Driving methods can be classified as follows:
1. Constant Current Type:
a. The output current of a constant current driving circuit is constant, while the output DC voltage varies within a certain range depending on the load resistance. A smaller load resistance results in a lower output voltage, and a larger load resistance results in a higher output voltage.
b. Constant current circuits are not afraid of short circuits, but a completely open circuit is strictly prohibited.
c. Constant current driving circuits are ideal for driving LEDs, but are relatively expensive.
d. Attention should be paid to the maximum current and voltage values used, as this limits the number of LEDs that can be used.
2. Voltage Regulated Type:
a. Once the parameters in the voltage regulated circuit are determined, the output voltage is fixed, while the output current varies with the load.
b. Voltage regulated circuits are not afraid of open circuits, but a completely short circuit is strictly prohibited.
c. When driving LEDs with a voltage regulated driving circuit, each string needs to have a suitable resistor to ensure that the brightness of each string of LEDs is average.
d. Brightness is affected by changes in the rectified voltage.
Circuit Structure Classification
(1) Resistor and Capacitor Voltage Reduction: Voltage reduction via capacitor. During flashing operation, the instantaneous current through the LED is extremely large due to the charging and discharging action, which can easily damage the chip. It is susceptible to fluctuations in the mains voltage, resulting in low power supply efficiency and low reliability.
(2) Resistor Voltage Reduction: Voltage reduction via resistor. It is greatly affected by changes in the mains voltage, making it difficult to make into a regulated power supply. The voltage reduction resistor consumes a large portion of the energy, so this power supply method has very low power efficiency and low system reliability.
(3) Conventional Transformer Voltage Reduction: The power supply is small in size and heavy, and the power efficiency is also very low, generally only 45% to 60%, so it is rarely used and has low reliability.
(4) Electronic Transformer Voltage Reduction: The power supply efficiency is low, the voltage range is not wide, generally 180 to 240V, and the ripple interference is large.
(5) RCC Voltage Reduction Switching Power Supply: The voltage regulation range is relatively wide, the power supply efficiency is relatively high, generally 70% to 80%, and it is widely used. Because the oscillation frequency of this control method is discontinuous, the switching frequency is not easy to control, the load voltage ripple coefficient is also relatively large, and the adaptability to abnormal loads is poor.
(6) PWM control method switching power supply: mainly composed of four parts, input rectification and filtering section, output rectification and filtering section, PWM voltage regulation control section, and switching energy conversion section. The basic working principle of PWM switching voltage regulation is that under the condition of changes in input voltage, internal parameters and external load, the control circuit uses the difference between the controlled signal and the reference signal to perform closed-loop feedback, adjust the pulse width of the main circuit switching device to make the output voltage or current of the switching power supply stable (i.e., the corresponding regulated power supply or constant current power supply). The power supply efficiency is extremely high, generally reaching 80% to 90%, and the output voltage and current are stable. Generally, this type of circuit has complete protection measures and is a high reliability power supply.
3. Classification by power supply installation position
The driving 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 a power supply installed outside. Generally, the voltage is relatively high and there is a safety hazard to people, so an external power supply is required. The difference between a built-in power supply and a lamp with an internal power supply is that the power supply has an outer casing. Common examples include streetlights.
(2) Built-in power supply: The power supply is installed inside the lamp. It usually has a low voltage, from 12V to 24V, which poses no safety hazard to people. Common examples include bulb lamps.
