soft start circuit...

J

John Larkin

Guest
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.
 
On Tuesday, June 20, 2023 at 6:05:32 PM UTC-4, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.
Click to expand...

Can you put the schematic in dropbox?
 
On Tue, 20 Jun 2023 15:32:11 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, June 20, 2023 at 6:05:32?PM UTC-4, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.

Can you put the schematic in dropbox?
Click to expand...

https://www.dropbox.com/scl/fi/burb5r50ptgcj6sqsedxv/P944_Soft_Start_2.jpg?dl=0&rlkey=ig8yieipdyv88h3sz25icok5g

You should run LT Spice. It\'s free and super cool and not hard to
learn.
 
On 2023-06-20 18:05, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


snip pretty circuit
Click to expand...

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.
Click to expand...

Nice, I like it--controlling the ramp rate at the output via AC feedback.

I usually do it using a series resistor for the soft start and shorting
it out after a delay. Which is better depends on how much energy you
have to dump into the caps--you can stuff more joules into a wirewound
resistor than a SOT23 FET, I expect.

I recently designed a 5V->3.3V LDO that needed really, really good load
transient response. The load is that imaging lidar chip, which pulls 7A
at 3.3V to run all the fast TIAs. It goes from 600 mA to 7A in under a
microsecond, which isn\'t a really great neighbor. ;)

At that kind of dissipation, we can\'t afford to run much of a duty
cycle(*), so the TIA can\'t run for more than 20-30 us at a time. Thus
the supply has to recover to < 1% in < 3 us to leave time for further
settling, and of course for the measurements. The proto looks a good
bit better than that, so it\'s quite doable.

The upstream supply is a Murata \'1/16-brick\' DC-DC converter, the
IRS-5/10-Q12PF-C. It turns 9-36V into isolated 5V at 10 A, with 4-wire
sensing. Pretty swoopy gizmo for $45 at qty 50.

Charging up all the reservoir caps for that LDO needs the soft start.

Cheers

Phil Hobbs

(*) 20W isn\'t much for a processor, say, but we need the top of the chip
bare, because, ya know, light has to come in. That makes cooling more
complicated.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 20 Jun 2023 22:06:46 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-20 18:05, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


snip pretty circuit

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.


Nice, I like it--controlling the ramp rate at the output via AC feedback.

I usually do it using a series resistor for the soft start and shorting
it out after a delay. Which is better depends on how much energy you
have to dump into the caps--you can stuff more joules into a wirewound
resistor than a SOT23 FET, I expect.
Click to expand...

I\'d use a DPAK, which wouldn\'t get very hot; it\'s only going to gulp
1.5 joules.

But a wirewound resistor and a p-fet switch isn\'t at all a bad
alternative, although it won\'t get up to the full +48 before the
switchover. There may be no resistor value that works.

I want to apply the square wave drives to the full bridge, and then
ramp up the supply. The other way, supply up first and then start
switching, makes nasty hundreds-of-amps pulses. Enormous inductors
right after the rectifiers can make it into a sort of forward
converter, which also tames the startup, but the inductors are giant
and expensive.

I recently designed a 5V->3.3V LDO that needed really, really good load
transient response. The load is that imaging lidar chip, which pulls 7A
at 3.3V to run all the fast TIAs. It goes from 600 mA to 7A in under a
microsecond, which isn\'t a really great neighbor. ;)
Click to expand...

So, you need a clever, very fast feedback loop, or a mess of polymer
and ceramic caps.

At that kind of dissipation, we can\'t afford to run much of a duty
cycle(*), so the TIA can\'t run for more than 20-30 us at a time. Thus
the supply has to recover to < 1% in < 3 us to leave time for further
settling, and of course for the measurements. The proto looks a good
bit better than that, so it\'s quite doable.

The upstream supply is a Murata \'1/16-brick\' DC-DC converter, the
IRS-5/10-Q12PF-C. It turns 9-36V into isolated 5V at 10 A, with 4-wire
sensing. Pretty swoopy gizmo for $45 at qty 50.
Click to expand...

Murata makes nice dc/dc things.

Charging up all the reservoir caps for that LDO needs the soft start.

Cheers

Phil Hobbs

(*) 20W isn\'t much for a processor, say, but we need the top of the chip
bare, because, ya know, light has to come in. That makes cooling more
complicated.
Click to expand...

Oil bath! Oil is transparent!
 
On 21-06-2023 04:34, John Larkin wrote:
On Tue, 20 Jun 2023 22:06:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-20 18:05, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


snip pretty circuit

Nice idea about the feedback mechanism :)
Click to expand...

Just be away that many FETs cannot be run safely in linear mode due to
the spirito effect.
 
On 21/06/2023 01:56, John Larkin wrote:
On Tue, 20 Jun 2023 15:32:11 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, June 20, 2023 at 6:05:32?PM UTC-4, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.

Can you put the schematic in dropbox?

https://www.dropbox.com/scl/fi/burb5r50ptgcj6sqsedxv/P944_Soft_Start_2.jpg?dl=0&rlkey=ig8yieipdyv88h3sz25icok5g

You should run LT Spice. It\'s free and super cool and not hard to
learn.
Click to expand...

Thanks for the dropbox pic, saves having to fire up LT spice. I have
always used a resistor shunted by mosfet but your idea is interesting.

What is the M1 abs max Vgs Fiddling R1/R2 might limit Vgs but D1 gets in
the way?

piglet
 
On 21/06/2023 08:43, piglet wrote:
On 21/06/2023 01:56, John Larkin wrote:
On Tue, 20 Jun 2023 15:32:11 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, June 20, 2023 at 6:05:32?PM UTC-4, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.

Can you put the schematic in dropbox?

https://www.dropbox.com/scl/fi/burb5r50ptgcj6sqsedxv/P944_Soft_Start_2.jpg?dl=0&rlkey=ig8yieipdyv88h3sz25icok5g

You should run LT Spice. It\'s free and super cool and not hard to
learn.


Thanks for the dropbox pic, saves having to fire up LT spice. I have
always used a resistor shunted by mosfet but your idea is interesting.

What is the M1 abs max Vgs Fiddling R1/R2 might limit Vgs but D1 gets in
the way?

piglet
Click to expand...

Ignore that, I see the enable voltage is 3.3V now so you have very
nicely taken care of Vgs max etc.

piglet
 
On Wed, 21 Jun 2023 08:43:05 +0100, piglet <erichpwagner@hotmail.com>
wrote:

On 21/06/2023 01:56, John Larkin wrote:
On Tue, 20 Jun 2023 15:32:11 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, June 20, 2023 at 6:05:32?PM UTC-4, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


Version 4
SHEET 1 880 680
WIRE -192 -192 -320 -192
WIRE -112 -192 -192 -192
WIRE 80 -192 -112 -192
WIRE 240 -192 176 -192
WIRE 288 -192 240 -192
WIRE 416 -192 368 -192
WIRE 512 -192 416 -192
WIRE 592 -192 512 -192
WIRE 656 -192 592 -192
WIRE -320 -144 -320 -192
WIRE 240 -96 240 -192
WIRE 416 -96 416 -192
WIRE 592 -96 592 -192
WIRE -320 -16 -320 -64
WIRE -192 -16 -192 -192
WIRE -112 -16 -192 -16
WIRE 48 -16 -32 -16
WIRE 96 -16 96 -144
WIRE 96 -16 48 -16
WIRE 240 32 240 -32
WIRE 416 32 416 -32
WIRE 592 32 592 -16
WIRE 96 96 96 -16
WIRE -272 144 -320 144
WIRE -208 144 -272 144
WIRE -48 144 -128 144
WIRE 32 144 -48 144
WIRE -320 192 -320 144
WIRE -48 224 -48 144
WIRE 96 224 96 192
WIRE 240 224 240 112
WIRE 240 224 96 224
WIRE 96 240 96 224
WIRE 240 256 240 224
WIRE -320 320 -320 272
WIRE -48 352 -48 288
WIRE 96 352 96 320
WIRE 240 352 240 320
FLAG -320 -16 0
FLAG 96 352 0
FLAG -320 320 0
FLAG 416 32 0
FLAG 592 32 0
FLAG 512 -192 Vsoft
FLAG -112 -192 +48
FLAG 48 -16 G
FLAG -48 352 0
FLAG -272 144 ENAB
FLAG 240 352 0
SYMBOL voltage -320 -160 R0
WINDOW 0 36 158 Left 2
WINDOW 3 -52 194 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 48 1m 1m 1m 9)
SYMBOL res -16 -32 R90
WINDOW 0 -10 85 VBottom 2
WINDOW 3 -37 25 VTop 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL pmos 176 -144 M270
WINDOW 0 20 180 VLeft 2
WINDOW 3 -10 216 VLeft 2
SYMATTR InstName M1
SYMATTR Value Si7461DP
SYMBOL cap -32 288 R180
WINDOW 0 49 41 Left 2
WINDOW 3 43 11 Left 2
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 112 336 R180
WINDOW 0 55 73 Left 2
WINDOW 3 55 42 Left 2
SYMATTR InstName R2
SYMATTR Value 2K
SYMBOL voltage -320 176 R0
WINDOW 0 50 144 Left 2
WINDOW 3 -46 187 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 3.3 5m 1u 1u 2)
SYMBOL cap 400 -96 R0
WINDOW 0 66 24 Left 2
WINDOW 3 65 53 Left 2
SYMATTR InstName C2
SYMATTR Value 1m
SYMBOL res 576 -112 R0
WINDOW 0 63 40 Left 2
WINDOW 3 59 69 Left 2
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res 272 -176 R270
WINDOW 0 -40 58 VTop 2
WINDOW 3 -44 57 VBottom 2
SYMATTR InstName R4
SYMATTR Value 1m
SYMBOL npn 32 96 R0
WINDOW 0 -44 -52 Left 2
WINDOW 3 -74 -22 Left 2
SYMATTR InstName Q1
SYMATTR Value 2N5210
SYMBOL res -112 128 R90
WINDOW 0 67 54 VBottom 2
WINDOW 3 72 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL cap 224 -96 R0
WINDOW 0 -47 24 Left 2
WINDOW 3 -45 55 Left 2
SYMATTR InstName C3
SYMATTR Value 1µ
SYMBOL res 224 16 R0
WINDOW 0 -48 39 Left 2
WINDOW 3 -51 69 Left 2
SYMATTR InstName R6
SYMATTR Value 500
SYMBOL zener 256 320 R180
WINDOW 0 -68 51 Left 2
WINDOW 3 -86 20 Left 2
SYMATTR InstName D1
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
TEXT 488 216 Left 2 !.tran 200m
TEXT 464 128 Left 2 ;P944 Soft Start
TEXT 448 168 Left 2 ;JL June 20 2023
TEXT -40 104 Left 2 ;BCX70
TEXT -48 -104 Left 2 ;IRFR9120N

Peak startup current is just over an amp. We can drive the inverter
logic inputs at startup, enable the soft start, and things will ramp
up gently.

Can you put the schematic in dropbox?

https://www.dropbox.com/scl/fi/burb5r50ptgcj6sqsedxv/P944_Soft_Start_2.jpg?dl=0&rlkey=ig8yieipdyv88h3sz25icok5g

You should run LT Spice. It\'s free and super cool and not hard to
learn.


Thanks for the dropbox pic, saves having to fire up LT spice. I have
always used a resistor shunted by mosfet but your idea is interesting.

What is the M1 abs max Vgs Fiddling R1/R2 might limit Vgs but D1 gets in
the way?

piglet
Click to expand...

I\'d have to order a new pfet, and may as well get one that is gate
protected, just in case. They typically zener around 22 volts.

It probably doesn\'t need D1. That\'s just to protect the npn in case
something goofy happens to a power rail. I certainly don\'t need it in
Spice! It\'s just a reminder.
 
On Wed, 21 Jun 2023 09:37:18 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

On 21-06-2023 04:34, John Larkin wrote:
On Tue, 20 Jun 2023 22:06:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-20 18:05, John Larkin wrote:
We have a giant 48 volt bus, and one plugin board (a jet engine
alternator simulator) will have a hunky full-bridge dc/dc converter
making +-60 volts. Startup makes hundreds-of-amps current pulses with
side effects, so soft start is a good thing.

Here it is:


snip pretty circuit

Nice idea about the feedback mechanism :)

Just be away that many FETs cannot be run safely in linear mode due to
the spirito effect.
Click to expand...

Yes, I\'ve blown up lots of big fets that way.

This one won\'t work very hard during the ramp-up.
 
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