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Slow Start Switched DC Output

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.
 
M

martin griffith

Jan 1, 1970
0
On 8 May 2007 03:36:17 -0700, in sci.electronics.design
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.

LT1910 from linear, check out fig 5 in the data sheet


martin
 
J

John Fields

Jan 1, 1970
0
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>


LTSPICE circuit list:

Version 4
SHEET 1 880 680
WIRE -128 144 -256 144
WIRE 32 144 -128 144
WIRE 176 144 128 144
WIRE 288 144 176 144
WIRE -128 176 -128 144
WIRE 176 256 176 144
WIRE 288 256 288 144
WIRE -128 288 -128 240
WIRE -80 288 -128 288
WIRE 48 288 48 192
WIRE 48 288 -16 288
WIRE -256 336 -256 144
WIRE -128 336 -128 288
WIRE -256 448 -256 416
WIRE -128 448 -128 416
WIRE -128 448 -256 448
WIRE 176 448 176 320
WIRE 176 448 -128 448
WIRE 288 448 288 336
WIRE 288 448 176 448
WIRE -256 480 -256 448
FLAG -256 480 0
SYMBOL res -144 320 R0
WINDOW 0 43 40 Left 0
WINDOW 3 38 69 Left 0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL cap -144 176 R0
WINDOW 0 -39 31 Left 0
WINDOW 3 -45 60 Left 0
SYMATTR InstName C1
SYMATTR Value 10e-6
SYMBOL voltage -256 320 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 28 0 1e-6)
SYMBOL res 272 240 R0
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL pmos 128 192 M270
SYMATTR InstName M1
SYMATTR Value Si7469DP
SYMBOL zener -80 304 R270
WINDOW 0 24 90 VTop 0
WINDOW 3 5 112 VBottom 0
SYMATTR InstName D1
SYMATTR Value BZX84C15L
SYMBOL cap 160 256 R0
WINDOW 0 43 29 Left 0
SYMATTR InstName C2
SYMATTR Value 1e-6
TEXT -242 466 Left 0 !.tran .1
 
M

MooseFET

Jan 1, 1970
0
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>

That ASCII art looks wrong to me. I assume the Zener's location is an
error. The zener should be from the source to the gate.


You should also put a diode across the resistor. If the 28V input
goes to zero and then back up to 28, the output would follow without
delay. With the diode, the slow start would repeat.
 
F

Fred Bartoli

Jan 1, 1970
0
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).

A prefered way would be using the fet as a miller integrator:

28V >--+------+^+-----+-------> out
| ||| |
| === |
| | |
12V z | |
A .-. |
| | | |
| 100R| | |
| '-' |
| | || |
+------+---||--'
| | ||
| .-. 10n
- | |
^ | | 330K
| '-'
| |
| |
=== ===
GND GND
 
J

John Fields

Jan 1, 1970
0
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)
 
F

Fred Bartoli

Jan 1, 1970
0
John Fields a écrit :
John Fields a écrit :
On 8 May 2007 03:36:17 -0700, [email protected] wrote:

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

You're right: in a hurry I got it wrong and the integrator reference
should have been GND, not the 28V input :-(

So:

.-------------.
| |
28V >--+-------+-----+^+-----)----+--> out
| | ||| | |
| | === | |
| | | | |
12V z | | 330K.-. |
A 330K.-. .-. | | --- 10n
| | | | | | | ---
| | | | | '-' |
| '-' '-'100R | |
| | | | |
'-------+-----+ .---+ |
| | | |
\| | |/ |
|-+-| |
<| | |> |
| - | |
| ^ | |
| | | |
+---+--------+
| | |
.-. .-. -
| | | | ^
10K| | 10K| | |
'-' '-' |
| | |
=== === ===
GND GND GND

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:

But you're still in error: your circuit is a current source, which means
that the dv/dt depends on the load. Now make the output load 100R or 1K
or 10K and see what happens.
 
J

John Fields

Jan 1, 1970
0
John Fields a écrit :
John Fields a écrit :
On 8 May 2007 03:36:17 -0700, [email protected] wrote:

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

You're right: in a hurry I got it wrong and the integrator reference
should have been GND, not the 28V input :-(

So:

.-------------.
| |
28V >--+-------+-----+^+-----)----+--> out
| | ||| | |
| | === | |
| | | | |
12V z | | 330K.-. |
A 330K.-. .-. | | --- 10n
| | | | | | | ---
| | | | | '-' |
| '-' '-'100R | |
| | | | |
'-------+-----+ .---+ |
| | | |
\| | |/ |
|-+-| |
<| | |> |
| - | |
| ^ | |
| | | |
+---+--------+
| | |
.-. .-. -
| | | | ^
10K| | 10K| | |
'-' '-' |
| | |
=== === ===
GND GND GND

It still doesn't work:


Version 4
SHEET 1 880 804
WIRE -32 -80 -304 -80
WIRE 400 -80 -32 -80
WIRE -32 64 -32 -80
WIRE 64 64 -32 64
WIRE 160 64 64 64
WIRE 576 64 256 64
WIRE 688 64 576 64
WIRE -32 144 -32 64
WIRE 64 144 64 64
WIRE 176 144 176 112
WIRE 400 144 400 -80
WIRE 576 240 576 64
WIRE -32 256 -32 208
WIRE 64 256 64 224
WIRE 64 256 -32 256
WIRE 176 256 176 224
WIRE 176 256 64 256
WIRE 176 288 176 256
WIRE 400 288 400 224
WIRE 288 336 240 336
WIRE 336 336 288 336
WIRE 688 336 688 64
WIRE 288 400 288 336
WIRE 176 512 176 384
WIRE 288 512 288 464
WIRE 288 512 176 512
WIRE 576 512 576 304
WIRE 576 512 288 512
WIRE -304 560 -304 -80
WIRE 176 576 176 512
WIRE 400 576 400 384
WIRE 576 576 576 512
WIRE -304 704 -304 640
WIRE 176 704 176 656
WIRE 176 704 -304 704
WIRE 400 704 400 656
WIRE 400 704 176 704
WIRE 576 704 576 640
WIRE 576 704 400 704
WIRE 688 704 688 416
WIRE 688 704 576 704
WIRE -304 784 -304 704
FLAG -304 784 0
SYMBOL voltage -304 544 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 pmos 256 112 M270
SYMATTR InstName M1
SYMATTR Value Si7469DP
SYMBOL cap 560 240 R0
SYMATTR InstName C2
SYMATTR Value 10e-9
SYMBOL res 672 320 R0
SYMATTR InstName R2
SYMATTR Value 100
SYMBOL npn 240 288 M0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL npn 336 288 R0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL diode 304 464 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL res 384 560 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 160 560 R0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL diode 592 640 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL res 160 128 R0
SYMATTR InstName R4
SYMATTR Value 100
SYMBOL res 384 128 R0
SYMATTR InstName R5
SYMATTR Value 330k
SYMBOL zener -16 208 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D3
SYMATTR Value BZX84C12L
SYMBOL res 48 128 R0
SYMATTR InstName R6
SYMATTR Value 330k
TEXT -280 768 Left 0 !.tran 10

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:

But you're still in error: your circuit is a current source, which means
that the dv/dt depends on the load. Now make the output load 100R or 1K
or 10K and see what happens.
 
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