NTC thermistor surge circuit analysis.Turkey PIR Lens

　　1. Causes of surge suppression

　　When the PC is cold started, a large surge current will be generated, that is, the AC 220V mains will give the PC a large power-on inrush current. This large surge current may burn the power supply and the internal circuit of the host. For this reason It is necessary to set up a circuit for suppressing surge, so that when the PC is powered on, the surge current is small, and after booting, it can restore the normal 220V power supply state.

　　2. NTC thermistor location

　　Open the PC's switching power supply case, you can find a disc-type ceramic capacitor on the outside, usually olive green. It is an NTC thermistor used to suppress inrush current, as shown in the figure.

　　3. Circuit Analysis

　　It can be seen from the circuit that NTCR1 is connected in series in the 220V power supply loop as part of the 220V AC mains load. When the PC is cold-started, since the resistance value of NTCR1 is large at normal temperature (zero power), this limits the current of the 220V loop when it is turned on, so that it cannot be too large.

　　After power-on, current flows through NTCR1, its temperature rises, and the resistance begins to drop. After the PC is turned on for a short time, the temperature of the NTCR1 resistor rises to the working range, and its resistance value drops to a very low value, which can be ignored. At this time, the 220V mains power supply enters the normal state, and the resistance value of NTCR1 is very small at this time, and it will not generate too much power consumption.

　　Automotive Grade Glass Encapsulated Protected NTC Thermistor

　　Device R25 resistance includes 1 kW and 1.5 kW low resistance and 5 kW resistance, suitable for IGBT and power MOSFET modules in EV and HEV vehicles

　　MALVERN, PA — April 11, 2022 — Vishay Intertechnology, Inc. (NYSE: VSH) today announced that the NTCS0603E3.....T and NTCS0805E3.....T series of automotive-grade glass packages protect thermal Resistor Expanded 0603 and 0805 form factors, new resistance devices at +25 °C (R25). The device is AEC-Q200 qualified, with R25 resistance values including 1 kW and 1.5 kW low resistance and a new 5 kW resistance value, suitable for IGBT and power MOSFET module protection in electric vehicles (EV) and hybrid electric vehicles (HEV).

　　Enhanced thermistors are glass-encapsulated for full protection, with R25 resistance and beta (B25/85) tolerances down to ± 1 %, enabling accurate temperature sensing from -40 °C to +150 °C, Protection and compensation. NTCS0603E3.....T and NTCS0805E3.....T series devices are smaller than MELF resistors, easy to assemble, and have extremely high flexural strength, suitable for automotive buck-boost converters, LED modules, battery packs, electric vehicles Charging piles, wind and solar panel inverters and office equipment

　　NTC thermistor adopts SMD structure, nickel-tin terminal, suitable for wave soldering and reflow soldering. The devices are RoHS-compliant, halogen-free, and packaged in reels of 4,000-count perforated paper tape.

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