How to Design a 12V-to-60V Boost Converter with Low Temperature Rise Using eGaN FETs

Modern displays, such as laptops and PC monitors, typically require a low power boost converter. In this application, the screen intensity is low to moderate and the converter is operated at light load most of the time, so the light-load efficiency is very important. The low switching loss of eGaN FETs can help address this challenge. This GaN Talk will examine the design of a 12V to 60V, 50W DC/DC power module with low temperature rise using eGaN FETs in the simple and low-cost synchronous boost topology.

Design of a small and Highly Efficient eGaN^®-FET-based synchronous boost converter

The synchronous boost topology is popular in DC/DC step-down converter design for its simplicity, easiness in control, and low cost. The schematic diagram of the eGaN FET-based synchronous boost converter is shown in Figure 1. The 100V rated eGaN FET EPC2052 with RDSon of 6mΩ is selected for the 12V to 60V, 50W power stage. The uP1966E gate driver that features high driving strength is used to drive the FETs. The synchronous bootstrap circuit with EPC2038 that ensures 4.9V gate voltage is used for the high-side gate drive. Digital control that allows sub-10ns dead time and flexibility in control scheme development is employed. To optimize efficiency, two small on-board switch-mode power supply circuits are used to generate the housekeeping 5V and 3.1V voltages for the gate driver and the digital controller respectively. The house keeping power can also be powered from either high or low voltage port using the simple diode“OR”circuit, which enables bi-directional operation.

Figure 1. Simplified schematic of the eGaN FET-based synchronous boost converter. The design is bi-directional capable.

The switching frequency of the converter is designed at 500kHz for high light-load efficiencies, and the inductor is a 10μH TDK ferrite inductor. At light load, the inductor core and AC copper losses are dominating factors. Therefore, a larger inductor improves the light-load efficiency because of decreased ripple and thus lower core losses and AC copper losses.

Design Validation

The synchronous boost converter EPC9162 is shown in Figure 2. The switch-node voltage, V_SW waveform at 0.15A output current is presented in Figure 3, which shows the switching to be fast and clean.

The overall power efficiency and power loss of the synchronous boost converter operating at different input voltages are given in Figure 4 with a peak efficiency of 95.3% at 12V input and 60V and 0.85A output.

Figure 2. Photograph of the 1 V to 60V, 50W synchronous boost converter EPC9162

Figure 3. Switch-node voltage vSW, waveform at 0.15A output current

Figure 4. Total system efficiency, including the housekeeping power consumption at 20V output

The thermal image of the converter operating at 12V to 60V, 0.85A output current without forced-air cooling is shown in Figure 5. A temperature rise of just 40°C is achieved. It is clear that the GaN FETs are capable of carrying more current given a relaxed temperature rise or with forced-air cooling.

Figure 5. Thermal image of the synchronous boost converter operating at 12V to 60V and 0.85A output and thermal steady state without forced-air cooling

Conclusions

A 12V to 60V, 50W eGaN-FET-based synchronous boost converter achieves 95.3% peak efficiency and only 40°C temperature rise with the small die size of 2.25mm². In applications where light-load efficiency is critical such as LED backlighting for laptops and monitors, the fast switching speed of eGaN FETs significantly reduces switching losses for higher efficiency. Additionally, the low temperature rise prevents equipment overheating and the synchronous boost topology provides a simple, low-cost solution.