NTC熱敏電阻器系由配置的金屬氧化物陶瓷材料制成，它可用來抑制高的突波電流。相對于受保護電路,熱敏電阻器具有較高的電阻。因此會抑制突波電流約1~2秒，在這一段時間內(nèi)熱敏電阻的電阻將因溫度升高而下降，直至熱敏電阻兩端壓降到可被忽略的電阻值為止。如圖A以電源供應(yīng)器為例, 在電源開的，電容器一般阻低，橋式整流器通常承受很大的電流，熱敏電阻器使用于保護電源供應(yīng)器。
Shanghai mec  eleronic  NTC Thermistor devic are made of a specially formulated metal oxide ceramic material which is capable of supprsing high inrush current surg.
Thermistor devic, being of relatively high ristance, shall limit the inrush current for 1~2 seconds during which time the device decreased in ristance substantially to a point where its voltage drop is negligible .The devic are pecially useful in power suppli (see Fig A) because of the extremely low impedance of the capacitor being charged, of which the bridge is ususlly subjeed to an exceedingly high current surge at turnon point.
特征
●抑止突波電流。
●穩(wěn)定狀態(tài)下功率損耗小(通常有1W或小于50W)。
●熱及電特性穩(wěn)定性高。
●寬廣的電性規(guī)格可供選擇。
FEATUR
●High inrush current rtriion effe
●all power loss in stationary state
●(Normally ls than 50W power)
●High thermal and elerical stability.
●Wide seleion of elerical performanc
應(yīng)用概述
如圖B所示，將一NTC熱敏電阻與一白熱燈絲串聯(lián)時，可以消除突波電流。若一只NTC熱敏電阻無法提供之突流限制功能時，二只或更多的熱敏電阻可用于串聯(lián)電路上或供應(yīng)電路的各個分路上(如圖A)。但要注意的是NTC熱敏電阻，不可并聯(lián)于電路上，因為其中一只NTC就可能會傳導(dǎo)幾乎的電流。熱敏電阻用于圖A所示AC電路的A1或A2處，或是DC電路D1或D2處。
在設(shè)計上，當(dāng)電路剛被打開的，NTC熱敏電阻的阻值高于電路上白熱燈絲的總電阻值。當(dāng)電流開始通過時，熱敏電阻產(chǎn)生「自然」現(xiàn)象，并在1到2秒內(nèi)，阻值會降到幾可忽略。以同樣的構(gòu)想來看電動馬達(dá)的突波電流，亦可以被抑制到限度。圖C表示應(yīng)用熱敏電阻保護直流馬達(dá)前后突波電流波形的差異。
APPLICATION
As shown in Fig.B, the current surge can be eliminated by placing a NTC thermistor in seri with a filament string. Yet, if the ristance of one NTC thermistor do not provide sufficient inrush current limiting funions for your applicantion, 2 or more may be used in seri or in separate legs of the supply circuit (Fig.A). Be noticed, the thermistor can not be used in parallel since one unit will tend to condu nearly all the current available. Thus, thermistor may be used in the AC (point A1or A2)or the DC (point D1or D2) locations in the circuit. (see Fig.A)
The ristance of NTC thermistor is digned higher than the total ristance of NIC thermistor is digned higher than the total ristance of filaments when thermistor shall immediately self-heat. Then, in 1~2 seconds, its ristance will be reduced to a minimum and become insignificant to the total ristance of a circuit. With the same concept, current surg in eleric motors can be held to minimum. Fig.C shows a tical DC motor s turn on surge before and after the application of a thermistor to the circuit
選用原則
1.熱敏電阻器的工作電流＞實際電源回路的工作電流
2.熱敏電阻器的標(biāo)稱電阻值
R≥         式中E為線路電壓  l m為浪涌電流
                對于轉(zhuǎn)換電源、逆變電源、開關(guān)電源、
                UPS電源l m=100倍工作電流
                對于燈絲、加熱器等回路l m=30倍工作電流
1.Maximum operating current >Aual operating current in the power loop
2.Reted zero power ristance at 25℃

of which, E: loop voltage, lm: Surge current.
For conversion power, reversion power, switch power,
UPS power, lm=100 tim. operating current
For filament, heater, lm=30 tim operating current
電壓電流特性
當(dāng)NTCR熱敏電阻在小電流下工作時（如圖F），由于功率太底，其電阻保持固定而表現(xiàn)線性關(guān)系（合歐姆定律V/R=1）。如果電流增加，NTC熱敏電阻就會產(chǎn)生焦耳效應(yīng)(P =V&tim;1)而使自己發(fā)熱，其電阻值隨即減小表現(xiàn)「電流增加,電壓下降」的狀態(tài)。
When operating low current (see fig.F), due to very low power is unable to make the NTC thermistor self-heated, so its ristance value is thus maintained constant and displayed with a linear curve (in conformity with ohm-law V/R=1).If the current is increased, the NTC thermistor will follow Joule-efficiency(P= V&tim;1) and make itself self-heated that rults in a ristace value decreasing and thus displays with a status of voltage dcending while current increased.

(如圖F)，說明NTC元件與環(huán)境達(dá)成熱平衡所需的時間，主要決定于材料熱容量（G）及散熱系數(shù)（δ）。當(dāng)元件溫度由T1降到T0，則可得到下列平衡式：
  －HdT=δ(T－T0)dt   其中－HdT=元件熱損失
                    δ(T－T0)dt:元件散熱量
  積分后可得溫度與時間關(guān)系式T－T1= (T0－T1)&tim;e－t/t
  其中τ=H/δ
As shown in fig.G which explains the time needed to reach thermal equilibrium of NTC components with the enviroment. This charaeristic depends on two important parameters. If a step change in temperature is applied to a component e.g. form high (T1) to low (T0) temperature, the energy lost (δ(T0－T1)dt) by the component (－HdT) is equal to the energy dissipated by it.
      －HdT=δ(T－T0)dt
      This equation yields: T－T1= (T0－T1)&tim;e－t/t
      τ=H/δ