Power Integrations ZVS controller needs no external parts
Power Integrations has developed a controller for zero voltage switching (ZVS) that needs no additional external parts.
The two variants in the InnoSwitch5-Pro family developed by Power Integrations support VZS power adaptor designs up to 135W and 220W for the emerging USB PD EPR (Extended Power Range) protocol.
“With more power and smaller size we need to increase efficiency. Now we are over 95% efficiency using PowiGaN transistors with ZVS and variable frequency control,” Andy Smith, director of training at Power Integrations tells eeNews Power.
“Rapid charging and all the different standards are causing strong growth in the market with a doubling of design slots before 2028. Notebook adaptors are adopting USB-PD so its growing into new areas that require a lot more power than cell phones and new standards such as UFCS in China mean we have to work with a wider range of standards.
- Taking GaN over 1200V
- Programmable ZVS power-supply ICs in small form factor
- 900V GaN flyback switcher ICs eliminate need for heat sink
The key thing is the ability to control both the primary and secondary sides very accurately.
“Implementing ZVS without adding components is the interesting part,” he said. “Normally you need current flow to discharge the primary side but we use the secondary side synchronous transistor in an unconventional way. Because we control both switches we turn that secondary side transistor on briefly just before we switch the primary transistor and the timing of that is critical.”
“The benefit of this is we don’t need other components, The tricky part is controlling precisely the switching so you discharge all the charge in the primary switch but don’t risk conduction for a few microseconds. It’s also variable so we dynamically adjust it as the load conditions change.”
Compared to quasiresonant (QR) switching this gives a 0.5 to 0.6% improvement in efficiency at high line which is a 12% reduction in heat, he says. “That’s what you would get with an active clamp circuit with more components.”
An enhanced I2C interface uses the system microcontroller for the power conversion algorithm.
“The 5-Pro has an I2C interface so it doesn’t care what algorithm you use, so it just responds to the I2C commands so the nuances of the different standards don’t matter to us and we’ll work with anything,” he said. “The difference for this version of Pro is the higher efficiency and tweaks in the output current and voltage steps and some of the I2C functions have been tweaked to reduce the bus traffic. We also do telemetry reporting with 20bit storage in the IC to tell developers why there is a shutdown. That’s very useful when you are debugging designs.
The response to faults in the system is managed by the 5-pro and this is dependent on the control algorithm.
The InnoSwitch5 family has GaN transistors rated at either 750 or 900V.
“We do 900V because India wants more headroom. The different devices we scale the size of the primary side transistor for more power and lower conduction loss. There is almost no difference in the performance of the switch,” said Smith.
“750V is standard for a 265V to address the reflections with some headroom. In some areas you get voltage swells up from 240 to 400V with mismatches between phases so what happens increasingly if people are making an adaptor for India they want more headroom.”
The INN53 family supports voltages up to 265V and power up to 135W without power factor correction (PFS). The INN54 family supports PFC at 385V up to 220W.
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