Version 4.1 SHEET 1 3696 680 WIRE -32 -608 -64 -608 WIRE 96 -608 48 -608 WIRE 96 -592 96 -608 WIRE -64 -512 -64 -608 WIRE -64 -400 -64 -512 WIRE -336 -352 -384 -352 WIRE -272 -352 -336 -352 WIRE -144 -352 -192 -352 WIRE 96 -352 96 -512 WIRE 96 -352 -48 -352 WIRE 160 -352 96 -352 WIRE 176 -352 160 -352 WIRE 272 -352 176 -352 WIRE 384 -352 336 -352 WIRE 448 -352 384 -352 WIRE 496 -352 448 -352 WIRE -384 -288 -384 -352 WIRE 384 -288 384 -352 WIRE 496 -288 496 -352 WIRE 160 -256 160 -352 WIRE -384 -112 -384 -208 WIRE 160 -112 160 -176 WIRE 160 -112 -384 -112 WIRE 384 -112 384 -224 WIRE 384 -112 160 -112 WIRE 496 -112 496 -208 WIRE 496 -112 384 -112 WIRE -384 -64 -384 -112 FLAG -384 -64 0 FLAG -64 -512 V_gate FLAG 176 -352 V_inductor FLAG 448 -352 V_out FLAG -336 -352 V_in SYMBOL ind 176 -272 M0 SYMATTR InstName L1 SYMATTR Value 100µ SYMATTR SpiceLine Rser=1m SYMBOL nmos -144 -400 M90 WINDOW 3 56 72 Invisible 2 SYMATTR Value BSC600N25NS3 SYMATTR InstName M1 SYMBOL diode 336 -368 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMBOL cap 368 -288 R0 SYMATTR InstName C1 SYMATTR Value 100µ SYMBOL res 480 -304 R0 SYMATTR InstName R_Load SYMATTR Value 10R SYMBOL voltage -384 -304 R0 SYMATTR InstName V_in SYMATTR Value 100V SYMBOL voltage 96 -608 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 -97 119 Left 2 SYMATTR Value PULSE(0 10 0 10n 10n 4u 10u) SYMATTR InstName V_control SYMBOL res 64 -624 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 2R SYMBOL res -288 -368 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R_in_Isense SYMATTR Value 1m TEXT -168 -1368 Left 5 ;The flyback SMPS topology. TEXT -464 -552 Left 2 !.tran 0 5m 4m TEXT 736 -552 Left 4 ;uses of the flyback TEXT 744 -504 Left 2 ;the flyback is an inverting topology.\nhowever it becomes more usefull when the inductor becomes a coupled inductor with two or more isolated windings.\nit can then have many secondary windings and hence many outputs, they don't have to be inverting as you just \nswap their terminals.\nAs the transformer secondaries can be closely magnetically coupled to each other, the voltages on these outputs \nthen closely track each other, as there are no inductors between the transformer and the outputs. TEXT 808 -1032 Left 2 ;This simulation is the circuit in its simplest form with no control loop, \nno synchronous rectification, and no input output isolation, its too simple to be a practical \ncircuit, but I have deliberately kept things simple in order to explain the basic topology.\n \nAt the start of the cycle the FET turns on and applies the input voltage to the inductor, \nthis builds the inductor current up,\nthe FET then turns off so the input voltage is disconnected from the inductor,\nso the inductor current then switches to the diode, this creates the output voltage, \nif the input voltage is positive then the output voltage has to be negative.\n \nThe settled output Voltage is calculated from the voltage across the inductor averaging to \nzero Volts over a cycle, as otherwise the circuit has not settled to its steady state condition. TEXT -464 -1088 Left 4 ;Instructions TEXT -464 -1040 Left 2 ;click on run\nwhile holding the mouse key down, click on V_gate then drag the mouse \nacross to V_inductor and release,\nthis should plot V_gate - V_inductor\nthis is the voltage that turns the FET on and off.\nclick on the plot window, then on plot settings/add plot pane.\nthen click on "V_in" to plot its Voltage\nthen click on "V_out" to plot its Voltage\nthen click on "V_inductor" to plot its Voltage\nZoom the time axis so you can see the individual cycles\nyou can see that the inductor voltage switches between Vin and Vout.\nVin and Vout are of opposite polarity and the average inductor voltage is zero.\nclick on the plot window, then on plot settings/add plot pane.\nthen click on "L1" to plot its current TEXT 800 -1080 Left 4 ;Simple circuit description. TEXT 808 -672 Left 2 ;If the load current becomes less than half the inductor ripple current then the description of the \ncircuit operation changes, see the section "Discontinuous inductor current", in the text file that \naccompanies this circuit. TEXT -328 -1304 Left 4 ;The flyback inverts the input voltage to create a negative output Voltage, \nbut if you make the inductor a "coupled inductor" with 2 or more isolated windings, then it doesn't have to invert.\nStart off with the "Instructions" section to plot some waveforms, \nThen the rest of the text might make more sense.