High Performance Current Mode PWM Controller. Designed for high-cost AC / DC converter. Up to 12W continuous output power is provided in the wide voltage range of 85V-265V, and the peak output power can be more than 18W. Optimized high-syndrome circuit design combines high performance ratio bipolar production processes to minimize the overall cost of products. The power controller can operate in a typical flyback circuit topology that constitutes a concise AD / DC converter. The startup circuit inside the IC is designed to be a unique current inhalation method, which can be started using the amplification of the power switch tube itself, which significantly reduces the power consumption of the start resistance; and the IC will automatically reduce the operating frequency when the output power is small. Thereby achieving extremely low standby power consumption. When the power tube is closed, the internal circuit reverse the power tube reversely biased directly with the CB high pressure resistance characteristics of the bipolar transistor, which greatly improves the high pressure of the power tube until 700V, which guarantees the safety of the power tube. . The IC also provides comprehensive anti-over-vehicle prevention and prevention, but also prevents the overload, the transformer saturation, the output short circuit, etc., improves the reliability of the power supply. The current limit and clock frequencies can be set by external devices. It is available in DIP8 standard packaging and environmentally-friendly-free packages that meet European standards.
THX203H working principle
Start stage
When power-on, VR is closed; the FB pull-up current source is closed; OE inputs the current to the VCC; OB control the base current of the power tube, limits the power tube set electrode current (ie THX203H start receiving current), thereby ensuring power tube Safety; in the VCC voltage rose to 8.8V, the startup phase ends, and enters the normal phase.
Normal stage
The VCC voltage should be maintained at 4.8 ~ 9.0V, VR output 2.5V benchmark; FB pull-up current source is turned on; the oscillator output OSC1 determines the maximum duty cycle, the output OSC2 is trying to trigger the power supply to enter the opening cycle, and the shield power tube open current peak; If FB is less than 1.8V (about 1.2-1.8V) The oscillator cycle will increase, the smaller the smaller oscillator cycle is wider until the oscillator is stopped (this characteristic reduces the standby power consumption of the switching power supply);
If peripheral feedback tries to make VCC greater than 9.6V, the inner circuit feeds back to FB to make VCC regulated at 9.6V (using this characteristic without using peripheral feedback circuit, the output voltage is stabilized by the internal circuit, but the voltage regulator is low); The period, OB provides base current, OE pull-down power tube emission electrode to IS, and OB uses a ramp current driving (referring to the function of the OB current is IS, when IS = 0V is powered by about 40mA, then OB The electric current increases with the linearity of the IS. When IS is increased to 0.6V, the OB is powered on by about 120mA. This characteristic effectively utilizes the OB output current, reducing the power consumption of THX203H), if IS detects FB specified current, enter the correlation cycle ; Off period, OB pull-down, power tube does not turn off immediately, but the OE clamp 1.5V (the base reverse bias after power tube is turned off, increase the pressure required); in the open or off period, such as detected power The tube super-upper current, then the upper current current trigger is prioritized, forced FB to drop, the duty cycle is small, thereby protecting power tubes and transformers;
At the beginning of the next level, the starting edge or FB is less than 1.8V, and the upper current trigger is reset. Further, the THX203H has a heat protection, and the cycle of the width oscillator is adjusted in the inner temperature than 140 ° C, so that the THX203H temperature does not exceed 150 ° C; the built-in ramp compensation, the THX203H duty cycle or continuous current mode can stably open / off cycle.
Normal phase switching cycle waveform
If the VCC drops to 4.3V, the oscillator is turned off, OSC1, OSC2 low, power retention cycle;
The VCC continues to fall to around 3.7V, and THX203H re-enters the startup phase.
Global waveform
THX203H internal structure
Internal circuit block diagram
THX203H pin and function, technology area
Isolated power supply design needs to develop the best topology
Medium power, inefficient regulator heat dissipation, power module cannot be ignored!
Related knowledge about switching power supplies
Can the switch power EMC can't? PCB drawing board engineers have unbacked responsibilities!
USB OTG VBUS power block diagram and application plan
Our other product:
