 tell me what you think of this IH circuit
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kell
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Tue Aug 31 2010, 05:46PM
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Registered Member #142
Joined: Sat Feb 11 2006, 01:19PM
Location:
Posts: 102
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Somebody showed me this induction heater circuit. Load into LTSpice:
Version 4
SHEET 1 1476 916
WIRE -224 -336 -496 -336
WIRE 32 -336 -224 -336
WIRE 208 -336 32 -336
WIRE 32 -288 32 -336
WIRE 208 -240 208 -336
WIRE -112 -192 -304 -192
WIRE 32 -160 32 -208
WIRE 160 -160 32 -160
WIRE -224 -144 -224 -336
WIRE -304 -128 -304 -192
WIRE -256 -128 -304 -128
WIRE 32 -128 32 -160
WIRE -112 -112 -112 -192
WIRE -112 -112 -192 -112
WIRE -256 -96 -352 -96
WIRE -224 -48 -224 -80
WIRE 32 -16 32 -64
WIRE -112 96 -112 -112
WIRE -112 96 -304 96
WIRE 32 96 32 48
WIRE -496 128 -496 -336
WIRE -224 128 -496 128
WIRE -224 160 -224 128
WIRE -304 176 -304 96
WIRE -256 176 -304 176
WIRE -112 192 -112 96
WIRE -112 192 -192 192
WIRE 32 192 32 160
WIRE 32 192 -112 192
WIRE 208 192 208 -144
WIRE 352 192 208 192
WIRE -352 208 -352 -96
WIRE -256 208 -352 208
WIRE -352 224 -352 208
WIRE 32 224 32 192
WIRE 352 240 352 192
WIRE -352 320 -352 304
WIRE 352 320 352 304
WIRE 352 320 -352 320
WIRE 32 368 32 288
WIRE 352 384 352 320
WIRE 32 448 32 432
WIRE 208 528 208 192
WIRE 32 544 32 512
WIRE 160 544 32 544
WIRE 352 544 352 464
WIRE -496 576 -496 128
WIRE 32 592 32 544
WIRE -496 720 -496 656
WIRE -224 720 -224 224
WIRE -224 720 -496 720
WIRE 32 720 32 672
WIRE 32 720 -224 720
WIRE 208 720 208 624
WIRE 208 720 32 720
WIRE 352 720 352 624
WIRE 352 720 208 720
WIRE -496 816 -496 720
FLAG -496 816 0
FLAG -224 -48 0
SYMBOL voltage -496 560 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL res -368 208 R0
WINDOW 0 -38 37 Left 0
WINDOW 3 -62 80 Left 0
SYMATTR InstName R3
SYMATTR Value 1e6
SYMBOL nmos 160 -240 R0
SYMATTR InstName M1
SYMATTR Value Si7868DP
SYMBOL pmos 160 624 M180
SYMATTR InstName M2
SYMATTR Value FDS4465
SYMBOL res 16 -304 R0
SYMATTR InstName R6
SYMATTR Value 510
SYMBOL res 48 688 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R8
SYMATTR Value 510
SYMBOL diode 16 -128 R0
WINDOW 3 36 32 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D3
SYMBOL diode 16 448 R0
WINDOW 3 41 30 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D1
SYMBOL diode 16 96 R0
WINDOW 3 37 34 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D2
SYMBOL diode 16 224 R0
WINDOW 3 41 32 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D4
SYMBOL diode 16 -16 R0
WINDOW 3 41 31 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D5
SYMBOL diode 16 368 R0
WINDOW 3 43 32 Left 0
SYMATTR Value 1N4148
SYMATTR InstName D6
SYMBOL ind2 336 368 R0
WINDOW 0 61 31 Left 0
WINDOW 3 39 65 Left 0
SYMATTR InstName L1
SYMATTR Value 1.59e-5
SYMATTR Type ind
SYMBOL cap 336 240 R0
WINDOW 0 -39 5 Left 0
WINDOW 3 -84 59 Left 0
SYMATTR InstName C2
SYMATTR Value 1.59e-7
SYMBOL res 336 528 R0
SYMATTR InstName R1
SYMATTR Value .2
SYMBOL Opamps\\LT1498 -224 -176 R0
SYMATTR InstName U2
SYMBOL Opamps\\LT1498 -224 128 R0
SYMATTR InstName U1
TEXT -480 760 Left 0 !;ac oct 256 20 1000000
TEXT -480 792 Left 0 !.tran .001 startup
In the big picture this is simply a positive feedback loop; as long as the voltage at the work coil is positive, the loop reinforces that by providing a positive drive from the inverter, and when the voltage at the work coil is negative, by the same token the inverter reinforces that. The end result is to drive the tank at resonance. That much I think I understand. I just saw this circuit for the first time yesterday.
I'm offering it up for consideration and comments. I'm going to see if I can use this circuit for a low power (100-200 watts) induction heater. I might try to do it with discretes instead of the op-amp. What's the informed opinion on using a bipolar totem-pole for a voltage follower?
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