Driven by the spur of energy conservation and environmental protection and the latest energy efficiency regulations around the world, improving energy efficiency has become the consensus of the industry. Compared to hard switching techniques such as flyback, forward, two-switch flyback, two-switch forward and full bridge, dual inductor plus single capacitor (LLC), active clamp flyback, active clamp forward, non- Soft switching technologies such as symmetrical half bridges (AHB) and phase-shifted full bridges provide higher energy efficiency. Therefore, in applications that focus on energy efficiency, soft switching technology is increasingly favored by designers.
On the other hand, the half-bridge configuration is best suited for medium and low power applications that offer high energy efficiency/high power density. The half-bridge configuration involves two basic types of MOSFET drivers, namely high-side drivers and low-side drivers. The high side indicates that the source of the MOSFET can float between ground and the high voltage input, while the low end indicates that the source of the MOSFET is always grounded, see Figure 1. When the high-side switch turns from off, the MOSFET source voltage rises from ground to the high-voltage input, which means that the voltage applied to the MOSFET gate must also rise. This requires some form of isolation or floating gate drive circuit. In contrast, the source of the low-side MOSFET is always grounded, so the gate drive voltage can also be grounded, making it easier to drive the gate of the low-side MOSFET.
Table 1: Cross-referencing of silicon drivers for ON Semiconductor's high-side MOSFET drivers.
The program comparison and ON Semiconductor recommended that we compare the two solutions with a 24 V@10 A LLC half-bridge circuit using a transformer drive scheme and a silicon driver scheme. Both schemes use the LLC controller NCP1395 with dual DRV outputs, except that the former uses a transformer to drive the MOSFET of the LLC converter, and the latter uses the NCP5181 driver IC to drive the MOSFET of the LLC converter. The waveforms of the two look similar, but comparing the waveforms when the high-side MOSFET is turned off, the driver IC turns off the MOSFET more quickly, and the driver IC turns off the MOSFET for 70 ns, which reduces switching losses. When the high-side MOSFET turns on, The driver IC maintains a safe and sufficient dead time between the high-side and low-side MOSFETs, which is superior to the transformer drive scheme. In terms of energy efficiency, there is no significant difference in energy efficiency between the two solutions at the same input power (see Reference 1 for details).
Which of these two options should you choose? In fact, if you design it carefully, both options are fine. As the premier high-performance, energy-efficient silicon solution provider for green electronics, ON Semiconductor's proposal is to choose a silicon driver solution because the silicon solution simplifies wiring and simplifies design, eliminating the need for manual insertion of the transformer. And can eliminate the problems in the transformer scheme such as the isolation is broken, the magnetic flux is broken, and the unexpected ringing occurs after the shutdown. Moreover, to support slim design, the height of the transformer in the flat power supply is a problem, and the silicon chip drive scheme does not have this problem.
to sum up:
For applications that require energy efficiency, half-bridge topologies using soft-switching technology are increasingly favored by designers. But to drive high-side MOSFETs in a half-bridge topology, designers are faced with the choice of choosing different drivers for their transformers or silicon chips. This paper analyzes the design considerations, related problems and solutions of different drive schemes, and compares the two drive schemes from multiple perspectives. Although well designed, both drive solutions work well, but ON Semiconductor recommends a silicon driver solution such as the NCP5181 to simplify wiring and design while avoiding many of the problems with transformer drive solutions. Personnel shorten the design cycle and speed up the product launch process.
Reference materials:
1. Half-bridge driver: Transformer or full-silicon driver, ON Semiconductor training course, ,%20a%20Transformer-Based%20Solution%20or %20an%20All-Silicon%20Drive%20-%20bilingual.rev0.pdf
2. NCP5181 data sheet, http://
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