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© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

Preliminary data sheet

Rev. 01 — 28 May 2004

10 of 27

Philips Semiconductors

TEA1532

GreenChip

™II SMPS control IC

7.14 Brown-out protection

During the so called brown-out test, the input voltage is slowly decreased. Since the

device. This is prevented by stopping the converter when the input voltage drops too low.

When the voltage on pin DEM drops below

−50 mV during the on-time (QR mode), the

maximum on-time is set to 25

µs. The maximum on-time will be reached while V

safe restart can be set with a demag resistor. During the primary stroke, the rectified

mains input voltage is measured by sensing the current drawn from pin DEM. This current

depends on the mains voltage, according to the following formula:

Where:

The latter function requires an on-time of at least 2

µs. This on-time ensures that a reliable

demag current can be measured.

(1) Start of new cycle at lowest drain voltage.

(2) Start of new cycle in a classical PWM system at high drain voltage.

Fig 8.

Signals for valley switching.

drain

secondary

stroke

mgu235

secondary

ringing

primary

stroke

valley

(2)

(1)

secondary

stroke

oscillator

I

DEM

()

V

aux

R

DEM

---------------

NV

mains

×

R

DEM

--------------------------

≈≈

N

N

aux

N

p

------------

=