I found this neat soft-start circuit on the eevblog forum. Its neatness
is that the gate threshold voltage occurs immediately and then the RC
softness kicks in.
V+ ________________________ V+
|
|
1M ___________ V-
|___1u___|
| |
| |--
|------|
|--
|
V- ____________|
As neat as that is, I have a situation where the motor may be run in
either direction (either polarity on the input) and the soft start
circuit won't handle that. To use it with either polarity, I plan to
use 2 of them & isolate with diodes:
_______
V+/- -x-----D>--| |---------x-----V+/-
| | | |
| | |-----x---------V-/+
V-/+ -----x-<D--|_______| | |
| | | |
| | _______ | |
| |_D>__| |_____| |
| | | |
|_____<D__| |_________|
|_______|
It looks OK to me, but what do I know & I'd like to hear what you think.
Am I missing anything?
Thanks, Bob
BTW - anybody know of software that will do schematics with keyboard
characters?
DC motor soft start
Started by ●November 22, 2021
Reply by ●November 23, 20212021-11-23
On 2021-11-23, Bob Engelhardt <BobEngelhardt@comcast.net> wrote:> I found this neat soft-start circuit on the eevblog forum. Its neatness > is that the gate threshold voltage occurs immediately and then the RC > softness kicks in. > > V+ ________________________ V+ > | > | > 1M ___________ V- > |___1u___| > | | > | |-- > |------| > |-- > | > V- ____________| > > > As neat as that is, I have a situation where the motor may be run in > either direction (either polarity on the input) and the soft start > circuit won't handle that. To use it with either polarity, I plan to > use 2 of them & isolate with diodes: > > _______ > V+/- -x-----D>--| |---------x-----V+/- > | | | | > | | |-----x---------V-/+ > V-/+ -----x-<D--|_______| | | > | | | | > | | _______ | | > | |_D>__| |_____| | > | | | | > |_____<D__| |_________| > |_______| > > It looks OK to me, but what do I know & I'd like to hear what you think. > Am I missing anything?could do this perhaps? __________ V +/- .--S<--| | | | --| | |------. | --| | | |___1u___| V+/- ___L______| | | | | 1M 1M | | _________L__ V-/+ |___1u___| | | | | | |-- | |------| | |-- | | | V-/+ ____________|-->S--' maybe add a diode parallel with the 1Ms to make faster resets.> BTW - anybody know of software that will do schematics with keyboard > characters?None that's worth bothering with. -- Jasen.
Reply by ●November 24, 20212021-11-24
On 11/23/2021 2:11 AM, Jasen Betts wrote:> > could do this perhaps? > > __________ V +/- > .--S<--| > | | > | --| > | |------. > | --| | > | |___1u___| > V+/- ___L______| | > | | > | 1M > 1M | > | _________L__ V-/+ > |___1u___| | > | | | > | |-- | > |------| | > |-- | > | | > V-/+ ____________|-->S--' > > > maybe add a diode parallel with the 1Ms to make faster resets. > ...That would work ... clever, too. Thanks. I'm guessing that the "S<" is a Shottky diode. Preferable for the lower forward drop?
Reply by ●November 24, 20212021-11-24
On 2021-11-24, Bob Engelhardt <BobEngelhardt@comcast.net> wrote:> On 11/23/2021 2:11 AM, Jasen Betts wrote: > >> >> could do this perhaps?...>> | | >> V-/+ ____________|-->S--' >>> That would work ... clever, too. Thanks. > > I'm guessing that the "S<" is a Shottky diode. Preferable for the lower > forward drop?Yes. mainly to have a lower drop than the substrate diode of the MOSFET. yes. -- Jasen.
Reply by ●November 25, 20212021-11-25
On 11/22/2021 9:20 PM, Bob Engelhardt wrote:> I found this neat soft-start circuit on the eevblog forum. Its neatness > is that the gate threshold voltage occurs immediately and then the RC > softness kicks in. > > V+ ________________________ V+ > | > | > 1M ___________ V- > |___1u___| > | | > | |-- > |------| > |-- > | > V- ____________| >... OK ... I built this and tried it out. Didn't work as expected & when I put my scope (Tek 465) on it, I couldn't see the trace. It's a 1-shot sort of event & the scope doesn't have the persistence (let alone storage) to see it. Any good tricks for seeing non-repetitive events? Thanks, Bob
Reply by ●November 25, 20212021-11-25
On 2021-11-25, Bob Engelhardt <BobEngelhardt@comcast.net> wrote:> On 11/22/2021 9:20 PM, Bob Engelhardt wrote: >> I found this neat soft-start circuit on the eevblog forum. Its neatness >> is that the gate threshold voltage occurs immediately and then the RC >> softness kicks in. >> >> V+ ________________________ V+ >> | >> | >> 1M ___________ V- >> |___1u___| >> | | >> | |-- >> |------| >> |-- >> | >> V- ____________| >> > ... > > OK ... I built this and tried it out. Didn't work as expected & when I > put my scope (Tek 465) on it, I couldn't see the trace. It's a 1-shot > sort of event & the scope doesn't have the persistence (let alone > storage) to see it. Any good tricks for seeing non-repetitive events? > > Thanks, Boblong exposure photography on your scope screen. take a video recording of the scope get a storage oscilloscope. use a sound-card and software PC oscilloscope -- Jasen.
Reply by ●November 27, 20212021-11-27
On 11/25/2021 9:42 PM, Jasen Betts wrote:> On 2021-11-25, Bob Engelhardt <BobEngelhardt@comcast.net> wrote:>> ... Any good tricks for seeing non-repetitive events? >> > > long exposure photography on your scope screen. > take a video recording of the scope > get a storage oscilloscope. > use a sound-card and software PC oscilloscope >I have an iPhone camera - no shutter control. But I just found a feature that does a virtual long exposure (Live photos & Effects). I'm gonna' try it.
