self-energized synchronous rectifer circuit?

"starfire" wrote in message news:0tidnS2-T5SOEevVnZ2dnUVZ snipped-for-privacy@supernews.com...

I found this using

I made a simulation of a sort of a synchronous rectifier which uses transistors to lower the forward voltage drop for a low voltage supply, in this case down to 260 mV maximum at 600 mA. It could probably be done just as well with Schottkys, but I wonder if this concept is viable for some applications. This is for a FWCT DC supply, not a switching regulator. I got efficiency of 83% for a 1.8 VDC output at 217 mW, for example. This would not be possible for MOSFETs because of the body diode, but it should work as shown with BJTs up to about 6 v P-P. LTSpice file follows.

Paul

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Version 4 SHEET 1 880 680 WIRE 144 -160 -48 -160 WIRE 192 -160 144 -160 WIRE 400 -160 288 -160 WIRE 512 -160 400 -160 WIRE 608 -160 512 -160 WIRE 144 -80 144 -160 WIRE -144 -64 -288 -64 WIRE -288 -32 -288 -64 WIRE -144 -32 -144 -64 WIRE -48 16 -48 -80 WIRE 32 16 -48 16 WIRE 144 32 144 0 WIRE 176 32 144 32 WIRE 144 64 144 32 WIRE -288 80 -288 48 WIRE -144 80 -144 48 WIRE -144 80 -288 80 WIRE -48 96 -48 16 WIRE 32 128 32 16 WIRE 144 128 32 128 WIRE 240 128 240 80 WIRE 240 128 144 128 WIRE 144 176 -48 176 WIRE 192 176 144 176 WIRE 400 176 400 -160 WIRE 400 176 288 176 WIRE 144 240 144 176 WIRE 144 368 144 320 WIRE 176 368 144 368 WIRE 144 416 144 368 WIRE 32 480 32 128 WIRE 144 480 32 480 WIRE 240 480 240 416 WIRE 240 480 144 480 FLAG -288 80 0 FLAG 32 480 0 FLAG 608 -80 0 FLAG 512 -96 0 SYMBOL ind2 -32 -176 M0 SYMATTR InstName L1 SYMATTR Value 50m SYMATTR Type ind SYMBOL ind2 -32 80 M0 SYMATTR InstName L2 SYMATTR Value 50m SYMATTR Type ind SYMBOL pnp 288 -96 M270 WINDOW 0 48 34 Left 0 WINDOW 3 45 65 Left 0 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL pnp 288 240 M270 WINDOW 0 50 32 Left 0 WINDOW 3 45 65 Left 0 SYMATTR InstName Q2 SYMATTR Value 2N3906 SYMBOL npn 176 -16 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL npn 176 320 R0 SYMATTR InstName Q4 SYMATTR Value 2N3904 SYMBOL res 224 -112 R0 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL res 224 224 R0 SYMATTR InstName R2 SYMATTR Value 100 SYMBOL res 128 -96 R0 SYMATTR InstName R3 SYMATTR Value 5k SYMBOL res 128 224 R0 SYMATTR InstName R4 SYMATTR Value 5k SYMBOL diode 160 128 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 160 480 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL ind2 -160 -48 R0 SYMATTR InstName L3 SYMATTR Value 100m SYMATTR Type ind SYMBOL voltage -288 -48 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 3 60 0 0 0 100) SYMATTR SpiceLine Rser=.1 SYMBOL cap 496 -160 R0 SYMATTR InstName C1 SYMATTR Value 4700µ SYMBOL res 592 -176 R0 SYMATTR InstName R5 SYMATTR Value 15 TEXT -144 240 Left 0 !K1 L1 L2 L3 1 TEXT -322 504 Left 0 !.tran 1 startup

Thanks very much, Paul.

I'll take a look at it. It looks very promising, although I was hoping to do this without a transformer. This is for an application within a strong magnetic field and the transformer may be affected or affect the system operation. This principles look good, though.

Dave

The transformer is not really necessary for operation. You could use half of the circuit if half wave is OK. Your choice of design depends on what you are trying to do. Good luck.

Paul

I'm not sure what its upper frequency limit is, but an air core transformer might be a possibility, especially if resonated with capacitance.