light output. Most drivers require an external 10VDc source to operate 1-10V dimming. NB this technique does not dim the LEDs to zero output.

Triac Dimming LED drivers are compatible with traditional trailing edge dimmers. Triac dimming LED drivers can vary the light output between 1-100%. Care must be taken to ensure that the load requirement of the dimmer is met to ensure smooth Triac dimming over the 1-100% range.

Dali Dimming LED drivers utilise DALI addressable programmers to control light levels and functionality. Multiple DALI dimming LED drivers can be controlled by a single pair of wires. Within a DALI network each DALI diming LED driver can be given individual lighting instructions.

FRIWO’s range of LED drivers can be dimmed by all these methods either on their own or by using DIMMBox.

Yes they can.

LEDs are diodes and only allow power to pass in one direction – they must be powered from a DC source that limits the current flowing through them. If LEDs are connected directly to the UK 230v AC mains supply without any current limiting LED driver or LED power supply they will most likely fail immediately and catastrophically with possible damage to the fixture.

If LEDs are powered via an LED driver or Power Supply that supplies an incorrect voltage several outcomes are possible. If the current and/or voltage is too low the LEDs will appear too dim or fail to light. If the current and /or voltage is too high the LEDs could age prematurely (in the case of minor overdrive) or at the other extreme fail catastrophically.

To determine this you need to understand the voltage drop in the wiring between the LED driver and the LED module. Too much voltage drop can reduce the light output from the LED system. The acceptable distance is determined by the load and the conductor size. With Constant Voltage applications you are limited since the voltage is normally fixed at either 12V or 24V and with a significant drop in voltage you may visually be able to see the difference in light output.

With Constant Current drivers there is far more flexibility since the driver will automatically supply more voltage in order to provide the necessary current. The exception to this is if the LED module was already using the entire output voltage capability of the driver in which case the distance would be limited in a similar way to the Constant Voltage drivers.

Voltage Drop is the loss of voltage along a length of cable due to the electrical resistance of the copper conductors inside the cable. The longer the cable and/or higher the current the greater the amount of voltage lost. Increasing the cable Cross Sectional Area (CSA) will mitigate against the loss of voltage. Voltage drops can be pre-determined using a simple calculation.

Miscellaneous Questions

IEC defines a SELV system as “an electrical system in which the voltage cannot exceed ELV under normal conditions, and under single fault conditions, including earth faults in other circuits”.

There exists some confusion regarding the origin of the acronym SELV.

It stands for "separated extra-low voltage" in installation standards and for "safety extra-low voltage" in appliance standards.

A SELV circuit must have:

  • Protective-separation (i.e., double insulation, reinforced insulation or protective screening) from all circuits other than SELV and PELV (i.e., all circuits that might carry higher voltages).
  • simple separation from other SELV systems, from PELV systems and from earth (ground).

The safety of a SELV circuit is provided by

  • the extra-low voltage
  • the low risk of accidental contact with a higher voltage;
  • the lack of a return path through earth (ground) that electric current could take in case of contact with a human body.

The design of a SELV circuit typically involves an isolating transformer, guaranteed minimum distances between conductors and electrical insulation barriers. The electrical connectors of SELV circuits should be designed such that they do not mate with connectors commonly used for non-SELV circuits.

FRIWO′s LED drivers are all passed SELV equivalent according to BS EN60335 and meet the safety standards according to EN61347-2-13 and EN61347-1.

Power Factor Correction (PFC) is associated with PSUs that have a mains input and a low voltage output and describes the ratio between Real Power and Apparent Power. PFC is given as a maximum figure of 1.0. The nearer to this the better – the smoother the Power Supply’s input current pull is, drastically reduces the amount of energy required to produce the low voltage and current output.

EN61000-3-2 -states that it is not allowed to use a LED driver with a power consumption > 25W without active PFC.

FRIWO′s LED drivers all have PFC.

Instead of coupling the charging condenser directly to the rectifier a boost convertor is interconnected. The boost convertor triggers an always constant direct voltage on the link capacitor out of the restified sinus signal.

EN61000-3-2 states that it is not allowed to use a LED driver with a power consumption > 25W without active PFC.

FRIWO′s LED drivers have active PFC on all relevant parts.

Efficiency is the ratio between the consumed input and given output power. The emerged difference is called energy loss.

Causes of energy loss include:

  • Ohmic losses by transformer and leads
  • Switching losses of SMPS
  • Inserted filters for EMC activities
  • Losses by multi stage (eg PFC & current control of LED drivers)
  • Losses by processing the IC

FRIWO′s LED drivers have efficiency levels of up to 95% (full load).

The Digital Addressable Lighting Interface.

Whilst Analog 1-10V control interface is traditionally the most common industry standard for the dimming of electronic ballasts DALI has been designed to become a well-respected and accepted standard in the lighting market. It strength and success has arisen from its flexibility and ease of installation.

DALI is an International Standard that guarantees the exchangeability of dimmable ballasts from different manufacturers giving specifiers; installers building owners and end users the confidence of supply from many sources.