tea1506 NXP Semiconductors, tea1506 Datasheet - Page 9

• Manufacturer Part Number: tea1506
• Description: Greenchip Smps Control Ic
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Valley switching
A new cycle starts when the power MOSFET is switched
on (see Fig.9). After the ‘on-time’ (which is 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
where L
and C
As soon as the oscillator voltage is high again and the
secondary stroke has ended, the circuit waits for the
2003 Sep 09
handbook, full pagewidth
GreenChip II SMPS control IC
A: Start of new cycle at lowest drain voltage.
B: Start of new cycle in a classical PWM system at high drain voltage.
d
is the capacitance on the drain node.
p
is the primary self inductance of the transformer
secondary
oscillator
stroke
valley
drain
---------------------------------------------- -
2
primary
stroke
Fig.9 Signals for valley switching.
1
L
p
secondary
stroke
C
d
9
lowest drain voltage before starting a new primary stroke.
This method is called valley detection.
Figure 9 shows the drain voltage together with the valley
signal, the signal indicating the secondary stroke 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 very possible, preventing large
capacitive switching losses
and allowing high frequency operation, which results in
small and cost effective inductors.
secondary
ringing
TEA1506P; TEA1506AP;
B
TEA1506T; TEA1506AT
MGU235
A
P
=
1
-- -
2
Product specification
C V
2
f