(Very) Wide input voltage range DC-DC power supply design - Page 1
Forum section: electronics / projects

author: mister_jay
author_rank: Newbie
timestamp: July 28, 2022, 08:32:43 am
content: Hello there, this is my first post on this platform, so please excuse any violations of best practices.I currently need to design a piece of test equipment that measures Voltage & Current in a current range from 10mA all the way to 32A @ 12 to 450V AC or DC.The wide range current measurement itself is definitely a problem on its own, however - the real obstacle i stumbled across appears to be the power supply needed for the sensing & processing of the gathered data.This would not be a problem with external power input or even a battery (which would be sucked empty pretty fast thanks to WiFi capability), nevertheless the only available input source for some power would be the lines voltage & current is measured on, which - as stated - has an extremely wide voltage range of 12V all the way up to 450V.Such a wide input voltage range seems to be an ungodly task for your everyday DC-DC converter to handle at acceptable efficiency.(Power usage itself would not be a problem - heat dissipation, however, is)I planned on going discrete from the beginning due to part shortages and not wanting to rely on the supply chain stability of such a niche semiconductor (if such a part would be available, that is).Maybe i got limited in my thought process because i hyper-focussed and narrowed down too much, which happens fairly often to be honest...Key Data:Input Voltage:12-450V DC (Let's neglect AC)Output Voltage:Either 5V or 3.3V (Preferably 3.3V since that would save me from using inefficient LDOs)Output Current max.:500mAOutput Current nominal:250mASince the Equipment would be in a thickly overmolded housing (no touchy) - input isolation is not necessary (also has space reasons).My problem:I think i am a little bit biased towards buck converters, cutting out potentially better solutions for this problem. Also - if buck converters are the best option - i have no idea on how to supply the necessary components with the correct voltage in a efficient way - zener supplies barely work in such a wide input voltage range without reaching sun's temperature...I also thought about including several supplies (One for 12V to maybe 60V, one for 60V to 120V and so on...) but i am not sure on how to select the proper supply without user interaction (power is fed on the same input pins) and how to handle overlapping.I did drew some basic synchronous buck converter schematics, since it would not have made any sense...

author: mariush
author_rank: Super Contributor
timestamp: July 28, 2022, 09:33:24 am
content: 3.3v and 250mA / 500mA max is not A LOT of power. It's 1-2 watts.You could probably shove a bunch of 18650 batteries (or pouch style / flat battery) and get several hours worth of operation out of the battery.Add a QI charger on the back of the device, and people could charge the device through its housing, you could charge in the car from the car's usb / cigarette lighter, or in fast food place while they're taking their break. Add a standard 2.5 /5.5 barrel jack (consider having it on separate pcb for easy replacement/repair as that is more likely to break, or some rugged version if you think it matters) and a dc-dc converter to support 5v...24v input to fast charge the battery with a proper fast charge capable charger IC. or a usb type-c with a charger chip that can negotiate 5v / 9v / 12v for faster charging.Optionally, You could design your product to accept a commercially available lithium battery format, like the battery packs for construction tools .. see :https://www.amazon.com/s?k=lithium+makita+batteriesTake out battery and put it in charger, plug new battery in your device.. job done.

author: mister_jay
author_rank: Newbie
timestamp: July 28, 2022, 09:41:38 am
content: Sorry, my bad... I should probably have clarified that the device itself is not human operated, nor will it be accessible for service along its lifespan to e.g. charge/change batteries. It will be in duty 24/7. That is why having a battery is simply not feasible.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 28, 2022, 10:01:59 am
content: You can use a typical high voltage buck converter to cover most of the range. Eg: AL17050WT, but then one that can do your rated voltage. Go find one that is in stock. There are hundreds.However, drawbacks of these chips is their minimum input voltage. They have a undervoltage lockout basically inhibiting their functionality up to say 35V, heavily derated of course, until the circuit optimal of 85-264 typically.For that lower bit you can use a depletion mode mosfet zener voltage clamp, in parallel with the buck. The key thing you have toensureis that the mosfet is forced off when the input voltage is enough for the buck to work. Otherwise smoke.I can't share many more details because it's what I do at work, and we spent quite a long time on it picking and testing parts.The other option, but your power requirement is probably too high, is a capacitive resistor dropper as used in many of those wide range timer relays.

author: Someone
author_rank: Super Contributor
timestamp: July 28, 2022, 10:10:22 am
content: It is doable in one step if you can afford EMI challenges and plenty of bulk capacitance, a micropower regulator running from a bootstrap zener shunt regulator on the primary side. Like a very scaled down universal input voltage flyback. At 2W of output power, why synchronous? single switch topologies is where I would start.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 01:03:00 pm
content: I have a flyback inverter here in qucs, model made for a previous job. Fairly low parts count.It looks feasible for wide range of DC Input using constant on-time pulse period control. ( that is, the off time extends as Input rises)A 1200 V switching device would be needed along with a special transformer.A 2:1 would give a DC link of about 12 V, constant 24 Ohm load with 12 V in and high duty cycle, then the off time increases as the Input voltage risesThis transient model needs nanosec time steps for the snubber etc so takes a long time to solve as the input voltage gets high, needing a long time window. I did not run it up to 450 VDC, so there may be issues not observed yet.

author: mister_jay
author_rank: Newbie
timestamp: July 29, 2022, 03:05:29 pm
content: First of all - thanks for all the replies and the diverse hints and ideas about designs and technologies. I opted for a (rather) conventional synchronous buck design with external MOSFETs and the rather supply chain stable NCP81161 OnSemi High & Low Side MOSFET driver IC.PWM gets generated using the notorious 555 Timer IC, whose availability is out of question too.This whole driving circuit gets supplied with the needed power using the suggested bootstrap zener shunt regulator circuit.To answer "Someone's" question on why synchronous - the broad input voltage range is pretty inefficient itself. Using a synchronous design approach i try getting at least a bit of performance back.Simulation and Prototyping will eventually show if it is more economical to use single switch topology with a low RDSMOSFET or the synchronous topology (Economical not only in terms of BOM cost, but also in an increase of lifespan through reduced thermal stresses and power usage).Also note, that i forgot to add the Schottky diode in the schematics, connecting 3V3 & GND in parallel to the low side MOSFET. This will (hopefully) further increase efficiency by bypassing the internal diode in the LS MOSFET.Handling AC input is not a problem - however, i still have to evaluate (or rather calculate) whether using diode bridge or an active rectifier is better. (It would not make sense to increase BOM Cost for the more efficient active rectifier, just for efficiency gains to get vanished by the active rectifier IC / discrete components)I'll keep you updated and post the schematics once all the calculations are done and the basic simulations & tests were acceptable.Best wishes!P.S. Please feel free to further contribute to this topic - I definitely appreciate any kind of input regarding optimization or even completely new ideas!P.P.S Regarding mag_therm's Flyback inverter - the required transformer would be pretty large in dimension, right?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2022, 05:12:53 pm
content: Attempting to use a 555 for an application it is really not suited to, suggests a level of experience that isn't equipped to develop wide range, high voltage, or synchronous converters... Pace yourself, know your strengths.The suggestion for a wide range IC based solution, in parallel with a linear one, is a relatively easy one. Using Fig.10:https://www.infineon.com/dgdl/Infineon-Application_Note_Applications_for_Depletion_MOSFETs-AN-v01_00-EN.pdf?fileId=5546d4624cb7f111014cd63d1a197d94set for a voltage somewhat below nominal, so it will provide adequate startup current, then go away once the switcher pulls in. The maximum dissipation while the switcher is in UVLO can be managed by choosing a relatively large device (D2PAK and TO-220 sizes are available). A thermal protection circuit may be desirable, if this may be subject to abject environmental conditions (poor circulation / high ambient temps).Tim

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 05:41:48 pm
content: Hi Jay,The concern about using the small signal inverter types usually discussed on this forum is that you intend it will be running it from 450 V DC.In the "likely" event of prototype or end use failure , you have to guard against a big bang and schrapnel flying around.Also comply with good practice and the fire standards in destination country eg NFPA in USA I am sure similar in EU.DC overcurrent protection at low currents is a problem: "Let through energy" etc has to be controlled.The components eg main switcher and conductor in the transformer etc will then have to be sized for that let through I^2*tAnd remember that, when a FET or IGBT fails, there can be arc back to gate circuit.So yes, components would be larger -no matter what topology you select..When I ran the period control constant pulse flyback inverter this morning, I did not get to the stage of running at 450 V as mentioned.If using that method, main switcher and the rectifier diodes and transformer will have to be rated for the peak currents even though the duty is unusually low.Maybe you should look at alternatives to running this on 450 V DC.

author: mister_jay
author_rank: Newbie
timestamp: July 29, 2022, 05:54:52 pm
content: Quote from: T3sl4co1l on July 29, 2022, 05:12:53 pmHello Tim,thanks for your input. I wonder if you could clarify, why the 555 timer IC would not suited for PWM signal generation?Putting the 555 in astable mode generates an oscillation.Using an LM555 instead of your "normal" NE555, output should be fairly independent of temperature and supply voltage.

author: Warhawk
author_rank: Frequent Contributor
timestamp: July 29, 2022, 06:20:01 pm
content: You can have a look at TI reference designs (https://www.ti.com/tool/PMP10200)The flyback topology is probably what you want to look at.What about Innoswitch 3 from PI?

author: exmadscientist
author_rank: Frequent Contributor
timestamp: July 29, 2022, 06:24:52 pm
content: Quote from: T3sl4co1l on July 29, 2022, 05:12:53 pmAgreed, this is NOT the easy part of this line of work! Be careful! And remember that 450 VAC is around 640 VDC peak, so banish all thoughts of 450 VDC from your thoughts if this is to work out. Of course, it gets worse, much worse, if this is mains 450 VAC, because mains hungers to kill things.QuoteSome advice, don't choose a plain DPAK for a job like this. They're smallish, and D2PAK has many more choices if you want a different part. (IXYS Littelfuse has a pretty good line, if not the cheapest.) The failure mode of a DPAK will probably be heating up enough to desolder itself... which honestly is kind of impressive that they live long enough to do that. 450V in is a lot of power to drop!

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 06:54:32 pm
content: Difficult job,1. The purpose is to get regulated 3.3 V 500 mA. from 12 ~ 450 V2. The converter controls are going to need something like that too.Doing 1. is going to require 2. ?Reminiscent of the song "There's a hole in the bucket, dear Liza, dear Liza, a hole "

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 29, 2022, 07:28:24 pm
content: If you want to go from 450Vdc to 5Vdc with a buck regulator, that means your switch has a duty cycle of roughly 1%. And if you also want to regulate the 5V accurately, then you need to have accurate modulation around that 1% duty cycle. Such a large input voltage to output voltage difference also means a large inductance for the filtering and this reduces the accuracy for changing current needs.I guess the easiest approach is to do it in two steps. Put two different buck regulators in series. The first one is able to tolerate 450Vcd on it's input, and it reduces that to something below 40V or so. When the input voltage drops below 40Vdc, then the switch in this pre-regulator wil simply always be on, so it's input and output have the same voltage (apart from diode drops, the series inductor etc).Then, the second buck converter takes this (up to) 40V input and regulates it down to the required output voltage.The second buck converter is one of the many standard circuits, while the first one can be quite simple because it does not have to regulate accurately. The high voltage regulator can be as simple as a reference voltage with a comparator and hysteresis.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2022, 10:42:40 pm
content: Quote from: Doctorandus_P on July 29, 2022, 07:28:24 pmYep, and even if you're as slow as 50kHz (20µs period), that's a 200ns pulse. Good luck getting a 555 to do that consistently. Sure it could be even slower still, but that's still only 500ns at 20kHz, and you don't want to be much below 20kHz because of audible noise.What's missing is, sure, you're making PWM... but that's notallyou're doing.What you're doingfirst,is charging current into the inductor. Current goes up, current goes down. In steady state during one cycle, the rise and fall are equal. V = L dI/dt, for which we can change the dees to deltas with straight-line waveforms (square voltage, triangle current), and so a pulse of for example 400V * 200ns into a 100uH inductor is a rise of 800mA.Note that's voltage across the inductor, so in a buck, it's Vin-Vout during on-pulse, -Vout during off-pulse (until current decays to zero, unless in forced CCM with sync rect).Then, inductor current charges output capacitor, which sets output voltage. If you go straight from PWM to Vout, you incur a double pole transfer function, putting up to 180° phase shift into your control loop.And for point of reference: you definitely don't do a pure timing based control, like pulse width inverse with supply voltage, or delay proportional to. Obviously you can't do fixed PWM% here, but even if Vin and Vout were fixed, you wouldn't, because there are too many sources of error to simply used fixed timing -- at least if you need any kind of regulation. Like, expect 5% or poorer regulation (defined as: change in Vout, as Iout varies from say 10-100% or 50-100% of rated).So that justifies the control loop. And you control inductor current first (typically with a peak or average current mode loop), to limit switch current (especially important when dI/dt can be so high), output current, and to break the double pole (so both current and voltage loops can be stable without any hackery).Speaking of which, between the two [current modes], peak is almost certainly better. With a fast comparator and driver, response can be within a 100ns or so, meaning the output current doesn't rise very much with input voltage, for a given current setpoint. Whereas raw PWM ("voltage mode" control), the modulator gain is directly proportional to Vin, so the control loop has to do a LOT of work accounting for that. And it's very hard to stabilize a control loop over a nearlytwo decadegain range. (Average current mode, means using an inner current loop, whose error amp sets PWM% based on setpoint minus inductor current. So, PWM is still done by comparison to a fixed ramp. Naively, anyway; you would definitely drive the ramp from Vin, so some combination of its slope/amplitude/frequency is precooked to help out here.)So you use two loops, an inner loop (probably peak current mode i.e. a comparator sensing switch current, turns off when crossing threshold), and an outer loop (setting that threshold, based on Vout). See UC3843 for a classic introduction to the method.And then you also get automatic current limiting, during startup and output fault. You wholly eliminate one possible failure mode (excess switch current). It can still fail due to excess voltage or temperature, but even just one of them is big.Output fault is kinda not so much solved by peak current mode, as most of the time is spent in flyback (catch diode on, or nothing / free ringdown) when there is no monitoring of inductor current. That is, if the output voltage is near zero, then dI/dt will likewise be tiny, and current won't have dropped much before the next pulse, which can only be so short, and as a result, output current continually ramps up. On the upside, with the low output voltage, a high-side current sense might be used to sense inductor current directly; level shifting isn't a big deal here. You can also reduce Fsw at low Vout, which is often used by ICs (either proportionally or stepwise -- depending, I suppose, on how good the mfg's analog vs. digital design engineers are..).This all may seem unimportant to you ("Vout = Vin * duty, what could be easier!?"), or you're not aware of the dynamic issues (control response), or edge cases (like startup and fault conditions). Or you suspect it's solvable in the control just by tweaking values (well, again, not over a two decade range you won't!). The system is the whole thing, and you can solve issues anywhere in the system that fits; it doesn't have to be locked into a particular structure, like having a fixed-frequency PWM into a switch. The switch itself can solve issues for you (like if it shuts off after a particular time, or peak current). Make use of all opportunities -- you will need them!(To be clear: you can compensate such a system, but what you will get is stable and fast response at maximum Vin, and extremely slow, lumpy behavior at minimum Vin. The output ripple (dynamic regulation, peak change in Vout for e.g. a step change in Iout) may be so high the output completely drops out, because the controller has to respond at a slow enough rate to handle max Vin but it's hardly getting any input error at min Vin. The challenge is to get stableand fastresponse at all conditions, so that output impedance stays usefully low.)QuoteYeah, cascading isn't a bad idea, maybe not necessary -- the LinkSwitch and things PI has (and similar from others I think?), are made for this kind of range -- well, nearly anyway. But that approach can afford a more "conventional" solution (i.e. ordinary type regulators/controllers). Beware of either bootstrap power prohibiting 100% duty, or switch drop when not. Which really isn't a big deal, maybe you lose 2-5V out of a 12V input (1-2.5W) (using a non-bootstrap type), but that's less dissipation than say, full load current through a depletion MOS, in the 12-30V range before the LinkSwitch thing wakes up (potentially ~15W).I don't know offhand what all regulators offer such features, though. LM2592 for example illustrates 100% duty but a higher voltage drop (the internal structure is a common-emitter PNP pulling up an NPN emitter follower), but doesn't go up to such high voltages. A discrete solution could be created, but that's a tough design, and it'll still be rather bulky and expensive.Bootstrap kinds, at least the maximum duty isn't an issue here!In any case, watch out for minimum duty cycle / pulse width. Don't want to be stuck grinding on burst threshold instead of normal operation (that is, even if load is high enough to be in normal continuous operation, it might not be able to switch at a low enough duty cycle for the desired output voltage, driving the controller into cutoff; as a result, it shuts down, either reducing Fsw, skipping pulses, or something else noisy like that).Tim

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 11:37:20 pm
content: I started thinking about the bucket brigade capacitor device from the 1970'sThen took a 2.2 uF and a 5 uF MKP and charged only the 2.2 to 45 Volt ( 1/10 just as a model.)Then with clip leads, connected them in parallel. As we know, the voltage equalises and is 45 * 2.2/( 5+ 2.2) =13.7 VThen disconnecting , the 5 uF cap is bigger and carries 13.7 VSo with a succession of steps, the voltage can be reduced and the process is fairly efficient, (losses by the ESR and loss tangent)With a succession of "buckets" it might be feasible to get from 450 V down to a workable voltage without losing too much energy.Say it ended up with 50 Volt on a 1500 uF : E = C*(V^2)/2 = 1.875 JouleThe load is 3.3 V * 500 mA = 1.65 Watt =1.65 Joule/secSo if the bucket brigade could get down from 450 V in 1 second or less, , there should be enough energy down at practical voltage ( neglecting switching and capacitor losses, also there is energy needed to run the controls etc).To get the controls up from a cold start, a big dropping resistor can be switched in just for msec until the controls are active, then opened.I have done that before on inverters.Add: The other advantage if bucket brigade works is that it is safer.I don't think trying to connect 450VDC onto the drain of a small FET is feasible.The first element at 450 V on the bucket brigade is the smallest capacitor, and a switch is not needed on the 450 V side of it.Add Again, The simple calc of energy transfer shown above is optimistic and not correct because of the residual charge left on the capacitors.

author: mariush
author_rank: Super Contributor
timestamp: July 30, 2022, 08:37:01 am
content: I think it would probably be easier to have two separate power inputs , one max 48v AC/DC and one for 48v AC - 480v DCbut it if must be only one universal input .i was thinking that maybe you can have some very low current circuit which measures the input voltage and turns on one of the power supplies (one low voltage and one high voltage ex one max 60v dc, one 60v - 450v maybe using an ac switcher of some sort like those LNK or ST Viper chips)There's some high voltage linear regulator ICs that can do 450v DC down to 3.3v / 5v at a few mA but the input voltage usually has to be above 12-16v - you'd have just enough to control a microcontroller or something to switch a mosfet or mechanical relay between inputs - so you could then have afor example LR8 from Microchip :https://www.microchip.com/en-us/product/LR8- 13.2v to 450v input voltage, 12v dropout voltage so with 13.2v in, you'd get 1.2v out but even that would be enough to power some 8 bit micro to measure the input voltageother examplesncp785a 10mA out, 450v in, fixed 3.3v/5v/12v/15v :https://www.onsemi.com/products/power-management/linear-regulators-ldo/ncp785abut I think it needs a minimum of 25v to output 3.3v, min 55v to output 12v according to datasheet.ncp786l 5mA out, 450v in, adj 1.27..15v :https://www.onsemi.com/products/power-management/linear-regulators-ldo/ncp786lbut this one seems to need min 30v for 1.27v out, recommended 55v minimum for whole range.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 30, 2022, 02:03:03 pm
content: Here is a scrot of the first bucket brigade simulation.It has 4 stages 450 V down to 12 Volt ready for a 3 terminal regulator. at 3.3V 500 mA.A load resistor on last stage is drawing 500 mA, hence the ripple.I have not determined yet how many stages are needed, or if just 2 stages will work.This model is running at very low frequency, 6.66 Hz ( yes, 6.66 Hertz)https://app.box.com/s/n1pwschdwvy3gpn6iufph0aggjnaiy0k

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 31, 2022, 02:03:52 pm
content: More work in qucs on the bucket brigade topology, showed that the number of stages can be reduced to 2.The switching device then becomes a half bridge with both on the high side, fired alternatelyThe power circuit has low component count, refer to:https://app.box.com/s/jpdqgq8rw3ng4sjfwhrri0qql74lldvo(Note the model has ideal voltage controlled switches in place of IGBT to minimize qucs time.)I did some work on a hypothetical battery charger powered from rectified 220V via bucket brigade,... to findimpracticalsnubber losses.So the bucket brigade is only suitable for powers of a few 10's Watt being transferred down from hundreds+ volt.The switching rate needs to be low, < 100 Hz to contain the pulse losses.The low side output capacitor, electrolytic 25V + pulse rated capacitors, needs to be set for ripple at max load.The high side is much smaller, the value sets the step down ratio, and this bank consists of 600V pulse capacitors.Here are some waveforms: Firstly with 450 V input at 6.66 Hz:https://app.box.com/s/xg6vhi2u3wjj1f3yjiwnacyed4gazgsoThen with the voltage down at 200V, needing the pulse rate to increase:https://app.box.com/s/1l9spqwze6edcswkqhxkph0cgpkj4nqhEdit: The addition of 2 anti-flywheel diodes today has reduced capacitor values and reduced snubber loss from about 200 W to around 20 Watt maybe.The above links are updated to Ver.2