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TEA1533AT データシート(PDF) 8 Page - NXP Semiconductors |
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TEA1533AT データシート(HTML) 8 Page - NXP Semiconductors |
8 / 24 page 2002 Aug 23 8 Philips Semiconductors Product specification GreenChipTMII SMPS control IC TEA1533T; TEA1533AT OverVoltage Protection (OVP) An OVP mode is implemented in the GreenChip series. This works for the TEA1533 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, an internal counter starts counting subsequent OVP events. The counter has been added to prevent incorrect OVP detections which might occur during ESD or lightning events. If the output voltage exceeds the OVP trip level a few times and not again in a subsequent cycle, the internal counter will count down with twice the speed compared with counting up. However, when typical 10 cycles of subsequent OVP events are detected, the IC assumes a true OVP and the OVP circuit switches the power MOSFET off. Next, the controller waits until the UVLO level is reached on pin VCC. When VCC drops to UVLO, capacitor CVCC will be recharged to the Vstart level. Regarding the TEA1533T, this IC will not start switching again. Subsequently, VCC will drop again to the UVLO level, etc. Operation only recommences when the VCC voltage drops below a level of approximately 4.5 V (practically when Vmains has been disconnected for a short period). Regarding the TEA1533AT, switching starts again (safe restart mode) when the Vstart level is reached. This process is repeated as long as the OVP condition exists. The output voltage Vo(OVP) at which the OVP function trips, 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 I(OVP)(DEM) is internally trimmed. The value of RDEM can be adjusted to the turns ratio of the transformer, thus making an accurate OVP possible. Valley switching A new cycle starts when the power MOSFET is switched on (see Fig.8). 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 Lp is the primary self inductance of the transformer and Cd is the capacitance on 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 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. V o OVP () N s N aux ----------- I(OVP)(DEM) RDEM × V clamp(DEM)(pos) + {} = 1 2 π × L p C d × () × ----------------------------------------------- P 1 2 --- CV 2 × f × × = |
同様の部品番号 - TEA1533AT |
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同様の説明 - TEA1533AT |
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