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AN3142 Arkusz danych(PDF) 7 Page - STMicroelectronics |
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AN3142 Arkusz danych(HTML) 7 Page - STMicroelectronics |
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7 / 44 page ![]() AN3142 The circuit implementing the line-modulated fixed-off-time with the new L6563S Doc ID 17005 Rev 3 7/44 Equation 3 and V''ZCD(t) decreases from Vmult+VBE to VZCDtrigger = 0.7 V level in the following time period t'': Equation 4 Figure 7 illustrates the signal on the ZCD pin with the two discharging time constants depending on the two resistors R, R0 and the L6563S parameters, particularly the upper clamp voltage and the triggering voltage of the ZCD pin. Figure 7. ZCD pin signal with the fixed off-time generator circuit The sum of the two time periods is the off-time function: Equation 5 In this way, once the multiplier operating point (that is, the Vmult / VAC ratio) is fixed, with a proper selection of R and R0 it is possible to increase TOFF with the line voltage so that, at maximum line voltage, it is always TON>TONmin = 450 ns for the L6563S [4]. This is a condition needed in order to avoid line distortion [ 5]. () () ⎥⎥⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⋅ + − + ⋅ ⋅ + ⋅ ⋅ + ⋅ − = ′ R V V ) R R ( V R V V ln C R R R R t BE mult 0 ZCDclamp 0 BE mult 0 0 ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + ⋅ − = ′′ BE mult ZCDtrigger V V V ln RC t () () () ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟⎟⎠ ⎞ ⎜⎜⎝ ⎛ + + ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⋅ + − + ⋅ ⋅ + ⋅ + ⋅ − = BE mult ZCDtrigger BE mult 0 ZCDclamp 0 BE mult 0 0 OFF V V V ln R V V ) R R ( V R V V ln R R R RC T |
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