Table of Contents
An LED driver should be selected against the coldest and hottest string voltages, not only the nominal voltage printed beside an LED symbol. The same design must also regulate current at minimum brightness, survive a disconnected string, and remain within its thermal limits.
This guide covers board-level LED driver selection for controlled lighting and indication. It does not assume that a general-purpose DC/DC converter or a display-matrix driver is interchangeable with a constant-current lighting driver.
String voltage and driver topology
Add the forward-voltage range of all series LEDs at the intended current and relevant temperatures. Include wiring drop and the headroom required by the chosen current-regulation path.
For an illustrative string of six LEDs, assume each device spans 2.7–3.3 V over the design conditions. The string spans 16.2–19.8 V before wiring and regulator headroom. If the supply spans 18–24 V, a simple buck driver cannot maintain current through every combination: the highest string requirement exceeds the lowest supply.
A topology that handles the crossing voltage ranges, a different string arrangement, or a narrower operating envelope may be required. TI’s LED-driver overview, accessed September 15, 2026, organizes selection by LED function and power topology and points to separate dimming resources.
Architecture choices across the voltage envelope
| Application condition | Candidate approach | Additional check |
|---|---|---|
| Supply consistently above string requirement | Buck current regulation | Minimum on-time, dropout/headroom, and fault behavior |
| Supply consistently below string requirement | Boost current regulation | Open-string voltage and input-to-output path |
| Supply crosses the required string voltage | Suitable buck-boost or related topology | Efficiency, control range, and component stress |
| Several independently controlled strings | Multiple regulated channels | Current matching, thermal distribution, and fault isolation |
| Low voltage difference and modest dissipation | Linear current regulation | Worst-case power loss and PCB temperature |
These are architecture-screening choices. Exact operating limits come from the selected driver’s datasheet and reference design.
The buck-converter selection guide covers voltage-converter constraints. An LED design additionally needs a defined current-control and fault strategy.
LED current and sensing error
Where a driver sets current from a sense threshold and resistor, the nominal relation is current equals sense voltage divided by resistance. Include both threshold accuracy and resistor tolerance, then consider drift, layout, sensing method, and switching ripple.
Assume an illustrative 0.1 V threshold and a 0.2 Ω resistor. The nominal current is 0.5 A, and the resistor dissipates 0.05 W at that current. This arithmetic does not select the resistor’s power rating; ambient temperature, derating, pulses, and layout still matter.
For multiple strings, distinguish absolute current accuracy from channel-to-channel matching. Equal total current does not prove that each parallel string receives an acceptable share.
Minimum brightness and PWM pulse duration
At 1 kHz PWM, the period is 1 ms. A 0.1% duty cycle gives a one-microsecond on-time. If the driver’s current does not settle within that interval, an ideal duty-cycle calculation will not describe the emitted light.
Check the supported PWM range, delay, current rise and fall times, and behavior at minimum brightness. Analog dimming changes the current amplitude; PWM dimming changes the time pattern. Either method needs validation against the required optical output and operating environment.
Use measurements appropriate to the application, including camera interaction or visible modulation where relevant. Electrical average current alone cannot establish that the optical behavior meets the product requirement.
Thermal and fault acceptance
Calculate the losses relevant to the selected topology and measure on representative hardware. A linear regulator dropping 3 V at 0.5 A would dissipate 1.5 W in that path; a switching driver distributes losses differently among the IC, inductor, switches, and other components.
Test open string, shorted LED or string where applicable, hot connection if permitted, startup, and thermal recovery. Confirm that the fault response does not overstress another component or leave the load in an unintended state.
For industrial electronics, record the approved string, thermal arrangement, dimming settings, and fault limits with the driver ordering code. A candidate substitute should be compared against that operating envelope rather than only against maximum current and package size.
That record gives purchasing a clear boundary: which variants can enter evaluation and which changes require a new design decision.
Frequently Asked Questions (FAQ)
Can a constant-voltage converter directly replace a constant-current LED driver?
Not without a circuit that provides the required current regulation and protection. LED forward voltage varies with operating conditions, so a voltage setting alone does not define a controlled LED current.
Does a high PWM dimming ratio guarantee good low-brightness performance?
No. Check the supported PWM frequency, minimum pulse duration, current rise and fall behavior, and actual optical result. A ratio quoted under different conditions may not apply.
Is the driver's maximum output current the allowed continuous application current?
Not by itself. Package dissipation, PCB thermal performance, input and output conditions, external components, and LED limits determine the usable continuous operating point.
