NTC Thermistor Resistors 33D-5 0.5A 33 Ohm Inrush Current Limiter Temperature

Product Specification

NTC Thermistor Resistors 33D-5 0.5A 33 Ohm Inrush Current Limiter Temperature Sensors 50D-5

Applications Of The NTC Thermistor Resistors 33D-5

Inrush current limiting, e.g. in switch-mode power supplies, soft-start motors

Features Of The NTC Thermistor Resistors 33D-5

* Leaded and coated NTC thermistors

* Tinned copper wire, kinked

* Coating material flame retardant to UL 94 V-0

* Highly stable electrical characteristics

Approvals Of The NTC Thermistor Resistors 33D-5

* UL 1434 

* TUV

* CQC

Specification Of The NTC Thermistor Resistors 33D-5

Why should use power NTC thermistors

In order to prevent the surge current that occurs at the moment of power-on in the electronic circuit, a power NTC thermistor is connected in series in the power supply circuit, which can effectively suppress the surge current during power-on, and after the surge current suppression effect is completed, due to the Through the continuous effect of its current, the resistance value of the power type thermistor will drop to a very small degree, and the power it consumes can be ignored, and it will not affect the normal operating current, so the power type thermistor is used in the power circuit. NTC thermistor is the most concise and effective way to suppress the power-on surge current to protect electronic equipment from damage.

Selection criteria for power NTC thermistors

1. The maximum operating current of the resistor> the operating current of the actual power circuit
2. Nominal resistance value of power resistors
R≥1.414*E/Im
where E is the line voltage Im is the surge current
About conversion power supply, inverter power supply, switching power supply, UPS power supply, Im=100 times the operating current
About the filament, heater and other circuits Im=30 times the operating current
3. The larger the B value, the smaller the remaining resistance and the smaller the temperature rise during operation.
4. Generally speaking, the greater the product of the time constant and the dissipation factor, the greater the thermal capacity of the resistor and the stronger the resistor's ability to suppress inrush current.

NTC Negative Temperature Coefficient Thermistor Terminology

Zero power resistance value RT (Ω)

RT refers to the resistance value measured by the measurement power that causes the change in resistance value to be negligible relative to the total measurement error at the specified temperature T.

The relationship between resistance value and temperature change is:

RT = RN expB(1/T – 1/TN)

RT : NTC thermistor resistance value at temperature T (K).
RN: NTC thermistor resistance value at extra temperature TN (K).
T: Regular temperature (K).
B: The data constant of the NTC thermistor, also known as the thermal index.
exp : The exponent to the base e of the natural number ( e = 2.71828 … ).

This relationship is an empirical formula and only has a certain accuracy within a limited range of the additional temperature TN or the additional resistance value RN, since the material constant B itself is also a function of the temperature T.

Additional zero power resistor value R25 (Ω)

According to the national standard rules, the additional zero-power resistance value is the resistance value R25 of the NTC thermistor measured at the reference temperature of 25 ℃, and this resistance value is the nominal resistance value of the NTC thermistor. Generally speaking, the resistance value of the NTC thermistor also refers to this value.

Maximum steady state current

The maximum continuous current allowed to be applied to the thermistor at an ambient temperature of 25°C.

Approximate resistance value (Ω) at maximum current at 25°C

The approximate resistance value at the maximum current at 25°C is the remaining resistance value of the thermistor when the allowed maximum continuous current is applied to the thermistor at an ambient temperature of 25°C, also known as the maximum remaining resistance value.