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LTC3766 数据表(PDF) 13 Page - Linear Technology |
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LTC3766 数据表(HTML) 13 Page - Linear Technology |
13 / 48 page LT8311 13 8311f For more information www.linear.com/LT8311 OPERATION TheLT8311controlsthesynchronousMOSFETsandopto- coupler on the secondary side of a forward converter. SynchronouscontroloflowRDS(ON)MOSFETscantypically lead to lower power dissipation in forward converters. The lower power dissipation can improve converter efficiency, resultinginlongtermcostsavingsbyloweringinputpower requirements to support a certain level of output power. Improved efficiency can also reduce the size of heat sinks required to dissipate the heat generated in the rectifiers; consequentlyincreasingtheoperatingambienttemperature rangewhichmaybeusefulinmanyindustrialapplications. The LT8311 also offers opto-coupler control for accurate output voltage regulation over line and load. The LT8311’s opto-couplercontrolcircuitrycomeswithahostofstart-up and steady-state functions to ensure robust transient re- sponseduringpower-onandoutputshort-circuitrecovery. FUNDAMENTALS OF FORWARD CONVERTER OPERATION IN CCM The timing diagram of a forward converter operating in continuous conduction mode (CCM) is shown in Figure 2. Thetimingdiagramisbrokenintosixregionsofoperation. Please refer to Figures 1 and 2 for the following explana- tion of each region of operation. Region 1 (Figure 2) When OUT goes high, M1 turns on. CG should already be at 0V before OUT goes high, to ensure that MCG does not cross conduct with M1. The LT8311’s preactive mode, which will be explained later, is an innovative scheme to turn off MCG before M1 turns on. FG must be high during this period to keep the forward MOSFET, MFG on, thereby conducting the output inductor current, ILOUT, (via the transformer’s secondary winding) through a low imped- ance path. During this phase, magnetizing current, ILMAG, builds up in the transformer’s magnetic core, and flows from VIN to GND through M1. Output inductor current, ILOUT, ramps up at a rate of (VCSW – VOUT)/ LOUT. Region 2 (Figure 2) When OUT goes low, and turns off M1, the transformer becomes high impedance, and stops conducting ILOUT. Since current in the output inductor cannot go to zero instantaneously, it pulls the drain of the catch MOSFET, CSW, towards ground. Ultimately CSW gets clamped at a diode voltage below ground by MCG’s body diode which nowsourcestheoutputinductorcurrent(similartoacatch diode in a traditional buck converter). CSW collapsing equivalently causes the transformer’s secondary winding voltage to become smaller. Through transformer action, Figure 1. Forward Converter with Active Clamp Reset (in Red) or Resonant Reset (in Blue) 8311 F01 VIN VDRAIN_M2 • • NS NP PRIMARY IC OUT VOUT COUT LOUT ILOUT CSW SECONDARY IC FSW SWP ILMAG LMAG MFG M1 RLOAD MCG VCL CCL AOUT M2 CAOUT CRST D2 FG CG ACTIVE CLAMP RESET (RED) RESONANT RESET (BLUE) + – |
类似零件编号 - LTC3766 |
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类似说明 - LTC3766 |
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