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NCP1608 Datasheet(PDF) 12 Page - ON Semiconductor |
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NCP1608 Datasheet(HTML) 12 Page - ON Semiconductor |
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12 / 24 page  NCP1608 http://onsemi.com 12 When the switch is closed, the inductor current increases linearly to the peak value. When the switch opens, the inductor current linearly decreases to zero. When the inductor current decreases to zero, the drain voltage of the switch (Vdrain) is floating and begins to decrease. If the next switching cycle does not begin, then Vdrain rings towards Vin. A derivation of equations found in AND8123 leads to the result that high power factor in CrM operation is achieved when the on time (ton) of the switch is constant during an ac cycle and is calculated using Equation 1. ton + 2 @ Pout @ L h @ Vac2 (eq. 1) Where Pout is the output power, L is the inductor value, h is the efficiency, and Vac is the rms input voltage. A description of the switching over an ac line cycle is illustrated in Figure 28. The on time is constant, but the off time varies and is dependent on the instantaneous line voltage. The constant on time causes the peak inductor current (IL(peak)) to scale with the ac line voltage. The NCP1608 represents an ideal method to implement a constant on time CrM control in a cost−effective and robust solution by incorporating an accurate regulation circuit, a low current consumption startup circuit, and advanced protection features. Figure 28. Inductor Waveform During CrM Operation ON OFF MOSFET Iin(t) IL(t) Vin(t) Vin(peak) IL(peak) Iin(peak) Error Amplifier Regulation The NCP1608 regulates the boost output voltage using an internal error amplifier (EA). The negative terminal of the EA is pinned out to FB, the positive terminal is connected to a 2.5 V ± 1.6% reference (VREF), and the EA output is pinned out to Control (Figure 29). A feature of using a transconductance error amplifier is that the FB pin voltage is only determined by the resistor divider network connected to the output voltage, not the operation of the amplifier. This enables the FB pin to be used for sensing overvoltage or undervoltage conditions independently of the error amplifier. Figure 29. Error Amplifier and On Time Regulation Circuits FB Control EA PWM BLOCK gm UVP OVP OVP Fault (Enable EA) UVP Fault CCOMP VControl VREF Vout Rout1 Rout2 RFB ton ton(MAX) + − + − + − VOVP VUVP POK VControl VEAH Ct(offset) tPWM Slope + Ct Icharge |
Similar Part No. - NCP1608_10 |
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Similar Description - NCP1608_10 |
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