The THX203H is a switching power supply controller IC that delivers up to 12W of continuous output power over a wide voltage range of 85V-265V with a peak output power of 18W.
Thx203h pin diagram
Thx203h internal circuit diagram
Note: PCB layout should keep a safe distance of more than 1mm between Pin6 and Pin7 to avoid discharge.
Thx203h pin voltage1. Start-up phase: CR is turned off at power-on; FB pull-up current source is turned off; OE is driven by power tube to start current to VCC; OB controls the base current of power tube, limiting power tube electrode current (ie, THX203H starts receiving current), Thereby ensuring the safety of the power tube; when the VCC voltage rises to 8.8V, the startup phase ends and enters the normal phase.
2, the normal phase: VCC voltage should be maintained at 4.8-9.0V, VR output 2.5V reference; FB pull-up current source is turned on; oscillator output OSC1 determines the maximum duty cycle, output OSC2 attempts to trigger power into the open cycle, and shield power The transistor turns on the current peak; if the FB is less than 1.8V (about 1.2-1.8V), the oscillator period will increase. The smaller the FB, the wider the oscillator period until the oscillator stops. This feature reduces the initial power supply. Standby power consumption); if the peripheral feedback tries to make VCC greater than 9.6V, the internal circuit feeds back to FB to stabilize VCC at 9.6V. (This feature can be used without external feedback circuit, and the output voltage is stabilized by the internal circuit, but the voltage regulation accuracy Lower); open period, OB provides base current for power tube, OE pulls down the emitter of the power tube to IS, and OB is driven by ramp current (refer to OB open current is a function of IS, OB open current when IS=0V About 40 mA.
Normal phase switching cycle waveform
Then the OB open current increases linearly with IS. When the IS increases to 0.6V, the OB open current is about 120mA. This characteristic effectively selects the output current of OB, which reduces the power consumption of THX203H. If IS detects the FB specified current, it enters. Off cycle; off cycle, OB pulldown, power tube will not be judged immediately, but OE clamp 1.5V (the power tube judges the base reverse bias, which improves the withstand voltage); in the on or off cycle, if the power is detected When the tube exceeds the upper limit current, the upper limit current trigger is preferentially set, forcing the FB to decrease, and the duty ratio becomes smaller, thereby protecting the power tube and the transformer; at the beginning of the next off period or the FB is less than 1.8V, the upper limit current trigger is reset. In addition, THX203H has built-in thermal protection, widening the period of the oscillator after the internal temperature is higher than 140 °C, so that the temperature of THX203H does not exceed 150 °C; built-in slope compensation, stable on/off in THX203H large duty cycle or continuous current mode cycle.
3. Conversion phase: If VCC drops to about 4.3V, the oscillator is turned off, OSC1 and OSC2 are low, and the power supply remains off; VCC continues to drop to about 3.7V, and THX203H re-enters the startup phase.
Global waveform
Thx203h related article: thx203h switch circuit diagram Daquan (five thx203h switch circuit)
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