PWM controller cuts drain for CRT TV supplies

A GreenPoint reference design for CRT-TV power supplies delivers standby power of less than 1W.

ON Semiconductor has unveiled a GreenPoint reference design for CRT-TV power supplies that delivers standby power of less than 1W.

This energy-efficient 160W reference design addresses all functional blocks of the power supply and meets international regulations for low standby power dissipation.

"We developed, built and fully tested this CRT-TV power supply reference design to further demonstrate ON Semiconductor's ability to help deliver industry-leading power efficient consumer products to the market", said Andy Williams, Vice President of ON Semiconductor's Power Conversion Division.

"When developing this design - and all our GreenPoint power solutions - we worked closely with our worldwide customers to assure the creation of effective solutions that directly address present and future power needs".

"ON Semiconductor plans to continue to deliver 'green' solutions that ease the design burden on our customers for power supplies that are more and more efficient".

To achieve breakthrough performance, the new CRT-TV GreenPoint reference design uses a number of ON Semiconductor's advanced power management devices and draws from the company's industry-leading discrete component portfolio.

The enabling device for the reference design is the newly introduced NCP1337, an enhanced pulsewidth modulation (PWM) current-mode controller that eases the design of free running quasiresonant power supplies such as those found in CRT-TVs.

It combines a true current-mode modulator and a demagnetisation detector - that ensures full borderline/critical conduction mode in any load/line.

The device eliminates the need for an external signal, by providing internal transformer core reset detection.

Frequency is internally limited to 130kHz to facilitate the compliance with EMI conducted emission standards, the lowest limit being 150kHz.

By monitoring the feedback pin activity, this controller enters ripple mode as soon as the power demand falls below a predetermined level.

The standby power of a 160W CRT TV can be reduced to less than 1W, while adapter no load consumption can match the most strengthens requirements.

Because restart is softened by an internal soft-start and the frequency cannot fall below 25kHz, no audible noise is emitted.

The NCP1337 features an efficient protective circuitry that, in the presence of an overcurrent condition, disables the output pulses and enters a safe burst mode when trying to restart.

Once the default has gone, the device auto-recovers and the power supply resume operation.

Additional features include a bulk voltage monitoring function known as brown-out protection, an adjustable overpower compensation that tackles the effect of the input voltage variation on the maximum power a quasiresonant PSU can deliver, and overvoltage protection on the Vcc.

An internal 4.0ms soft-start eliminates the traditional startup stress.

The NCP1337 is ideal use in power supplies in CRT-TVs, notebook AC/DC adapters, offline battery chargers, other consumer electronics such as DVD players and set-top boxes, and any power supply where efficiency and low EMI signature are needed.

The device is offered in both an SOIC-7 and a PDIP-7 package and priced at $1.04 per unit in 2500 unit quantities.

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