To build an AC/DC converter solution using the high-performance PWM controller chip SE3910 - News - Global IC Trade Starts Here Free Products

At present, in the power scheme below 100W, pulse width modulation (PWM) control chip is generally used to realize PWM modulation, and the switch control mode has high working efficiency with respect to the DC working mode, and the system is improved by using the flyback offline working mode. The safety of work is very suitable for portable charging devices and power adapters, such as mobile phone chargers, power adapters, etc. Therefore, the demand for AC/DC PWM switching power supply chips is very large in the market. However, the traditional AC/DC power supply scheme uses the transformer secondary coil feedback mode (SSR). The secondary feedback mode of the transformer requires a constant voltage-constant current control chip on the low voltage side to assist in voltage conversion and constant current. The application scheme increases the complexity of the system application, and also increases the design cost of the system solution. The AC/DC power control chip to be introduced in this paper is the SE3910 of Siwang Electronics, which is a transformer primary coil feedback mode (PSR) PWM. Control chip. SE3910 technical features

The SE3910 is a green mode PWM controller chip for low-power AC/DC chargers, adapters and LED driver solutions. The chip is available in SOP-8 package. The PWM mode operates with a fixed switching frequency of 40KHz. The constant current control module uses the PSR mode, which omits the optocoupler, constant voltage/constant current control chip and its surrounding circuits in the traditional scheme, which greatly simplifies the application cost of the chip and reduces the complexity of the system application.

The EMI is specially designed for the chip design. The frequency jitter function is specially designed for the switching frequency module. Eight different switching frequencies appear in the designed sequence every 3.2ms period, and the electromagnetic interference spectrum is transferred to a relatively wide frequency. Bandwidth to achieve the goal of optimizing system EMI.

At the same time, the working state of SE3910 uses multi-mode adjustment function. When no load or light load, the chip will automatically enter the PFM working mode to ensure the precise input of the input energy and output energy of the power system, preventing excessive energy during light load or no load. When the load rises to the heavy-duty design value set by the chip, the chip will automatically enter the PWM working mode, which greatly optimizes the system's working efficiency, so that the system efficiency can reach 80% or more, and the no-load is also reduced. And output ripple at light load conditions.

The chip design has a soft start function, which greatly suppresses the large current when the system is powered on, protects the damage of the circuit board, and reduces the influence of the large current on the system power consumption when the system is started; the chip also has the power supply undervoltage protection. Function, LEB function, over temperature protection function, etc., to maximize the reliability and safety of the chip operation; the chip is suitable for power supply solutions below 5W and 5W.

Typical application

SE3910 can be widely used in various low-power AC/DC switching power supply solutions, such as mobile phone chargers, power adapters, etc. In addition, because the chip integrates constant current function, it can also be widely used in low-power LED driving solutions. .

Figure 1 shows the basic application circuit of SE3910, in which the negative feedback path is composed of transformer/output stage/R3/R4/SE3910, etc., the switching energy of the transformer is adjusted by adjusting the duty cycle of the switching signal at GATE, so that the system is stable in the setting work. status. The AC voltage is first converted into a high voltage DC signal through a bridge rectifier circuit, R1 and C2 form the system startup circuit, VIN is the startup PIN of SE3910, and R5, C6 and C7 on COMV PIN form the system compensation circuit to ensure the system is stable. Frequency response, FB is the output voltage detection PIN. By setting R3/R4, the voltage on the secondary side of the transformer can be adjusted. According to the principle that the transformer voltage ratio is proportional to the turns ratio, the DC output voltage can be adjusted. GATE is PWM output PIN, which is used to control the power tube 13003 to control the peak current of the primary side of the transformer to control the conversion energy of the transformer. CS PIN is used to detect the peak current of the transformer. When the system works in constant current mode, CS PIN The voltage on the voltage will be fixed at the set maximum value, which will determine the maximum peak current of the primary side of the transformer, so that the output will also be constant current. The output constant current value can be flexibly adjusted by adjusting the R6 resistor.

Figure 2 shows an example of the current popular SE3910 application solution, one for the charger solution and the other for the LED driver solution. The key point in system design is the output constant voltage and constant current value design.

The design of the output constant voltage value:

The constant voltage implementation principle of the system is to stabilize the sampled value of the output voltage signal negatively fed back by the transformer on the chip FB PIN by the operational amplifier in the SE3910 to a constant value of the ref set by the chip, and ref is a bandgap reference source inside the chip. The constant voltage output by the module is 1.5V, which achieves the purpose of stabilizing the output voltage.