By drive mode
(1) Constant current type
a. The output current of a constant current drive circuit is constant, while the output DC voltage varies within a certain range with the size of the load resistance. When the load resistance is small, the output voltage is low, and the larger the load resistance, the higher the output voltage;
b. A constant current circuit is not afraid of load short circuits, but it is strictly prohibited to completely open the load.
c. The constant current drive circuit is ideal for driving LEDs, but relatively expensive.
d. Attention should be paid to the maximum withstand current and voltage values used, which limit the number of LEDs used;
(2) Stable voltage:
a. After the various parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, while the output current changes with the increase or decrease of the load;
b. The voltage stabilizing circuit is not afraid of open circuit of the load, but it is strictly prohibited to have a complete short circuit of the load.
c. Drive the LED with a voltage stabilizing driving circuit, and add appropriate resistors to each string in order to make the brightness of each LED display average;
d. The brightness will be affected by the voltage changes caused by rectification.
(3) Pulse drive
Many LED applications require dimming functions, such as LED backlighting or building lighting dimming. Dimming function can be achieved by adjusting the brightness and contrast of LED. Simply reducing the current of the device may be able to adjust the LED emission, but allowing the LED to operate below the rated current can cause many adverse consequences, such as color difference issues. The method to replace simple current adjustment is to integrate a pulse width modulation (PWM) controller into the LED driver. The PWM signal is not directly used to control the LED, but to control a switch, such as a MOSFET, to provide the required current to the LED. PWM controllers typically operate at a fixed frequency and adjust the pulse width to match the required duty cycle. Currently, most LED chips use PWM to control LED illumination. To ensure that people do not feel obvious flickering, the frequency of PWM pulses must be greater than 100Hz. The main advantage of PWM control is that the dimming current of PWM is more precise, minimizing the color difference when LED emits light. [1]
(4) AC drive
AC drives can also be divided into three types based on different applications: step-down, step-up, and converter. The difference between AC drives and DC drives lies not only in the need for rectification and filtering of the input AC power, but also in the issue of isolation and non isolation from a safety perspective.
The AC input driver is mainly used for modified lamps: for ten PAR (Parabolic Aluminum Reflector, a common lamp on professional stages) lamps, standard light bulbs, etc., they operate under 100V, 120V, or 230V AC input; For the MR16 lamp, it needs to operate under a 12V AC input. Due to some complex issues, such as the dimming ability of standard three terminal bidirectional thyristor switches or leading edge and trailing edge dimmers, as well as compatibility issues with electronic transformers (i.e. no flicker operation) that generate 12V AC power from the AC line voltage when MR16 lamps operate), the field involved in AC input drivers is more complex compared to DC input drivers. [1]
AC power supply (mains drive) is applied to LED drive, which generally needs to go through steps such as voltage reduction, rectification, filtering, voltage stabilization (or current stabilization) to convert AC power into DC power. Then, suitable driving circuits are used to provide suitable working current for LED, with high conversion efficiency, small size, and low cost, while solving safety isolation problems. Considering the impact on the power grid, it is also necessary to address electromagnetic interference and power factor issues. For small and medium power LEDs, the optimal circuit structure is an isolated single ended flyback converter circuit; For high-power applications, a bridge converter circuit should be used. [1]
According to circuit structure
(1) Resistance and capacitor voltage reduction method: By reducing voltage through the capacitor, during flashing use, due to the effect of charging and discharging, the instantaneous current passing through the LED is extremely high, which is easy to damage the chip. Easy to be affected by voltage fluctuations in the power grid, resulting in low power efficiency and reliability.
(2) Resistance voltage reduction method: By reducing voltage through resistance, it is greatly affected by changes in grid voltage, making it difficult to make a stable power supply. The voltage reduction resistor consumes a large amount of energy, so this power supply method has low power efficiency and low system reliability.
(3) Conventional transformer voltage reduction methods: The power supply is small in size, heavy in weight, and has low power efficiency, usually only 45% to 60%, so it is rarely used and has low reliability.
(4) Electronic transformer voltage reduction method: The power efficiency is low, and the voltage range is not wide, usually 180-240V, with large ripple interference.
(5) RCC voltage reduction switch mode power supply: The voltage stabilization range is relatively wide, the power efficiency is relatively high, and it can generally reach 70% to 80%, and it is also widely used. Due to the discontinuous oscillation frequency of this control method, the switching frequency is difficult to control, and the load voltage ripple coefficient is also relatively large, resulting in poor adaptability to abnormal loads.
(6) PWM control mode switching power supply: mainly composed of four parts: input rectification and filtering part, output rectification and filtering part, PWM voltage stabilization control part, and switching energy conversion part. The basic working principle of PWM switching voltage regulator is to provide closed-loop feedback through the difference between the controlled signal and the reference signal in the control circuit, in the event of changes in input voltage, internal parameters, and external loads. This adjusts the pulse width of the main circuit switching device to stabilize the output voltage or current of the switching power supply (i.e., the corresponding voltage regulator or constant current power supply). The power efficiency is extremely high, usually reaching 80% to 90%, and the output voltage and current are stable. Generally, this type of circuit has complete protection measures and belongs to a high reliability power supply.
Classification of power installation positions
The driver power supply can be divided into external power supply and internal power supply according to the installation position.
(1) External power supply
As the name suggests, an external power supply is one that installs the power supply outside. Generally, if the voltage is relatively high and poses a safety hazard to people, an external power supply is required. The difference from the built-in power supply is that the power supply is equipped with a casing, commonly known as a street light.
(2) Built in power supply
It means installing the power supply inside the lamp, usually with a relatively low voltage ranging from 12V to 24V, which poses no safety hazards to people. This common one is a bubble lamp.