On cold days, a car seat can cause discomfort and even a source of various chronic diseases. To avoid this, some car enthusiasts connect heating to their car seats. Doctors testify that with reasonable operation, the heating device has a beneficial effect on the body, preventing radiculitis, renal diseases and osteochondrosis. For men, doctors advise not to set the heating to the maximum level and turn it off periodically.
Heated seats are of 2 types: built-in heaters and seat covers. Seat covers fit onto the chair and plug into the cigarette lighter.
Built-in heaters consist of an electronic control unit and a heater made in the form of a resistive element.
The control unit contains 4 functional units:
- PWM controller, which generates an impulse signal;
- the output stage, which is a powerful transistor, to the drain of which a heater is connected, and a pulse signal from a PWM controller is fed to the gate;
- timer providing automatic shutdown of the heater after a certain time interval;
- a protection unit that ensures the safety of a powerful transistor in the event of a short circuit of the drain to the power bus, as well as disconnection of the PWM controller with a simultaneous break in the circuit of two heaters.
The heater control unit can be implemented in different ways. In particular, it can be performed on discrete elements using universal ICs. In this case, there must be at least three ICs, a powerful transistor and a number of passive components.
In the modes "Weak heating", "Strong heating" and "Medium heating", the division coefficient of the frequency divider (frequency divider) is maximum, which provides a reset of the output signal after 30 minutes. In the "Intensive heating" mode, the DC generates a control signal after 4 minutes, which, through the control signal generator (FUS), enters the control unit and automatically sets the "Strong heating" mode, with further shutdown after 30 minutes.
If in any mode there is a short circuit of the transistor drain to the power bus, the protection unit generates a reset signal when the circuit of two heaters is simultaneously open. In this case, the FUS ensures the supply of alternating antiphase signals (with a frequency of 1 Hz) from the DC to the LEDs, as a result of which their alternate blinking appears.
