Power Supply PCB question - Page 1
Forum section: electronics / projects

author: han
author_rank: Frequent Contributor
timestamp: May 02, 2014, 08:07:01 am
content: Frist.. please be gentle at meI'm in the process of modification switching P/S. And just realize one thing.From almost all P/S board i ever see(mains P/S), almost every board is made with single layer PCB.Even laptop P/S is using single layer PCB with tiny SMD component.Is there is concern using multilayer PCB on mains voltage?

author: poorchava
author_rank: Super Contributor
timestamp: May 02, 2014, 08:12:49 am
content: Not really, maybe aside from the fact that you should not route primary and secondary one under another on 2 sides of pcb.Other than than it's only for the sake of cost. Those circuits are relatively simple and use large components, so if they can route it on cheap single sided pcb - they do.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:10:13 pm
content: Double sided boards cost twice as much as single sided boards. If you can get the circuit to operate with a single sided board it's worth the extra engineering time.

author: han
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:18:20 pm
content: I din't expect the PCB pricing is a matter, since even Expensive brand PS still using single layer PCB..

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:37:24 pm
content: Every cent you can save on a high volume product is profit. If you can make an expensive product work with a single sided board then great.Most industrial switchmode power supplies however use double sided boards since they provide a convenient low impedance ground plane that really helps with steep edged waveforms such as current feedback and gate drives.Also, with high power density designs the electronics is usually packed very tightly and often nearby the power transformer or output inductor. The ground plane can then effectively shield the low level electronics from the high dv/dt's generated by the power components.Incidently, those single sided boards you see in Chinese products are paper based and punched due to the huge volume. Most low to medium volume product PCB's are FR4 material and drilled.

author: han
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:48:55 pm
content: @RichardHmm, I don't think it just cost problem.In this High voltage block have same configuration.And this one not cheap Chinese product, its quite expensive at it's time..

author: SeanB
author_rank: Super Contributor
timestamp: May 02, 2014, 12:50:45 pm
content: In older copiers they went to rather ridiculous methods to maintain using a single side board. One main board I saw was single sided SRBP, but there were over 200 jumper wires in 4 different lengths soldered to the board to do links. Considering that the only things other than jumpers on the board were around a half dozen keyboard buttons, a single mask microcontroller and a half dozen or so resistors and 5 connectors and a few LED's it was rather overkill, but as the wires were all probably auto inserted it probably made sense to the manufacturer. Funny thing was the other 2 boards in the machine were actually 2 sided FR4 material, one was the power supply, and the other was the main microcontroller board. These also had link wires, but not as many.

author: han
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:55:20 pm
content: Quote from: SeanB on May 02, 2014, 12:50:45 pmWow.. 200 Jumper wire..Is there any pick and place machine for jumper wire? or they insert it manually?

author: SeanB
author_rank: Super Contributor
timestamp: May 02, 2014, 01:01:08 pm
content: wired component auto inserters handle jumpers easily, as they cut the components out of the reel, and bend the leads to length then insert. They simply have a reel with straight wires and it just cuts to length. I have even seen 0 ohm jumpers consisting of a wire with a white ceramic sleeve sealed to the wire for the machine to grip.

author: han
author_rank: Frequent Contributor
timestamp: May 02, 2014, 01:06:21 pm
content: Quote from: SeanB on May 02, 2014, 01:01:08 pmhmm, Interesting. i did't know such a machine exist...If i sell/made that kind machine, i will name it breadboard master

author: macboy
author_rank: Super Contributor
timestamp: May 02, 2014, 01:24:48 pm
content: Quote from: SeanB on May 02, 2014, 01:01:08 pmI have also seen plenty of cheap phenolic/paper single sided boards with many jumpers, and wondered why they didn't use a 2 layer. But I guess that inserting all those jumpers is on a paper PCB is still cheaper than a 2-layer FR4.Instead of wire links, it is also common to see "0 ohm" resistors, both through hole (marked only with a single black band) and SMD (marked "0" or "0R"). The SMD zero ohm resistors are also sometimes used as a type of fuse, often as the current breaking element for crowbar diode reverse-voltage protection.

author: SeanB
author_rank: Super Contributor
timestamp: May 02, 2014, 01:35:44 pm
content: I have seen reels of wire ended components, where you have a variety of components in the reel, so that the auto inserter does not have to change reels often. You might find a reel with multiple resistor values, and the odd other component like diodes and capacitors that are the same spacing and diameter for insertion in a mass produced board.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 05, 2014, 07:43:13 am
content: That CRT monitor PCB in the photo uses a single sided board just for cost reasons. The voltage rating I don't think has anything to do with it.I agree with SeanB regarding manufacturers using single sided boards and jumpers rather than double sided boards.Often equipment manufacturers use bought out PSU's and CRT displays. My spectrum analyser for example uses a bought out switchmode PSU and CRT assy. Many manufacturers consider these bought out units throw-away items and provide no circuit diagrams or information at all.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2014, 11:31:34 am
content: Often the power supply, CRT, etc. module comes from an outside supplier, so for one, the design style may be dramatically different from the rest of the product. For two, the design is probably much more tightly cost optimized, hence the use of single side phenolic and stuff like that.Tim

author: fcb
author_rank: Super Contributor
timestamp: May 05, 2014, 11:38:27 am
content: Single sided phenolic boards made using the "punch & crunch" technique are VERY low cost. Bear-in-mind that it's only in recent years that Chinese PCB houses have been available. I went round GSPK (near Harrogate, UK) back in the mid 90's - they still had a punch&crunch line operating.One of the main reasons for punch&crunch boards is that you can do isolation slots easily - they used to be expensive to route.Also, pretty much all SMPSU design is based on 70's or 80's topologies and is easy to layout on single-sided, it helps that the chip manufacturers designed the pin-outs to help with single-sided.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 05, 2014, 01:05:58 pm
content: fcbIt's amazing that the majority of commercial switchmode power supplies that I see are ancient technology units.I suppose when price is more important than power density old technology wins.

author: fcb
author_rank: Super Contributor
timestamp: May 05, 2014, 09:35:10 pm
content: Quote from: Richard Head on May 05, 2014, 01:05:58 pmI guess.If there's no need for high density or extreme efficiency why bother spending more.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2014, 10:40:22 pm
content: TOPSwitch and related devices are displacing things I think, but you'll still see single (or two) transistor blocking oscillators. They always seemed to use them in VCRs. It's been a while since I cracked open a DVD player or whatever, don't know if that's still common.Tim

author: SeanB
author_rank: Super Contributor
timestamp: May 06, 2014, 05:05:24 am
content: I see a lot of single package controllers, and often you see the package cracked in half where the integrated power switch blew it open. Mostly generic mystery manufacturer devices, never a topswitch but often a clone. The 2 transistor self oscillating ones are often used on cheap phone chargers, and they use only a plastic power device and a SMT control transistor, with a primary side feedback loop only. Regulation is at best described as "ball park" as they might do between 3-7V depending on load and the incoming mains voltage.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 06, 2014, 06:17:27 am
content: Quote from: fcb on May 05, 2014, 09:35:10 pmAnd then where the opposite is true, stuff like this happens;https://dl.dropboxusercontent.com/u/677635/IMG_0291.JPGhttps://dl.dropboxusercontent.com/u/677635/IMG_0292.JPGhttps://dl.dropboxusercontent.com/u/677635/IMG_0293.JPG