Delta Elektronika ES030-10 Power Supply Review,Teardown and Tests - Page 1
Forum section: electronics / testgear

author: Floyo
author_rank: Regular Contributor
timestamp: November 15, 2015, 02:21:35 pm
content: Ok, here goes my first review of a bit of gear. I wrote this because I finally have a piece of equipment that bothhasn't been reviewed to death already, and is still in production. It's a bit long, so I'll try to keep it organized.Intro:Delta Elektronika is a Dutch company with a very solid reputation within the Netherlands, both for reliability but also customer support.They go through the effort to supply schematics or support for their (older) gear to everyone, including hobbyists. The supplies are found inalmost all educational electronics institutions, usually the "ancient" 30v 1a model, or the symmetrical output version of that supply, great forlittle dual-rail analogue circuits.These days they mostly make very hefty industrial power-supplies in the multi-kilowatt range, though there are still some more lab oriented units.I got one of the smaller units second hand, the ES030-10 (as the name suggests a 30v 10a unit), for some projects involving a bunch ofled strips at 12/5V and other high power applications.The units aren't cheap by any means, though good deals can be had on the (Dutch) second-hand market.Overview:The front of the unit is pretty bare-bones, two 3.5 digit readouts for voltage and current, a "real" power switch, two ten-turn pots, and the output terminals.These are the 4mm + binding post type.On the back of the unit there is the mains input, switches for switching between front panel control or remote analogue programming via the DB-15 connector, also situated on the back.The programming connector offers a "remote shutdown" pin, the reference voltage output, I and V inputs for remote programming, I and V monitor outputs, a CC status led and a +12v line.(models with various digital control options are available, as well as rear output terminals).Performance:Delta takes great pride in the noise performance of their supplies, quoting that actual performance is often better than the banner spec.I have tested a few key parameters to any high-performance power supply, but since I lack quite a bit of the proper equipment some improvisation wasneeded here and there.All scope plots were made with a DS2072 at 20Mhz bandwidth limiting, AC coupling for the noise measurements and dynamic loading, DC for the rest.The supply was set for the maximum output settings, 33 V, 10.3A in all tests (this supply has the "10% extra output power" option). The test load was 4 Ohms unless otherwise mentioned (this gives close to the maximum load).Probing was done using a 1X probe connected with a probe-to-bnc adaptor directly fed into a 4MM banana adapter inserted into the output jacks.This setup minimizes stray noise pickup.Turn on/off behaviour:Lets start with the basics, the turn on behaviour. This is something that a lot of supplies, especially low quality ones, get wrong.The goal is to have no overshoot on or other weirdness. As can be seen scope plots, turn on with no loadattached is as should be. The same test with a 4 ohm load attached is a bit weirder, the control loop seems to take a bit of time to get settled, thoughthere is no overshoot. The same test with the supply being set to 30V instead of 33V doesn't show this little triangle wiggle.Programming:Next up is the remote shutdown function, a 5v signal on the RSD pin brings the output of the supply down to 0V. Since this actively brings the voltagedown the "no load" falling edge is much faster compared to just switching the unit off via the mains switch. The waveforms when using the analogueprogramming connector(V) show similar rise-times as described in the manual, the supply responds within 2ms, both rise and fall.Output Noise:Onto output noise, SMPSs typically have quite a bit of switching residue on their output, which could upset equipment connected to it.Especially HAM radio operators often still prefer linear supplies for that reason. Here the supply also lives up to the specs and stayswithin the limits at all times, quite impressive for a switching supply.Step Response:Another important parameter for a power supply is its ability to recover from a sudden step in load. If the supply is too slow in respondingthe output voltage can drop, which can result in a brown-out of the circuit being powered.Since I don't have an electronic load (Jim Williams's AN133 would be a good fit here) (yet) I had to improvise a little.Instead of using some kind of actively controlled current source I used an N-MOSFET driven by a gate driver, which in turn was driven froma pulse generator. The FET alone would cause a dead short, so two 10 Ohm 1/2 watt resistors were added in parallel, for a 5 ohm load during the FETs on period.When using this setup it is rather important to keep the duty cycle low enough so the dissipation in the resistors does not get out of hand. Larger wirewound resistorsare less suitable for this test because of their large inductance, this inductance impedes the current flow and thus skews the results.When stepping the load from 0A to 6.6A (FET off vs. 5 ohm connected) the result of the test wasn't too great, the output dipped over 5 volts, and recoveredwith a little overshoot. Audible ticking was emitted by the supply, presumably because of the sudden change in mechanical stress in the inductors.To test the dynamic performance in a way that better resembles the datasheet spec I connected an 8 Ohm static load (big wirewound resistors) in parallel withthe FET+5Ohm arrangement. This gives approximately the 50-100% loadstep as described in the specs. The results match a lot better now, with the maximumdip now being 400mV and the supply recovering fully within 150µS. There is some discrepancy still, but the test setup might be to blame.ThermalThermal management in a high power unit is important, if a long product life at full load is to be desired. Since this is a 300Wunit this also means that 300W of heat needs to be dissipated if the unit is to be fully stressed. To do this with stuff I had laying aroundsome improv was needed again, 100Watts worth of dissipation was provided by 4 4Ohm resistors connected in parallel to give 1Ohm. the remaining 2Ohms were formedby my somewhat large collection of speaker and mains wiring, all connected in series and shorted at one end. A little bit of tweaking gave a nice steady 2Ohms, a room fan kept the temperatureof the bundle of wires in check. It isnt pretty but it works fine in a pinch (the resistance of the copper wire has quite some temperature drift though).I let the unit run for 1.5ish hours, with the case off so I could carefully probe components with a thermocouple. The highest tempswere the inductors, at 60ish degrees Celsius. The heatsink hardly got warm at all (+-40C). With the lid on the results would likely be better,because the airflow works as designed then. Ambient temperature during this experiment was 23C.If there is any interest I could get access to an IR thermal camera to take some more detailed measurements.Output harmonics and "EMC":The last test was a to have a look at the output harmonics. For this I used an Analog Discovery as a "spectrum analyzer". The result from its14 bit ADC is a lot more useful than the 8 bits of an average digital scope. The goal of this experiment was to see if this primitive setupcould give any sort of indication of the EMC produced with respect to something like the official norms. These results need to be takenwith the largest grain of salt you can be bothered to find, but having said that, the harmonics seem to lie below the EN55022 limits with thepeaks at -75dbV (45dbµV). This experiment was just a bit of fun, and I'd like to hear your thoughts on it.Teardown:Ok, time to take this thing apart. The top of the case comes of with just three screws. the whole thing is constructed out of a single board.Interesting to note is that there isn't a single SMD component to be found, except for on the panel meters. All components are of well known, proper, brandsthethe filter cap is Rubicon, the small red caps are Wima, and the potmeters are Bourns. Another point of interest is the fact that there are noelectrolytics in the output circuitry, just a massive amount of paralleled 10µF 50V ceramic caps tacked straight on the output. This should givevery good ESR at high frequencies, and very good reliability over a long lifetime compared to electrolytics. 20 of these are situated directly at the output terminals, and 8 are used before the output common mode choke. The remaining three are part of a little LC filter network.There is a copper shield behind the panel meters, presumably to shield the holes left by the cutouts for the meters.Circuit topology:The signal path is quite easy to follow, first the mains input passes through two common mode chokes and some more filtering.the voltage is then rectified and fed into the active PFC section, ending in the mains filter cap.From there the 370ish volts DC passes through the only user replaceable fuse in the product into the main switching FETs.These FETs are driven from a pair of TC4420's which in turn get their signals from the two red pulse transformers right of the main filter cap.The switching topology is an interleaved forward converter,as far as I can tell. This has quite some benefits over a single transformer design,the main one being lower ripple, but lower i^2*r losses and a lower profile transformer probably also had to do with that.IC's used:PFC: UC3854BNFET driver: TC4420Main switching controller: IP3P125 (SG1525A is similar)Current sense opamp: OP177Reference: REF02 (not sure what this is used for yet, since the switching controller also has a 5.1V reference)Output Diodes: STTH1302CFPOther opamps: tl084Assorted 74HC logic chips.So, that concludes my review for now, I'd like to hear your thoughts.(P.s. I'll see if I can embed the images in logical places in the post, and the Analog Discovery plots are coming)

author: Floyo
author_rank: Regular Contributor
timestamp: November 15, 2015, 02:23:09 pm
content: The plots from the Analog Discovery. the same 1X high impedance probing setup used as in the rest of the tests.

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 03:32:22 pm
content: Can you please make some more hi-res photos of the circuitry? I am quite interested to see how does that thing work. Especially - I see no ellytics on the output. Only a bunch of blue ceramics there.

author: wblock
author_rank: Regular Contributor
timestamp: November 15, 2015, 03:40:26 pm
content: Floyo, this review is the next best thing to me actually having one of these power supplies. Thank you!Quote from: Yansi on November 15, 2015, 03:32:22 pmSee the Teardown section, the ceramic capacitors are mentioned.

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 03:46:02 pm
content: Okay theres enough detail, but still, these Delta supplies are just pure AWESOME, so I wanted to see some more details...We have at work some old ('79) switchmode supply from Delta and that is also one hell of a beast. (60V 10A), very nice built.

author: Floyo
author_rank: Regular Contributor
timestamp: November 15, 2015, 04:31:30 pm
content: Here is a closeup of the output terminals with associated caps. I think this arrangement together with the interleaved converters contributes a large amount to the low noise.I reverse engineered the output circuitry (I think its correct) , and it is surprisingly low in complexity. One thing to note is that both the current shunt and the filtering inductor are in the negative line. The overall topology differs a bit from the versions I came across in literature (e.ghttp://www.deltartp.com/dpel/dpelconferencepapers/Apec95%20interleaved%20magnetics.pdffig 3.). Maybe someone with more experience can shed some light on how this configuration would work.

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 05:20:00 pm
content: Yeah, should be correct. Let me five minutes to redraw it.Here it is. Quite simple. The 1) image shows a "classic" forward converter with the doublediode and a choke. We can easily agree, that the choke can be moved to the negative rail without any change of the circuit behavior. Now let's add second forward converter, running 180° out of phase, givving pulses to the choke when the other converter is demagnetizing the transformer. That way you'll get double the output frequency, so half the ripple per same inductance.Still dunno why the choke is in the negative rail, but that doesn't matter. I'd be more interested about how they did the control of the two forward convertors and how is the power sharing done.BTW, as nice and clean as the build looks, the power electronics inside the unit doesn't look clean at all. Just look at the EMI input filter and notice the parallel traces from the filter input and output, running parallel to each other. I'd say that's a no no. Also the primary side power traces are long as hell, there must be a fuckton of switching transients on the power mosfets. Hence why the tons of R-C snubbers everywhere.

author: nctnico
author_rank: Super Contributor
timestamp: November 15, 2015, 05:45:26 pm
content: Quote from: Yansi on November 15, 2015, 03:32:22 pmAnd that is exactly the problem with these power supplies. Their control loop cannot keep up when a large capacitive load is attached to the output so it's output will drop consirably in such an event. If you power multiple devices from this PSU this lack of capacitance at the output can cause issues.

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 06:07:30 pm
content: nctnico: I have designed a SMPS without ellytics once, but that was for a 300W DC brushed motor. I have used only I think 10uF output capacitance, but that was mainly because the motor had to be connected with a length of cable. EMI from the long cable and mostly its capacitance was the main reasons to construct the converter like this, only with small filter capacitance.Back to the topic: One more thought about this supply:This Delta supply seems to be a singleswitch(?) interleaved forward convertor. I see only one reason for them to choose interleaved forward instead of a halfbridge:Both of these topologies share the same benefit of twice the switching frequency on the output choke. But the halfbridge topology would require symetrical pulses on the primary. This is usually solved by slowing down the regulators. Delta obviously wanted to minimize output capacitance and gain some speed for the regulation loop. That can't be done with the halfbridge topology, not easily enough. So they did the interleaved forward. (But still... two transformers instead of one, each transformer demagnetizing winding over the top, four secondary diodes instead of two, 800+V mosfets...)The one Delta supply we have at work, it is also forward, but single switch with a fucking BUV98A//BUV98AV datasheet, similar package, BUV98A has fastons instead of screws

author: nctnico
author_rank: Super Contributor
timestamp: November 15, 2015, 07:03:27 pm
content: Quote from: Yansi on November 15, 2015, 06:07:30 pmI'm not saying it is a bad topology perse, it just isn't the most ideal one for a lab power supply. If you switch on a load which has 10000uf of capacitance inside you can easely get a current surge of 300A and getting to 1kA isn't impossible. Just look at the output stage of a 2kW HP power supply:It has 80000uf of output capacitance to deal with these kind of situations and to make the output impedance as low as possible over a wide frequency range. Oh and before I forget: I have hands on experience with the Delta power supplies and that is how I found out about the less than ideal dynamic load handling.

author: Yansi
author_rank: Super Contributor
timestamp: November 15, 2015, 07:30:45 pm
content: Neither have I said that it is bad. Just seem to be more complex topology for something achievable more easily.80mF seems quite bloated. (low voltage and low frequency may be the culprits?) What voltage is that HP supply? Having too much capacitance won't help with fast current regulation. Thats what I see as the most limiting factor with pure switchmode regulated supplies.Also hybrid PSU designs are quite interesting. One of my "relaxation projects" is eaxactly a such hybrid: 2Amp 30V linear supply with tracking preregulator. Also not anywhere ideal, but gets ya some improvement. But thats completely another matter...Floyo: Can you please confirm it is a single switch forward convertor? What type of mosfet (or even BJT?!) is there?Also where's the current sensing? Seems like some source shunts present there...

author: Floyo
author_rank: Regular Contributor
timestamp: November 15, 2015, 08:15:02 pm
content: Yansi: I think its a single switch per transformer, I cant tell you what device it is, they are covered by some rather thin insulating "socks", which are also rather stuck. I don't want to damage those, since a switch with compromised isolation would be quite bad. They're driven from a FET driver though, so I'm betting its a FET. The 1/4 watt resistors below the switches are in connected in parallel, so those are probably used for primary side current limiting.The secondary side shunt is visible on the right side of the fan, just above the earthing wire.(that BUV98A is quite something though :p)R.e. output capacitance. Though the brute force approach of just adding more capacitance does get you better transient response for extremely large surges, it also has the disadvantage if quick and accurate current limiting is desired. When using the supply as an CC led driver for example, with a compliance voltage above the forward voltage (to accommodate both single and series strands) the difference in voltage stored in the output caps would discharge through the diode, possibly causing damage. So the capacitance is a bit of a trade-off.

author: nctnico
author_rank: Super Contributor
timestamp: November 15, 2015, 09:42:00 pm
content: A standard general purpose bench PSU design will always need a decent amount of capacitance at its output for control loop stability and for dynamic load handling. Such a PSU is basically a voltage source with some current limiting (sourcing) capabilities bolted on. Creating a close to ideal and yet general purpose current source is hard (close to impossible) since so much depends on the load to get the control loop stable. There are very specialistic power supplies (more like amplifiers) which have zero overshoot on their current limiting but expect to pay a lot for those. I don't think LEDs will have a problem to deal with an inrush current. In general diodes are capable of handling their rated current many times over for a short period.The picture I posted above is from a HP6572A 20V/100A switching power supply. It does have a 'down programmer' which helps to discharge the capacitors during an overcurrent event but I doubt it does much to save a really sensitive circuit.

author: Yansi
author_rank: Super Contributor
timestamp: November 16, 2015, 01:12:59 am
content: Okay, those 100 amps at 20V explain the capacitance.

author: Floyo
author_rank: Regular Contributor
timestamp: November 16, 2015, 06:52:43 pm
content: I decided to do a little experiment today with a diode/ power led to satisfy my curiosity regarding the inrush current. Test setup was as follows: Supply at 12V, Current limit at 0.35A. +-Diode-->Fet-->25mOhm shunt-gnd. Fet driven with a low duty cycle pulse, on time a couple of milliseconds.The inrush current works out to be around 160 amps, with the 300odd µF of capacitance the pulse lasts around 100µs. The 1n4007 lived fine for as long as I tested (couple dozen pulses). The Cree 3W power led died on the first pulse, and I forgot to arm the scope, so no trace of that one. Now, since this led was missing its the top of its lens (junkbin led, sheared off at some point) I'm not sure it was totally representative, and the sample size is one either way, so no real conclusions can be drawn from this experiment.The 1n4007 has a peak current rating of 30a for 8.3ms, nominal 1A. A random power led from Nichia has a 2.4A peak value for 10ms, nominal 0.7A. So LEDs seem to be a bit more sensitive with regards to peak current handling. (http://www.nichia.co.jp/en/product/led_product_data.html?type=%27NVSW119C%27)I didn't quite feel like cobbling together a lot more capacitance to hook up, it wouldn't increase the magnitude of the pulse anyway, just the duration. So I put the circuit into LT-Spice, the results match practice quite well, the peak current is higher at 200A, but pulse shape and duration are similar. Increasing the capacitance 0.08F just increased the duration, as expected.Moral of the story, beware of your supplies output capacitance, regardless of how much it is, and use the right tool for the job.@ntnico, That is true of course, getting a control loop stable (and fast) with a known load is hard enough, let alone with an unknown one.@Yansi, was there anything else you'd like to know about the circuitry, I could try to figure it out.

author: Yansi
author_rank: Super Contributor
timestamp: November 17, 2015, 11:05:17 pm
content: Yea, one more question I have! What is the switching frequency of the PSU please?

author: Floyo
author_rank: Regular Contributor
timestamp: November 21, 2015, 08:56:30 pm
content: Sorry for the late reply, I was busy for a few days.The output ripple is at 200Khz, and it being an interleaved converter the switching freq. would be 100Khz. The output FFTs confirm this, showing 100Khz as the fundamental. the 200Khz harmonic is stronger in amplitude though, again because of the interleaving.