Power Integrations’ New Switcher IC Family Reduces Standby Power by up to 60%

Power Integrations' (PI) LinkSwitch-TNZ family offers lossless zero-cross detection, offline power conversion, and X-capacitor discharge functions in a single, compact SO-8C package. Members of the series can form the core of universal input isolated flyback designs offering up to 12-watt output or for non-isolated buck and buck-boost power supplies with up to 575 mA output.

Image courtesy of Power Integrations

Appliances Waste Too Much Power in Standby Mode

Because most appliances and Home and Building Automation (HBA) infrastructure equipment spend the majority of their time in standby mode, international regulations set strict limits on standby or no-load consumption.

“The new LinkSwitch-TNZ ICs provide an accurate signal indicating that the sinusoidal AC line is at zero volts. This signal is used by smart home and building automation (HBA) products and appliances to control the switching of relays, IGBTs and TRIACs to minimize switching stress and system in-rush current. LinkSwitch-TNZ’s detection of the zero-cross point consumes less than 5 mW, allowing systems to reduce standby power losses versus alternative approaches that require ten or more discrete components and burn 50 to 100 mW of continuous power," said Adnaan Lokhandwala, product marketing manager at Power Integrations.

What is Zero Crossing?

As an AC signal travels on its sinusoidal pathway from +115V to -115V, it crosses a “sweet spot” of 0 volts. This “zero crossing”  is where an appliance turns on its subsystems, such as motors or compressors, in order to minimize switching losses, inrush current, and a host of other issues. The problem is that circuitry to detect zero crossing, which must always be active, is itself a significant user of power.

Image courtesy of Power Integrations.

With its own integrated lossless AC zero-cross detection feature, LinkSwitch-TNZ ICs cut down on waste. PI states that the use of its TNZ family of ICs for zero-crossing detection instead of discrete circuitry will also cut the component count by 40% or more.

X-Capacitor Discharge

X-capacitors, such as filter capacitors, is connected “line to line”, and as such are charged to a potentially hazardous voltage level. To avoid danger, they often have “bleeder” resistors connected across their terminals to dissipate the accumulated charge. This is a tremendous source of waste, as the bleeders draw away power (and generate heat)  at all times, not just when necessary.

The LinkSwitch-TNZ ICs are capable of discharging the resistors when the time is appropriate, and will not impose a wasteful, continuous power drain.

Members of the LinkSwitch-TNZ

In these descriptions, CCM and MDCM are power supply technologies that stand for “continuous conduction mode” and “mostly discontinuous-mode," respectively.

	Buck Technology	Flyback Technology
	MDCM / CCM	230 VAC / 85-265 VAC
LNK33x2	63 mA / 80 mA	5 Watt / 3 Watt
LNK33x4	120 mA / 170 mA	10 Watt / 6 Watt
LNK33x6	225 mA / 360 mA	18 Watt / 12 Watt
LNK33x7	360 mA / 575 mA	18 Watt / 12 Watt

Getting to Market Faster

PI offers four reference designs employing the LinkSwitch-TNZ IC.

As illustrated, the practical examples offered to utilize the new components in both non-isolated buck and in isolated flyback configurations.

Image courtesy of Power Integrations presentation.