Microelectronics THX203H is produced through a high performance current mode PWM controller, it is designed for cost-effective AD / I) C converter is designed to provide continuous output power of 12W in a wide voltage range of AC85V ~ 265V peak output power of up to 18W. Suppliers can win because the circuit design with an optimized, it is widely used in DVD, digital satellite receiver and power adapter switching power supply, such as a natural TD 759 uses a digital satellite receiver is present as the primary conversion circuit chip.
Switching power supply maintenance experience
A power switch does not start oscillation, we usually need to see the switching frequency is correct, whether the blocking protection circuit, voltage feedback circuit, the current feedback circuit was not any problem, whether the switch and breakdown.
Switching power supply transformer or heat issue "dth buzz", the switching frequency typically does.
Output voltage of the switching power supply indicator flashing is generally of secondary short circuit.
switching power supply works thx203h
DIP8 THX203H in most of the package, the pin functions shown in Figure 1, a typical application circuit shown in Figure 2. (Note: This figure is applied to the nine receivers, DVB receivers in general, the output voltage slightly difference). After power, + 300V voltage to the internal circuit to THX203H ② feet EC3 external capacitor charges the capacitor, when the voltage across EC3 reaches 88V, the internal oscillation circuit start Ic, switching power supply enters the normal working state. At this time, the switch becomes an induced electromotive force is T③ ④ winding, after D6, EC3 rectified and filtered to power THX2 {13H. T for normal, THX203H ~) pin must be between 4.8V-9.0V in.
figure 1
figure 2
THX203H 5 pin is the feedback voltage input, and the normal voltage is approximately 1.2V to 1.8V. When the output voltage increases, the precision three-terminal regulator IC3 (TL431) is electrically R rises, the voltage drop K, light emitting diode in the optocoupler IC2 enhancement between its ③, ④ the feet contact the photosensitive the transistor is turned on a deeper level, C, e electrode resistance is decreased, the voltage drop THX203H⑤ pin, the internal oscillator output pulse Ic is narrowed, i.e., the duty ratio becomes smaller, so that the transmission rate of the pipe and H {electrical transformer. If the output voltage decreases, which is opposite to the above regulation process.
Further, THX203H built-in thermal protection circuit. After the internal temperature is higher than 14O ℃ width modulation cycle of the oscillator THX203H that the temperature did not exceed 150 deg.] C; stable / off cycle of the built-in slope compensation circuit, the duty cycle or THX203H in large continuous current mode. If VCC drops of 4.3 V, the oscillator is shut off power holding period; continue if VCC drops to 3.7v, THX203H new Ying into the startup phase.
Troubleshooting examples
Example 1: FIG boot no silent, without any indication panel.
Analysis of maintenance: Open the cover, check the fuse F1 is not blown, measured at both ends with a 300V DC voltage EC2, 300V rectifier filter circuit 1 described two properly.
Then measuring the switching power supply output voltage, 20V, 15V, 3.3V power supply voltage output group were weak, to be described as the core THX203H main conversion circuit is normal, a failure occurs in the sampling voltage feedback network, check the voltage sampled focus 3.3V power supply voltage and a sample group of IC2, IC3 main elements of a feedback circuit. Each element sample was checked no abnormal voltage feedback circuit, the power pack 3.3V check rectifying diode D7 source shorted rectifier diode D7 shorted group, after renewed troubleshooting.
Example 2: same as in Example 1:
Analysis of maintenance: check fuse F1 is not blown, as measured across the capacitor after the bridge rectifier EC2 filter circuit has a normal voltage of 300V DC, the switching power supply output terminal of each group were weak voltage supply, the main inverter circuit described can be started normally. When the main inverter circuit enters the normal operation phase of the induced voltage generated by the feedback winding of the rectifier D6, EC3 filtered after injection IC1 (THX203H) ② feet, so that the main inverter circuit is small for the duration. According to this principle, the focus of the switching power supply feedback winding examination, rectifying diode D6 and the smoothing capacitor EC3, found EC3 has expired, the renewal troubleshooting.
Example 3: same as in Example 1.
Analysis of maintenance: measured at both ends with a 300V DC voltage EC2, described 300V rectifier, filter circuit is working properly.
Analysis of the working process of the switching power supply: DC voltage of 300V, all the way through the primary winding of switching transformer added THX203H⑦, ⑧ pin (internal power collector of the switching tube), another pass is added to the starting resistor R2 THX203H① foot. Technology area
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