Discrete SMPS have any advantages? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: April 01, 2024, 05:32:48 pm
content: Hi,As you know, certain SMPS have no control chips, they just use discrete transistors and diodes, and kind of set up some kind of self oscillation.Is there any advantage of these kind of converters over "Control IC based" SMPS's?Like are they more immune to ESD damage? or more immune to Nuclear Magnetic Pulse? or more immune to higher levels of atmospheric radiation which they may recieve at high altitude?

author: Gyro
author_rank: Super Contributor
timestamp: April 01, 2024, 05:48:00 pm
content: Quote from: Faringdon on April 01, 2024, 05:32:48 pmOk, where are you going with that one?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 01, 2024, 05:51:14 pm
content: Nope.They were cheaper, back before single-chip regulators got super cheap out of China. No transient immunity that can't be solved better by protective components, and modern PF and efficiency specs generally demand IC functionality.Maybe you'd reach for some toobs to handle nuclear EMP, but I'd still feel better doing it with proper semiconductor components inside a thick fuckin' box o' metal.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: April 03, 2024, 02:52:27 pm
content: Quote from: Faringdon on April 01, 2024, 05:32:48 pmIf you want to have better immune to ESD and EM pulse from nuke, you can try to build SMPS with using tubes instead of semiconductor components

author: mtwieg
author_rank: Frequent Contributor
timestamp: April 04, 2024, 01:51:49 pm
content: Usually choosing discrete designs is driven by concerns over sourcing components, especially if you have to commit to a 20-year product lifespan. Obsolescence, export restrictions, tariffs, etc.The decision is also sometimes based on a need for exceptional reliability in some applications. But that's not to say that discrete components are generally more reliable than specialized ICs.

author: Faringdon
author_rank: Super Contributor
timestamp: April 04, 2024, 07:01:27 pm
content: Thanks, another point though, is that i used to work at a company that supplied 230VAC, 250W Linear regulators to the Nuclear industry....mains transformer followed by diode bridge/smoothing cap, then large power BJTs in pllel, with emitter degen....no chips.....they weighed a ton.Word on the factory floor was that they needed to be like that for reliable back up power supplies in the nuclear environment, since chips just werent as rugged to the neutrons and protons.

author: Xena E
author_rank: Frequent Contributor
timestamp: April 04, 2024, 09:18:07 pm
content: Quote from: Faringdon on April 01, 2024, 05:32:48 pmNo!Then...Quote from: Faringdon on April 04, 2024, 07:01:27 pmChips are more rugged in the presence of radiation if they have been covered in dip or ketchup.You don't get the problems you outline in the OP in a nuclear power installation, particularly EMP... or you should hope not, that would be a one time event precluding any worry about the failure of some piddling SMPS.If you did, you'd already be fucked...

author: Faringdon
author_rank: Super Contributor
timestamp: April 05, 2024, 04:42:06 am
content: QuoteThanks, but discrete components dont need this "dip" to become rugged? Since they are already more rugged than chips?

author: David Aurora
author_rank: Frequent Contributor
timestamp: April 05, 2024, 05:58:09 am
content: Quote from: Faringdon on April 05, 2024, 04:42:06 amHow about we just skip to the part where you drop a conspiracy theory about China and tell us about the 15th place you've been "wrongly" fired from this week and we all move on?

author: mtwieg
author_rank: Frequent Contributor
timestamp: April 05, 2024, 11:56:57 am
content: Quote from: Faringdon on April 05, 2024, 04:42:06 amAgain, discrete components are not generally "more rugged" than chips. If you took an IC and somehow singulated each of its components into its own die and packaged them discretely, it wouldn't be any more robust (likely much less so). Engineers who work in hi-rel applications understand their failure modes and how they relate to the devices' properties and construction.

author: ftg
author_rank: Frequent Contributor
timestamp: April 05, 2024, 01:04:20 pm
content: Quote from: Faringdon on April 01, 2024, 05:32:48 pmThe reason one sees discrete SMPS designs in satellites is the challenge that is getting new parts through the approval and qualification process.So in some cases the designers are working with a very limited pool of qualified parts.One might bother to go throught the qualification process for some new GaN RF transistor for example, but possibly not for some SMPS controller.That's my take anyway.

author: AnalogTodd
author_rank: Regular Contributor
timestamp: April 05, 2024, 02:05:58 pm
content: Quote from: ftg on April 05, 2024, 01:04:20 pmIt's a very good point. What OP does not apparently know about is radiation effects. I would recommend he get a copy ofIntegrated Circuit Design for Radiation Environmentsby Gaul, Van Vonno, et al. as one place to look for information. It's not that chips are not rugged to neutrons and protons (after all any semiconductor junction can be considered a 'chip') but instead what effects radiation, heavy ions, neutrons, protons, and more all have on the chip.Why can't you take a commercial product and put it in these environments?One of the first things is total ionizing dose radiation (TID). TID will shift thresholds of MOS devices, degrade bipolar device betas, damage semiconductor crystal lattice and cause leakages among the main effects. This can be enough to cause many circuits to fail to function. Things can be better or worse depending on the rate at which the circuit receives the dosage (go look up HDR vs. ELDRS).The next major hurdle is single event effects (SEE). This comes from a charged particle striking the semiconductor and causing any of a number of issues. Go research SEB, SEFI, SET, SEU, SEL, SEGR, and SEDR. To have these chips simply survive, they often need to be derated significantly from what they might be able to achieve in a commercial environment, often by a factor of three or more. I have seen circuits that have been subjected to this testing at their commercial ratings get destroyed.Neutron damage is much more rare (neutrons lack charge and must collide with particles in the semiconductor to have an issue as opposed to protons) and is often not as critical.As stated above, qualifying products for these environments isn't a simple matter. Have a Cobalt-60 source at hand? Now you can test TID. To test SEE, you need a cyclotron and there are only a handful of those worldwide. These are just testing; if a chip fails testing you are back to the beginning of trying to find a new chip to use. A better option might be to spend the money to use a chip that is radiation hardened or tolerant. Of course, be ready to pay a LOT more than you would for a commercial product (a commercial version may be $1 where the RH version is $1000).Building a discrete solution may be a viable option as individual transistors/devices can be characterized with this testing (and one can now know where failure occurs) and then used within a limited operating range.

author: Faringdon
author_rank: Super Contributor
timestamp: April 06, 2024, 12:49:13 pm
content: QuoteThanks, and from your kind post, i take it that the "jury is out" as to whether or not chips are more sensitive to radiation than discrete semiconductors.....it would need expensive equipment to ascertain and so we wont know.But from what you say, its cheaper to certify an all discrete design for radiation-environment use, (compared to a chip based design) and so there is going to be a definite market for all-discrete designs."intuition" does tend to tell me that a SOT23 NPN is going to be more resilient to radiation damage than a tiny tiny NPN on a chip......there's more volume that needs destroying on the SOT23, so its bound to be more resilient to radiation(?). Like the difference between trying to smash a wall down with a hammer is going to take time.....trying to totally smash a bit of brick to dust is going to be quicker.Also, ive worked on down-hole designs which were pretty much all discrete (apart from the famous UC2843 which everyone knows about) due to those discretes already having been certified.And of course, bipolar stuff is always more resilient to anything than CMOS, because CMOS has gate junctions which are thin and delicate...this is why NPN's are more resilient than MOSFETs. And the UC2843 is one of the only power supply chips that is all bipolar, so it is of course, very resilient....(and very cheap). The introduction of the UCC28C43, (pin for pin with UC2843 but made of CMOS instead) which has far less bias current,, has in no way obseleted the UC2843...for the very reason i discuss here.If a proton hits a FET junction, then that junction gets smashed up bad.....the smaller the junction, the worse it gets smashed up.(this is why chips are less resilient than discrete, which tend to be larger) ...if a proton hits a PN junction inside a BJT, the damage is nowhere near as bad.

author: AnalogTodd
author_rank: Regular Contributor
timestamp: April 08, 2024, 01:55:14 pm
content: Quote from: Faringdon on April 06, 2024, 12:49:13 pmYou're reading a lot more into what I wrote than you should. There is a lot of information out there on radiation effects and how any semiconductor handles it, the "jury is out" is not the case. Any discrete device will be affected by radiation in a fashion similar to a full chip. It does take expensive equipment to ascertain radiation effects, but the difference is that once you have it figured out, a box full of discrete devices can be reconfigured in a lot of ways that a full chip cannot.QuoteIt is not necessarily cheaper to do, no. You still need to do the same testing either way. The difference is that once the testing is done and you know how things respond, you can build the discrete devices into something different and know how that circuit will respond. The same discrete devices can be used to make an amplifier, a regulator, or any of a number of circuits without needing testing as you know how the individual devices respond. The cost difference is that buying a radiation hardened chip has had the manufacturer do all the design and testing for you and you get all the data supporting that when you buy the parts. Buying commercial discrete devices may be cheaper, but you must now do all the testing and make models and then do the design yourself. How much does that cost?QuoteSpend time learning about radiation effects, please. Larger devices are not necessarily going to be more resilient. The larger volumes can actually work against you as particle strikes inject charge into a junction based on how far it goes through that junction. A 15 micron thick junction will get three times the charge as a 5 micron thick one does. Leakages may actually be worse in the larger device as there is a larger area between junctions where damage can occur. Remember, this isn't just about particle strikes, but ionizing radiation as well and a small NPN on a chip can have less than 1% of the junction area of a discrete device that can leak. That same size difference also comes into play with particle strikes as the rate at which you can expect a particle to strike the larger device as opposed to the smaller device is directly related to the size. When you get a charged particle every X number of days through a 1 sq. cm area, the larger device gets hit more often than the smaller one.QuoteI've worked with people doing down-hole designs as well. The biggest challenge there is temperature effects as the environment can run above 150C. The market for down-hole devices is so small that most chip manufacturers don't want to go after it. They're more than happy to rate devices to a 125C maximum junction temperature for commercial/industrial stuff and have been going to 150C for automotive stuff going under the hood. These markets are millions of dollars in size. The few times that I have seen chip manufacturers selling into down-hole designs is when they found that a circuit can withstand 175-185C and still function properly (a happy accident in their opinion).QuoteAgain, take the time to learn radiation effects. Bipolar devices are worse for some radiation effects compared to CMOS. This is why the radiation sensitive community has now switched to doing low dose rate testing vs. high dose rates for ionizing radiation. High ionizing radiation dose rates can get you a result in a short period of time, but don't reflect how dosing actually occurs in the environment. Any MOS device isn't really more fragile, it's different effects. A charged particle going through a gate oxide can create an ionized track that can allow current to flow if there is enough electric field across the oxide (usually seen with high drain voltages). That allows for the discharge of the capacitances through the channel; not a problem for a small device on a chip since it's a tiny capacitance, but a large MOS device can have enough capacitance to create high currents and destroy the oxide (single event gate rupture or SEGR). Bipolar vs. MOS devices change in different ways with ionizing radiation; bipolars tend to have beta drop, while MOS devices have a threshold shift from electrons getting knocked out of the gate oxide. N-channel devices have their gate thresholds drop and P-channel devices see an increase.Having a particle strike isn't just 'smashing' junctions. Go back to look at the size of protons relative to the size of an atom--there's a lot of empty space in there. What charged particle strikes tend to do is create a track of electron-hole pairs in a material as their charge attracts and repels protons and electrons and any electric field causes those to drift in different directions. Hence you get a net electrical charge injected into the junction. Neutrons have no charge so they only cause an issue when they collide with electrons or the nucleus of an atom and that is rare given the space in an atom.A discrete design can give options that a chip doesn't. Need everything to run low voltage except for one transistor? You don't need a high voltage process for everything on chip, you just buy the one device to be rated appropriately. However, when you look at it from a reliability standpoint, a discrete design is much worse overall because you have so many possible failure points as opposed to just the one chip. On top of all this, don't forget the fact that many chip functions aren't built in a radiation hardened solution. The number of radiation hardened products out there is tiny compared to the commercial and industrial spaces, and the number of companies and engineers actually designing specifically for that market is tiny (I might estimate a few hundred worldwide). So you may be stuck doing a discrete design in that environment because there might not be an existing solution.