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[FAQ] UCC28C43-Q1: How can I use current mode PWM controllers in an automotive high-voltage contactor economizer?

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Part Number: UCC28C43-Q1

How can I use current mode PWM controllers in an automotive high-voltage contactor economizer?

A high-voltage electric battery in HEV/EVs is used to power the traction inverter and other high-voltage loads such as the AC compressor. To connect the battery to the loads, the battery power lines are routed through electronically controlled, high-voltage switches called contactors.

Figure 1 shows a typical high-power vehicle boardnet with contactors in the battery disconnect unit (BDU) and power distribution module (PDM).

Figure 1: Typical high-voltage power boardnet with contactors in HEV/EVs

The high-voltage contactor is electronically controlled by powering a low-voltage coil inside the contactor. The low-voltage contactor control circuit, called the economizer, drives this low-voltage coil inside the contactor and is powered by the low-voltage bus in the vehicle; for example 12-V bus. Further, the control signals for switching the high-voltage contactors on or off are generated by control modules such as the vehicle control unit (VCU) or the HVAC control module in the vehicle.

Figure 2 shows the profile of the current in the low-voltage coil. This current profile, called a pull-in-and-hold profile; when the contactor is first switched on, the current in the coil is initially high. This is the pull-in current, represented by ipull in Figure 2. The pull-in current is followed by constant-hold current, represented by ihold in Figure 2, for the remainder of time that contactor is on. The pull-in current ensures that the contact is made while the hold current ensures the contacts remain in place.

Figure 2: Pull and hold current in contactor

As shown in Figure 2, one of the key functions of an economizer is to regulate the current in the low-voltage control coil. Texas Instruments wide portfolio of current mode PWM controllers that includes devices such as the UC2843A-Q1 and UCC28C43-Q1 are well suited to regulate the current in the low-voltage coil.

The devices feature a simple yet effective control architecture. With only eight pins, the UC2843A-Q1 and UCC28C43-Q1 can drive MOSFET gates directly. Furthermore, these industry-proven devices offer a flexible and scalable controller solution for the high-voltage to low-voltage conversion and can also support wide-input range applications.

Figure 3 shows a circuit concept for economizer with the PWM controller.

Figure 3: Current mode PWM controller shown in contactor economizers

The economizer in Figure 3 also includes power supply and current set point generator blocks. These blocks can be easily realized by using Texas Instruments wide portfolio of LDOs, analog multiplexers, operational amplifiers and comparators.