TEA1507 Philips Semiconductors, TEA1507 Datasheet - Page 8

• Manufacturer Part Number: TEA1507
• Description: GreenChipII SMPS control IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
OverVoltage Protection (OVP)
An OVP mode is implemented in the GreenChip
For the TEA1507, this works by sensing the auxiliary
voltage via the current flowing into pin DEM during the
secondary stroke. The auxiliary winding voltage is a
well-defined replica of the output voltage. Any voltage
spikes are averaged by an internal filter.
If the output voltage exceeds the OVP trip level, the OVP
circuit switches the power MOSFET off. Next, the
controller waits until the UVLO level is reached on pin V
This is followed by a safe restart cycle, after which
switching starts again. This process is repeated as long as
the OVP condition exists.
The output voltage at which the OVP function trips, V
can be set by the demagnetization resistor, R
Where N
number of auxiliary turns of the transformer.
Current I
The value of the demagnetization resistor (R
adjusted to the turns ratio of the transformer, thus making
an accurate OVP possible.
OverCurrent Protection (OCP)
The cycle-by-cycle peak drain current limit circuit uses the
external source resistor to measure the current accurately.
This allows optimum size determination of the transformer
core (cost issue). The circuit is activated after the leading
edge blanking time, t
the ‘sense’ voltage to an internal level.
OverPower Protection (OPP)
During the primary stroke, the rectified mains input voltage
is measured by sensing the current drawn from pin DEM.
This current is dependent on the mains voltage, according
to the following formula:
Where:
The current information is used to adjust the peak drain
current, which is measured via pin I
compensation is such that an almost mains independent
maximum output power can be realized.
The OPP curve is given in Fig.8.
2000 Dec 05
V
o OVP
GreenChip II SMPS control IC
N
s
ref
=
is the number of secondary turns and N
=
is internally trimmed.
-----------
N
N
aux
N
----------- -
s
N
aux
p
I
(OVP)(DEM)
leb
. The OCP protection circuit limits
I
DEM
R
-------------- -
R
DEM
V
DEM
sense
aux
+
V
. The internal
clamp DEM pos
N V
--------------------------
R
DEM
DEM
DEM
mains
) can be
aux
:
series.
o(OVP)
is the
CC
.
8
Short winding protection
After the leading edge blanking time, the short winding
protection circuit is also activated. If the ‘sense’ voltage
exceeds the short winding protection voltage V
converter will stop switching. Once V
UVLO level, capacitor C
supply will restart again. This cycle will be repeated until
the short circuit is removed (safe restart mode).
The short winding protection will also protect in case of a
secondary diode short circuit.
Overtemperature protection
An accurate temperature protection is provided in the
circuit. When the junction temperature exceeds the
thermal shutdown temperature, the IC will stop switching.
When V
recharged to the V
high, V
restart mode).
Operation recommences when the junction temperature
drops 8 degrees typically.
handbook, halfpage
CC
MGU236
CC
100 A
(typ)
will drop again to the UVLO level, etc. (safe
drops to UVLO, capacitor C
Fig.8 OPP correction curve.
start
I DEM
level. If the temperature is still too
VCC
will be recharged and the
24 A
(typ)
Preliminary specification
CC
VCC
drops below the
0.50 V
(typ)
0.3 V
(typ)
V sense(max)
TEA1507
will be
swp
, the