Quick answer: Choose an LED driver by matching the LED load’s required current or voltage, then its output range, power and dimming method. According to Mean Well’s HLG-240H datasheet, a driver can support both constant-current and constant-voltage operation, so the operating mode matters as much as the wattage.
This guide covers driver selection, low-voltage calculations and replacement checks. It does not provide mains wiring instructions. Use a qualified electrician for mains-voltage installation or replacement.
What does an LED driver do?
An LED driver supplies controlled DC power; when the source is AC mains, the driver converts it to the DC power the LEDs need. That is the basic role described in Wikipedia’s LED lamp article.
Start by separating the input rating from the output rating. According to Mean Well’s datasheet, the HLG-240H family accepts 90–305 VAC input, while its models have rated outputs from 12–54 V. Those ranges describe this family, not every LED driver. The input range tells you about the supply; the output rating tells you about the load it can serve.
Should you choose constant current or constant voltage?
Match the regulation method to the LED circuit. According to Wikipedia’s LED circuit article, a constant-current driver changes its output voltage while keeping current constant, including when the load varies. Constant voltage means the regulated quantity is voltage instead.
| Driver mode | Selection priority | What the cited example establishes |
|---|---|---|
| Constant current (CC) | Required LED current and the string’s voltage range | Current stays constant while voltage changes, according to Wikipedia. |
| Constant voltage (CV) | Required supply voltage and how the LED circuit controls current | Mean Well describes CV operation as usually using an additional DC/DC driver, according to its datasheet. |
| Combined CV + CC | The operating region in which the load will run | Mean Well’s HLG-240H supports both modes, with direct LED drive in CC mode, according to its datasheet. |
Do not select a replacement from wattage alone. A power value does not uniquely specify voltage or current: P = V × I. Establish which quantity the load requires you to regulate before comparing power ratings.
How do you match voltage, current and watts?
For a CC load, match the required current and keep the string voltage within the driver’s CC operating window. As a concrete reference, according to Mean Well’s datasheet, the HLG-240H-24 has a 24 V output rating, 10 A rated current and a 12–24 V constant-current region. Its rated output power follows P = 24 × 10 = 240 W. That voltage window alone does not make it suitable for a lower-current LED string.
Worked example: a constant-current string
Assumed inputs: a series string of 6 LEDs, each with 3.0 V forward voltage at a required 350 mA, and a hypothetical driver regulating 350 mA over 15–21 V.
- String voltage = LED count × forward voltage = 6 × 3.0 = 18 V.
- Current in amps = 350 ÷ 1,000 = 0.350 A.
- LED power = voltage × current = 18 × 0.350 = 6.3 W.
- Voltage-window comparison: 15 V ≤ 18 V ≤ 21 V.
The assumed operating point fits. It does not establish the string’s entire operating range: according to Wikipedia’s LED article, forward-voltage manufacturing tolerances also affect current sharing. Use the actual LED voltage limits when assessing the complete design.
Worked example: a constant-voltage load
Assumed inputs: a module specified for 24 V constant-voltage input, with its own current control, consuming 96 W.
Required current = power ÷ voltage = 96 ÷ 24 = 4 A.
The output requirement is therefore 24 V at 4 A, or 96 W, at the assumed operating point. This is load arithmetic, not a universal spare-capacity percentage. Compare the result with the candidate driver’s permitted operating conditions.
For the low-voltage cable run, use the voltage drop calculator to evaluate V_drop = I × R_loop. The wire gauge calculator compares voltage drop and its current-capacity planning limits; these tools help assess the cable separately from the driver.
When is a resistor enough for a small LED circuit?
A series resistor is the simplest LED drive circuit, according to Wikipedia’s LED circuit article. The same source gives R = (V_supply − V_forward − V_switch) ÷ I_LED and notes that most LED datasheets specify a maximum continuous DC current. This is a low-voltage circuit calculation, not a mains-driver design.
Assumed inputs: a 12 V DC supply, 3 series LEDs with 3 V forward voltage each, a target current of 20 mA, and 0 V switch drop. The LED resistor calculator uses the same series-load calculation without a separate switch-drop term:
- Total LED voltage = 3 × 3 = 9 V.
- Resistor voltage = 12 − 9 − 0 = 3 V.
- Current = 20 ÷ 1,000 = 0.020 A.
- Resistance = 3 ÷ 0.020 = 150 Ω.
- Resistor dissipation = I² × R = 0.020² × 150 = 0.0004 × 150 = 0.060 W.
That dissipation is the calculated heat load, not a selected resistor power rating. According to Wikipedia’s LED article, parallel LED strings can share current unevenly because of forward-voltage tolerances, and a shared current source may cause failures as devices warm. Do not treat a shared total current as proof of equal branch currents.
Will the driver work with your dimmer?
Match the dimming interface, not just the word “dimmable.” According to the DOE GATEWAY dimming report, forward phase-cut removes the leading part of the AC waveform, while reverse phase-cut removes the trailing part. DOE attributes many dimming problems to compatibility between the LED source and phase-cut dimmer.
A separate control input is a different interface. According to Mean Well’s datasheet, HLG-240H B/AB types adjust output current using 1–10 VDC, a 10 V PWM signal at 100 Hz–3 kHz, or resistance. For that dimming arrangement, the datasheet suggests direct LED connection rather than additional drivers. Those details must match the planned control system.
What should you compare before replacing a driver?
Compare regulation, output limits, dimming and protection behavior. According to Mean Well’s datasheet, this family uses constant-current limiting for over-current, hiccup protection for a short circuit, latch-off for over-voltage, and automatic recovery after an over-temperature shutdown cools down. Protection behavior is therefore part of the replacement comparison.
Use this selection checklist:
- Match the load’s CC or CV requirement, including current and voltage window.
- Calculate load power and compare it with permitted driver output.
- Match the dimming interface and relevant model variant.
- Match the enclosure protection to the installation environment.
For enclosure markings, the first IP digit describes solid-object protection and the second describes water protection. IP65 is dust-tight with protection against water jets from a 6.3 mm nozzle; IP67 is dust-tight with immersion protection up to 1 m, as described in Wikipedia’s IP Code article. These are different water-exposure categories, so choose by the stated exposure.
FAQ
Is an LED driver just a power supply?
It supplies power with the regulation the LED circuit needs. According to Mean Well’s datasheet, the same driver family can operate in CC or CV mode, so the label “power supply” alone does not establish compatibility.
Can I choose a driver with more watts?
Extra wattage alone does not establish a match. In the assumed CV example, 96 W ÷ 24 V = 4 A; the required voltage remains part of the selection even if a candidate has a higher power rating.
Can parallel LED strings share a constant-current driver?
Do not assume equal current sharing. According to Wikipedia’s LED article, forward-voltage tolerances cause unequal sharing and may lead to failure as the LEDs warm.
Will an old TRIAC dimmer work?
The pairing needs to be compatible. According to the DOE GATEWAY report, LED source and phase-cut dimmer compatibility often explains dimming problems; a dimmable-driver label does not establish that pairing.
Can I replace a driver with the same voltage rating?
Voltage alone is insufficient. According to Wikipedia’s LED circuit article, a CC driver regulates current while voltage changes, so the replacement also needs the correct current and operating window.
Jack Shi
Founder & editor, LEDaskJack Shi builds and writes LEDask, an independent LED-lighting tools project operated by clooms. He designs the calculators, checks their formulas and reference values against published engineering data, and writes the guides across the site.
