John Fields a écrit :
I want to switch DC power to an instrument "slowly". I am using a FET
to switch the power to the instrument. Could someone direct me to a
circuit that would slowly turn on the FET so that the voltage to the
instrument ramps up from 0 to 28 V at a rate not to exceed 10V/
millisecond. Thanks in advance.
---
View in Courier:
P CHANNEL MOSFET
/
/
28IN>------+----------S D---+-----28OUT>
| G |
[C] | |
| | |
+--[ZENER>]--+ [1µF]
| |
[R] |
| |
GND>-------+------------------+----GND>
This is certainly not the best way to do this (highly dependent on
mosfet gm).
---
Shouldn't matter too much, since all he's looking for is a _minimum_
rise time,
---
A prefered way would be using the fet as a miller integrator:
28V >--+------+^+-----+-------> out
| ||| |
| === |
| | |
12V z | |
A .-. |
| | | |
| 100R| | |
| '-' |
| | || |
+------+---||--'
| | ||
| .-. 10n
- | |
^ | | 330K
| '-'
| |
| |
=== ===
GND GND
---
Except that (Unless I did something wrong) it doesn't work:
Version 4
SHEET 1 1240 680
WIRE -64 144 -192 144
WIRE 112 144 -64 144
WIRE 256 144 208 144
WIRE 368 144 256 144
WIRE -64 192 -64 144
WIRE 128 208 128 192
WIRE 368 288 368 144
WIRE -64 320 -64 256
WIRE 128 320 128 288
WIRE 128 320 -64 320
WIRE 192 320 128 320
WIRE 256 320 256 144
WIRE -192 368 -192 144
WIRE -64 368 -64 320
WIRE 128 368 128 320
WIRE -192 480 -192 448
WIRE -64 480 -64 432
WIRE -64 480 -192 480
WIRE 128 480 128 448
WIRE 128 480 -64 480
WIRE 368 480 368 368
WIRE 368 480 128 480
WIRE -192 512 -192 480
FLAG -192 512 0
SYMBOL cap 256 304 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value 10e-9
SYMBOL voltage -192 352 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 28 0 1e-6 1e-6 .05 .1)
SYMATTR InstName V1
SYMBOL res 352 272 R0
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL pmos 208 192 M270
SYMATTR InstName M1
SYMATTR Value Si7469DP
SYMBOL zener -48 256 R180
WINDOW 0 -52 30 Left 0
WINDOW 3 -132 -8 Left 0
SYMATTR InstName D1
SYMATTR Value BZX84C12L
SYMBOL res 112 192 R0
WINDOW 0 43 40 Left 0
WINDOW 3 38 69 Left 0
SYMATTR InstName R5
SYMATTR Value 100
SYMBOL res 112 352 R0
WINDOW 0 43 40 Left 0
WINDOW 3 38 69 Left 0
SYMATTR InstName R6
SYMATTR Value 330k
SYMBOL diode -48 432 R180
WINDOW 0 -46 29 Left 0
WINDOW 3 -90 -5 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
TEXT -176 496 Left 0 !.tran .2
Also, I had some errors in my original circuit which I fixed:
P CHANNEL MOSFET
/
/
..28IN>--+---+----------S D--------28OUT>
.. | | G
.. | [C] |
.. | | |
.. | +--[DIODE>]--+
.. [R] | |
.. | +--[<DIODE]--+
.. | | |K
.. | [R] [DIODE]
.. | | |
..GND>---+---+------------+----------GND>
and it seems to run OK now:
Version 4
SHEET 1 880 680
WIRE 128 64 -16 64
WIRE 256 64 128 64
WIRE 416 64 256 64
WIRE 688 64 512 64
WIRE 256 96 256 64
WIRE -16 176 -16 64
WIRE 64 192 32 192
WIRE 256 208 256 160
WIRE 320 208 256 208
WIRE 432 208 432 112
WIRE 432 208 384 208
WIRE 688 224 688 64
WIRE 128 256 128 64
WIRE -16 288 -16 256
WIRE 32 288 32 240
WIRE 32 288 -16 288
WIRE 256 320 256 208
WIRE 320 320 256 320
WIRE 432 320 432 208
WIRE 432 320 384 320
WIRE -16 336 -16 288
WIRE 256 368 256 320
WIRE 432 368 432 320
WIRE -16 480 -16 416
WIRE 64 480 64 192
WIRE 64 480 -16 480
WIRE 128 480 128 336
WIRE 128 480 64 480
WIRE 256 480 256 448
WIRE 256 480 128 480
WIRE 432 480 432 432
WIRE 432 480 256 480
WIRE 688 480 688 304
WIRE 688 480 432 480
WIRE -16 560 -16 480
FLAG -16 560 0
SYMBOL res 240 352 R0
WINDOW 0 43 34 Left 0
WINDOW 3 38 61 Left 0
SYMATTR InstName R1
SYMATTR Value 100k
SYMBOL cap 240 96 R0
WINDOW 0 -39 31 Left 0
WINDOW 3 -45 60 Left 0
SYMATTR InstName C1
SYMATTR Value 10e-6
SYMBOL voltage -16 320 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 28 0 1e-6 1e-6 1 2)
SYMATTR InstName V1
SYMBOL res 672 208 R0
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL pmos 512 112 M270
SYMATTR InstName M1
SYMATTR Value Si7469DP
SYMBOL diode 448 432 R180
WINDOW 0 -46 29 Left 0
WINDOW 3 -75 -4 Left 0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode 320 336 R270
WINDOW 0 36 32 VTop 0
WINDOW 3 -4 32 VBottom 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMATTR Description Zener Diode
SYMATTR Type zener
SYMBOL diode 384 192 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMATTR Description Zener Diode
SYMATTR Type zener
SYMBOL sw -16 160 M0
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S1
SYMBOL res 112 240 R0
SYMATTR InstName R3
SYMATTR Value 1000
TEXT -8 536 Left 0 !.tran 3
TEXT -8 504 Left 0 !.model SW SW(Ron=1e-3 Roff=10Meg Vt=0.5Vh=0)
