This reference design (TIDA-01407) from Texas Instruments is a 400W dc-dc power supply that generates a 12Vdc rail from the 48Vdc car battery in a mild hybrid electric vehicle (MHEV) system. The design implements a phase-shifted full-bridge topology which is capable of delivering 400W of output power and handling an input voltage range of 36Vdc to 60Vdc without losing regulation.
The design is extendable to 500W with appropriate heatsinking and is easily customizable to meet a variety of system requirements. Typical applications can include HEV/EV traction inverter, dry double-clutch transmission, electronic control units, HEV/EV dc-dc converter, and so on.
The input voltage withstand rating can be increased by increasing the MOSFET blocking voltage for the LV148 standard compliance.
The enhanced, phase-shifted full-bridge controller UCC28951-Q1 implements programmable delays which ensure zero voltage switching (ZVS) over a wide range of operating conditions.
The output side implements synchronous rectification, which enables fast transient response and a high loop bandwidth. The system regulates 12V at no load with less than 100mW of standby power.
Pseudo isolation is achieved through the use of a transformer, which means the 48V does not apply to the load if the MOSFETs are shorted.
The half-bridge gate drivers, which drive the high side and low side MOSFETs together at the primary side, can withstand a maximum boot voltage of 120Vdc.
The controller regulates the output voltage through the transformer primary side, which eliminates the use of an optocoupler and leads to a higher reliability and smaller form-factor board.
Figure 1 shows a block diagram example of the 48V battery-inverter-driven motor system. The TIDA-01407 serves as a redundant supply to the 12V battery voltage rail.
As the diagram shows, the isolated dc-dc (TIDA-01407) is connected to the 48-V battery side and the non-isolated dc-dc is connected to the 12V battery side (TIDA-01179).
Both designs are in ORing configuration and provide the power to the downstream loads. TIDA-01179, which includes a buck-boost converter and a buck converter, creates the front-end power for the 12V car battery.
System Block Diagram
Figure 2 (above) shows the system block diagram. The design consists of three main functional elements.
- Current sensing at the primary side through the current transformer – This feature is for cycle-by-cycle overcurrent protection and adaptive delay control.
- Power stage of the phase-shifted full-bridge at the primary side – This power stage implements the zero voltage soft-switching scheme and variable power-saving features for improving the efficiency over a wide load current range. The device can tolerate automotive electronics operating from a car battery, which experiences transient loads such as cold cranks and load dumps that can range up to 80V and are easily scalable to 100V.
- Synchronous rectification MOSFETs at the secondary side – This element offers several benefits and functions to:
- Boost the system efficiency by reducing the voltage drop over the drain-to-source
- Reduce voltage overshoots and undershoots caused by the load steps
- Enable fast transient response and a high loop bandwidth
Summary of features
- Phase-shifted full-bridge converter over input voltage of 36-V to 60-V DC; output power up to 400W
- Extendable to 500W with heatsinking; easy to customize per customer requirements
- Soft-Switching, Phase-Shifted Full Bridge Using UCC28951-Q1, Grade 1
- Synchronization Achievable for Multiple Phase Operation
- Regulated 12 V With 36-V to 60-V Input and at No Load With < 100-mW Standby Power
- Pseudo-Isolation Through Transformer; Load Does Not Register 48 V if MOSFETs Short
- Synchronous Rectification for High Efficiency
- Adaptive Delay for High Efficiency Across Load Range