On 25-July-23 8:41 am, John Larkin wrote:> > https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 > > I like C1, with just a high-enough-voltage mosfet that it survives the > max flyback voltage.I'd be concerned that whatever I thought the max flyback voltage could be, there will be a combination of circumstances that conspire to produce something higher on the day when that's most inconvenient. E lets you choose the turn-off time as a trade against FET drain voltage. Sylvia.
many relay drivers
Started by ●July 24, 2023
Reply by ●July 25, 20232023-07-25
Reply by ●July 25, 20232023-07-25
On a sunny day (Mon, 24 Jul 2023 15:41:16 -0700) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <m9vtbidjnfs514s4s26nhj59m1ojp8q2m1@4ax.com>:> >https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 > >I like C1, with just a high-enough-voltage mosfet that it survives the >max flyback voltage. > >C2 would use some exotic avalanche-rated thing. > >Everthing else needs more parts. > >Any more?I would use A to be safe, pevents RF oscillations and delivers power back into the supply ;-)
Reply by ●July 25, 20232023-07-25
On 25/07/2023 11:56 am, John Larkin wrote:> On Mon, 24 Jul 2023 18:38:15 -0700, boB <boB@K7IQ.com> wrote: > >> On Mon, 24 Jul 2023 18:15:44 -0700, John Larkin >> <jlarkin@highlandSNIPMEtechnology.com> wrote: >> >>> On Mon, 24 Jul 2023 23:25:47 -0000 (UTC), Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>>> >>>>> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >>>>> >>>>> I like C1, with just a high-enough-voltage mosfet that it survives the >>>>> max flyback voltage. >>>>> >>>>> C2 would use some exotic avalanche-rated thing. >>>>> >>>>> Everthing else needs more parts. >>>>> >>>>> Any more? >>>>> >>>>> >>>> >>>> TVS across the coil. That sometimes helps a bit with keeping the rail >>>> clean, and (unlike the shunt rectifier approach) lets the contacts open at >>>> full speed. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> I'd like to use a sot-23 fet and nothing else. I'll brickwall 120 >>> 7x20mm relays and have to put the drivers between the pins on the >>> bottom side of the board and I need room for hundreds of fat traces >>> too. >>> >>> It's tough to get a flyback boost of 10:1, and I'm hoping that a relay >>> coil can't do that. I could use a 100 or 150 volt fet and the spike >>> voltage might not get that high. >>> >>> Dropout would be fast! >> >> Yes, the high voltage transistor can do the work as long a it can take >> the energy. I do that too when I need turn-off to be fast. >> Otherwise, I just use a cache diode across the coil. >> >> The circulating current with a regular diode will slow the switch off >> but quite a lot. Sometimes it's ok but sometimes, like with line >> connected inverter/charger, we need it to turn off in a couple of ms >> rather than 10 ms or so. >> >> boB > > In some cases we can measure the contact currents and open the relay > if the customer pumps in too many amps. In that case, we'd prefer to > open the contacts as fast as possible. > > If I do add a part, it may as well be a zener to ground. >What I usually do if there are multiple coils is share one zener between all of the coil drivers, and have an individual diode from each drain to the shared zener. Having the zener to the supply rail rather than to ground is slightly more energy-efficient, if the relays switch often, but requires some amount of bulk capacitance to be present on the supply rail, which there usually is anyway.
Reply by ●July 25, 20232023-07-25
On 25/07/2023 9:49 pm, Chris Jones wrote:> On 25/07/2023 11:56 am, John Larkin wrote: >> On Mon, 24 Jul 2023 18:38:15 -0700, boB <boB@K7IQ.com> wrote: >> >>> On Mon, 24 Jul 2023 18:15:44 -0700, John Larkin >>> <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> >>>> On Mon, 24 Jul 2023 23:25:47 -0000 (UTC), Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>>>> >>>>>> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >>>>>> >>>>>> I like C1, with just a high-enough-voltage mosfet that it survives >>>>>> the >>>>>> max flyback voltage. >>>>>> >>>>>> C2 would use some exotic avalanche-rated thing. >>>>>> >>>>>> Everthing else needs more parts. >>>>>> >>>>>> Any more? >>>>>> >>>>>> >>>>> >>>>> TVS across the coil. That sometimes helps a bit with keeping the rail >>>>> clean, and (unlike the shunt rectifier approach) lets the contacts >>>>> open at >>>>> full speed. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> I'd like to use a sot-23 fet and nothing else. I'll brickwall 120 >>>> 7x20mm relays and have to put the drivers between the pins on the >>>> bottom side of the board and I need room for hundreds of fat traces >>>> too. >>>> >>>> It's tough to get a flyback boost of 10:1, and I'm hoping that a relay >>>> coil can't do that. I could use a 100 or 150 volt fet and the spike >>>> voltage might not get that high. >>>> >>>> Dropout would be fast! >>> >>> Yes, the high voltage transistor can do the work as long a it can take >>> the energy. I do that too when I need turn-off to be fast. >>> Otherwise, I just use a cache diode across the coil. >>> >>> The circulating current with a regular diode will slow the switch off >>> but quite a lot. Sometimes it's ok but sometimes, like with line >>> connected inverter/charger, we need it to turn off in a couple of ms >>> rather than 10 ms or so. >>> >>> boB >> >> In some cases we can measure the contact currents and open the relay >> if the customer pumps in too many amps. In that case, we'd prefer to >> open the contacts as fast as possible. >> >> If I do add a part, it may as well be a zener to ground. >> > > What I usually do if there are multiple coils is share one zener between > all of the coil drivers, and have an individual diode from each drain to > the shared zener. > > Having the zener to the supply rail rather than to ground is slightly > more energy-efficient, if the relays switch often, but requires some > amount of bulk capacitance to be present on the supply rail, which there > usually is anyway.(on further thought the capacitance is only more necessary (than with the zener to ground) if there is long wiring to the power supply, with significant inductance)
Reply by ●July 25, 20232023-07-25
On 24/07/2023 23:41, John Larkin wrote:> > https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 > > I like C1, with just a high-enough-voltage mosfet that it survives the > max flyback voltage. > > C2 would use some exotic avalanche-rated thing. > > Everthing else needs more parts. > > Any more? >I have used slew rate limited ... <https://www.dropbox.com/scl/fi/oyf7ocfaolxbr0zf6zi68/slewrelaydrive.jpg?rlkey=3zpl2gkfu62k5ua46hk9j92vh&raw=1> a less minimal version of your "G". I also like "B" it is very cheap very reliable and can tailor release time and peak voltage just the way you like. piglet
Reply by ●July 25, 20232023-07-25
On Tue, 25 Jul 2023 21:49:49 +1000, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 25/07/2023 11:56 am, John Larkin wrote: >> On Mon, 24 Jul 2023 18:38:15 -0700, boB <boB@K7IQ.com> wrote: >> >>> On Mon, 24 Jul 2023 18:15:44 -0700, John Larkin >>> <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> >>>> On Mon, 24 Jul 2023 23:25:47 -0000 (UTC), Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>>>> >>>>>> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >>>>>> >>>>>> I like C1, with just a high-enough-voltage mosfet that it survives the >>>>>> max flyback voltage. >>>>>> >>>>>> C2 would use some exotic avalanche-rated thing. >>>>>> >>>>>> Everthing else needs more parts. >>>>>> >>>>>> Any more? >>>>>> >>>>>> >>>>> >>>>> TVS across the coil. That sometimes helps a bit with keeping the rail >>>>> clean, and (unlike the shunt rectifier approach) lets the contacts open at >>>>> full speed. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> I'd like to use a sot-23 fet and nothing else. I'll brickwall 120 >>>> 7x20mm relays and have to put the drivers between the pins on the >>>> bottom side of the board and I need room for hundreds of fat traces >>>> too. >>>> >>>> It's tough to get a flyback boost of 10:1, and I'm hoping that a relay >>>> coil can't do that. I could use a 100 or 150 volt fet and the spike >>>> voltage might not get that high. >>>> >>>> Dropout would be fast! >>> >>> Yes, the high voltage transistor can do the work as long a it can take >>> the energy. I do that too when I need turn-off to be fast. >>> Otherwise, I just use a cache diode across the coil. >>> >>> The circulating current with a regular diode will slow the switch off >>> but quite a lot. Sometimes it's ok but sometimes, like with line >>> connected inverter/charger, we need it to turn off in a couple of ms >>> rather than 10 ms or so. >>> >>> boB >> >> In some cases we can measure the contact currents and open the relay >> if the customer pumps in too many amps. In that case, we'd prefer to >> open the contacts as fast as possible. >> >> If I do add a part, it may as well be a zener to ground. >> > >What I usually do if there are multiple coils is share one zener between >all of the coil drivers, and have an individual diode from each drain to >the shared zener. > >Having the zener to the supply rail rather than to ground is slightly >more energy-efficient, if the relays switch often, but requires some >amount of bulk capacitance to be present on the supply rail, which there >usually is anyway.Yes, there could be a clamp supply that is some multiple of my +12 relay coil supply. But I'd have to distribute it to all 120 relays, which would probably add another layer to the PC board. A zener can dump to ground. I don't think we'd switch often enough to fry a zener. Relays don't specify coil inductance, so I'll have to measure a few to estimate stored energy. I guess some of the energy is stored mechanically, so static inductance isn't the whole story. This is what I have so far: https://www.dropbox.com/scl/fi/pt0s654nj3549ox9wys11/P948_7mm_5.jpg?rlkey=m8su7owc3k3c9o3n59ouc1wje&raw=1 Little SOT23 mosfets under each relay and an FPGA driving them. Lots of traces.
Reply by ●July 25, 20232023-07-25
On Tue, 25 Jul 2023 13:15:20 +1000, Sylvia Else <sylvia@email.invalid> wrote:>On 25-July-23 8:41 am, John Larkin wrote: >> >> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >> >> I like C1, with just a high-enough-voltage mosfet that it survives the >> max flyback voltage. > >I'd be concerned that whatever I thought the max flyback voltage could >be, there will be a combination of circumstances that conspire to >produce something higher on the day when that's most inconvenient. > >E lets you choose the turn-off time as a trade against FET drain voltage. > >Sylvia.Sure, but I need to route fat traces to 120 relays on a 6-layer board. Parts get in the way.
Reply by ●July 25, 20232023-07-25
On Tue, 25 Jul 2023 05:20:21 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Mon, 24 Jul 2023 15:41:16 -0700) it happened John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote in ><m9vtbidjnfs514s4s26nhj59m1ojp8q2m1@4ax.com>: > >> >>https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >> >>I like C1, with just a high-enough-voltage mosfet that it survives the >>max flyback voltage. >> >>C2 would use some exotic avalanche-rated thing. >> >>Everthing else needs more parts. >> >>Any more? > >I would use A to be safe, pevents RF oscillations and delivers power back into the supply ;-)That's no fun. Everybody does that. The stored energy is dissipated in the diode and the coil resistance.
Reply by ●July 25, 20232023-07-25
On Tue, 25 Jul 2023 15:04:59 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 24/07/2023 23:41, John Larkin wrote: >> >> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 >> >> I like C1, with just a high-enough-voltage mosfet that it survives the >> max flyback voltage. >> >> C2 would use some exotic avalanche-rated thing. >> >> Everthing else needs more parts. >> >> Any more? >> > >I have used slew rate limited ... > ><https://www.dropbox.com/scl/fi/oyf7ocfaolxbr0zf6zi68/slewrelaydrive.jpg?rlkey=3zpl2gkfu62k5ua46hk9j92vh&raw=1> > >a less minimal version of your "G". I also like "B" it is very cheap >very reliable and can tailor release time and peak voltage just the way >you like. > >pigletB loses power when the relay is on, but the numbers aren't bad. The relays use 200 mW and if the resistor is 4x the coil resistance, the resistor loses 50 mW and the flyback is about 60 volts.
Reply by ●July 25, 20232023-07-25
On Monday, July 24, 2023 at 6:41:33 PM UTC-4, John Larkin wrote:> https://www.dropbox.com/scl/fi/40slcbgbngggdcwwt95vi/Relay_Drivers.jpg?rlkey=gfai2trx0n6bnja2yl4hber7i&raw=1 > > I like C1, with just a high-enough-voltage mosfet that it survives the > max flyback voltage. > > C2 would use some exotic avalanche-rated thing. > > Everthing else needs more parts. > > Any more?Is that a 200mW coil? So at 5V they have Rc = 25/0.2= 125R. But the abbreviated data sheet says it's Rc of 720R, which makes no sense whatsoever, unless "coil power rating DC" means just that for applications using overvoltage ( allows for 12V) speed-up. That kind of coil resistance makes me suspect the L/R is quite small, making the coil magnetic circuit quite speedy compared to armature movement. Do you have the actuate/ release times? And is this an 80/20 pull-in/ drop-out type, or something else? The actual delay from application of pull-in current to contact make can be measured, same for the drop-out current to contact break. I'm guessing the drop-out break is longer because they all use contact over-travel on make to preserve contact material and reduce bounce. Anyway, getting a handle on those times and currents will determine the best reverse voltage method. TE says some of that PCJ series are pending obsolescence.
