The 4 categories and characteristics of LED driver

LED driver is a power converter that converts power into a specific voltage and current to drive LED light. In general: the input of LED drivers includes high-voltage industrial frequency AC (i.e. utility power), low-voltage DC, high-voltage DC, low-voltage, and high-voltage. frequency AC (such as the output of electronic transformers), etc.

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-According to the driving method.

(1) Constant-current LED driver

  • The output current of the constant current driving circuit is constant, but the output DC voltage will vary within a specific range with the size of the load resistance. The smaller the load resistance, the lower the output voltage. The higher the load resistance, the higher the output voltage.
  • A constant current circuit is not afraid of load short circuit, but it is strictly forbidden to disconnect the load entirely.
  • Very suitable for constant-current driver circuits for driving LEDs, but relatively expensive.
  • Attention to the maximum withstands current and voltage values, which limits the number of LEDs used.

(2) Regulated LED driver

  • When the various parameters in the regulator circuit are determined, the output voltage is fixed, but the output current changes as the load increases or decreases.
  • The regulated circuit is not afraid of the open circuit of the load, but it is strictly forbidden to short circuit the load entirely.
  • LEDs are driven by the voltage regulator driver circuit, and each string needs to add a suitable resistor so that each string of LEDs shows average brightness.
  • The brightness will be affected by the change of rectifier voltage.

-Classification of the LED drive.

(3) Pulsed LED Driver

Many LED applications require dimming functions, such as LED backlighting or architectural lighting dimming. The dimming function can be achieved by adjusting the brightness and contrast of the LEDs. LEDs can be adjusted by simply reducing the current of the device but allowing LEDs to operate at lower than rated current can have many undesirable consequences, such as chromatic aberrations. An alternative to simple current adjustment is to integrate a pulse width modulation (PWM) controller in the LED driver.

The PWM signal is not used to control the LED directly, but rather controls a switch, such as a MOSFET, that provides the desired current to the LED. PWM controllers typically operate at a fixed frequency and adjust the pulse width to match the desired duty cycle. Most LED chips today use PWM to control LED luminescence.

To ensure that one does not perceive significant flicker, the frequency of the PWM pulses must be greater than 100 HZ. The main advantage of PWM control is that the dimming current through PWM is more accurate and minimizes the color difference when the LED is illuminated.

(4) AC LED drive

Depending on the application, AC drives can also be divided into three types: step-down, step-up, and converter. The difference between AC drive and DC drive, in addition to the need for rectification and filtering of the input AC, there are also issues of isolation and non-isolation from a safety point of view.

AC input drivers are mainly used for retrofit lamps: for ten PAR (parabolic aluminum reflector, common lamps on professional stages) lamps, standard lamps, etc., they work at 100V, 120V, or 230V AC For MR16 lamps, it needs to work at 12V AC input.

The area covered by AC input drivers is more complex than that of DC input drivers due to complex issues such as the dimming capability of standard SCRs or leading and trailing edge dimmers, and performance issues with electronic transformer compatibility (i.e. flicker-free operation) from AC line voltage to generate 12V AC for MR16 lamp operation.

AC power supply (mains drive) applied to LED drive, generally through the steps of step-down, rectification, filtering, voltage regulation (or current regulation), AC power conversion to DC power, and then provide the right LED through the appropriate drive circuit operating current must have high conversion efficiency, small size, and low cost, while addressing the safety isolation issues.

Considering the impact on the grid, electromagnetic interference and power factor issues must also be addressed. For low to medium power LEDs, the best circuit structure is an isolated single-ended flyback converter circuit; for high-power applications, a bridge converter circuit should be used.

Power supply installation location classification.

Drive power supply can be divided into the external power supply and built-in power supply according to the installation location.

(1) External power supply
As the name suggests, an external power supply is installed the power supply outside. Generally higher voltage, there are safety risks to people, the need for external power supply. The difference with the built-in power supply is that the power supply has a shell, and street lights are common.

(2) Built-in power supply
The power supply is installed in the lamp. The general voltage is lower, from 12v to 24v, with no safety hazard to people. This commonly has an LED bulb.

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