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Steinchen  HeadWizer Joined: Oct. 12, 2005 |  Message [#1] posted on: 12-26-2005 05:26 PM CST (US).   |  |  I'm going to build a PSU dedicated for my Dynalos. Due to problems with sourcing some parts for the Dynahi PSU in Europe and the extensive casework/heatsinking the Dynahi PSU needs I want to create a new pcb and don't want to populate a Dynahi PSU pcb with different parts. Main goals: suitable TO-220 replacements for opa541 are opa544 (TO-220 5-lead) and opa548 (TO-220 7-lead). Specs (current and voltage rating, voltage swing, etc) are quite similar, the current limit function of opa548 is not needed, I'm afraid this could deteriorate transient response, additionally the LM317 preregulators sports some kind of 1.5A current limit to the PSU first thoughts about schematics: Thoughts and suggestions are very appreciated |
| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#2] posted on: 12-26-2005 06:35 PM CST (US). | | Personally, I quite like the layout of the dynahi PSU-board although I will agree that it is unnecessarily large for dynalo-use. I can see the appeal of on-board heat sinks, but for me the ideal PSU for the dynalo would be a dynahi board scaled to accept 18mm caps and OPA548 op-amps. This board could be made app. half the size of the current dynahi boards and if the output voltage is kept under 18V or so, you could still use fair-sized caps (3300uF/35V shouldn't be a problem, even in low-esr types). 
PS: If the dissipation in the regulators isn't anymore than a couple of watts, I find the SK129s overkill. SK104s may run a little hotter but will yield a much smaller board. |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#3] posted on: 12-28-2005 03:26 AM CST (US). | | the SK104 are sufficient for the Dynalo, but to some extend I want to keep the PSU versatile, e.g. use it with a MH or M³, so the PSU should be able to deliver 300mA to 400mA easily. With the 10K/W of the SK104 they would run pretty warm (about 35°C or 40°C above ambient). Space is no concern, likely I'm gonna stick with SK129. Regarding the opamp I decided to use opa544, it has higher continuous output current (2A vs 0.5A), higher slew rate (8V vs 6V/uSec) and the extra pin of opa547 with the current limit function is not needed.
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| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#4] posted on: 01-02-2006 04:34 AM CST (US). | | I changed the voltage reference from REF02 to REF102, with one small resistor change either of the two can be used, in case of REF02 just omit the noise suppression cap. I haven't made a decision concerning the preregulator layout yet, the upper and the lower prereg layout are different atm, is there a characteristic that makes one superior to the other ?
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| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#5] posted on: 01-08-2006 12:33 PM CST (US). | | OK, I had some time to work on my version (see attached images). It's a scaled down version of AMB's diagram using GBU-type bridges (for space reasons) and OPA548 opamps. The main capacitors are 22mm diameter and the board measures app. 8.5 x 10cm (compared to something like 11 x 15.5 cm for the group-buy PCBs). The only thing I'm not really happy about is the thin trace going between the pins of one opamp (top right in the second picture). It is much thinner than the others (32 mil vs. 50 or 70 mils everywhere else), but I don't know if this is a problem. Questions, comments, critique most welcome
PS: Steinchen, I hope it's OK that I borrow your thread? [Edited by Nisbeth on 01-08-2006 at 12:40 PM.] Attachment: C1302.gif,C1303.gif |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#6] posted on: 01-08-2006 02:50 PM CST (US). | | 32mil is about 0.8mm, that shouldn't be a prob. With a 35u copper layer you'd need about 1.5A for a 10°C temperature rise of the trace, with only 200 to 250mA for the Dynalo we are far from a prob here. Since the trace is short resistance shouldn't be a prob, either. Nice layout, the monolithic rectifier bridge and the absence of snubbers save a lot of space. |
dgardner HeadWizer Joined: Sep. 27, 2004 | Message [#7] posted on: 01-08-2006 07:07 PM CST (US). | | Both these layouts look nice. One thing... If you go back into the history of the original Gilmore Dynamic power supply with the OPA548, there were lots of poeple who had oscillation troubles on the -16V output. The OPA548 in inverting mode was unstable. I don't know about the OPA544. Anyone breadboarded this yet and played with it? If the intent is to share this design, I will certainly be a customer. I would be willing to chip in for the tooling charges to debug it as well. |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#8] posted on: 01-09-2006 03:32 AM CST (US). | | I'm going to prototype the psu soon. Given that the design works and there is interest I'd gladly provide the board for GBs. |
| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#9] posted on: 01-09-2006 04:17 AM CST (US). | | Unfortunately I will be too busy to do much about my design for at least another month, but if anyone else is interested in prototyping the layout I have no problems with given out the files
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Pars HeadWizer Joined: Nov. 12, 2003 | Message [#10] posted on: 01-09-2006 09:05 AM CST (US). | | Yeah, I recall that people were having probs in this area, originally attributed to not fast enough caps (like the IC ones that Kevin used). The Headamp V2 board that I built has never had any problems with oscillation, and this is using Wima 4.7uf. It does have several additional ceramics and a couple of resistors in this area that weren't in the original design, but I'd have to ohm the board out to figure out how exactly they are configured (which I will do if anyone needs it). The PSU on this has always impressed me with its stability and tracking. |
| dgardner HeadWizer Joined: Sep. 27, 2004 | Message [#11] posted on: 01-09-2006 09:50 AM CST (US). | | The role of the series resistors on the opamp outputs is still a bit of a question in my mind. If this contributes to the stabilty, then this should be confirmed and should be included in the design layout, IMHO. |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#12] posted on: 01-09-2006 09:56 AM CST (US). | | the 4.7uF Wima, are they MKS (Polyester) or MKP (Polypropylene) ? For power rail bypassing of the preregulator stage or on the output of the opamps ? The datasheet for opa548 recommends a RC-snubber at the output when driving capacitive loads (of 1000pF or more) while it seems that opa541 doesn't need this, probably a reason why opa548 doesn't work reliably on the original board. |
| Pars HeadWizer Joined: Nov. 12, 2003 | Message [#13] posted on: 01-09-2006 09:57 AM CST (US). | | The headamp V2 board that I built was also setup for GBU bridges. I did up an Eagle file for 31DQ10 Schottky discretes as a vertical board which fit in the same space/pinout as the GBU bridges using some MillMax "L" shaped pins... these worked out really well. You are welcome to the board file if you want it. I posted some pics of these on head-fi if you want to see them (in the show us your amp thread). [Edited by Pars on 01-09-2006 at 11:12 AM.] |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#14] posted on: 01-09-2006 10:05 AM CST (US). | |
opa548 needs the resistor for current sensing and current limiting (0.2Ohms should result in a aprox 2.5A limit). The datasheet says nothing about driving capacitive loads. I doubt that 0.2Ohm is high enough to increase stability significantly. [Edited by Steinchen on 01-09-2006 at 10:06 AM.] |
| Pars HeadWizer Joined: Nov. 12, 2003 | Message [#15] posted on: 01-09-2006 12:45 PM CST (US). | | The std. Wima's used are MKS-4. |
| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#16] posted on: 01-15-2006 02:36 PM CST (US). | | Had time to play a little more in Eagle yesterday. Managed to tweak the dynahi-psu layout a bit and also attempt a dynalo-psu as well
EDIT: New version of the dynalo and dynahi added plus a "mini-mini" dynalo with GBU-type monolithic rectifier bridges instead of discrete diodes. [Edited by Nisbeth on 01-15-2006 at 06:15 PM.] Attachment: C1348.gif,C1346.gif,C1347.gif |
| dgardner HeadWizer Joined: Sep. 27, 2004 | Message [#17] posted on: 01-22-2006 01:56 PM CST (US). | | How's this project going? Any chance your guys are getting ready to order some first pass units? |
| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#18] posted on: 01-22-2006 03:14 PM CST (US). | | Don't know about Steinchen, but nothing's happening at my end for at least another month 
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| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#19] posted on: 01-22-2006 04:10 PM CST (US). | |
A prototype board has been ordered already, hopefully I get it in about 2 weeks. The parts needed for stuffing it are already here. |
| Steinchen HeadWizer Joined: Oct. 12, 2005 | Message [#20] posted on: 02-07-2006 08:30 AM CST (US). | | update: the proto pcb is delayed, now I expect to have the first board running about Feb 26th :/ |
atomboy Member Joined: Oct. 12, 2005 | Message [#21] posted on: 02-10-2006 12:13 PM CST (US). | | I've been trying to follow along and I've cooked this up with the idea of etching it at home.
The Eagle files are here: Parts are based on what I had already collected (OPA548, REF02) and what's cheap from Electronics Goldmine (2200uF 50V caps- two for a buck!). I have searched, but I can't find the discussion about the OPA548 being unstable in inverted mode. The datasheet seems to be prety insistant about the power bypass caps, so I've put them in. Would this help address oscilation? How would I know if it did oscilate beyond the audible range? Dogs barking in the neighborhood? I've left the adjustment pots off the LM317 sections. I'm thinking they don't matter since they don't control the final output anyway, no? |
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