(1) Constant current type: a. The output current of the constant current drive circuit is constant, but the output DC voltage changes within a certain range with the size of the load resistance. The load resistance is small, and the output voltage is low. The larger the load resistance value, the higher the output voltage; b. The constant current circuit is not afraid of short circuit of the load, but it is strictly forbidden to open the load completely. C. The constant current drive circuit is ideal for driving LEDs, but the price is relatively high. d. Pay attention to the maximum current and voltage used, which limits the number of LEDs used; (2) Voltage stabilization: 稳压 a. After the parameters of the voltage stabilization circuit are determined, the output voltage is fixed, and The output current changes with the increase and decrease of the load; b. The voltage stabilization circuit is not afraid of the open circuit of the load, but it is strictly forbidden to completely short the load. C. The LEDs are driven by a voltage-stabilized driving circuit. Each string needs to be added with a suitable resistor to make each string of LEDs display the average brightness. D. The brightness will be affected by the rectified voltage change.
Classification of circuit structure
(1) Step-down method of resistance and capacitance: When the capacitor is stepped down, when flashing, the instantaneous current through the LED is extremely large due to the charge and discharge effect, which easily damages the chip. Susceptible to the influence of power grid voltage fluctuations, the power supply has low efficiency and low reliability. (2) Resistance step-down method: The resistance step-down method is greatly affected by the change of the grid voltage, and it is not easy to make a regulated power supply. The step-down resistor consumes a large part of the energy, so this power supply method has low power efficiency , And the system is also less reliable. 3 (3) Conventional transformer step-down method: The power supply is small in size, heavy in weight, and the power efficiency is very low, generally only 45% to 60%, so it is rarely used and the reliability is not high. (4) Step-down method of electronic transformer: The power supply efficiency is low, and the voltage range is not wide, generally 180 ~ 240V, and the ripple interference is large. 5 (5) RCC step-down switching power supply: The voltage regulation range is relatively wide, and the power supply efficiency is relatively high. Generally, it can achieve 70% to 80%, and it is also 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 relatively large, and the abnormal load has poor adaptability. (6) PWM control mode switching power supply: It is mainly composed of four parts, the input rectification filtering part, the output rectification filtering part, the PWM voltage stabilization control part, and the switching energy conversion part. The basic working principle of PWM switching regulator is that under the condition of input voltage, internal parameters and external load changes, the control circuit performs closed-loop feedback through the difference between the controlled signal and the reference signal, and adjusts the pulse width of the main circuit switching device. Make the output voltage or current of the switching power supply stable (that is, the corresponding regulated power supply or constant current power supply). The efficiency of the power supply is extremely high, generally 80% to 90%, and the output voltage and current are stable. Generally, this kind of circuit has perfect protection measures and belongs to high reliability power supply. 3. Classification according to the installation position of the power supply: The drive power supply can be divided into external power supply and built-in 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 if it is dangerous to people, an external power supply is required. The difference from the built-in power supply is that the power supply has a shell, and there are common street lights. (2) Built-in power supply is to install the power supply in the lamp, generally the voltage is relatively low, 12v to 24v, there is no hidden danger to people. This common one is a bulb lamp.