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TEA1507P View Datasheet(PDF) - Philips Electronics

Part Name
Description
Manufacturer
TEA1507P
Philips
Philips Electronics Philips
TEA1507P Datasheet PDF : 20 Pages
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Philips Semiconductors
GreenChipII SMPS control IC
Preliminary specification
TEA1507
OverVoltage Protection (OVP)
An OVP mode is implemented in the GreenChipseries.
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 VCC.
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, Vo(OVP)
can be set by the demagnetization resistor, RDEM:
Vo(OVP) = N---N--a---us--x- × (I(OVP)(DEM) × RDEM + Vclamp(DEM)(pos))
Where Ns is the number of secondary turns and Naux is the
number of auxiliary turns of the transformer.
Current Iref is internally trimmed.
The value of the demagnetization resistor (RDEM) can be
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, tleb. The OCP protection circuit limits
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: I(DEM) R--V---D--a--Eu---xM-- N------×-R----VD----Em---M-a---i-n--s-
Where: N = -N--N--a---pu---x
The current information is used to adjust the peak drain
current, which is measured via pin Isense. The internal
compensation is such that an almost mains independent
maximum output power can be realized.
The OPP curve is given in Fig.8.
MGU236
handbook, halfpage
Vsense(max)
0.50 V
(typ)
0.3 V
(typ)
100 µA
(typ)
IDEM
24 µA
(typ)
Fig.8 OPP correction curve.
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 Vswp, the
converter will stop switching. Once VCC drops below the
UVLO level, capacitor CVCC will be recharged and the
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 VCC drops to UVLO, capacitor CVCC will be
recharged to the Vstart level. If the temperature is still too
high, VCC will drop again to the UVLO level, etc. (safe
restart mode).
Operation recommences when the junction temperature
drops 8 degrees typically.
2000 Dec 05
8
 

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