Thermistor in charger

Charging thermistors are generally based on PTC ceramics and are used in smoothing power capacitors. When the charger has an unexpected failure or short circuit, it can control the current to a guaranteed range. Generally, ordinary resistors are used to control the current when the capacitor is charged, but this also has certain technical risks. Self-protecting rechargeable thermistors are based on PTC (Positive Temperature Coefficient) ceramics and are used to smooth capacitors in power supplies. When a short circuit occurs, they limit the current to a level, such as when the capacitor is shorted, if the capacitor is shorted or the relay fails, the resistor will continue to be exposed to high power levels.

When the capacitor is charged, a resistor is usually required in series to control the charging current, so as not to generate a strong current peak that exceeds the allowable range. This function is generally implemented by a fixed ordinary resistor or a negative temperature coefficient (NTC) thermistor. In most cases, a time- or voltage-controlled relay is used to short-circuit the current-limiting element after charging.

The restriction of the charging current is very important for the rectifier and converter system, because if the peak value of the inrush current is not controlled, it may trigger the fuse or subject the rectifier to a strong current exceeding the allowable range. If there is no interference during operation, the above-mentioned combination of ordinary resistors and relays is sufficient to control the charging current. However, interference that occurs during or after charging can cause these thermistors to fail completely, and thus cause the failure of other components of the system.