PTC Thermistor Application Example
Keep electrical equipment from overcurrent and overheating damage; As a kind of heating PTC ceramic element, it is a kind of temperature auto-control heater. It is widely used in heaters, hair dryers, mosquito-repellent incense, iron and other electrical appliances which need to maintain constant temperature. It can save a set of temperature control circuit.
(1) Load over current, overheat protection
The picture on the right shows the protection of the thermistor to the load circuit.
When the battery of the mobile phone is overcharged or short-circuited, the battery heats up, and the resistance of the PTC on the internal circuit board of the battery rises, limiting the current to a safe range. Some parallel mobile phone batteries use ordinary resistors instead of PTCR inside, and the protection is very poor in the event of a short circuit fault.
(2) Application of PTCR in TV PTC Degaussing Circuit
The grids, shadows and other components of color kinescope are made of metal materials. They are susceptible to the influence of geomagnetic field or stray magnetic field inside and outside the machine, which will magnetize these metal components and make the image color abnormal. Therefore, color TV sets are equipped with automatic degaussing circuit.
The degaussing coil attached to the picture tube is connected in series with the PTCR to form a degaussing circuit. When it is turned on, the PTCR cold resistance is very small (about 12 to 18 Ω), and the 50 Hz current flowing through the degaussing coil is very large, resulting in a strong alternating magnetic field. Current also flows through PTCR, making its temperature rise, its resistance value increases rapidly in a few seconds, the current decreases gradually, showing attenuation waveform, and the magnetic field decreases gradually to play the role of demagnetization. To reduce the holding current, a small power heating resistor can be placed next to the PTCR to keep the PTCR at a high temperature during the operation of the TV. The current flowing through the degaussing coil can be maintained at a small level to reduce power consumption.
Current time curve of PTC degaussing circuit
(3) Application of PTCR in motor starting
Application of PTC in motor starting circuit
Connecting the PTCR in series in the motor starting coil circuit, and having a large starting current within a few seconds of starting the motor; When the motor is started, the current flowing through the starting coil is small.
(4) Application of PTCR in motor overheat protection
The PTCR is buried in the motor coil. When the motor coil is overheated, the PTCR is reduced, the motor protection circuit is activated, and the power of the motor is cut off. In this example, the motor current does not flow through the PTCR, which is quite different from the previous examples. The PTCR only functions to detect temperature, not as a recoverable fuse.