Topology for 140W LED boost driver (two switch forward maybe) - Page 1
Forum section: electronics / projects

author: Zipdox
author_rank: Regular Contributor
timestamp: February 01, 2022, 09:40:51 pm
content: So I previously posted on this forum asking for helpdesigning a tapped boost converter driverfor a BXRC-50G10K1-C-73-SE LED, andit did work, but it had some flaws.Approximate ratings:Input voltage: 12-24VOutput voltage: 70VOutput current: 2AObviously using an SMD MOSFET was a stupid idea cooling-wise, it should be replaced with a THT MOSFET that can be mounted to a heatsink.Another issue I noticed is coil whine. Although the drive frequency is way above the range of human hearing, in the higher output power range the inductor seems to whine at an audible frequency, which I think is caused by the current feedback loop.The output current ripple is also pretty bad, because it's driving an LED and as such a tiny amount of voltage ripple causes a lot of current ripple when the LED is just barely turning on.I don't know if the efficiency of my design is optimal. I think that maybe creating a new design using a different topology will allow for a higher efficiency.After some reading, namelyhttps://www.digikey.nl/en/articles/dc-dc-converter-topologies-and-techniques-to-obtain-high-boost-ratioshttps://www.sunpower-uk.com/glossary/what-is-a-forward-converter/I think that designing a two switch forward booster will mitigate a number of problems that exist in my current design.First of all, using a two switch forward will eliminate the voltage overshoots and ringing associated with traditional boost converters. This is due to the clamping diodes, which also eliminate the need for a snubber network. This will allow for lower voltage ratings on the MOSFETs, which will allow for lower forward voltage MOSFETs and thus lower power loss.I think the output inductor would also result in a reduction in ripple on the output, though that's just a guess, I don't know if it will make a difference.I'm not sure about the power losses in the clamping diodes though, considering they will be conducting quite a bit of current due to the boost topology. Two switch forward converters are usually used in step-down mode so I couldn't find any documentation on such a scenario.I also don't know if there will be any voltage overshoots on the secondary side, and what diodes should be picked for it.Obviously a two switch forward is more complex than a tapped boost converter. I'd have to either use a different controller IC that is capable of high-side and low-side switching, or I'd have to add a separate gate driver.I'm really an amateur when it comes to these kinds of things, so any insight would be appreciated.

author: ogden
author_rank: Super Contributor
timestamp: February 01, 2022, 10:12:37 pm
content: Copyinspire from existing design. In your case I would try following or similar multiphase boost converter, converted to current mode regulation:AN-1820 LM5032 Interleaved Boost Converter (Rev. A). Diode rectification is good enough for 2A, no need for sync rectifier which will increase complexity and price. I do not see input fuse in your existing design - always have one.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 01, 2022, 11:10:56 pm
content: Quote from: ogden on February 01, 2022, 10:12:37 pmWhat advantages would an interleaved boost converter give me besides the reduced ripple? It would increase cost and complexity, not to mention a significant chunk of board space.

author: uer166
author_rank: Super Contributor
timestamp: February 02, 2022, 12:11:28 am
content: Quote from: Zipdox on February 01, 2022, 11:10:56 pmI hate to say it, but Treez is right! In this case you have ~16A RMS input current, which translates to quite a high peak input current ( if you're doing a normal boost converter. Of course with a forward the peak current is not nearly as high, but it's still pretty substantial.I would make a 2 or 4-phase interleaved boost (not tapped, just normal boost) for something like this. No way you could reasonably devise a single stage boost with this ratio and power levels. A multiphase solution will be much smaller and more efficient. I don't see why a forward wouldn't work here, but it's more work with the isolation and transformer design, boost is quite straightforward and here it's at the upper edge of reasonable step-up ratio.

author: ogden
author_rank: Super Contributor
timestamp: February 02, 2022, 12:13:36 am
content: Quote from: Zipdox on February 01, 2022, 11:10:56 pmChip manufacturers do not agree to you. Main benefits I see in multiphase - smaller & lower cost inductances, option of higher switching frequencies, smaller switches, not to mention lower input/output capacitor requirements. All that may lead to actually lower volume of converter compared to single phase. If offered design is too complex for you - don't pick it obviously.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 02, 2022, 01:21:29 am
content: Quote from: uer166 on February 02, 2022, 12:11:28 amUsing a non-tapped boost converter has the advantage of not having negative swinging voltage on the rectifier diode, but will it be able to achieve the desired output voltage?On second thought, you are right about a forward converter being more complicated. I guess I'll make a multiphase booster converter.One thing I have on mind me though, is what the best way to do current sensing. The LM5032 datasheet shows current transformers but I don't know if I wanna go that way. I'd rather just use a shunt and a current sense/instrumentation amplifier. The LM5032 isn't suitable by the way because of its minimum supply voltage, so I'll have to find something else.But I need to ask, does the current sensing have a purpose besides making sure the MOSFETs don't exceed their rated current? Because the way that my LED drivers works is using the voltage feedback pin of the driver.

author: ogden
author_rank: Super Contributor
timestamp: February 02, 2022, 06:37:02 am
content: Quote from: Zipdox on February 02, 2022, 01:21:29 amCurrent sensing incurrent modePWM converters is not about MOSFET but inductor current. Make sure to meet required loop bandwidth of current sense circuit, better use offered by manufacturer solution(s). Don't limit your options to LC5032. For example OnSemi NCV78702 could do the job. I would buy IC first, then design because you may get close to none availability for part of your choice.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 02, 2022, 05:26:47 pm
content: Quote from: ogden on February 02, 2022, 06:37:02 amI'm a little lost. I don't know what loop bandwidth means. The things I found aren't related to switching supplies.The NCV78702 is controlled via SPI, which is outside of the scope of my project. I'd rather do it all analog. I'll look for alternatives.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 02, 2022, 06:17:33 pm
content: Right, loop bandwidth is not specific to SMPS. It's any control system. So, it has to do with the error amp between pins 1-2 of the UC3843, or, for the NCV78702, between VBOOSTDIV and COMP (note this is a transconductance type, so the feedback network is not required, just an RC network to GND; the effect is the same). Or the LM5032 in terms of current loop maybe, but it looks like that chip actually requires an external error amp, so, a TL(V)431 say, with compensation in the usual way.Tim

author: ogden
author_rank: Super Contributor
timestamp: February 02, 2022, 06:21:45 pm
content: Quote from: Zipdox on February 02, 2022, 05:26:47 pmNo worries. Then simply do not redesign/reinvent current feedback circuit. Leave as per reference design.QuoteAgain - no worries. As long as you can get LM5032, you can ignore any other IC including NCV78702.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 02, 2022, 07:04:52 pm
content: I did some searching on Analog's site and the LTC7840 seems a like a good contender. Thoughts?

author: ogden
author_rank: Super Contributor
timestamp: February 02, 2022, 07:35:47 pm
content: Quote from: Zipdox on February 02, 2022, 07:04:52 pmYes indeed good contender, in 2-phase config.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 02, 2022, 07:43:08 pm
content: I also found the LTC3862, which allows clock output and customizing the phase, so you can make 2-, 3-,4-, 6- or 12-phase boosters. It's available on TME, so I might go with this one if there aren't any problems.

author: langwadt
author_rank: Super Contributor
timestamp: February 02, 2022, 08:08:06 pm
content: Quote from: uer166 on February 02, 2022, 12:11:28 amif a suitable coupled inductor can be found or you have to wind it anyway, why not tapped?

author: uer166
author_rank: Super Contributor
timestamp: February 02, 2022, 08:26:51 pm
content: Quote from: langwadt on February 02, 2022, 08:08:06 pmBecause you run into leakage inductance, snubber design, and negative voltage swing of the output tap. It's a much harder thing to design than a boost, and only marginally simpler than a full-on flyback.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 02, 2022, 11:33:09 pm
content: Actually the LTC3862 isn't suitable because it drives the MOSFETs at 5V, so I'd need a gate driver.

author: langwadt
author_rank: Super Contributor
timestamp: February 03, 2022, 12:50:50 am
content: Quote from: Zipdox on February 02, 2022, 11:33:09 pmLM5122 ?https://www.ti.com/tool/PMP9595

author: Zipdox
author_rank: Regular Contributor
timestamp: February 03, 2022, 01:40:16 am
content: Quote from: langwadt on February 03, 2022, 12:50:50 amThat would require two chips. I'm already workings on a design with the LTC7840, which has lots of easily customizable parameters.

author: Zipdox
author_rank: Regular Contributor
timestamp: February 04, 2022, 12:31:34 am
content: So I made a design.It's supposed to run at 140kHz.I probably forgot some things, but one thing I have no clue how to figure out is the ITHpins. I know they're for a capacitor and a resistor for adjusting the loop response, but the datasheet doesn't really have a clear explanation of how to choose values.

author: poorchava
author_rank: Super Contributor
timestamp: February 04, 2022, 07:17:12 pm
content: I would just go with a normal single phase boost. No need to overcoplicate it. I mean I have a 3.5kW boost pfc and it works no problem. 140W should be doable. Boost ratio of 5 doesn't call for a transformer, a normal boost will do.At those voltages switching losses are usually not a problem either unless you use some really shit fet and diode.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 04, 2022, 07:56:11 pm
content: Two phase is nice because it lets you use much smaller capacitors. For example I did a compact 1kW buck module a few years back, single phase would've needed massive capacitors like 2mF 160V at the input, literally taking up more space than the second phase. Whereas a couple hundred uF is enough with 2ph. Plus inductors of that rating aren't easy to get commercially, but halfsies, no problem.Also very popular for PFC, even at fairly low levels (100W+). It can run quite fast, saving even more component size; usually doing something like quasi-resonant boost to save on switching loss. (QR requires BCM, so, 100% current ripple, so does incur a bit more cost in the inductors, probably being custom ferrite parts.)For this, the tapped inductor is fine if you're doing a custom wind anyway, I mean, why not, right? Makes the switching a bit easier. Doing it without, just straight boost, also isn't a problem, as has been stated. It's on the upper end of what's practical, so you will invest a bit more in component ratings to do it, but not by a ridiculous amount. Good for builds using all off-the-shelf parts.Quote from: Zipdox on February 04, 2022, 12:31:34 amLooks fine. Ith pins are error amp outputs; they're also transconductance (gm) type, so an impedance to ground serves for compensation. Also means they can be overdriven, say if you want to use an external error amp (like, connecting an opto here for an isolated converter), or wired in parallel (they won't fight each other, as would be the case for a voltage-mode output). So, wire them together to get equal current setpoints for both channels, which is all you need to ensure current sharing between the two phases. Fig.7 shows this.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: February 04, 2022, 08:48:54 pm
content: Quote from: T3sl4co1l on February 04, 2022, 07:56:11 pmOk so I connect them together, but is nothing else required? Like I said I absolutely no idea what to do with them at this point.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 04, 2022, 10:08:38 pm
content: You need the RC compensation network...Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 17, 2022, 12:46:02 am
content: I made a spice simulation. There seems to be a loop where the converter switches on and off at several kHz. Is this what the compensation network is for?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2022, 06:35:41 am
content: You need to tie the Ith's and SS's together too.Check waveforms and values on C9-C11, and value of R16 (assuming you retain those parts and remove C12, C13, R17). Probably C9 has to be smaller and C11 much larger.Don't forget to put the overvoltage clamp back in later!FYI, units are incorrect (R doesn't exist, L is liter, C is coulomb), though I don't mind 'R' shorthand for Ω. More importantly, SPICE ignores any suffixes that aren't unit multipliers (f (10^-15), p, n, u, m, k, meg, g, t (10^12)), so this complaint has no effect on the model; they can be left blank just as well for simulation purposes.Tim

author: oz2cpu
author_rank: Frequent Contributor
timestamp: March 17, 2022, 08:35:24 am
content: D1 ?? and D2 ??is that a good idea for stability and regulation loop ??I would change D1 to a resistorand remove D2also what is R18 good for ?? remove it.ZD1 ?? not a good idea, its capacitance will affect you loop and regulation, remove it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2022, 02:12:07 pm
content: Quote from: oz2cpu on March 17, 2022, 08:35:24 amOn what? This one?https://www.eevblog.com/forum/projects/topology-for-140w-led-boost-driver-(two-switch-forward-maybe)/?action=dlattach;attach=1400402;imageThose were discussed in earlier threads, it's overvoltage (LED open circuit) protection.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 17, 2022, 07:54:52 pm
content: Quote from: T3sl4co1l on March 17, 2022, 06:35:41 amRight, I forgot about SS needing to be tied. I was confused about Ith, I thought they were out of phase but after looking at the block diagram in the datasheet again I see I was mistaken.Quote from: T3sl4co1l on March 17, 2022, 06:35:41 amI'm not sure what I should look for.Quote from: T3sl4co1l on March 17, 2022, 06:35:41 amShould my goal be to make the loop respond faster to a rising LED current?Quote from: T3sl4co1l on March 17, 2022, 06:35:41 amLeft them out of the simulation because AFAIK they aren't relevant unless the LEDs go open circuit.Quote from: T3sl4co1l on March 17, 2022, 06:35:41 amYeah I left them in cause I wasn't sure. I'll remove them.Quote from: oz2cpu on March 17, 2022, 08:35:24 amThis is the LED current feedback. It is already intended to be RC filtered so the diode's capacitance is irrelevant.

author: Zipdox
author_rank: Regular Contributor
timestamp: March 17, 2022, 10:47:40 pm
content: I gotta be honest, I have no idea what I'm doing. I need to read up on control loop theory. If anyone would like to have a look at my spice model, I've attached it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2022, 11:07:56 pm
content: In particular, that the waveform / modulation / oscillation is the same between those locations, but phase shifted; which is your hint that one or more of those RCs needs to increase or decrease substantially to maintain a stable loop. I would guess C9 is much too large (it's not really needed at all, or some 100s pF to "take the edge off"), C10 isn't very relevant (a token ~47p might be used?), and C11 is much too small. A good approach is to set C11 overly large (100n?), then adjust the others (including R16) for good step response (with respect to V2, I take it?). Then adjust C11 downward, tweaking R16 to maintain good response, until response is optimal (can't go any faster without making step response worse).Compare to a normal SMPS: you have the inner loop (inductor pole near Fsw), into the filter cap and load resistance, the latter of which is the RC element you compensate the error amp for, being that it is much much lower than Fsw, and acting mostly single-pole you can fully compensate it with a type 2 network (the R+C on Ith). Which is to say, there is a fairly direct correspondence between load R and C components, and compensation R and C components. This however, has a dynamically very "stiff" load, and not only is the output voltage reflected very quickly by the LED current (i.e. the LEDs convert output voltage to sense current, and probably faster than anything else in the circuit so can be considered instantaneous), but the load impedance is much lower than usual (the incremental or dynamic resistance of the LED stack might be, say, 1/10th its average resistance*). Which puts that load RC much higher (closer to Fsw, still fractional I think), which makes the inductor pole more significant and you may find the earlier relation (between load RC and comp RC) doesn't quite hold anymore. Another thing to try in that case, increase C3 -- to decrease the load pole so it's easier to compensate again.*Average as in, take Vdc / Idc. As opposed to incremental/dynamic resistance, the ratio of a small change, dV/dI.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 12:00:55 am
content: Crap I think the OP-amp is too slow. Its output is too smoothed.

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 01:37:33 am
content: Never mind I got it working with these values. It works at 100% power as well as lower levels. Though I got some funny waveforms. I'll have to perfect it a bit further.

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 02:28:28 am
content: I made a more accurate model of the LED.

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 11:21:04 am
content: Anyway, I've already designed a PCB:https://oshwlab.com/zipdox/bridgelux-29-led-boost-driver-newI think the 7443634700 inductor I chose fits the requirements. But maybe the 74437529203470 is more appropriate as the inductance decreases less near saturation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 18, 2022, 01:00:21 pm
content: Do you want lower inductances to keep the current ripple up at full load?The waveform is perfectly normal BTW, just DCM at light load, ringing is on the switch node.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 01:57:59 pm
content: Quote from: T3sl4co1l on March 18, 2022, 01:00:21 pmIs that a bad thing? I suppose I could pick a different inductor.I think I'll use the PA4349.473ANLT

author: Zipdox
author_rank: Regular Contributor
timestamp: March 18, 2022, 05:26:59 pm
content: I've modeled in some parasitic inductance for the long trace on the PCB, and I arrived at these R and C values for the compensation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 19, 2022, 04:12:16 am
content: Will that trace really be >10cm??And the switching loops zero? (Between MOS, source resistor, diode and local cap, I'd expect absolute minimum like 4nH even for the smallest, widest SMT components; on up to THT, more like 20 with TO-220s and responsible layout.)C1 still seems quite large, but I forget how the error amp gain compares to others, maybe it's typical/normal anyway. If nothing else, I suppose you won't need much step response just for running LEDs, it's not like it's going to be a problem.Have you checked the sim at full load current yet? Overly large inductors cause subharmonic oscillation.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 19, 2022, 12:30:50 pm
content: Quote from: T3sl4co1l on March 19, 2022, 04:12:16 amNo it's 5cm. I don't know what you mean by switching loops zero. Did you have a look atmy PCB layout? I feel like the trace between the diode and the bulk output caps could be problematic, as in it would cause oscillation with the 4.7uF cap next to the diode.Quote from: T3sl4co1l on March 19, 2022, 04:12:16 amC1 needs to be this large to maintain a stable gate drive voltage according to the datasheet.Quote from: T3sl4co1l on March 19, 2022, 04:12:16 amI think there's some minor wobble in the duty cycle, but it doesn't seem to cause any instability.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 19, 2022, 04:31:18 pm
content: Quote from: Zipdox on March 19, 2022, 12:30:50 pmNot sure what's worse, the long traces between things, or the cut off grounds in front of the transistors...I mean the loop of identified components shows zero inductance on the schematic. A peculiar choice if you're going to add stray inductances, why not include all significant ones?QuoteGate...voltage? What schematic are you looking at? I'm looking at the last one posted.QuoteThat's the definition of instability though..?Note that a slow variation is most likely compensation being off, and likely more visible in output voltage (ripple) and at the error node (ITH). Subharmonic oscillation is a straight up alternation (or worse).Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 19, 2022, 08:01:45 pm
content: Quote from: T3sl4co1l on March 19, 2022, 04:31:18 pmWhat do you mean cut off grounds? The ground is connected though the shunt.Quote from: T3sl4co1l on March 19, 2022, 04:31:18 pmI added the one I thought was significant, which was the high current track from the diode to the bulk caps. But it isn't that big of a problem then?Quote from: T3sl4co1l on March 19, 2022, 04:31:18 pmOh you meant C1 in the spice mode. I thought you meant C1 in the original schematic.Anyway, I think I'm just swinging in the dark with that model. The current configuration seems to work reasonably well.Quote from: T3sl4co1l on March 19, 2022, 04:31:18 pmYeah you're probably right. But at least it's not looping.I'll see what I can do to make it better.But other than that, does the PCB layout look alright?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 20, 2022, 07:04:38 am
content: The loop inductance is increased from not having a solid ground under the loop. You might consider splitting the diode to each side, so the transistor, diode and 4.7uF cap can be closer together on each side. Don't worry about symmetry, you can't have it anyway with the transistor pinouts being as they are. Prioritize switching loop and power paths, then ground fill (consider filling top side too, stitching with vias), then find reasonable paths for gate drive and current sense, then find a safe spot for the controller. Making a big loop around the controller probably isn't the best, maybe having it off to the side, opposite the inductors. Note inductor placement is mostly irrelevant, the current varies much more slowly in them than in the switching loop. Likewise the input filtering isn't as critical (but depending on where it connects, you may want extra filtering). I do like that input and output are nearby: this reduces the loop area between them and thus common mode EMI that can be emitted by the wiring.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 20, 2022, 04:17:32 pm
content: Putting a ground plane on the top side is gonna make it difficult to separate the ISENSE- pins, because they're attached to the GND net. I'll try to move the output caps closer to the switches though.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 20, 2022, 04:49:55 pm
content: Yes, some design rules, or keepout/cutout areas will be needed to preserve Kelvin connections.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 20, 2022, 10:57:00 pm
content: I messed around with renaming nets and I think the kelvin connections are fine like this with a ground plane on both sides.https://easyeda.com/editor#id=9177022418934ed99dadbeeaef1196c1

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2022, 05:19:50 am
content: That helps. But I don't see stitching vias, just vias in pad? Which are best avoided as they make soldering worse. (Fine for the controller's thermal pad, don't have much choice there.) R1 can be pointed towards C19, so its ground return path is not cut off on the top layer. Maybe have to cross over the traces on their way back to the controller, no biggie.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 21, 2022, 12:24:38 pm
content: I stitched the planes.But I don't understand why rotating R1 makes a difference. As far as I know no current flows between C19 and R1. When the MOSFET is switched on, current flows from the input caps, through the inductor, through the MOSFET, through R1 to ground. When the MOSFET is switched off, current flows from the input caps, through the inductor, and through the diode to C19. R1 doesn't conduct any current when C19 is being charged, so I'm not sure what you mean.https://easyeda.com/editor#id=ea242f4d98fd471ab8c3ed6c36d257c1

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2022, 03:15:19 pm
content: Yes, precisely.So when the MOSFET stops conducting, it doesn't stop instantaneously. It is limited by device and circuit properties, in particular the inductance of the source lead and R1 for example. The current doesn't simply stop, it reduces at some finite rate, meanwhile the drain voltage shoots upwards, limited by the difference in current and the node capacitance(s). Eventually, the diode begins conducting, and current is transferred from MOSFET to diode. As MOSFET current falls, a voltage is developed by the loop --the complete loop, from capacitor to diode to MOSFET to resistor-- putting a peak, and some ringing (MOSFET Coss * stray loop Ls) on the node.If this peak voltage is excessive, it will cause MOSFET destruction. Or if the loop area is excessive, and poorly shielded, the induction to nearby connections can cause malfunction, EMI problems (remember, the drain voltage, with ringing, is capacitively coupled through the heatsink/tab insulator), etc.Conversely at turn-on, in CCM, the diode is carrying load current, then the MOSFET begins to turn on, carrying more and more current (through the same loop) until the diode turns off and voltage begins to swing downward. (Or, well, the voltage will begin swinging downward already, due to V = Ls * dI/dt.) As the voltage settles at the bottom, it rebounds, ringing with Ls * diode Cjo.So, for ballpark 20nH and ~500pF, expect a resonant peak around 50MHz (this will not be excited if the risetime is significantly slower, i.e. much more than 10ns). Which, eh, with the parts shown, you might see some peaking and ringing. If so, consider increasing the gate resistors.If you decide to add a snubber, values around R = sqrt(Ls/Coss) ~ 6 ohm and C > Coss say 1nF should prove effective. The R+C network must be placed as close to the diode and/or MOSFET as possible (which isn't very feasible with the long leads of the TO-220s adding some 7nH+ already, but it'll still give some help).Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 21, 2022, 08:36:52 pm
content: Ok I rotated R1, but what about R2?https://easyeda.com/editor#id=966b1cf455724c2da975b6c0ed6dfcde

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2022, 09:14:42 pm
content: That's fine, just connect it from the backside so there's better ground fill. Like uh... lemme see here. Oh, it won't let me save without an account, of course. Looks like... should be able to paste this in?https://www.seventransistorlabs.com/PCB_PCB_BridgeLux%2029%20LED%20Boost%20Driver%20Final_2022-03-21.jsonalso cleaned up some routes, reduced the via arrays because they don't need to be nearly so dense, or wide.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 21, 2022, 09:52:17 pm
content: Quote from: T3sl4co1l on March 21, 2022, 09:14:42 pmAre 5 vias really enough for near 10A pulses?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 22, 2022, 12:08:00 am
content: Yup. 20 mil traces and 12 mil vias (~what's here) are good for like 2A at low temp rise, even more with higher allowable temp rise and the wide pours sinking them.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: March 22, 2022, 12:32:26 am
content: Since JLCPCB is so cheap I'll order both the one with your modifications and my version since I'm stubborn. We'll see what works. I can always change the compensation network component values.

author: Zipdox
author_rank: Regular Contributor
timestamp: April 04, 2022, 09:53:55 pm
content: Well, it appears I have made a fatal mistake. Nothing that a little track cutting can't fix though. Update the design. If I make a second one (if I can get my hands on more Nichicon caps) I'll order new boards.

author: uer166
author_rank: Super Contributor
timestamp: April 04, 2022, 11:15:57 pm
content: Quote from: Zipdox on April 04, 2022, 09:53:55 pmSounds like a DRC check fail. This should have been caught automatically. Any idea what happened there?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 04, 2022, 11:25:43 pm
content: This has been your daily reminder to repour polygons and run DRC; at least it was easily solved.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: April 05, 2022, 02:30:35 pm
content: Quote from: uer166 on April 04, 2022, 11:15:57 pmImplying I didn't skip DRC because of false errors...

author: Zipdox
author_rank: Regular Contributor
timestamp: April 05, 2022, 02:37:49 pm
content: Well, I got it working, but not really. It whines, and the scope shows it's looping like it would without a proper compensation network. I also triggers hiccup mode above 25% power output. Back to LTspice I guess...

author: Zipdox
author_rank: Regular Contributor
timestamp: June 30, 2022, 02:38:01 pm
content: I think maybe the LM358 is a problem. So I'm looking for a faster replacement with the same pinout. Does anyone have any suggestions?

author: Zipdox
author_rank: Regular Contributor
timestamp: July 07, 2022, 07:13:35 pm
content: I replaced it with the LM833 but now it's doing something really weird.The second channel is outputting 9V for some reason, while the non inverting input is at 0V.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 07, 2022, 10:13:44 pm
content: 833 isn't rail to rail.TLV2372 is, though not much faster than LM358. Something like, uh, let me see here, TSX9292, LM7322, etc. should be fine? Think there was a CAxxxx something or other still around too, single supply type, don't remember the number though.Tim

author: Zipdox
author_rank: Regular Contributor
timestamp: July 08, 2022, 09:18:37 am
content: TLV2372IDR is the only one I can find in stock on TME. I'll also order an LMV722M.