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TEA1507P Folha de dados(PDF) 8 Page - NXP Semiconductors |
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TEA1507P Folha de dados(HTML) 8 Page - NXP Semiconductors |
8 / 20 page 2000 Dec 05 8 Philips Semiconductors Preliminary specification GreenChip ™II SMPS control IC TEA1507 OverVoltage Protection (OVP) An OVP mode is implemented in the GreenChip ™ series. 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: 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: Where: 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. 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. V o OVP () N s N aux ----------- I (OVP)(DEM) R DEM V clamp DEM () pos () + × () × = I DEM () V aux R DEM --------------- NV mains × R DEM -------------------------- ≈≈ N N aux N p ------------ = handbook, halfpage MGU236 0.50 V (typ) 0.3 V (typ) IDEM Vsense(max) −24 µA (typ) −100 µA (typ) Fig.8 OPP correction curve. |
Nº de peça semelhante - TEA1507P |
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Descrição semelhante - TEA1507P |
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