LED Driver Symbol
Definition: The LED Driver symbol represents the AC-to-DC power conversion unit that supplies regulated voltage or current to LED loads — drawn as a rectangle with 'LED DRV' text or a diode mark, AC input terminals (AC L, AC N) on the left and DC output terminals (DC+, DC−) on the right — listed to UL 8750 in North America and IEC 61347-2-13 internationally.
Also known as: LED power supply, constant-voltage driver, constant-current driver, LED transformer, Class 2 driver, dimmable LED driver, electronic LED control gear.
What the LED Driver symbol means
The LED Driver symbol denotes the electronic control gear between mains AC power and an LED load. LEDs cannot connect directly to 120/240 V AC: they need rectified, regulated DC, and because an LED's current rises steeply with tiny voltage increases, the supply must actively regulate. The driver performs rectification, power-factor correction (on better units), switching conversion, and regulation in one enclosed unit, presenting mains terminals (AC L, AC N, often earth) on one side and low-voltage DC terminals (DC+, DC−) on the other.
Drivers come in two fundamentally different regulation modes. A constant-voltage (CV) driver holds a fixed output voltage — 12 V or 24 V — and lets the load (an LED strip or module with its own resistors) set the current; it behaves like a stiff DC supply. A constant-current (CC) driver holds a fixed output current — 350 mA, 700 mA, 1050 mA are common — while its voltage swings across a compliance range to suit however many LEDs are in the series string; it is used with bare COB modules and downlight engines. Connecting the wrong type destroys LEDs, so the symbol or its label in a diagram should always state CV/CC and the rating.
How to identify the LED Driver symbol
In diagrams the LED driver is a rectangle with the AC input on the left (terminals AC L and AC N, sometimes a ground) and the DC output on the right (DC+ and DC−), labelled 'LED DRV', 'DRIVER', or with a small diode/LED mark inside. Ratings text beside the symbol — for example '24 V DC, 60 W, Class 2' or '700 mA CC, 15–42 V' — tells you the regulation mode. Dimmable drivers add control terminals: a violet/gray pair for 0–10 V dimming, or DALI bus terminals, drawn on the top or bottom edge.
IEC-style drawings may render it as the generic converter symbol — a rectangle split diagonally with '~' (AC) in one triangle and '=' (DC) in the other, per IEC 60617 — the same convention used for any rectifier or power supply. Distinguish an LED driver from a plain low-voltage transformer symbol: a magnetic transformer shows two windings and outputs AC (for halogen systems), while a driver always shows the AC-in/DC-out converter form.
Function in a circuit
The driver takes 120 V or 277 V AC (or 220–240 V internationally; most commercial drivers accept 100–277 V universal input), rectifies it, and runs a switch-mode converter that regulates the output. A CV driver for strip lighting behaves like a stiff 12/24 V source and must be sized so the connected strip load is no more than about 80% of the driver's wattage. A CC driver for a downlight or COB engine pushes its rated current through the LED string and 'finds' whatever voltage that string needs within the driver's compliance window.
In a typical residential circuit the driver's AC side is wired like any luminaire: switched hot to AC L, neutral to AC N, on a 15/20 A lighting circuit. Dimming happens one of two ways: phase-cut (TRIAC/ELV) dimmable drivers accept a chopped AC waveform from an ordinary wall dimmer, while 0–10 V, DALI, or PWM-input drivers keep clean AC and take a separate low-voltage control signal. Class 2 output drivers (≤60 W at 12 V, ≤100 VA generally, per NEC 725) allow the DC side to be wired with light-duty methods, which is the main reason strip-light installs favor them.
Standards: IEC vs ANSI
| IEC 60617 | IEC 61347-2-13 covers safety of DC- or AC-supplied electronic control gear for LED modules; IEC 62384 covers performance. SELV output classification per IEC 61140 applies to 12/24 V drivers. The drawing convention is the IEC 60617 converter symbol (rectangle with ~/= halves) or a labelled rectangle. Dimming interfaces follow IEC 62386 (DALI). |
|---|---|
| ANSI/IEEE 315 | UL 8750 is the North American safety standard for LED drivers (as part of lighting products), with Class 2 output circuits defined by UL 1310 and NEC Article 725 (max 100 VA, 60 W at 12 V, current-limited). NEC Article 410 governs luminaire wiring and Article 411 low-voltage lighting systems. ANSI C82.77 covers harmonics/power quality for lighting gear; 0–10 V dimming follows ANSI/ESTA E1.3 and IEC 60929 Annex E conventions. |
| Key difference | Symbol-wise both traditions use a labelled AC-in/DC-out rectangle; IEC formalizes it with the ~/= converter glyph. The regulatory split matters more: North America leans on the Class 2 concept (inherently limited output allowing relaxed low-voltage wiring methods), while IEC territory uses SELV classification for the same idea with different limits (≤60 V DC). Dimming ecosystems also differ — TRIAC and 0–10 V dominate the US; DALI is far more common in European commercial work. |
Terminals / pins
| Pin | Name |
|---|---|
| ac_l | AC L |
| ac_n | AC N |
| dc_pos | DC+ |
| dc_neg | DC- |
Typical values
Constant-voltage drivers: 12 V and 24 V outputs, 20–320 W, with 60 W (at 12 V) the ceiling for a single Class 2 output. Constant-current drivers: 350 mA, 500 mA, 700 mA, 1050 mA outputs with compliance voltages like 15–42 V, powers of 10–50 W typical for downlights. Input is 120 V, 277 V, or 100–277 V universal at 50/60 Hz; efficiency runs 80–93%; power factor ≥0.9 on commercial-grade units. Dimming ranges are typically 100–10% for TRIAC and 100–1% (or 0.1%) for 0–10 V/DALI drivers. Ambient ratings around tc = 70–90 °C case temperature set driver life, commonly 50,000 hours.
Where the LED Driver symbol is used
- Under-cabinet and cove LED strip systems, with a remote CV driver hidden in a cabinet, closet, or attic
- Recessed LED downlights, each with its own small CC driver in or beside the housing
- Landscape and deck lighting retrofits replacing magnetic halogen transformers with 12/24 V DC drivers
- Commercial troffers and linear fixtures using 0–10 V dimmable programmable drivers on 277 V circuits
- LED signage and channel letters, fed by weatherproof (IP65–IP67) CV drivers per UL 48 sign practice
- Smart-home lighting, where TRIAC/ELV-dimmable drivers sit behind wall dimmers or a smart PWM controller sits on the DC side
Example
In an under-cabinet lighting diagram, the wall switch's switched hot lands on the driver's AC L terminal and the circuit neutral on AC N; the driver is a 24 V, 96 W Class 2 unit. Its DC+ terminal feeds the positive rail of two strip runs (wired in parallel, star topology) and DC− returns from both strips' GND rails. The connected strip load totals 70 W — about 73% of driver capacity, inside the 80% sizing rule — and dimming is handled upstream by an ELV-compatible wall dimmer chopping the AC feed to this TRIAC-dimmable driver.
Key facts
- An LED driver converts mains AC to regulated DC; LEDs cannot run from AC directly because their current rises uncontrollably with small voltage increases.
- The two regulation modes are not interchangeable: constant-voltage (12/24 V) drivers feed strips and modules that self-limit current; constant-current (350/700/1050 mA) drivers feed bare LED strings and let voltage float.
- Class 2 drivers (NEC 725 / UL 1310: max 100 VA, 60 W at 12 V) allow the low-voltage DC side to be run with relaxed wiring methods — the backbone of US strip-light installs.
- Size a CV driver so the LED load is no more than about 80% of its rated wattage, for headroom and driver life.
- Dimming interfaces: TRIAC/ELV phase-cut (uses the existing wall-dimmer wiring), 0–10 V (two extra control wires), DALI (digital bus), and DC-side PWM controllers.
- UL 8750 is the North American driver safety standard; IEC 61347-2-13 is the international equivalent; 12/24 V outputs are SELV under IEC rules.
- Driver case temperature (tc point) is the dominant life factor — enclosed, unventilated locations shorten the typical 50,000-hour rating.
- A 'LED transformer' sold for retrofit is usually a driver; true magnetic transformers output AC and suit halogen, not most LED, loads.
Frequently asked questions
What is the difference between a constant-voltage and a constant-current LED driver?
A constant-voltage driver holds a fixed 12 V or 24 V output and the load determines the current — it powers LED strips and modules that contain their own resistors or regulators. A constant-current driver holds a fixed current (say 700 mA) and its voltage floats across a range to match the LED string — it powers bare LED arrays in downlights and COB fixtures. Feeding a bare LED string from a CV driver, or a strip from a CC driver, will overdrive and destroy the LEDs.
What does Class 2 mean on an LED driver?
Class 2 (NEC Article 725 / UL 1310) means the output is power-limited to levels considered safe from fire and shock — no more than 100 VA, and 60 W at 12 V. Wiring on a Class 2 output can use light-duty low-voltage methods instead of full chapter-3 wiring. It is unrelated to 'Class II' insulation (the double-insulation symbol), a common point of confusion on datasheets.
Can I dim an LED driver with a regular wall dimmer?
Only if the driver is explicitly TRIAC- or ELV-dimmable — these accept the phase-cut AC waveform a wall dimmer produces. A non-dimmable driver on a wall dimmer will flicker, buzz, or fail. The alternatives are 0–10 V or DALI drivers (which need extra control wires to a compatible dimmer) or leaving the driver at full output and dimming on the DC side with a PWM controller between driver and strip.
How do I size an LED driver for my strip?
Multiply the strip's watts-per-foot (or per meter) by the total length, then choose a driver rated at least 25% higher (equivalently, load the driver to no more than 80%). Example: 16 ft of 3 W/ft strip = 48 W, so use a 60 W driver. Match the voltage exactly (12 V strip on a 12 V driver) and, for US installs, prefer a UL-listed Class 2 unit.
What is the difference between an LED driver and a transformer?
A transformer is a magnetic AC-to-AC device — a 12 V halogen transformer outputs 12 V AC. An LED driver is an electronic AC-to-DC converter with active regulation. Many LED strips will not run (or will flicker at half-wave) on AC from an old halogen transformer, and magnetic transformers are not current-regulated, so LED retrofits of halogen systems normally replace the transformer with a proper DC driver.
Why did my LED driver fail early?
Heat is the usual killer. Driver lifetime ratings (typically 50,000 hours) are specified at a maximum case temperature (the tc point); burying a driver in an unventilated joist bay or enclosure pushes it past that temperature and dries out its electrolytic capacitors years early. Other common causes: loading it near 100% continuously, sustained overvoltage, or using a non-dimmable unit on a phase-cut dimmer.
Related symbols
- Buck Converter Module symbol
- Dimmer Switch symbol
- LED symbol
- Low Voltage Transformer symbol
- Power Supply 24V DC symbol
- Transformer symbol
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