What is an LED driving power supply, what are its different types, and what standards are classified according to? Are there shortcomings in the overall constant current and road-by-channel constant current working methods? Guangdong Zhenglian Power Co., Ltd. will take you to understand them one by one!

 

According to the requirements of different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.

 

LED drive power is a power converter that converts the power supply into a specific voltage and current to drive LED light. Generally, the input of LED drive power includes high-voltage power frequency AC (that is, mains), low-voltage DC, high-voltage DC, low-voltage Frequency AC (such as the output of an electronic transformer).

 

The output of the LED driving power is mostly a constant current source that can change the voltage as the forward voltage drop of the LED changes.

 

 

 

    There are two types of LED driving power supply control, one is Voltage Mode Contml, and the other is Constant Current Control. Both have their own advantages and disadvantages, it is difficult to say which type of control is best for all applications, and should be selected according to the actual situation.

 

Voltage Controlled LED Driver

 

    Voltage control is the most commonly used type of control. Take the step-down switching regulator (ie Buck converter) as an example, the basic principle and working waveform of the voltage control type. The characteristic of the voltage control type is that by first sampling the output voltage (if necessary, a sampling resistor divider can be added), the obtained sampling voltage UQ is used as the input signal of the control loop; then the sampling voltage Un and the reference voltage UI <. , To compare and amplify the comparison result to the error voltage U, and then U. Send to PWM comparator and sawtooth voltage U. The comparison is performed to obtain a modulation signal whose pulse width is proportional to the error voltage. B. The oscillator in the picture has two outputs, one is a clock signal (square wave or rectangular wave), and the other is a sawtooth wave signal. This is the timing capacitor for the sawtooth oscillator. T is a high-frequency transformer, and VT is a power switch. The step-down output circuit consists of rectifier VD, freewheeling diode VI). 、 Energy storage inductor I. And filter capacitor G. In the pM latch, R is the reset terminal, S is the set terminal, and Q is the latch output terminal.

 

Voltage-controlled LED drive power has the following advantages:

 

    (1) It belongs to a closed-loop control system and has only one voltage feedback loop (that is, a voltage control loop), and the circuit design is relatively simple.

 

    (2) It works stably during the modulation process.

 

    (3) The output impedance is low, and multiple power sources can be used to power the same load.

 

    The main disadvantages of the voltage control type are as follows:

 

    (1) The response speed is slow. Although the current detection resistor Rs is used in the voltage control type circuit, R is not connected to the control loop. Therefore, when the input voltage changes, the pulse width must be adjusted after the output voltage changes. Due to the lag time of the filter circuit, the change in output voltage can only manifest itself after several cycles. Therefore, the response time of the voltage control type is longer, and the stability of the output voltage is also affected to some extent.

 

    (2) An overcurrent protection circuit needs to be designed separately.

 

    (3) The phase compensation of the control loop is more complicated, and the closed-loop gain changes with the input voltage.

 

Classification by driving method

 

(1) Constant current

 

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 smaller the load resistance, the lower the output voltage, and the larger the load resistance, the higher the output voltage. The higher;

 

The constant current circuit is not afraid of short circuit of the load, but it is strictly forbidden that the load is completely open;

 

Constant current driving circuit is ideal for driving LED, but the price is relatively high;

 

It should be noted that the maximum withstand current and voltage values ​​are used, which limits the number of LEDs used.

 

(2) Regulated

 

When the parameters in the voltage stabilization circuit are determined, the output voltage is fixed, but the output current changes as the load increases or decreases;

 

The voltage stabilization circuit is not afraid of the open circuit of the load, but it is strictly forbidden that the load is completely short-circuited;

 

Drive the LEDs with a voltage-stabilized driving circuit, and each string needs to be added with a suitable resistor to make each string of LEDs display the average brightness;

 

Brightness is affected by rectified voltage changes.