Brief Analysis of Tesla MODEL 3 Control Panel Relay Drive Circuit

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Brief Analysis of Tesla MODEL 3 Control Panel Relay Drive Circuit [Copy link]

Introducing the BMS controller of MODEL 3, this time I will summarize the relay drive circuit (as shown in the figure below). Please take the trouble to read it again, haha.

The topology of the entire drive circuit is as shown in the figure below: the relay power supply is input from P1, the relay drive signal and power supply are output from P2, and a total of four low-side drive signals are output to the outside; note that there are two high-side switches here, which is a bit special and will be discussed later.

The relay drive output signals of the MODEL 3 controller are all concentrated on the P2 connector, as shown below: This connector is 44PIN, from the manufacturer JST, model S44B-RAD1AK; you can see that there are many diodes near the B-side connector, which are used for port protection.

The relay-related pin definitions of the P2 connector are as follows. There are a total of 4 relay drivers: the main relay and the fast-charge relay. Note that there is no pre-charge relay driver because its pre-charge function is implemented using DC\DC.

The power supply for the relay drive circuit comes from the P1 connector, as shown in the figure below: After passing through the port protection on the T side, this power supply line is punched to the B side, and then goes through the wide copper sheet to the relay drive circuit.

The key modules of the entire relay drive circuit are shown in the figure below: ① is the power supply anti-reverse circuit, ② is the fast charging relay power switch, ③ is the main relay power switch, ④ is the fast charging relay drive circuit, and ⑤ is the main relay drive circuit; in ② and ③, in addition to the PMOS switch, there is also a current detection circuit for the purpose of current limiting.

Let’s take a look at the key components of the circuit, as shown below:

• ①, Anti-reverse PMOS tube: Infineon-IPD50P04P44L-11

• ②, PMOS power switch: Infineon-IPD50P04P44L-11

• ③. Current detection resistor: 0.02Ω

• ④. Filter inductor: 100uH

• ⑤. Filter inductor: 220uH

• ⑥. Energy storage capacitor: 680uF/35V

• ⑦. Dual-channel PMOS high-side switch: VISHAY-SQJ963EP

• ⑧, Quad low-side driver switch: NEXPERIA-BUK9Y107-80E

Low-side drive circuit for two main relays

The circuit diagram is as follows. The key point is to use a single diode as the coil freewheeling circuit, and add TVS protection to the drive output port, and also to the power output port.

Two-way fast charging relay low-side drive circuit

The fast charging drive circuit has changed from the previous one. One of the circuits is shown in the figure below: The relay drive protection circuit uses a combination of diode + TVS tube, and the TVS tube is also connected in parallel with a resistor. As mentioned in a previous article, this TVS tube can accelerate the discharge of the inductor, and this resistor can also accelerate the discharge of the inductor. The two can complement each other, so I think this resistor is also used to discharge the inductor. At the same time, it was found that a PMOS high-side switch was placed at both ends of the resistor, which can short-circuit the TVS + resistor, but is the purpose of the short circuit to reduce the clamping voltage and increase the discharge time?