CI SMD PWM FONTE TV TCL 283N20 PINO 1 E PINO 6 VAI PARA O FOTOACOPLADOR PINO 2 VAI PARA O MOSFET 70R380 PINO 3 VAI PARA CATOD DIODO 1N4148 QUE CI É ESSE

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Direct answer to the question – The SMD marked “283N20” on the primary side of TCL power‑supply boards is a house‑code used by the set‑maker for a current‑mode PWM controller of the UC384x family UC3842345 or an Asian second‑source equivalent. – Pin functions in the set match the standard UC384x pin‑out once the pin numbering on the board is taken into account: • COMP and FB pins 1 & 2 of the IC go to the optocoupler feedback network; • OUT pin 6 drives the gate of the external MOSFET 70R380; • VCC pin 7 is fed through the auxiliary diode 1N4148; • ISENSE pin 3 is returned to the current‑sense resistor in series with the MOSFET source. Detailed problem analysis 1. Why the UC384x fits the observed wiring • In every UC384x, two adjacent pins 1‑COMP, 2‑FB are devoted to the error‑amplifier loop and therefore meet the optocoupler. • Pin 6 is the only high‑current totem‑pole output capable of driving an external MOSFET; this matches the track you found from the IC to the gate of the 70R380. • VCC pin 7 normally receives the rectifiedfiltered auxiliary winding through a fast diode such as 1N4148; the diode you mention is therefore on the expected pin. • The device is manufactured by several suppliers ONSEMI, TI, ST, Silan, etc. who frequently deliver it to TV set OEMs with truncated or customised top‑markings; “283N20” is one of those. 2. Packagepin‑numbering confusion • On TCL boards the UC384x is usually supplied in the SOIC‑8 package 150 mil. • The first pad on the PCB is often identified by a square or a bevel; technicians sometimes start counting from the opposite end, hence the apparent mismatch you reported “pin 2” going to the MOSFET whereas, in datasheets, OUT is pin 6. Rotating the IC in the CAD view reconciles all connections with the standard pin map. 3. Electrical fingerprints you can measure to confirm – VCC UC384x pin 7: 12 – 28 V during normal operation, with a quick rise to ≈16 V at start‑up. – REF pin 8: steady 5.0 V reference often hidden under a decoupling capacitor on TCL boards. – OUT pin 6: 50 – 100 kHz rectangular waveform, duty‑cycle ≤ 50 %. – COMP pin 1: 1 – 3 V DC with a small saw‑tooth ripple. Current information and trends – UC384x remains ubiquitous in cost‑sensitive flyback supplies because of its robustness, wide second‑source availability and proven EMI behaviour. – Newer designs migrate to quasi‑resonant or primary‑side‑regulation ICs ICE2QS03, OB2269, NCP1251, etc. for higher efficiency and lower stand‑by loss, but many TCL chassis built up to 2022 still rely on UC384x‑type controllers. Supporting explanations and details – The four versions UC3842434445 differ only in under‑voltage‑lock‑out UVLO thresholds and maximum duty‑cycle; any of them will usually work in the same footprint if the start‑up network meets the UVLO limits. – Asian clones e.g., AJ3842, CRD2842, S3842G, SG5842 share the pin‑out and electrical limits; they are what you often receive when ordering “3842” from TV‑parts suppliers. Ethical and legal aspects – Use only certified replacements or reputable second‑sources to avoid counterfeit parts that could compromise safety risk of LPS ≠ SELV, fire, or electric‑shock. – When servicing SMPS, respect local regulations regarding isolation tests and leakage current. Practical guidelines 1. Removalreplacement – Unsolder with hot air at ≈330 °C, shielding neighbouring plastic parts. – Clean pads, inspect for lifted copper; apply fresh solder and flux before seating the new IC. 2. Start‑up check before power‑up – Series‑lamp or variac for first energising; monitor VCC to ensure the chip does not latch‑off. – Verify gate drive amplitude before inserting the main MOSFET if it was removed. 3. Common failure causes – Open start‑up resistor, dried auxiliary‑winding capacitor, shorted MOSFET, or over‑voltage on COMP pin due to bad optocoupler. Possible disclaimers or additional notes – Although 384x devices are pin‑compatible, substituting a UC3842 by a UC3844 lower max‑duty may prevent full‑load operation—check the duty‑cycle requirement of the flyback stage. – If the IC is marked “283N20‑A” the suffix can denote a lead‑free version or a particular duty‑cycle option. Suggestions for further research – Compare with datasheets of UC3842B ONSEMI and SG6841 if you wish to test a higher‑efficiency drop‑in. – Examine service manuals of TCL chassis MS82P, MT21X7, MT28N, where exactly the same house‑code appears. Brief summary The device identified on the TCL power‑supply PCB as “283N20” is a re‑marked member of the UC384x current‑mode PWM controller family. Mapping the board traces to the standard UC384x pin functions FB, COMP, OUT, VCC confirms the identification. Any reputable UC3842345‑compatible part in SOIC‑8 can be fitted, provided its UVLO and duty‑cycle limits suit the original supply design.

TCL TV Power Supply IC 283N20 Pinout and Equivalent UC384x PWM Controller Identification

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Direct answer to the question

Detailed problem analysis

Current information and trends

Supporting explanations and details

Ethical and legal aspects

Practical guidelines

Possible disclaimers or additional notes

Suggestions for further research

Brief summary