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Forum Index : Microcontroller and PC projects : 12v/24v DC power filter thing....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9754 |
Hi folks.  I want to use one of my projects in a vehicle, but I know that vehicle electrical supplies can be a bit nasty when it comes to running an MCU on them. Does anyone know of a filter thing, that works well as a DC filter AND as a load-dump protection/spike arrestor should the battery be disconnected with the engine(and alternator) running? I have so far found this thing at Jaycar, but I have no idea what is in it. I expect that it filters the DC to remove noise, but I doubt it has any load-dump protection or spike protection - but perhaps it does. I suppose I could buy one and cut it open to see what is inside it. If something off-the-shelf is available, it would just save me having to try to spend time researching and building one. But if members know of any schematics they could recommend, so much the better and I could possibly then include it on the main PCB with everything else. I am thinking something along the lines of this:  I already have the SEPIC buck/boost converter to deal with any input voltage from around 7v to 40v, and so am just thinking that I need an EMI filter in front of it as in the diagram above, perhaps with a juicy TVS diode or two across the filer. Thought and opinions would be very much appreciated. Thanks for any replies. Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru  Joined: 08/01/2014 Location: United StatesPosts: 925 |
Grogster, I have used this regulator for anything I use a microcontroller in a vehicle and it has NEVER failed me. A couple of logical filter caps and ALL is well. I have used these in MANY motorcycle and car projects. Maybe I'm lucky, but no failures or issues on any mobile project. From TI... The regulators are also suited for automotive applications, with built in protection from reverse battery connections, two-battery jumps and up to +60 V/−50 V load dump transients. Familiar regulator features such as short circuit and thermal shutdown protection are also built in |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9754 |
Hey there. Looks like a good device, but the load current is insufficient. I need at least 1-amp capability. I will remember this device though, and have saved the PDF. Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
This is also in TI's automotive catalog... requires 4 to 6 external components.... TL2575HV-33-Q1 1 amp capacity. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9754 |
This is a very interesting device!  What I particularly love about it, is that it can have up to 60v in(as with the one that Jim linked to above), but with the current I need. I could just about do without the SEPIC converter, and just use a couple of these with some filtering and TVS diodes to control the input spikes etc. I need to read more of the datasheet, as at 24v in especially, I would need to work out the heat dissipation. I only need the 1A load at about a 20% duty-cycle, so that should prevent the regulator from getting too hot. I will read the rest of this PDF! Anyone else with other ideas or other HV regulator part numbers, please do post. EDIT: OH! Jim! It's the same Jim for both post.  Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
I did a bunch of research for this particular type of application (automotive, mainly motorcycles) in order to put some fun uC projects on the bikes. My main goal was to keep it as simple as possible and cheap. The first reference is used the most. I try to keep all the uC stuff under this regulator and anything I can possibly use the 12v power for, I would using the uC to handle external low gate voltage mosfets etc. This way the 500ma capacity was never an issue. Don't know what you are trying to do... |
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KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1945 |
I've been running a big multi microprocessor and computer interface system in my older vehicle for almost 10 years, that includes around 13 USB devices and a palm sized 1/2" thick windows PC running everything (9 second power on to fully running). I have Interface micros to the climate control and vehicle control systems, iDrive manual control, steering wheel control and touch screen control of Climate systems, GPS, DAB-FM, Music and vehicle running status and so on. System microprocessors can run standalone if the PC fails, it never has. I built two low dropout 5A SMPS back then for powering all USB devices and hubs, they have never failed, filtered input and output as SMPS noise is a HUGE issue with GPS and DAB modules. The Tiny PC has a built in battery and does not supply any current to any USB device or external connection, it simply enables the two 5v SMPS units as USB voltage is enabled via the OS and Bios, one SMPS also drives the PC once USB is enabled. Never had a glitch or failure of any part of the system with the exception of a big USB flash drive that held music my library. Not bad for almost 10 years running. The system is impervious to cold cranking or IGN cycling at any time and in any operating state, it is fully automatic and appears to be part of the vehicle - there is no hint of a windows PC behind anything. Point is, it obviously depends on the vehicle, my old 2003 Honda was very advanced for it's time with full body control modules, computer management for engine, transmission, climate control and vehicle systems management. I've had a battery go open circuit in 48 C heatwave conditions in the middle of nowhere and never damaged a thing, not something I would ever do purposely. Likely saved by the load on the alternator from AirCon and big transmission and radiator fans all running full tilt at that 48c temp. You would think that interference comes from the output of an SMPS but it actually shows up more on the 12v supply side coming back from the SMPS into the 12v wiring. I used toroid cores and a Spectrum analyser to make the IO filters back then. Apology for rambling on. Mike. NANO Inverter: Full download - Only Hex Ver 8.1Ks |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2464 |
hi, what you want is a common-mode choke: https://en.wikipedia.org/wiki/Choke_(electronics)#Common-mode_choke https://en.wikipedia.org/wiki/Choke_(electronics)#Common-mode_choke (forum software is removing the brackets from the URL) you'll find one that can be salvaged on the input side of just about every 230v switch-mode power supply these days. they work remarkably well. cheers, rob :-) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9754 |
You mean like this kind of thing? This is designed for mains AC, so I don't know how well it would work on DC. Do you have any thoughts on that? Ditto the EMI filters inside pretty much any PSU - will they still be effective on low-voltage DC? How about this one? Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2464 |
mains AC is slow (50Hz), while common-mode chokes filter out the higher frequency stuff, hence they work just as well for DC. most industrial automotive electronic equipment will contain a common-mode choke on the supply input. however, there are some design limitations. most importantly is to not 'bypass' the common-mode choke by having any solid signal ground connection emerging from inside the equipment. you can get around this by either having an isolating PSU within the equipment, or by using a loosely coupled signal ground, or by keeping any externally connected switches, etc, floating with respect to the chassis. cheers, rob :-) addendum, lets see if this image works:  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9754 |
Ahhh, OK then. So circuit-ground must be isolated from chassis ground. Is that correct? This kind of idea:  I added TVS diode D1, but other then that, the rest is what I expect this filter to be. D1 would need to be a reasonably juicy one, so it can dissipate the energy if the voltage ever peaks above 60v. But as the alternator's own regulator will pull that voltage back down to where it should be in a load-dumping situation, and that this SHOULD happen with about 100mS or so, we should only need to suppress the short spikes. I'm thinking 6A diode at least. Thoughts? Comments? EDIT: Rob beat me! The SEPIC converter I am using has a common ground, but so long as IT'S ground and all the circuit ground, is on the ground side of the common-mode choke and NOT on the chassis side of the choke, that's OK - correct?Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2464 |
TVS's normally have a phenominal current/power rating (1000A or more) but only for a very short time. you may get good milage by putting a polyfuse in place of the regular fuse - it has been over a decade since i played with these things, and my memory is a little fuzzy. you can make a weak connection between circuit ground and chassis ground, for example through a 100 ohm resistor, but then noise on the 12v supply will be superimposed upon the signal you are measuring. this may or may not be an issue in your application - for a digital input the noise may be well below the switching threshold, for an analog input you may be able to filter out the noise in software. alternatively, use optocouplers for digital I/O and differential input buffers for analog inputs. cheers, rob :-) |
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