The use of integrated nitride-gallium (GaN) switches in highly efficient, economical offline power supplies.

For flyback offline power supply designers, the challenge is to ensure durability and reliability while further reducing costs, improving efficiency and reducing size to increase power density.

01.10.2021
 

The range of applications for compact 100-watt power supplies continues to grow, from AC chargers and AC adapters, USB Power Delivery (PD) chargers and fast charging (QC) adapters, to LED lighting, home appliances, motor drives, smart meters and industrial systems . For flyback offline power supply designers, the challenge is to ensure durability and reliability while further reducing costs, improving efficiency and reducing size to increase power density.

To solve many of these problems, designers can replace silicon (Si) power switches with devices based on wide band gap (WBG) technologies such as gallium nitride (GaN). This translates directly into an improvement in power efficiency and a reduction in cooling demand, which allows for an increase in power density. However, controlling nitride-gallium (GaN) switches is more difficult compared to silicon (Si) switches.

Designers can overcome fast switching problems such as parasitic capacitance and inductance and high frequency oscillations, but this requires additional time and cost. Instead, designers can choose high-degree offline flyback switching ICs with built-in gallium nitride (GaN) power devices.

This article briefly reviews the advantages of GaN technology and the challenges of designing it. Next, three offline flyback switching IC platforms with internal GaN power switches from Power Integrations were shown and how they can be used to manufacture high-efficiency power converters. Complementary MinE-CAP ICs for storage capacitor miniaturization and surge current management are discussed, as well as a useful online design environment.

What is Gallium Nitride (GaN) and what are its advantages?

Gallium nitride (GaN) is a wide band gap semiconductor material (WBG) which, compared to silicon (Si), has a low on-state resistance, high breakdown strength, fast switching and high thermal conductivity. The use of gallium nitride (GaN) in place of silicon (Si) enables the production of switches that have significantly lower switching losses on on and off. Moreover, GaN devices with equivalent resistance are much smaller than their silicon counterparts. As a result, for a given structure size, the GaN power switch has lower combined conduction losses and switching losses (Figure 1).


Figure 1: For a given structure size, GaN devices have lower turn-on resistance leading to lower total losses compared to silicon MOSFETs. (Image source: Power Integrations)

Gallium nitride (GaN) technology has distinct advantages, but it can be difficult to design for its application. For example, because of the extremely fast switching of GaN devices, control circuit systems can be very sensitive to capacitances and parasitic inductances from the circuit board and from discrete GaN systems. The rapid voltage spikes (dv / dt) and high frequency oscillations that can occur when controlling GaN devices generate greater electromagnetic interference (EMI) that must be filtered out to prevent inverter performance degradation. Moreover, the fast switching of GaN devices makes it difficult to protect them from disturbances, as they can be damaged sooner than the protection circuits can react.

 
 

Simplicity without sacrificing performance

Power Integrations solved these problems with the PowiGaN quasi-resonant switching chips: InnoSwitch3-CP, InnoSwitch3-EP, and InnoSwitch3-Pro (Figure 2). PowiGaN is a GaN power switch technology developed by Power Integrations that replaces the traditional primary silicon transistors in InnoSwitch3 offline flyback switching integrated circuits. Instead, it integrates primary, secondary, and feedback circuits in a single InSOP-24D surface-mounted (SMD) housing. In this way, the devices reduce driver chip complexity and electromagnetic interference (EMI) emissions while reducing conduction and switching losses, enabling the use of more efficient, lighter, smaller power supplies and chargers, and open frame power supplies.

Figure 2: Offline InnoSwitch3 flyback switching ICs with GaN switches are shipped in the space-saving InSOP-24D housing. (Image credit: Power Integrations)

The use of this approach allows power supply designers to focus on issues of power delivery, thermal performance, dimensions and other aspects of the application without addressing the difficulties of gallium nitride (GaN) technology.

The three InnoSwitch3 groups with PowiGaN technology are optimized for specific application classes:

  • The InnoSwitch3-CP is designed for applications such as battery charging that can use a fixed power profile.
  • The InnoSwitch3-EP is designed for open frame AC / DC power supplies in a wide range of consumer and industrial applications.
  • The InnoSwitch3-Pro devices have an I²C digital interface for the control of constant voltage (CV) and constant current (CC) setpoints, safety mode options and exception handling via software.

The InnoSwitch3 ICs feature quasi-resonant control, up to 95% efficiency over the full load range, and support accurate constant voltage (CV), constant current (CC) and constant power (CP) outputs to meet the needs of a wide variety of applications. They also incorporate lossless current measurement technology. The technology also eliminates the need for external current sensing resistors that degrade efficiency and that may even exceed the resistance of many GaN switches in discrete circuits.

Other key features of these switches are: secondary side measurement, dedicated driver for MOSFET transistors with synchronous rectification, integrated FluxLink inductive feedback connector between primary and secondary drivers with insulation> 4000V AC (V ~), compliance with global requirements in energy efficiency, low electromagnetic interference (EMI), compliance with regulations and safety standards (UL1577 and TUV approval (EN60950 and EN62368) and instantaneous impulse response for 100% load steps.

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