THX202H adopts patented technology to prevent overload and saturation, and can meet higher environmental protection standards. Suitable for low-power switching power supply devices such as mobile phone chargers. Features? Patented technology design for overload prevention and saturation prevention can prevent overload, switching transformer saturation, output short circuit and other faults in time;
The built-in power triode is used as the switch tube; At the same time, the power consumption of the starting resistor is reduced by more than 10 times by using its amplification function;
Built-in slope compensation circuit, thermal protection circuit and slope current drive circuit;
Wide voltage output 5.5W, 220Vac output 8W; No output power consumption can be lower than 0.25W W w.
Second, the block diagram:
Third, the pin description pin symbol pin description:
OB？ The base of that pow tube and the starting current control end.
CT？ Oscillator c input
GND ground terminal
Feedback input
VCC positive power supply terminal
OE？ Emitter and starting current input of power tube.
OC？ Power tube collector
On-chip test pin VR 2.5V reference on-chip test pin of OC power tube collector is power tube current.
Fourth, the principle description:
? After electrifying, it is the start-up stage. At this stage, VR has no output, transistor Q2 is turned off, and FB pull-up current source is turned off. The peripheral circuit inputs a small current (about 0.05~0.2mA) from OB to the base of the high-voltage power transistor Q 1, and inputs a starting current from the collector OC and emitter OE of Q 1 to VCC. ; The circuit in OB controls the base current of Q 1 and limits the collector OC current of Q 1 (i.e. THX202H start-up acceptance current, about 2mA), thus ensuring the safety of Q 1. When the VCC voltage rises to 8.8V, the start-up phase ends and enters the normal phase. ? In normal stage, VCC voltage should be kept at 4.75~9.8V, and VR output should be 2.5V reference; FB pull-up current source is turned on; The output OSC 1 of the oscillator determines the maximum duty cycle, and the output OSC2 tries to trigger the power supply to enter the conduction period and shield the peak value of the conduction current of the power tube. If FB is less than 1.8V (about 1.2- 1.8V), the smaller FB is, the wider the oscillator period will be until the oscillator stops oscillating (this characteristic reduces the standby power consumption of the switching power supply); If the peripheral feedback tries to make VCC greater than 9.8V, the internal circuit feeds back to FB to stabilize VCC at 9.8V (using this feature, the output voltage can be stabilized by the internal circuit without using the peripheral feedback circuit, but the voltage stabilization accuracy is low); During the open circuit, the base of Q 1 conducts current, and Q2 pulls the emitter of Q 1 down to IS, which IS driven by the ramp current (thIS means that the base conducting current of Q 1 is a function of IS, when IS=0V, the conducting current is about 24mA, and when IS increases to 0.6V, the conducting current is about 40mA, which is effectively utilized. During turn-off, the base of Q 1 is pulled low, and Q 1 will not be turned off immediately, but OE clamps 1.5V (after turn-off, the base of Q 1 is reversely biased, which improves the withstand voltage of Q 1); During the turn-on or turn-off period, if Q 1 exceeds the upper limit current, the upper limit current trigger will be set first, forcing FB to drop and reducing the duty cycle, thus protecting Q 1 and the transformer; When the starting edge of the next turn-off period or FB is less than 1.8V, the upper limit current triggers the reset. In addition, THX202H has built-in thermal protection. When the internal temperature is higher than 125℃, the period of the oscillator will be widened, so that the temperature of THX202H will not exceed 135℃. The built-in slope compensation can stabilize the on/off period of THX202H in large duty cycle or continuous current mode. ? If VCC drops to about 4.4V, the oscillator will turn off, OSC 1 and OSC2 will be low, and the power supply will remain off. VCC continues to drop to about 3.8V, and THX202H re-enters the startup phase.