Any insight for Automotive Sensor Inputs/ Front-End Protection.
in [Design]
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From: Grant on 30 Apr 2010 17:48 On Fri, 30 Apr 2010 08:26:04 -0700, Joerg <invalid(a)invalid.invalid> wrote: >JosephKK wrote: >> On Thu, 29 Apr 2010 10:09:51 -0700 (PDT), "miso(a)sushi.com" >> <miso(a)sushi.com> wrote: >> >>> On Apr 26, 3:35 pm, Johnny5 <dirtylogicdesi...(a)gmail.com> wrote: >>>> I was curious if anyone had any insight into protecting an Opto- >>>> isolator LED input from load dump, Jumpstarts, and many of the other >>>> signals in the auto environment. FETS,CLIPPERS,Clamps? >>>> Thank you in advance, >>>> It is an open drain SSR. >>> The automobile industry seriously needs to address providing DC to >>> their customers. They need a better connector instead of the cig plug, >>> and the DC should be conditioned. >>> >>> Ditto on transorb diodes. >> >> And what about the yammerheads that insist on plugging 700 W inverters >> into them? > > >That's where two wonderful inventions come into play: Fuses and breakers :-) Yes, but sometimes the fuse and main switching device break at the same time, oops! Way back when I worked on power converters the fast fuses (the big silver in sand type) cost about as much as the SCRs, and it was still a race which would break first. Grant. -- http://bugs.id.au/
From: Klaus Kragelund on 30 Apr 2010 18:15 On 29 Apr., 17:36, Joerg <inva...(a)invalid.invalid> wrote: > John Devereux wrote: > > Joerg <inva...(a)invalid.invalid> writes: > > >> Jim Thompson wrote: > >>> On Wed, 28 Apr 2010 18:09:18 +0100, John Devereux > >>> <j...(a)devereux.me.uk> wrote: > > >>>> Johnny5 <dirtylogicdesi...(a)gmail.com> writes: > > >>>>> On Apr 26, 6:35 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- > >>>>> Web-Site.com> wrote: > >>>>>> On Mon, 26 Apr 2010 16:18:05 -0700, Joerg <inva...(a)invalid.invalid> > >>>>>> wrote: > > >>>>>>> Jamie wrote: > >>>>>>>> Johnny5 wrote: > >>>>>>>>> I was curious if anyone had any insight into protecting an Opto- > >>>>>>>>> isolator LED input from load dump, Jumpstarts, and many of the other > >>>>>>>>> signals in the auto environment. FETS,CLIPPERS,Clamps? > >>>>>>>>> Thank you in advance, > >>>>>>>>> It is an open drain SSR. > >>>>>>>> TVS diodes. Transorbs is another name for them. > >>>>>>> Also Transzorb. And ST calls them Transil. It's trade names, like > >>>>>>> Kleenex or Kim Wipes. > >>>>>>> [...] > >>>>>> No canned answers. It depends on the circuitry. > > >>>> [...] > > >>>>> Thank you all for the input, a little more on the circuit . Sensors > >>>>> are pressure switches/Temp that are connected to Vbatt. Pressure High= > >>>>> relay that switches Vbatt on/off. No current Limit. So I was thinking > >>>>> it would be best use opto. HSR312 SSR, Vr=7v, Vf=1.6V , control > >>>>> current approx 2mA. > > >>>>> Automotive opto front end for Vbatt switched with no current limit > > >>>>> Bav99/ TVS with a current limiter suffice? ? > >>>>> polarity protection p channel fet as well? any choice on fet, dmos > >>>>> only? > >>>>> thks > >>>> Do you actually need to do anything? LEDS will survive brief overcurrent > >>>> just fine. If you size the LED resistor for 12V operation near the 2mA, > >>>> you will have to get up to 100V or so to even get to its rated 25mA > >>>> maximum. Any such pulses will be very brief, the LED won't mind. > > >>>> I would just use a series resistor and connect a signal diode in > >>>> anti-parallel across the LED. > >>> There you go! > > >>> So many posters here want to make simple problems difficult... TVS's, > >>> etc :-] > > >> Those posters tend to design reliable electronics :-) > > >> Figure 1, for a dose of reality: > >>http://www.automotivedesignline.com/howto/205101011 > > > Hi Jeorg, > > > That LTC part will likely blow up before the simple resistor+opto > > solution. The Ford load dump pulse is only 60V peak with 150ms decay > > time constant. The resistor+opto will survive 100V > > indefinitely. Furthermore is is extremely likely to survive pulses of > > much higher voltage, while the LTC part is extremely likely to fail. > > I only brought that link to show the shape of a load dump spike because > some readers may not know. In aerospace those spikes are a whole lot > tougher because the voltage can stay up there for a second, and it can > happen several events in a row. This gets tested so a product that fails > wouldn't even make it to field testing. And shouldn't. > > > Yes, of course you can make it still more robust with a R+TVS+R feeding > > the LED. > > Exactly. That's typically the lowest cost solution because TVS are > ubiquitous and very cheap. Not using them is, in many cases, like > driving around without wearing a seat belt. > > [...] Don't forget that the load dump pulse is distributed to all devices in the system, so although the the obvious design approach would be to use a low value TVS (to clamp as soon a possible), you may then be the device taking the majority of the dump energy (close to the battery, low impedance path). Chosing a larger voltage rating TVS, you may never actually see a large current in your device and the lifetime of your unit could be improved Regards Klaus
From: Joerg on 30 Apr 2010 18:57 Klaus Kragelund wrote: > On 29 Apr., 17:36, Joerg <inva...(a)invalid.invalid> wrote: >> John Devereux wrote: >>> Joerg <inva...(a)invalid.invalid> writes: >>>> Jim Thompson wrote: >>>>> On Wed, 28 Apr 2010 18:09:18 +0100, John Devereux >>>>> <j...(a)devereux.me.uk> wrote: >>>>>> Johnny5 <dirtylogicdesi...(a)gmail.com> writes: >>>>>>> On Apr 26, 6:35 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >>>>>>> Web-Site.com> wrote: >>>>>>>> On Mon, 26 Apr 2010 16:18:05 -0700, Joerg <inva...(a)invalid.invalid> >>>>>>>> wrote: >>>>>>>>> Jamie wrote: >>>>>>>>>> Johnny5 wrote: >>>>>>>>>>> I was curious if anyone had any insight into protecting an Opto- >>>>>>>>>>> isolator LED input from load dump, Jumpstarts, and many of the other >>>>>>>>>>> signals in the auto environment. FETS,CLIPPERS,Clamps? >>>>>>>>>>> Thank you in advance, >>>>>>>>>>> It is an open drain SSR. >>>>>>>>>> TVS diodes. Transorbs is another name for them. >>>>>>>>> Also Transzorb. And ST calls them Transil. It's trade names, like >>>>>>>>> Kleenex or Kim Wipes. >>>>>>>>> [...] >>>>>>>> No canned answers. It depends on the circuitry. >>>>>> [...] >>>>>>> Thank you all for the input, a little more on the circuit . Sensors >>>>>>> are pressure switches/Temp that are connected to Vbatt. Pressure High= >>>>>>> relay that switches Vbatt on/off. No current Limit. So I was thinking >>>>>>> it would be best use opto. HSR312 SSR, Vr=7v, Vf=1.6V , control >>>>>>> current approx 2mA. >>>>>>> Automotive opto front end for Vbatt switched with no current limit >>>>>>> Bav99/ TVS with a current limiter suffice? ? >>>>>>> polarity protection p channel fet as well? any choice on fet, dmos >>>>>>> only? >>>>>>> thks >>>>>> Do you actually need to do anything? LEDS will survive brief overcurrent >>>>>> just fine. If you size the LED resistor for 12V operation near the 2mA, >>>>>> you will have to get up to 100V or so to even get to its rated 25mA >>>>>> maximum. Any such pulses will be very brief, the LED won't mind. >>>>>> I would just use a series resistor and connect a signal diode in >>>>>> anti-parallel across the LED. >>>>> There you go! >>>>> So many posters here want to make simple problems difficult... TVS's, >>>>> etc :-] >>>> Those posters tend to design reliable electronics :-) >>>> Figure 1, for a dose of reality: >>>> http://www.automotivedesignline.com/howto/205101011 >>> Hi Jeorg, >>> That LTC part will likely blow up before the simple resistor+opto >>> solution. The Ford load dump pulse is only 60V peak with 150ms decay >>> time constant. The resistor+opto will survive 100V >>> indefinitely. Furthermore is is extremely likely to survive pulses of >>> much higher voltage, while the LTC part is extremely likely to fail. >> I only brought that link to show the shape of a load dump spike because >> some readers may not know. In aerospace those spikes are a whole lot >> tougher because the voltage can stay up there for a second, and it can >> happen several events in a row. This gets tested so a product that fails >> wouldn't even make it to field testing. And shouldn't. >> >>> Yes, of course you can make it still more robust with a R+TVS+R feeding >>> the LED. >> Exactly. That's typically the lowest cost solution because TVS are >> ubiquitous and very cheap. Not using them is, in many cases, like >> driving around without wearing a seat belt. >> >> [...] > > > Don't forget that the load dump pulse is distributed to all devices in > the system, so although the the obvious design approach would be to > use a low value TVS (to clamp as soon a possible), you may then be the > device taking the majority of the dump energy (close to the battery, > low impedance path). Chosing a larger voltage rating TVS, you may > never actually see a large current in your device and the lifetime of > your unit could be improved > True, you can't set the TVS at 15-20% above rated voltage unless it is behind a series resistor. With many of my designs the client would prefer that it keeps working through spikes even though the standard allows an interruption, so I try to oblige. Then any sort of overvoltage protection can be at about twice the rated voltage. Unfortunately that restricts my pick of PWM chips to very few :-( If for some reason there must be clamping as soon as possible the usual TVS devices are too small, then you almost have to resort to a TL431 approach with a big fat FET in there, with tons of SOA reserves. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 30 Apr 2010 19:37
Grant wrote: > On Fri, 30 Apr 2010 08:26:04 -0700, Joerg <invalid(a)invalid.invalid> wrote: > >> JosephKK wrote: >>> On Thu, 29 Apr 2010 10:09:51 -0700 (PDT), "miso(a)sushi.com" >>> <miso(a)sushi.com> wrote: >>> >>>> On Apr 26, 3:35 pm, Johnny5 <dirtylogicdesi...(a)gmail.com> wrote: >>>>> I was curious if anyone had any insight into protecting an Opto- >>>>> isolator LED input from load dump, Jumpstarts, and many of the other >>>>> signals in the auto environment. FETS,CLIPPERS,Clamps? >>>>> Thank you in advance, >>>>> It is an open drain SSR. >>>> The automobile industry seriously needs to address providing DC to >>>> their customers. They need a better connector instead of the cig plug, >>>> and the DC should be conditioned. >>>> >>>> Ditto on transorb diodes. >>> And what about the yammerheads that insist on plugging 700 W inverters >>> into them? >> >> That's where two wonderful inventions come into play: Fuses and breakers :-) > > Yes, but sometimes the fuse and main switching device break at the same > time, oops! Way back when I worked on power converters the fast fuses > (the big silver in sand type) cost about as much as the SCRs, and it was > still a race which would break first. > Sometimes I work on aerospace stuff and there nearly everything is behind a breaker. It's no problem, if the breaker comes then something is busted in the connected device already. The devices themselves must be designed so they can stomach the spike without tripping the breaker, otherwise they'd fail certification. In a car, if someone would plug in a 700W inverter, load it to the hilt and there was a 20A breaker it would simply trip. Nothing in the inverter should die. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |