PTC Protection Intelligent Home Appliance Circuit Design Scheme
- Oct 30, 2018 -

PTC protection intelligent home appliance circuit design scheme

In the soybean milk maker, blender, such as egg mixer in home appliance, to avoid a "tough" big motor locked-rotor and burned caused by design engineers usually design temperature or over-current protection measures, the commonly used are: 1 time over-current protection, recoverable temperature protection, also use PTC do locked-rotor protection today.When motor blocked in turn, flows through the armature current will be normal working current for several times, usually can achieve at least 4 ~ 5 times or more, such a large current flows through the motor armature, will cause the motor temperature rise sharply, lead to a significant reduction in the electrical insulation performance, finally cause the enameled wire insulation layer of the stator or rotor winding to melt, cause electrical short circuit burning and other dangerous phenomenon.Because the motor is started, in order to overcome the friction torque, moment of working current is big, and completion of launch, in the absence of blocked in turn, working current is a constant value, because once the fuse in its 2 times rated current, quickly action, expression is burn out, open circuit, the motor start failure, so the early use of one sex as a motor over-current protection, 1 to overcome the shortcomings of insurance, usually choose one of the fuse will be greater than the rated current of the motor's normal working current, so while avoiding the motor start the instantaneous error protection problems,However, if the motor is blocked or overheating, the protection will not be timely, affecting the protection effect.If choose bimetal thermostat as motor blocked or overheating protection, the impact of the moment motor start current before the heat of the engine does not translate into motor, bimetallic thermostat will not action, although can effectively avoid to choose 1 times the disadvantages of the fuse, but the installation position of bimetal thermostat is very exquisite, need to the thermostat clingy or exciting winding of the stator of the motor, otherwise, if the motor is blocked in turn, although the actual temperature is higher than the allowable values of the armature, but because of the heat conduction, not in time or the quantity of heat conduction to the thermostat is not enough, not enough to cause the thermostat action, will lead to protective effect.If use PTC as locked-rotor protection of motor, will effectively avoid the above problems, first of all, PTC as recoverable fuse of polymer materials, internal depend on joule's law Q = the I ^ 2 * R * T action, visible to internal heat and is proportional to the square of the flow of electric current, when the current is added, internal heat to the square of the current relationship has increased dramatically;The large current shock at the moment of motor start, because the heat accumulated is not enough to cause PTC action, so there will be no wrong protection.Once the motor is blocked, as the blocked current is several times the normal working current, PTC can start protection as long as the current flowing through is two times the normal working current. At this moment, the overall temperature of the motor does not rise, avoiding the impact of high temperature on the motor!PTC after startup protection, power need human intervention, the PTC heat dissipation can be restored to the factory after low resistance state, if not to cut off the current, the PTC will always have a small residual current flows through the PTC for high value, even if the user is charged at the moment blade of mixer, and ensure that the motor does not rotate, thus protecting the personal safety of users.

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