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

Preliminary data sheet

Rev. 01 — 28 May 2004

9 of 27

Philips Semiconductors

TEA1532

GreenChip

™II SMPS control IC

regulation (e.g. the control loop is open). In this case activating pin PROTECT

repeated until the fault condition is removed (safe restart mode)

drops below 4.5 V (typical value). The internal overtemperature protection will also

trigger this latch; see also Figure 1.

A voltage higher than 3 V on pin PROTECT will always latch the IC. This is independent of

the state of the IC.

7.13 Valley switching

Refer to Figure 8. A new cycle starts when the power switch is activated. After the on-time

(determined by the sense voltage and the internal control voltage), the switch is opened

and the secondary stroke starts. After the secondary stroke, the drain voltage shows an

oscillation with a frequency of approximately

the drain node.

As soon as the oscillator voltage is high again and the secondary stroke has ended, the

circuit waits for the lowest drain voltage before starting a new primary stroke. This method

is called valley detection. Figure 8 shows the drain voltage, valley signal, secondary stroke

signal and the oscillator signal.

In an optimum design, the reflected secondary voltage on the primary side will force the

drain voltage to zero. Thus, zero voltage switching is possible, preventing large capacitive

switching losses

, and allowing high frequency operation, which

results in small and cost effective magnetics.

1

2

π

×

L

p

C

d

×

(

)

×

(

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

P

1

2

---

CV

2

×

f

×

×

=

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