Comment les commandes DALI influencent-elles la tension de sortie ?

A panicked email reached our factory last spring: a client’s meter showed “wrong” voltage after sending DALI commands. Nothing was broken. That misunderstanding wastes hours, so let me untangle it.

DALI commands do not set a specific LED output voltage. They send a digital arc-power or light-output level from 0–254. The DALI LED driver interprets that command and regulates its own output voltage and current to reach the requested brightness for the connected LED load.

That single distinction explains most confusion around DALI dimming. In this article, I will walk through what the commands really change, how to verify driver behavior, why voltage moves during dimming, and how you can customize the response for your project.

What DALI Commands Actually Change My LED Driver’s Output Voltage?

On our end-of-line test bench, every DALI dimmable driver we ship gets hit with a full command sweep. Watching those test logs daily taught me exactly which commands matter.

DALI commands such as DAPC (Direct Arc Power Control), UP, DOWN, STEP UP, and RECALL MAX LEVEL change the driver’s target light level, not its voltage directly. The control gear then adjusts current, voltage, or PWM duty cycle internally to reach that requested target.

Think of the control chain like this: DALI command → requested light level → LED driver control loop → output voltage and current → LED light output. The driver, not the DALI bus, decides the actual electrical operating point. Under the IEC 62386 standard ¹, a Direct Arc Power Control command carries an 8-bit value. That value maps a dimming level 0–254 onto a logarithmic dimming curve, which matches how human eyes perceive brightness. The driver then acts like a digital-to-analog converter, translating that digital step into a physical output change.

Three Voltages People Confuse

Readers often mix up three completely different things. I separate them for every new customer, because the confusion is that common.

How the Driver Translates Commands

For a constant current driver ², the command changes the regulated current. The output voltage then settles wherever the LED string’s forward voltage sits. For a constant voltage driver, the voltage stays fixed, and the driver typically modulates the duty cycle of a high-frequency PWM signal instead. Configuration commands like FADE TIME and FADE RATE control how fast the transition happens. So a single UP command may shift output gradually over several seconds, not instantly.

How Can I Verify My DALI Driver Responds Correctly to Voltage Commands?

A lighting distributor in Singapore once messaged me on WhatsApp, worried our drivers were “ignoring” commands. Ten minutes of guided testing showed his meter was on the bus terminals, not the output.

Verify a DALI driver by checking bus voltage (about 16 VDC), sending a known dimming level 0–254, and measuring light output, not just LED voltage. Then use query commands, or D4i energy reporting on DALI-2 drivers, to confirm the driver reached the requested level.

Verification starts with the communication layer, not the load. If the DALI bus power supply is weak or overloaded, commands never arrive cleanly. The bus is current-limited at 250 mA; drawing more collapses the signal. During normal communication, the loop voltage fluctuates by roughly ±2–3 VDC, because devices briefly short the loop to transmit bits. That fluctuation is normal, not a fault.

A Step-by-Step Verification Process

1. Measure the idle bus voltage. It should sit near 16 VDC.
2. Send a DAPC command at a known level, for example 128.
3. Observe the light. It should move smoothly along the logarithmic dimming curve.
4. Query the driver’s actual level. It should echo the value you sent.
5. Only then measure LED output current and voltage against the datasheet.

Reading the Bus Correctly

Modern DALI-2 drivers ³ make verification even easier. D4i drivers built to Part 252 report real-time voltage, power, and energy data through query commands. In our own QC process, we log this feedback for every batch before export, because DALI-2 certification standardizes how command values map to output across manufacturers. That consistency is exactly what buyers like engineering companies need for multi-vendor projects.

Why Does My Output Voltage Fluctuate or Drop During DALI Dimming?

Early in my export career, a project team in Germany returned a batch they believed was defective. Every unit passed retesting. The lesson stuck: unexpected voltage readings usually mean misread physics, not bad drivers.

Output voltage changes during DALI dimming because a constant current driver lowers LED current, so the LED string’s forward voltage naturally drops. Fluctuation seen on a meter often comes from PWM dimming, fade transitions, or accidentally measuring the communication bus instead of the LED output.

Let me break this into cause and effect, because each source of “fluctuation” has a different fix. First, basic diode physics. LEDs have a forward voltage that falls slightly as current falls. So when a DALI command dims a constant current driver from 100% to 10%, the measured LED voltage drops a little. That is correct regulation, not a communication problem. If a technician measures an unexpected voltage after changing a DALI level, the first question should be whether the driver is correctly regulating the LED load, not whether DALI failed.

Second, PWM dimming. Many constant voltage drivers hold amplitude steady and chop the output at high frequency. An average-reading multimeter then shows a “voltage” that scales with duty cycle. The rail is not actually sagging; the meter is averaging pulses.

Common Causes and What They Really Mean

Third, fade behavior. FADE TIME and FADE RATE dictate the transition speed between output states. Advanced drivers use 16-bit internal interpolation across the 254-step range, so ultra-slow fades stay smooth with no visible stepping. During those long fades, output naturally drifts. Finally, some high-efficiency drivers use dynamic rail scaling, adjusting the internal DC-DC converter’s rail voltage at low dim levels to cut switching losses and heat. Voltage movement there is a feature, not a defect.

Can I Customize How DALI Commands Control Output Voltage for My Project?

Every custom order forces us to weigh a trade-off: locking parameters at the factory gives consistency, while leaving them programmable gives installers flexibility. We usually recommend a hybrid, and here is why.

Yes. You can customize how DALI commands shape output by configuring minimum level, maximum level, fade time, fade rate, power-on level, and system failure level, or by ordering drivers with tuned dimming curves, PWM frequency, and current settings matched to your project.

Customization happens at two layers, and understanding both saves money. The first layer is standard DALI configuration. Every compliant driver stores variables that reshape how commands translate into output. MIN LEVEL and MAX LEVEL cap the result internally; a command below the minimum simply lands at the floor. POWER ON LEVEL defines the output when mains power first arrives. SYSTEM FAILURE LEVEL defines the fallback if the bus signal disappears. Some drivers go to full output on power-up and drop to a preset level on signal loss, which means output can change even with no new command. For hotels and hospitals, we often preset these values before shipping so every fixture behaves identically out of the box.

Factory-Level Customization Options

The second layer is hardware and firmware tuning, which we handle at the design stage:

• Output current setting. We match a constant current driver’s regulation point to your exact LED module, so the same DALI level produces predictable light across the whole project.
• Dimming curve selection. Logarithmic suits human perception; linear suits daylight-harvesting sensors and control algorithms.
• PWM frequency. Higher frequencies avoid flicker on camera-heavy sites like studios or retail spaces.
• Deep-dimming performance. Drivers with 16-bit interpolation keep 1% dimming smooth for cinemas and conference rooms.
• Branding and documentation. We offer customizable logos and private designs for distributors building their own product lines.

One exception deserves a clear warning. A dedicated DALI-to-0–10V converter ⁴ deliberately translates DALI commands into an analog control voltage, mapping 0–254 onto a 0–10 V output. That is a downstream conversion device, not normal DALI driver behavior. If your project mixes DALI controllers with legacy 0-10V dimmable LED drivers, use that interface intentionally, and never expect a standard DALI driver to behave the same way.

Conclusion

DALI commands request light levels; the driver sets the voltage. Misreading that costs projects time and trust. Choose well-configured, DALI-2 certified drivers, and those surprises disappear.

Notes de bas de page

1. Official site for the international standard governing DALI technology. ↩︎
   

2. Authoritative source for electrical engineering standards and terminology related to power electronics. ↩︎
   

3. Official industry alliance providing certification and technical specifications for DALI-2 technology. ↩︎
   

4. Provides context on the DALI protocol and how it differs from analog dimming systems. ↩︎