There are some key words which are quite easy to be mixed together in the LED lighting industry like PWM dimming signal and PWM LED current, class 2 and class II, isolated power supply and isolated dimming, etc. This article will only focus on isolated dimming interface.
Isolated Dimming vs. Isolated Power Supply
Isolated dimming means that the dimming interface is isolated to both input and output. Sometimes the dimming signal is low voltage and safe 0-10V or PWM or digital with less than 20V peak voltage but the output voltage is high voltage which is not safe. But sometimes the dimming signal is not safe because the dimmer is powered by but not isolated from AC line voltage, so for the power supply if the dimming interface is not isolated from the output, the whole LED luminaire can be unsafe. This is the background of adopting isolated dimming interface of LED drivers.
Normally for a universal input LED driver, the dimming interface insulation voltage is required as below table shows.
| Unit: Vac | Input | Output | Dimming | Case |
|---|---|---|---|---|
| Input | – | 3750 | 3750 | 1554 |
| Output | 3750 | – | 1554 | 1554 |
| Dimming | 3750 | 1554 | – | 1554 |
| Case | 1554 | 1554 | 1554 | – |
Isolated Dimming vs. Non-isolated Dimming
Before the mandatory standards of isolating the dimming interface, all the LED driver dimming interface is non-isolated and shares the same electrical reference with LED secondary output.
| Unit: Vac | Input | Output | Dimming | Case |
|---|---|---|---|---|
| Input | – | 3750 | 3750 | 1554 |
| Output | 3750 | – | 0 | 1554 |
| Dimming | 3750 | 0 | – | 1554 |
| Case | 1554 | 1554 | 1554 | – |
Isolated Dimming Related Standards
UL8750 Supplement SF
Supplement SF was published as part of ANSI/UL 8750 in July 2017. In September 2017, UL’s certification organization set up an industry file review for the adoption of this supplement with an effective date of Nov. 2, 2020.
Chapter 15.4, IEC 61347-1,2015
IEC standards announced the requirement for isolated dimming earlier than UL as below.
Summary
Isolated dimming is more and more adopted in general lighting so the designers should understand the differences between the isolated dimming and isolated power supply so as to choose the right products for the luminaires. For more questions please contact with us by sales@upowertek.com.
