48v isolated dc/dc converter

This will have to work at up to 200 watts maybe; 48 in and out.

Those surface-mount Coilcraft planar transformers are wonderful.

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I suspect some air flow can sneak in between the flat kapton windings. I guess I should include the leakage inductances, but they are tiny.

The LTC gate drivers are a bit expensive but they work really nice. And they have a Spice model!

Version 4 SHEET 1 4320 1252 WIRE 2032 -400 2000 -400 WIRE 2080 -400 2032 -400 WIRE 2176 -400 2080 -400 WIRE 2224 -400 2176 -400 WIRE 2368 -400 2304 -400 WIRE 2432 -400 2368 -400 WIRE 2592 -400 2512 -400 WIRE 2592 -352 2592 -400 WIRE 1456 -320 1408 -320 WIRE 1504 -320 1456 -320 WIRE 1552 -320 1504 -320 WIRE 1712 -320 1616 -320 WIRE 1792 -320 1712 -320 WIRE 1920 -320 1856 -320 WIRE 2080 -320 2080 -400 WIRE 2176 -288 2176 -400 WIRE 2240 -288 2176 -288 WIRE 2368 -288 2368 -400 WIRE 2368 -288 2304 -288 WIRE 2032 -240 1984 -240 WIRE 1712 -224 1712 -320 WIRE 2592 -224 2592 -272 WIRE 1504 -160 1504 -320 WIRE 1584 -160 1504 -160 WIRE 1984 -160 1984 -240 WIRE 1984 -160 1840 -160 WIRE 1472 -80 1408 -80 WIRE 1584 -80 1472 -80 WIRE 1920 -80 1920 -320 WIRE 1920 -80 1840 -80 WIRE 2080 -80 2080 -224 WIRE 2080 -80 1920 -80 WIRE 2144 -80 2080 -80 WIRE 2352 -80 2144 -80 WIRE 2656 -80 2416 -80 WIRE 3040 -80 2864 -80 WIRE 3168 -80 3040 -80 WIRE 3344 -80 3232 -80 WIRE 992 -64 944 -64 WIRE 1024 -64 992 -64 WIRE 944 -32 944 -64 WIRE 1472 0 1408 0 WIRE 1584 0 1472 0 WIRE 1984 0 1840 0 WIRE 2080 32 2080 -80 WIRE 944 80 944 48 WIRE 3168 96 3120 96 WIRE 3344 96 3344 -80 WIRE 3344 96 3232 96 WIRE 3456 96 3344 96 WIRE 3536 96 3456 96 WIRE 1984 112 1984 0 WIRE 2032 112 1984 112 WIRE 2656 128 2656 -80 WIRE 2864 128 2864 -80 WIRE 1712 160 1712 64 WIRE 1024 192 944 192 WIRE 1088 192 1024 192 WIRE 1280 192 1216 192 WIRE 1328 192 1280 192 WIRE 2080 192 2080 128 WIRE 944 224 944 192 WIRE 1216 224 1216 192 WIRE 1088 240 1088 192 WIRE 1168 240 1088 240 WIRE 3344 256 3344 96 WIRE 3536 256 3536 96 WIRE 1168 288 1120 288 WIRE 944 336 944 304 WIRE 1120 336 1120 288 WIRE 1216 336 1216 304 WIRE 2656 336 2656 208 WIRE 2864 336 2864 208 WIRE 2048 368 2016 368 WIRE 2096 368 2048 368 WIRE 1216 448 1216 416 WIRE 1472 448 1424 448 WIRE 1520 448 1472 448 WIRE 1568 448 1520 448 WIRE 1728 448 1632 448 WIRE 1792 448 1728 448 WIRE 1920 448 1856 448 WIRE 2096 448 2096 368 WIRE 3040 512 3040 -80 WIRE 3168 512 3040 512 WIRE 3344 512 3344 320 WIRE 3344 512 3232 512 WIRE 3536 512 3536 336 WIRE 3536 512 3344 512 WIRE 2048 528 1984 528 WIRE 1728 544 1728 448 WIRE 1024 560 944 560 WIRE 1088 560 1024 560 WIRE 1520 608 1520 448 WIRE 1600 608 1520 608 WIRE 1984 608 1984 528 WIRE 1984 608 1856 608 WIRE 944 624 944 560 WIRE 1488 688 1424 688 WIRE 1600 688 1488 688 WIRE 1920 688 1920 448 WIRE 1920 688 1856 688 WIRE 2096 688 2096 544 WIRE 2096 688 1920 688 WIRE 2160 688 2096 688 WIRE 2656 688 2656 416 WIRE 2656 688 2160 688 WIRE 2864 688 2864 416 WIRE 3120 688 3120 96 WIRE 3120 688 2864 688 WIRE 3168 688 3120 688 WIRE 3344 688 3344 512 WIRE 3344 688 3232 688 WIRE 944 752 944 704 WIRE 1488 768 1424 768 WIRE 1600 768 1488 768 WIRE 1984 768 1856 768 WIRE 3344 768 3344 688 WIRE 2096 800 2096 688 WIRE 1984 880 1984 768 WIRE 2048 880 1984 880 WIRE 1728 928 1728 832 WIRE 2096 960 2096 896 FLAG 1216 448 0 FLAG 1728 928 0 FLAG 2096 960 0 FLAG 1488 768 PWM+ FLAG 1488 688 PWM- FLAG 1472 448 +12 FLAG 2048 368 +48 FLAG 944 80 0 FLAG 992 -64 +12 FLAG 1712 160 0 FLAG 2080 192 0 FLAG 1472 -80 PWM+ FLAG 1472 0 PWM- FLAG 1456 -320 +12 FLAG 2032 -400 +48 FLAG 2144 -80 PSW FLAG 2160 688 NSW FLAG 2592 -224 0 FLAG 1024 192 PWM+ FLAG 944 336 0 FLAG 1120 336 0 FLAG 1280 192 PWM- FLAG 3344 768 0 FLAG 3456 96 OUT FLAG 944 752 0 FLAG 1024 560 EFF SYMBOL voltage 1216 320 R0 WINDOW 0 61 43 Left 2 WINDOW 3 59 79 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL PowerProducts\\LTC4444 1728 688 R0 SYMATTR InstName U6 SYMBOL nmos 2048 448 R0 WINDOW 0 102 34 Left 2 WINDOW 3 73 72 Left 2 SYMATTR InstName M3 SYMATTR Value Si2318CDS SYMBOL schottky 1568 464 R270 WINDOW 0 86 31 VTop 2 WINDOW 3 76 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MBRS1100 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 1856 432 R90 WINDOW 0 -50 29 VBottom 2 WINDOW 3 -40 31 VTop 2 SYMATTR InstName C3 SYMATTR Value 100n SYMBOL nmos 2048 800 R0 WINDOW 0 102 32 Left 2 WINDOW 3 71 68 Left 2 SYMATTR InstName M1 SYMATTR Value Si2318CDS SYMBOL voltage 944 -48 R0 WINDOW 0 61 43 Left 2 WINDOW 3 59 79 Left 2 SYMATTR InstName V4 SYMATTR Value 12 SYMBOL voltage 2592 -368 M0 WINDOW 0 -80 37 Left 2 WINDOW 3 -79 68 Left 2 SYMATTR InstName V5 SYMATTR Value 48 SYMBOL PowerProducts\\LTC4444 1712 -80 R0 SYMATTR InstName U4 SYMBOL nmos 2032 -320 R0 WINDOW 0 97 85 Left 2 WINDOW 3 72 122 Left 2 SYMATTR InstName M2 SYMATTR Value Si2318CDS SYMBOL schottky 1552 -304 R270 WINDOW 0 86 31 VTop 2 WINDOW 3 76 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value MBRS1100 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 1856 -336 R90 WINDOW 0 -50 30 VBottom 2 WINDOW 3 -39 28 VTop 2 SYMATTR InstName C5 SYMATTR Value 100n SYMBOL nmos 2032 32 R0 WINDOW 0 102 32 Left 2 WINDOW 3 71 68 Left 2 SYMATTR InstName M4 SYMATTR Value Si2318CDS SYMBOL ind2 2640 320 R0 WINDOW 0 -60 31 Left 2 WINDOW 3 -61 68 Left 2 SYMATTR InstName L4 SYMATTR Value 75µ SYMATTR Type ind SYMBOL ind2 2848 320 R0 WINDOW 0 62 31 Left 2 WINDOW 3 53 68 Left 2 SYMATTR InstName L5 SYMATTR Value 75µ SYMATTR Type ind SYMBOL res 2640 112 R0 WINDOW 0 -78 43 Left 2 WINDOW 3 -83 79 Left 2 SYMATTR InstName R7 SYMATTR Value 4m SYMBOL res 2848 112 R0 WINDOW 0 55 40 Left 2 WINDOW 3 46 76 Left 2 SYMATTR InstName R11 SYMATTR Value 4m SYMBOL res 2320 -384 M270 WINDOW 0 -35 45 VTop 2 WINDOW 3 -37 44 VBottom 2 SYMATTR InstName R12 SYMATTR Value 20µ SYMBOL res 2528 -384 M270 WINDOW 0 -36 54 VTop 2 WINDOW 3 -40 51 VBottom 2 SYMATTR InstName R13 SYMATTR Value 20µ SYMBOL cap 2240 -304 M90 WINDOW 0 71 33 VBottom 2 WINDOW 3 76 35 VTop 2 SYMATTR InstName C10 SYMATTR Value 1 SYMBOL cap 2416 -96 R90 WINDOW 0 94 32 VBottom 2 WINDOW 3 105 34 VTop 2 SYMATTR InstName C1 SYMATTR Value 100µ SYMBOL voltage 944 208 R0 WINDOW 0 -71 115 Left 2 WINDOW 3 -118 184 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value PULSE(0 5 0 1n 1n 2u 4u 1e9) SYMBOL e 1216 208 R0 WINDOW 0 52 44 Left 2 WINDOW 3 53 76 Left 2 SYMATTR InstName E1 SYMATTR Value -1 SYMBOL schottky 3168 -64 R270 WINDOW 0 90 39 VTop 2 WINDOW 3 79 39 VBottom 2 SYMATTR InstName D3 SYMATTR Value RB088BM150 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 3168 112 R270 WINDOW 0 78 40 VTop 2 WINDOW 3 72 39 VBottom 2 SYMATTR InstName D4 SYMATTR Value RB088BM150 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 3232 496 R90 WINDOW 0 -47 28 VBottom 2 WINDOW 3 -41 27 VTop 2 SYMATTR InstName D7 SYMATTR Value RB088BM150 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 3232 672 R90 WINDOW 0 73 33 VBottom 2 WINDOW 3 82 36 VTop 2 SYMATTR InstName D5 SYMATTR Value RB088BM150 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 3328 256 R0 WINDOW 0 -69 12 Left 2 WINDOW 3 -81 48 Left 2 SYMATTR InstName C2 SYMATTR Value 100µ SYMBOL res 3520 240 R0 WINDOW 0 -68 29 Left 2 WINDOW 3 -67 64 Left 2 SYMATTR InstName R1 SYMATTR Value 25 SYMBOL bv 944 608 R0 WINDOW 0 69 42 Left 2 WINDOW 3 49 81 Left 2 SYMATTR InstName B1 SYMATTR Value V=V(out)*I(R1) / (48*I(R12)) TEXT 1048 -168 Left 2 !.tran 1m startup uic TEXT 2704 304 Left 2 !K1 L4 L5 1 TEXT 2728 0 Left 2 ;1:1 TEXT 2696 -48 Left 2 ;Transformer TEXT 2664 -152 Left 2 ;Coilcraft PL300-100L TEXT 2368 224 Left 2 ;primaries TEXT 2376 264 Left 2 ;parallel TEXT 1040 -296 Left 2 ;P940 DC/DC Converter TEXT 1064 -232 Left 2 ;JL June 9 2021 RECTANGLE Normal 2976 752 2528 -112 2

The transformer model is a bit rudimentary.

The coupling between the winding is supposed to be perfect - "K1 L4 L5 1" when anything much better than 0.99 is a bit unlikely.

This does specify the leakage inductance.

It's relatively easy to measure leakage inductance - you just short one coil and measure the inductance of the other one.

It's actually in the data sheet which says the primary inductance is 287uH (min) not 75uH and the leakage inductance 0.25uH (max).

For some odd reason, John hasn't included coil resistance - 7.2mR (max) - inside the inductance specification, and hasn't put in any parallel capacitance. The inter-winding capacitance is worth measuring too, and putting into the circuit model.

It's easy enough to measure the parallel capacitance - you just measure the self-resonant frequency of one of the coils. Most inductor data sheets include that.

The interwinding capacitance is even easier - a capacitance meter can measure it directly.

As a simulation, this does fall a bit short.