Design principle of electric heater
The PTC electric heater module consists of PTC heating components, controllers and internal pipelines. The heating component is installed in the aluminum die casting, the aluminum die casting and the plastic casing form a closed circulation pipeline, and the cooling liquid flows through the heating body in a meander structure.
The electrical control part is an aluminum die-cast body covered with a metal casing. The controller circuit board is secured with screws and the connector is directly attached to the circuit board. The electrical principle block diagram is shown in Figure 1 below:
Figure 1 Electrical principle block diagram
The high-voltage part is inside the red frame, and the low-voltage part is outside the red frame. The high-voltage control unit and the low-voltage control unit contain circuit components such as microprocessors.
The high-voltage part consists of 3 IGBTs (IGBT_A, IGBT_B, IGBT_C) and 3 sets of PTC components (PTC_A, PTC_B, PTC_C) to form 3 high-voltage heating branches, which can be independently powered on or off. Step-by-step power regulation control can be achieved by combining, as shown in Table 1 below.
The control unit realizes the current and voltage sampling of the high-voltage loop through the shunt and sampling resistance respectively, so as to realize the protection of abnormal work. The temperature sensor NTC_C is used to detect the temperature of the PCB and protect it in time when the temperature is too high.
There is TVS at the power supply inlet of the low-voltage part to effectively prevent surges. A high-frequency isolation transformer is used to provide auxiliary power for the high-voltage side. Communication information is exchanged between the high- and low-voltage control units through digital isolators. With hard-wired wake-up function, it can realize wake-up and sleep function. Input auxiliary power supply part current limiting protection function. The temperature sensors NCT_A and NTC_B located at the water inlet and water outlet respectively are used to detect the temperature of the coolant in real time and protect it in time when the temperature is too high.
