LED Driver
Power Supply
LEDs need controlled current, not just voltage — the driver converts mains to a regulated constant current (or constant voltage for strips), sets the brightness, and largely decides how long the light lives.
Schematic symbol
LED
How led driver appears in a circuit diagram.
Types & variants
Key specs
Output current
mAThe defining spec of a CC driver: 300/350/700/900/1050 mA classes. Must match the LED string's rated current.
Output voltage window
VCC drivers list a compliance range, e.g. 24–42 V — your LED string's total forward voltage must fall inside it.
Output power
WCurrent × voltage window top. CV drivers are rated in W at 12 or 24 V.
Power factor
—Quality drivers >0.9; regulations require it above certain wattages.
Ripple
%High output ripple = 100 Hz flicker — headaches and camera banding. Good drivers keep it low.
Protections
—Open-circuit, short-circuit, over-temperature and surge protection separate good drivers from bulb-killers.
Markings
Label lists input range, output current, voltage window and wattage, e.g. 'OUT: 36–48 V, 300 mA'. Strip PSUs read like normal SMPS: '12 V 5 A 60 W'.
Standard values
CC: 300 mA (up to ~15 W panels), 700 mA (COB spots), 1050/1400 mA (high bays). CV: 12 V and 24 V at 1–20 A for strips. Module form: MT7912/PT4115-style buck drivers for makers.
How to choose
1) CC for LED strings/COBs — match current exactly, check voltage window covers the string. 2) CV only for strips with built-in resistors. 3) Isolated for anything touchable. 4) Dimming type must match the wall control (TRIAC vs 0–10 V vs PWM are not interchangeable). 5) Derate 20% and ensure ventilation — heat is the killer.
Pinout & package
Input L/N, output +/− leads. Packages: caseless PCB (inside bulbs), plastic potted brick (panel lights), metal-case rail PSU (strips), and PCB modules with PWM/analog dim pins for makers.
Example circuits
- 18 W panel light: 300 mA CC driver feeding a 40-LED series string
- 5 m 12 V strip on a 60 W CV supply with PWM MOSFET dimmer
- PT4115 buck module driving a 3 W star LED from 12 V with PWM dimming
- 0–10 V dimmable office troffer on a DALI network
Common failures
Dried electrolytic capacitors (flicker, then no start), blown input bridge/fusible resistor after a surge, overheating in sealed ceilings, and mismatched replacements (over-current cooking the LEDs, or string voltage outside the window causing flashing).
How to test
Measure output: a CC driver with no load rises to its open-circuit voltage; on load it should hold its rated mA (verify with a meter in series). Flickering fixtures: swap in a known-good driver first — it's the culprit far more often than the LED board.
Substitutes
Replace with the same output current and a voltage window covering the string; wattage equal or higher. For strips, any quality 12/24 V SMPS of sufficient amps works. Dimmable must be replaced by the same dimming standard.