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Delve deeply and work diligently to achieve new heights
All colleagues unite and focus their efforts to write a new chapter of developmentOn the Classification of LED Driver Power Supplies
所属分类： Industry News
发布时间：2020-05-27
About LED driver power supply What are the classification criteria? How should LED driver power supplies be distinguished?
By drive type
(1) Constant-current type
a. In a constant-current driver circuit, the output current remains constant, while the output DC voltage varies within a certain range depending on the load resistance: a lower load resistance results in a lower output voltage, whereas a higher load resistance leads to a higher output voltage.
b. Constant-current circuits are tolerant of load short circuits, but must never be left with a completely open circuit.
c. Constant-current driver circuits are the most ideal for driving LEDs, but they are relatively more expensive.
d. Attention should be paid to the maximum current and voltage ratings of the components, as these limit the number of LEDs that can be used.
(2) Voltage-regulated type:
a. Once the parameters of the voltage regulator circuit are set, the output voltage remains constant, while the output current varies with changes in the load.
b. The voltage regulator circuit can tolerate an open‑circuit load, but a complete short circuit of the load is strictly prohibited.
c. Use a constant‑voltage driver circuit to power the LEDs; each string must be equipped with an appropriate series resistor to ensure uniform brightness across all LED strings.
d. Brightness is affected by fluctuations in the rectified voltage.
(3) Pulse Drive
Many LED applications require dimming functionality, such as LED backlighting or architectural lighting. Dimming can be achieved by adjusting the LED’s brightness and contrast. Simply reducing the device’s current may suffice to modulate light output, but operating LEDs below their rated current can lead to undesirable side effects, including color shift. An alternative to straightforward current adjustment is to integrate a pulse-width modulation (PWM) controller into the LED driver. The PWM signal does not directly drive the LED; instead, it controls a switching element—such as a MOSFET—to deliver the required current. PWM controllers typically operate at a fixed frequency while varying the pulse width to achieve the desired duty cycle. Today, most LED chips employ PWM to regulate light output; to prevent perceptible flicker, the PWM pulse frequency must exceed 100 Hz. The primary advantage of PWM control is its ability to modulate current more precisely, thereby minimizing color variation during operation.
(4) AC Drive
AC drives can also be classified into three types—buck, boost, and inverter—depending on the application. In addition to rectifying and filtering the incoming AC supply, AC drives differ from DC drives in that, from a safety standpoint, they must address the issue of isolation versus non-isolation.
AC‑input drivers are primarily used for retrofit lamps: for PAR (Parabolic Aluminum Reflector) fixtures—common on professional stages—and standard incandescent bulbs, they operate from 100 V, 120 V, or 230 V AC; meanwhile, MR16 lamps require a 12 V AC input. Due to certain complexities—such as the dimming capabilities of standard triac dimmers or leading‑edge/ trailing‑edge dimmers, and compatibility issues with electronic transformers that convert mains AC to the 12 V AC needed by MR16 lamps for flicker‑free operation—AC‑input drivers involve a more intricate design landscape than their DC‑input counterparts.
AC‑powered (mains‑driven) LED drivers typically undergo steps such as voltage reduction, rectification, filtering, and regulation (or current‑limiting) to convert the AC input into a DC supply. The resulting DC is then delivered to the LED via an appropriate driver circuit that provides the required operating current. Such systems must also feature high conversion efficiency, compact size, and low cost, while ensuring safe isolation. Furthermore, to minimize impact on the power grid, they must address electromagnetic interference and power‑factor issues. For medium‑ and low‑power LEDs, the optimal topology is an isolated single‑ended flyback converter; for high‑power applications, a bridge‑type converter is recommended.
According to the circuit structure
(1) Resistor–capacitor voltage‑dropping method: When used for flashing applications, the charging and discharging cycles cause a very high instantaneous current through the LED, which can easily damage the chip. This approach is also susceptible to fluctuations in mains voltage, resulting in low power efficiency and poor reliability.
(2) Resistive voltage‑dropping method: This approach is highly susceptible to fluctuations in the mains voltage, making it difficult to implement as a regulated power supply. Moreover, the series resistor dissipates a significant portion of the input power, resulting in low efficiency and reduced system reliability.
(3) Conventional transformer-based voltage reduction: This method features a compact power supply, but it is relatively heavy and has very low efficiency—typically only 45% to 60%—so it is seldom used and offers limited reliability.
(4) Voltage‑reduction method using an electronic transformer: This approach has relatively low power efficiency and a limited input voltage range—typically 180–240 V—and exhibits significant ripple interference.
(5) RCC buck‑type switching power supply: It offers a relatively wide regulation range and high efficiency, typically reaching 70%–80%, and is widely used. However, because this control scheme employs discontinuous oscillation, the switching frequency is difficult to regulate, the output voltage ripple is relatively large, and its ability to handle transient loads is poor.
(6) PWM‑controlled switching power supplies consist primarily of four sections: the input rectification and filtering stage, the output rectification and filtering stage, the PWM voltage‑regulation control stage, and the switching‑energy‑conversion stage. The fundamental operating principle of PWM switching regulation is that, under varying input voltages, internal parameters, and external loads, the control circuit maintains a closed‑loop feedback by comparing the error signal with the reference signal, thereby adjusting the pulse width of the main‑circuit switching devices to keep the output voltage or current stable—yielding either a regulated voltage supply or a constant‑current source. These supplies boast very high efficiency, typically reaching 80%–90%, while delivering stable output voltage and current. Such circuits usually incorporate comprehensive protection features, making them highly reliable power supplies.
Classification of Power Supply Installation Locations
Drive power supplies can be classified, according to their installation location, into external and internal types.
(1) External Power Supply
As the name suggests, an external power supply is one that is mounted outside the device. Typically, when the voltage is relatively high and poses a safety risk to humans, an external power supply is required. The key difference from an internal power supply is that the external unit is enclosed in a housing; streetlights are a common example.
(2) Built-in power supply
It involves installing the power supply inside the luminaire; typically, the voltage is relatively low—between 12 V and 24 V—posing no significant safety risk to people. A common example is the incandescent bulb.