1 Introduction

The bias power supply for HVLV DCDC converter can be mainly divided in to two parts: Isolated bias power supply and non-isolated bias power supply. Considering that the microcontroller is located in the LV secondary side of the converter, isolated gate drivers are required at the HV primary side. Therefore, isolated bias power supply are required to provide power to the isolated gate drivers. There are different topologies to design an isolated bias power supply. The most commonly used topologies are flyback, push-pull, LLC-resonant, and integrated transformer modules. Each topology provides specific advantages but at the same time has trade-offs and challenges. The choice of the topology depends largely on the overall architecture of the isolated bias power supply. Different Si, SiC, GaN, IGBT switches (and possibly others) need different input voltage range for gate-source voltage. Therefore, isolated bias power supply architecture and selection of devices also depend on the switches used in the design.

Considering the microcontroller is located at low voltage side and sharing same ground as low voltage battery, all devices like non-isolated gate drivers, active clamp circuit gate drivers, sensors, controller area network (CAN) and so forth of the secondary side of DCDC converter can be powered using non-isolated bias supply. From a low voltage battery, non-isolated DCDC converters like buck converter, Single-Ended Primary Inductor Converter (SEPIC) or a buck-boost converter can be used to generate a regulated voltage rail. This regulated voltage rail can be further used to distribute required bias power to the primary and secondary side devices.

Bias power devices take power either from the low-voltage battery or from the high-voltage battery of the HEV or EV. Based on the power source, the bias power supplies can be divided in two groups: low-voltage bias power supplies and high-voltage bias power supplies. The bias supply circuit can be directly connected to the battery or connected to the battery using the pre-regulators. The pre-regulators are needed depending on the wide input voltage range capability of the device. Although low-voltage batteries are common as a power source for isolated bias power supplies, sometimes both low-voltage and high-voltage batteries are used to provide redundancy in the system. A redundant power supply can lead to achieve higher functional safety of an overall system.

Figure 1-1 shows a generic HVLV DCDC converter circuit with DC-DC primary, and DC-DC secondary stages. The switches are named as Pri_HS_1, Pri_HS_2, and so forth. The first part of this nomenclature indicates that whether the switch belongs to DC-DC primary or DC-DC secondary stage of the converter. The second part shows whether the circuit uses a high-side or low-side switch. The third part shows the switch number of the high or low side. In the same fashion, consider the same nomenclature for the gate driver of each of these switches and the isolated bias power supply to the gate drivers. In the figures in this document, this nomenclature is used to describe the different isolated bias power supply architecture.

Figure 1-1 HVLV DCDC Generic Circuit