SLUAAS4 January 2024 LM5155-Q1 , LM51551-Q1 , LM5156-Q1 , LM51561-Q1 , LM51561H-Q1 , LM5156H-Q1 , LM5157-Q1 , LM51571-Q1 , LM5158-Q1 , LM51581-Q1 , UCC28700-Q1 , UCC28730-Q1 , UCC28740-Q1 , UCC28781-Q1 , UCC28C50-Q1 , UCC28C51-Q1 , UCC28C52-Q1 , UCC28C53-Q1 , UCC28C54-Q1 , UCC28C55-Q1 , UCC28C56H-Q1 , UCC28C56L-Q1 , UCC28C57H-Q1 , UCC28C57L-Q1 , UCC28C58-Q1 , UCC28C59-Q1
The automotive industry is transitioning from combustion engines to electric vehicles (EV) and hybrid electric vehicles (HEV). One of the key parts of an EV and HEV system is a Traction Inverter. The traction inverter takes the DC input power from the high-voltage (HV) battery and provides the controlled AC power to the e-motor. Along with power Switches and gate drivers, isolated bias power supply is a major portion in the traction inverter circuit. One of the main functions of the isolated bias supply is to provide the required power to the gate drivers. There are several possible architectures for the isolated bias power supply. These architectures also influence the choice of the topologies and associated devices.
Isolated bias supply provides power to the different gate-driver circuits in HEVs and EVs. 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.
Isolated bias power supplies take power either from the low-voltage (LV) battery or from the high-voltage battery of the HEV, EV. Based on the power source, the isolated bias power supplies can be divided in two groups: low-voltage isolated bias power supplies and high-voltage isolated bias power supplies. The isolated 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, LV batteries are common as a power source for isolated bias power supplies, often both LV and HV batteries are used to provide redundancy in the system. A redundant power supply can lead to achieve higher functional safety of overall system. Figure 1-1 shows a traction inverter block diagram.
Low-voltage isolated bias power supply circuits usually have a 12V battery as a power source in HEV and EV. Although there are some systems with 48V as a LV battery, this paper focuses on the 12V battery system. However, these architectures can be still relevant for 48V LV battery designs. In that case, one option is to have a converter to lower the voltage to use the same devices or another option is to have devices supporting an input voltage range designed for a 48V battery.
Considering the state of charge (SOC) of the 12V LV battery, the wider input voltage range needs to be supported by the isolated bias power supply (as an example: 8V–16V). In case of cold crank and load dump scenarios, the input voltage range requirement goes further down and up, respectively. There can be differences in this wide input voltage range of 12V LV battery depending on the OEM. Not all types of topologies and the associated devices can support this wide input voltage range. Therefore, in several designs a pre-regulator is needed between LV battery and isolated bias power supply to regulate the input voltage for the isolated bias power supply device.
Parameters | Open-Loop LLC | Push-Pull | Primary-Side-Regulated Flyback | Fully-Integrated Modules (Full Bridge + Transformer) |
---|---|---|---|---|
VIN minimum and maximum | 9V, 34V | 3V, 36V (1) | 4.5V, 65V(1) | 4.5V, 26.4V(1) |
POUT maximum | Up to 9W | Up to 7.5W (1) | Up to 30W(1) | Up to 2.5W(1) |
VOUT regulation | Unregulated | Unregulated, VIN controlled | Regulated | Regulated |
Switching Frequency | 0.1–1.2MHz | 0.1–2MHz | 20–350kHz | 11–15MHz |
Isolation | Depends on transformer used | Up to 5kV, basic or reinforced | ||
Supporting Devices | UCC25800-Q1 | SN6501-Q1 SN6505-Q1 SN6507-Q1 | LM518x-Q1 LM2518x-Q1 LM515x-Q1 LM34xxx-Q1 | UCC1413x-Q1 UCC1414x-Q1 UCC1424x-Q1 UCC1434x-Q1 UCC1524x-Q1 |
High-voltage isolated bias power supply circuits have an HV battery as a power source in HEV and EV. As an HV battery, 400V and 800V voltage batteries are the most common in HEVs and EVs. The isolated bias supply connected to the HV battery needs to support a wider input voltage range. The need for wide input voltage range support is similar to the LV battery: SOC and load dump scenarios of the HV battery. Based on the SOC of the battery, a wider input voltage range needs to be supported. For example, commonly considered voltage ranges are 240V–450V for a 400V battery and 550V–950V for an 800V battery. However, this voltage range can be different depending on the OEM requirement.
Although the HV battery can be used as a primary source for isolated bias power supply, mostly the battery is used to provide redundancy. Flyback topology is usually selected for such a high and wide input voltage range from a technical perspective as well with respect to minimizing costs.
Device | UCC28C5x-Q1 | UCC28700-Q1 | UCC28730-Q1 | UCC28740-Q1 | UCC28781-Q1 |
---|---|---|---|---|---|
Switching Type | Hard-switched | Valley switching | Valley switching | Valley switching | Zero-voltage switching (ZVS) |
Feedback Regulation(1) | Primary, Secondary (Optocoupler) | Primary | Primary | Secondary (Optocoupler) | Secondary (Optocoupler) |
Typical Power Levels | 20–100W | 2–50W | 2–50W | 2–50W | 50–150W |