Version 4.1 SHEET 1 2884 1232 WIRE 384 -368 352 -368 WIRE 496 -368 464 -368 WIRE 688 -368 560 -368 WIRE -768 -352 -800 -352 WIRE -496 -352 -768 -352 WIRE -368 -352 -416 -352 WIRE -240 -352 -368 -352 WIRE -160 -352 -240 -352 WIRE 80 -352 -160 -352 WIRE 80 -336 80 -352 WIRE -800 -288 -800 -352 WIRE -368 -288 -368 -352 WIRE -240 -288 -240 -352 WIRE 1376 -272 992 -272 WIRE 80 -224 80 -256 WIRE 144 -224 144 -256 WIRE 144 -224 80 -224 WIRE 192 -224 144 -224 WIRE 352 -224 352 -368 WIRE 352 -224 272 -224 WIRE 400 -224 352 -224 WIRE 992 -224 992 -272 WIRE 688 -208 688 -368 WIRE 688 -208 576 -208 WIRE 736 -208 688 -208 WIRE 1616 -192 1568 -192 WIRE 1744 -192 1616 -192 WIRE 80 -176 80 -224 WIRE 1568 -160 1568 -192 WIRE 576 -144 576 -208 WIRE 400 -128 352 -128 WIRE 352 -96 352 -128 WIRE -800 -16 -800 -208 WIRE -512 -16 -800 -16 WIRE -368 -16 -368 -224 WIRE -368 -16 -512 -16 WIRE -240 -16 -240 -208 WIRE -240 -16 -368 -16 WIRE 1568 -16 1568 -80 WIRE 80 16 80 -96 WIRE 352 16 352 -16 WIRE 352 16 80 16 WIRE 576 16 576 -64 WIRE 576 16 352 16 WIRE 848 16 576 16 WIRE 992 16 992 -144 WIRE 992 16 848 16 WIRE -512 32 -512 -16 WIRE 848 80 848 16 WIRE 448 448 416 448 WIRE 560 448 528 448 WIRE 752 448 624 448 WIRE -704 464 -736 464 WIRE -560 464 -704 464 WIRE -432 464 -480 464 WIRE -304 464 -432 464 WIRE -176 464 -304 464 WIRE -96 464 -176 464 WIRE 144 464 -96 464 WIRE 144 480 144 464 WIRE -736 528 -736 464 WIRE -432 528 -432 464 WIRE -176 528 -176 464 WIRE -304 544 -304 464 WIRE 1440 544 1056 544 WIRE 144 592 144 560 WIRE 208 592 208 560 WIRE 208 592 144 592 WIRE 256 592 208 592 WIRE 416 592 416 448 WIRE 416 592 336 592 WIRE 464 592 416 592 WIRE 1056 592 1056 544 WIRE 752 608 752 448 WIRE 752 608 640 608 WIRE 800 608 752 608 WIRE 1680 624 1632 624 WIRE 1808 624 1680 624 WIRE 144 640 144 592 WIRE 1632 656 1632 624 WIRE 640 672 640 608 WIRE -304 688 -304 624 WIRE 464 688 416 688 WIRE 416 720 416 688 WIRE -736 800 -736 608 WIRE -576 800 -736 800 WIRE -432 800 -432 592 WIRE -432 800 -576 800 WIRE -304 800 -304 752 WIRE -304 800 -432 800 WIRE -176 800 -176 608 WIRE -176 800 -304 800 WIRE 1632 800 1632 736 WIRE 144 832 144 720 WIRE 416 832 416 800 WIRE 416 832 144 832 WIRE 640 832 640 752 WIRE 640 832 416 832 WIRE 912 832 640 832 WIRE 1056 832 1056 672 WIRE 1056 832 912 832 WIRE -576 848 -576 800 WIRE 912 896 912 832 FLAG -160 -352 power_supply_output FLAG 848 80 0 FLAG -512 32 0 FLAG -768 -352 Vin FLAG 736 -208 error FLAG 1376 -272 power_trafo_pri FLAG 144 -256 pot_divided FLAG 400 -224 inv FLAG 400 -128 non_inv FLAG 1616 -192 power_trafo_sec FLAG 1568 -16 0 FLAG -96 464 power_supply_output-1 FLAG 912 896 0 FLAG -576 848 0 FLAG -704 464 Vin-1 FLAG 800 608 error-1 FLAG 1440 544 power_trafo_pri-1 FLAG 208 560 pot_divided-1 FLAG 464 592 inv-1 FLAG 464 688 non_inv-1 FLAG 1680 624 power_trafo_sec-1 FLAG 1632 800 0 SYMBOL ind -400 -368 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 39 60 56 VTop 2 SYMATTR InstName L1 SYMATTR Value 100µ SYMATTR SpiceLine Rser=1m SYMBOL cap -384 -288 R0 WINDOW 39 -24 82 Left 2 SYMATTR SpiceLine Rser=20m SYMATTR InstName C1 SYMATTR Value 100µ SYMBOL res -256 -304 R0 SYMATTR InstName R1 SYMATTR Value 10R SYMBOL res 96 -352 M0 SYMATTR InstName R3 SYMATTR Value 14k SYMBOL res 96 -192 M0 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL res 176 -240 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL cap 496 -384 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 220n SYMBOL res 368 -384 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL voltage -800 -304 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value ac 1. SYMBOL bv 992 -240 M0 WINDOW 3 -90 113 Left 2 SYMATTR Value V=24.5*V(error) SYMATTR InstName B1 SYMBOL bv 576 -160 M0 WINDOW 3 -195 111 Left 2 SYMATTR Value V=1E6*(V(non_inv)-V(inv)) SYMATTR InstName B2 SYMBOL res 368 -112 M0 SYMATTR InstName R7 SYMATTR Value 1m SYMBOL bv 1568 -176 M0 WINDOW 3 -90 113 Left 2 SYMATTR Value V=0.5*V(power_trafo_pri) SYMATTR InstName B5 SYMBOL ind -464 448 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 39 60 56 VTop 2 SYMATTR InstName L2 SYMATTR Value 100µ SYMATTR SpiceLine Rser=1m SYMBOL cap -448 528 R0 WINDOW 39 -24 82 Left 2 SYMATTR SpiceLine Rser=20m SYMATTR InstName C2 SYMATTR Value 100µ SYMBOL res -192 512 R0 SYMATTR InstName R2 SYMATTR Value 10R SYMBOL res 160 464 M0 SYMATTR InstName R8 SYMATTR Value 14k SYMBOL res 160 624 M0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL res 240 576 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL cap 560 432 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 22n SYMBOL res 432 432 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 10k SYMBOL voltage -736 512 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value ac 1. SYMBOL bv 1056 576 M0 WINDOW 3 -90 113 Left 2 SYMATTR Value V=24.5*V(error-1) SYMATTR InstName B3 SYMBOL bv 640 656 M0 WINDOW 3 -195 111 Left 2 SYMATTR Value V=1E6*(V(non_inv-1)-V(inv-1)) SYMATTR InstName B4 SYMBOL res 432 704 M0 SYMATTR InstName R12 SYMATTR Value 1m SYMBOL bv 1632 640 M0 WINDOW 3 -90 113 Left 2 SYMATTR Value V=0.5*V(power_trafo_pri-1) SYMATTR InstName B6 SYMBOL cap -320 688 R0 SYMATTR InstName C5 SYMATTR Value 330µ SYMBOL res -320 528 R0 SYMATTR InstName R13 SYMATTR Value 1R TEXT 744 -440 Left 2 ;this voltage gain of 49/2=24.5 is from\nthe input voltage divided by\nthe peak to peak sawtooth Voltage\nwe take half the input voltage as a half bridge\nonly puts half the input voltage\nacross the power tranformer primary. TEXT -464 -1328 Left 5 ;UC2875 full bridge, phase shift control, loop response, TEXT -1024 976 Left 2 !.ac dec 100 10 100k TEXT -808 -1248 Left 2 ;firstly we have to add realistic ESR to the output capacitors, I have put this in as 20 m Ohms.\nthen running this sim as is shows two problems.\nthe peak in the response of the LC filter which could cause ringing or oscillations at 750hz\nrequires to be damped.\nthe loop does not have enough bandwidth, this will make the power supply respond slowly to transients, \nso the resulting output voltage transients will be larger and last longer. \nfor the damping \n...in parrallel with the output capacitor, add a larger capacitor with a resistor in series\nthe convention is to add 3 times the present value of C, \nthe additional R in series is the impedance of the inductor at the 1.6khz resonant freq, this is 1 Ohm.\nadding this has removed the peaky response of the LC filter.\nin order to increase the bandwidth of the control loop, in the error amp circuit, increase the output R and C impedances.\n \nNow check that hte control loop is stable, so that it won't oscillate or ring.\nthat is check what the phase is when the gain goes through 0db, this is called the phase margin, this should be at least 25 degrees.\nif the phase goes through zero then check how much below 0dbs the gain is at this point, this is called the phase margin.\nfor this example the phase margin is about 30 degrees.\nthere is no gain margin as the phase does not go through 0 degrees. TEXT -688 -488 Left 4 ;LC filter and load TEXT -64 -496 Left 4 ;potential divider and error amp TEXT 840 -568 Left 4 ;supply volts\n/p-p sawtooth Volts TEXT -80 -592 Left 5 ;Original control loop TEXT -128 128 Left 5 ;Improved control loop TEXT -624 328 Left 4 ;LC filter and load TEXT 0 320 Left 4 ;potential divider and error amp TEXT 928 312 Left 4 ;supply volts\n/p-p sawtooth Volts TEXT -448 136 Left 2 ;changes are\nadding the RC (capacitive damper) in parallel with the output cap.\nThe capacvitor around the error amp behaves as an integrator,\nincreasing low frequency gain, I have reduced the value of this capacitor to give more low freq gain\nand to make this gain continue out to a higher frequency, \nthis makes the power supply settle to its output voltage more quickly LINE Normal 528 -304 528 -304 2 LINE Normal 592 512 592 512 2 RECTANGLE Normal -144 80 -688 -464 2 RECTANGLE Normal 720 80 0 -464 2 RECTANGLE Normal 1344 112 832 -464 2 RECTANGLE Normal -80 896 -624 352 2 RECTANGLE Normal 784 896 64 352 2 RECTANGLE Normal 1408 928 896 352 2