Hi All, I've got this power supply that is a bunch of CUI dc-dc converters. (+24, +15, -15, +5, -5) all made from a 24V wall wart. There's a limit on the input to output voltage on the CUI's so had to make the -15 from the +15.
Anyway because of the sequencing the +15V comes up 1 ms before the -15V. This was fine until a colleague tried to use it to run one of his circuits. It pukes when turned on and the -15V never get's there. (it sits at ~ +0.4 V) (I still have to look into his circuit.) I was thinking of switching the +15 so it only came on (at the output) with the -15. Below is my first crack at a circuit. (PFet is switched on by pnp that gets base drive from +15 -> 20V zener -> -15.)
So is this kosher? Is there some better way? I haven't thought that much about resistor values. TIA
George H. (hmm I could get rid of the pnp and just have the zener turn it on.)
Version 4 SHEET 1 880 680 WIRE -96 -64 -320 -64 WIRE 96 -64 -96 -64 WIRE 176 -64 96 -64 WIRE 368 -64 272 -64 WIRE -320 -48 -320 -64 WIRE 368 -16 368 -64 WIRE 96 48 96 16 WIRE 192 48 192 -16 WIRE 192 48 96 48 WIRE -320 80 -320 32 WIRE -240 80 -320 80 WIRE 96 80 96 48 WIRE -240 112 -240 80 WIRE 368 112 368 64 WIRE -320 160 -320 80 WIRE 96 224 96 160 WIRE -96 272 -96 16 WIRE -48 272 -96 272 WIRE -96 320 -96 272 WIRE -320 400 -320 240 WIRE -96 400 -96 384 WIRE -96 400 -320 400 WIRE 96 400 96 320 WIRE 96 400 -96 400 FLAG -240 112 0 FLAG 368 112 0 SYMBOL pmos 272 -16 M270 SYMATTR InstName M1 SYMATTR Value RSJ250P10 SYMBOL pnp 32 320 M180 SYMATTR InstName Q1 SYMBOL zener -80 384 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value PTZ20B SYMBOL voltage -320 -64 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value +15 SYMBOL voltage -320 144 R0 WINDOW 3 -332 50 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 15 10m 1u 0 1000m 1 1) SYMBOL res 80 -80 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 80 64 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res -112 -80 R0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL res 48 256 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res 352 -32 R0 SYMATTR InstName R5 SYMATTR Value 1k TEXT -354 410 Left 2 !.tran 0 20m 0 TEXT -56 344 Left 2 ;20V zener