STDA010 January   2026 LM25180-Q1 , LM5155-Q1 , SN6507-Q1 , UCC14240-Q1 , UCC34141-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Low-Voltage Isolated Bias Power Supply
    2. 1.2 High-Voltage Bias Power Supply
  5. 2Bias Power in Common-Source Configuration of Back-to-Back FETs
  6. 3Bias Power in Common Drain Configuration of Back-to-Back and Bidirectional FETs
    1. 3.1 Centralized Isolated Bias Power Supply Architecture
    2. 3.2 Semi-Distributed Isolated Bias Power Supply Architecture
    3. 3.3 Bias Power Supply Using a DC-DC Converter Module
  7. 4Isolated Bias Power Supply Using Gate Driver to Drive the Transformer
  8. 5Redundancy in the Isolated Bias Power Supply Architecture
  9. 6Summary
  10. 7Terminology

1.1 Low-Voltage Isolated Bias Power Supply

Low-voltage bias power supply circuits usually have a 12V battery as a power source in HEVs and EVs. Although there are some systems with 48V as a low-voltage battery, this paper focuses on the 12V battery system. However, these architectures are still relevant for 48V low-voltage battery designs. For example, in a 48V low-voltage battery design, one use-case is to use a converter to lower the voltage from 48V to 24V, 15V, or 12V to use the same isolated bias power devices as a 12V battery. Alternatively, another use-case is to have isolated bias power devices supporting an input voltage range designed for a 48V battery.

Considering the state of charge (SOC) of the 12V low-voltage battery, the wider input voltage range needs to be supported by the isolated bias power supply (for example: 8V–16V). In cold crank and load dump scenarios, the range requirement of the input voltage goes further down or further up, respectively. There can be differences in the wide input voltage range of a 12V low-voltage 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 preregulator is necessary between the low-voltage battery and the isolated bias power supply to regulate the input voltage for the isolated bias power supply device.

Table 1-1 Texas Instruments' Low-Voltage Isolated Bias Supply Topologies and Associated Devices
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 the 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
UCC1524x-Q1
UCC34141-Q1
UCC35131-Q1
Advantages High efficiency
Low EMI
High CMTI		 Wide Vin range
High line regulation		 High efficiency
Wide Vin range
High load and line regulation		 No external transformer
Robustness to vibration
Small size and low height
Challenges Requirement of preregulator Low efficiency at low Iout (<50mA) Parasitic capacitance across isolation barrier of flyback transformer Low efficiency
Power limitation
(1) Depends on the variant of the device.