New Member and an Automotive based Transient Filter Supply Question - Page 1
Forum section: electronics / projects

author: Docara
author_rank: Regular Contributor
timestamp: June 09, 2018, 02:05:03 pm
content: Hello Everyone - just a quick introduction,I have just joined the forum and would like to say a big hello to everyone and a thank you to everyone in advance for replying to any questions I submit.Just some background my first 'love' was electronics back in the day when a Z80 was cutting edge and datasheets used to come in books (1984 ish). I started off formally studying electronics but life, money and women forced me to stray from the path of 'enlightenment' and I have ended up up being a (bloody good) electrician. My interest has been rekindled thanks to Dave's fantastic digital power supply project on YouTube from a few years ago and a small project I have working on (intermittently) which I would like to move forward and would like some help.So, my level of knowledge is I know what I want to do and roughly how to do it, I know what to search for into Google and I have the capability to use reference designs and formula from datasheets. What I don't know is techniquesAnyway....I have been restoring a narrowboat in the UK with a friend of mine. During the process 'things' have presented themselves which I would like to do (electronically) but I no longer have the knowledge how to proceed.Cutting to the chase and keeping things very simple for now, The project I am working on (basically) is to connect two microcontrollers together using a CAN bus but not necessarily using the CAN protocol, allow remote wakeup and control of daisy chained UART Servo's at one end and a monitoring with a touch panel display the other.So my first question revolves around filtering for the regulated power supply feeding the electronics, assuming the installation is essentially identical to a diesel automotive installation BUT with battery isolation relays and an inverter charger in place there is going to be massive transients and noise on the cables so is would what I have included be sufficient to protect the following voltage regulator stage. I am allowing a 1-1.5A draw. Sorry I did try to include the jpg as a picture not an attachment but computer said no.Thanks againMatt

author: bitseeker
author_rank: Super Contributor
timestamp: June 09, 2018, 06:34:49 pm
content: Welcome to the forum, Matt. Automotive (or equivalent) power line noise suppression is outside my area, but I'm sure the right folks will be along in time. Including a bit about your question in the subject of your post will help catch those with aligned interest. For example, instead of just "New Member and a Question," something like "New Member with Question about Power Protection in Auto/Boat."Regarding pics, attaching them is advantageous for those with low bandwidth connections as the full image isn't downloaded until someone clicks on the thumbnail.

author: Docara
author_rank: Regular Contributor
timestamp: June 09, 2018, 09:05:14 pm
content: Hi Bitseeker ,Thanks for the reply, I have tweaked the title as you suggested. To be honest I am quite surprised the title block accepted such a long phrase - A lot of other forums are very limited in this area.I did try to sort the image out but I just couldn't, all I could get showing was twoplace holders up without a prompt for the file - is there a secret to this? I wonder if the problem is my end and browser based.Matt

author: bitseeker
author_rank: Super Contributor
timestamp: June 09, 2018, 09:13:42 pm
content: If you really want to have the image appear inline, here are the steps (assuming you're doing this on a computer, not phone/tablet):1. Attach the image to the message as usual.2. Post the message, even though you're not done, yet.3. Click on the thumbnail to enlarge it, then right-click on it to copy its URL.4. Edit your post and paste the image URL where you want the image to appear.5. Apply the image tag to the URL either by manually typing the bbCode or highlighting the URL and clicking the image button in the toolbar. (This step may be optional, depending on whether the URL is interpreted correctly and automatically by the forum.)6. Post the changes.

author: max_torque
author_rank: Super Contributor
timestamp: June 10, 2018, 04:02:31 pm
content: Given you have a TVS diode to clamp over voltage, i'd suggest some sort of fusing or current limiter to prevent that diode getting a kicking!Worst case is the alternator on the engine running at full current to charge the battery, but then the battery wire comes off, or some one opens an isolator etc. Here the magnetic flux in the alternator has nowhere to go, and a big voltage spike is generated, generally called "Load dump".As you total current required to pull from the supply is relatively small a self-resetting PTC fuse can be used inline, or you could of course use a conventional fuse.Another option, is to include a suitable series resistor that normally only drops a few volts, but under load dump situations can effectively share some of the power dissipation with the TVS diode. I've used 5w SMC resistors like this successfully before in a product that exceeds 24v load dump (212v peak!!):Choosing the resistance value is of course a compromise, but it can also be sized to take some of the heat load off the linear regulation stage (assuming you are using a linear dropper)

author: chuckb
author_rank: Frequent Contributor
timestamp: June 11, 2018, 01:56:30 am
content: At work, we had a similar problem with a 28V power source. We had to withstand a 110V surge (400 amp source) for several hours and intermittent 600V spikes (from lightning). We developed this circuit through several iterations over 20 years with thousands of units in the field.I will give example voltages here for a 14V system.Start with a series diode in the power line to eliminate issues with a negative voltage transient.Power the electronics from a switching supply so when the input voltage is three times normal the current is three times less. The lower current makes it easier on the other protective components.Use a Depletion mode MOSFET 100-200V with a 16V Zener on the gate to ground (the voltage is determined by the highest voltage the switcher can handle). Use a pull up resistor from the gate to source of 1k-10k to bias the zener. There will be about 2V across the gate to source when the Zener needs to work. Add a 0.1ufd cap across the Zener for a slower turn on to limit inrush current to your switcher filter capacitors. During normal operation the Depletion mode MOSFET will be fully on and it will look like a 0.1 ohm resistor (or less depending on the MOSFET). If the input voltage exceeds 16V the MOSFET will act as a very simple linear regulator at 18V (on the source). During startup it looks like a small resistor so it has a minimal affect on dropout voltage.To start with, look at the IXYS part IXTH16N20D2. It is 0.080 ohms, 200V and 16 amps. This is probably overkill but it saves doing a bunch of testing.With a 200 Vds MOSFET, use an 160V Transorb (600-1500 watts peak) on the input. When the transorb passes serious current the voltage will go up 20-30V. It's all in the datasheet. I would use a Bi-directional (clamps at +-160V) Transorb before the series diode. This lets you establish a 200 V PIV rating limit for the input diode.The common mode choke is fine as long as you do not have any sensor or load in the system connected to actual ground. If something is connected to actual metal ground it will bypass the choke and inject noise into the wrong part of your circuit. This will lead to the strangest problems you have ever experienced. We had one intermittent issue that took us years to isolate.NOTE: When Transorbs (or other semiconductors) are asked to absorb to much energy they will overheat and fail shorted. If you have a glass or hermetic package the little bitty bond wires will act as fuses and they will open under current overload. With epoxy packages the 20 ga copper lead is directly connected to the chip. I have overloaded Transorbs, they have failed shorted, then the 20 ga copper lead wire fused open (500 amps peak) or the epoxy package cracks and opens the circuit.Overloaded semiconductors always fail shorted initially, then there will be a little current surge or a large current surge until the power system clears the short.With a 160V Transorb that should not be happening to you. Be sure to use a fuse inline to cover chafed wiring. A Poly fuse is to slow to protect anything but a wire, maybe.The last bit of experience, don't use solid tantalum caps in a high current (>0.2 amp) circuit, ever.Hope this helps.Added Attachment -

author: Docara
author_rank: Regular Contributor
timestamp: June 11, 2018, 10:29:39 am
content: Hi,Thank you Chuckb and Max_torque.Wow a lot of information to digest.Max-torque.Good call I completely forgot about a fuse locally on this branch. Though there is an upstream fuse from the ignition switch for the whole of the Dashboard based system - of which this is a section.To clarify are you suggesting putting the power resistor in the supply line before the TVS or inline with the TVS? (I am presuming the first) Do I need to derate the VBR of the TVS because of this resistor?Due to other systems there is no possibility of isolating the battery when the engine is running - other than human interference with a spanner!FYI - My intention is a BUCK/BOOST after this filter stage then two linear VR's (probably LDO). I need low power dissipation from the linearsI have made another post here concerning CAN Transceivers, whatI would like to dois trigger the BB regulator to awaken from sleep via CAN.ChuckbAt time of writing this I haven't looked at your schematic yet. I have no idea of the levels of transients I might encounter so I have taken a lead from the major manufacturers advice on automotive filtering etc and tried to implement what they suggest. From Load dumps to cranking volt drops to reverse polarity protection. I do have a slight concern about actual or nearby lightning strike as the boat is fully metal. This is why the first TVS is in-place.Yes I do intend to use a switching Buck/Boost (as mentioned above.QuoteThiscouldbe a problem as at this stage I am not sure what the future holds! The only loads could be indicators and levels switches but these are just that a switch. Would you suggest just an inductor in the supply lines then?What is a "20 ga copper"?I will have a look at the schematic and report backThanks a gain to you bothMatt

author: Docara
author_rank: Regular Contributor
timestamp: June 11, 2018, 11:43:04 am
content: UpdateI've combine Chuckb and Max-power's advise -What are your thoughts on the following schematic?

author: chuckb
author_rank: Frequent Contributor
timestamp: June 12, 2018, 12:46:18 am
content: Quote from: Docara on June 11, 2018, 10:29:39 amYes I would suggest replacing the common mode choke with just an inductor in the powerline. It does not need to be a large inductor.Sorry "ga" is an abbreviation I use for American Wire Gauge (AWG). The transorb lead is copper and 1mm in diameter that's equivalent to 18 American Wire Gauge. My memory told me it was 20 AWG but the data sheet shows 18 AWG leads.