Transformer winding-wire query - 200W Multi-Output Half-Bridge PSU! - Page 1
Forum section: electronics / projects

author: Chris56000
author_rank: Frequent Contributor
timestamp: December 23, 2017, 07:18:08 pm
content: Hi!I'm stuck, along with my friend Steve, at work with a 200W Multi-Output Industrial Power Supply Module, which uses a Half-Bridge Topology with an SG3524N PWM chip that drives the switching transistors via a small ferrite-core transformer, using ferrite-ring cores about 25mm diameter and about 5mm high, with two isolated Base Drive Secondaries wound on top of the Primary connected to Pins 12/14 of the chip.The transformer is wound with insulated wire that looks to be about 0.2 mm diameter and the insulation is a soft black stuff that melts at well below soldering-temperatures and it also abrades very easily!Can anyone recognise this type of wire and can you buy it? I think I've seen it used in other colours (red, green, blue) as well on this sort of little ferrite-ring transformer where there needs to be three or four different separate windings.I've dealt with a number of industrial PSU modules in the course of my employment that use ferrite-ring transformers wound with this stuff, but more usually the core is fixed to a base that has integral PCB pins fitted to it so I don't have to touch the actual winding ends, but unfortunately the two PSUs I'm stuck with have the winding leads brought out direct to the PCB pads with a pair of long leads from one winding on each core run to the main PWM/Output Board.The PSU Modules are of British Manufacture, Zicon Electronics ZE200-541 and ZE200-553 Series, the Manufacturer apparently being the British OEM for XP Power PLC.I can't add any pics as my employer's broken up for Christmas and I didn't unfortunately take any before I left!Could I rewind these transformers using any other type of enamelled wire?Chris Williams

author: fourtytwo42
author_rank: Super Contributor
timestamp: December 23, 2017, 08:04:47 pm
content: Hi Chris, this sounds to me whats known as TIW (Triple Insulated Wire) especially as that gate/base drive transformer is crossing the safety barrier and should be good for re-enforced insulation.TIW has three layers of insulation and if this is the case MUST NOT be replaced with ordinary enamel or the end user is in serious shock hazard and this could get back to you as the repairer.You can easily buy TIW but usually in bobbins

author: Chris56000
author_rank: Frequent Contributor
timestamp: December 23, 2017, 10:58:17 pm
content: Hi!Member Forty-Two, thanks for your prompt reply!It certainly looks like it's T.I.W., and looking it up from various Chinese maker's websites suggests it's self-solderable as well which iswhat the stuff I came across in the PSU Modules appeared to be!AliExpress sell 20m spools of the stuff at reasonable prices (single figures!) so when I get back on duty I'll measure the remains of what's on the ferrite-ring cores with a digital micrometer and order a spool of the closest matching size!The ferrite-cores form (what appear to be!) the secondaries, with a primary flyback-winding from the main transformer connected from the collector/emitter mid-point of the two MJE13009 switching transistors, then via a 2u2 400V polyester film capacitor and two U-shaped copper-wire conductors that secure the plastic cases of the transformers to the board - are then returned to the centre-tap of the main primary-side H.T. bus smoothing-capacitors (680u @ 200V each) - am I correct in saying the 2u2 capacitor from the H.T. centre tap to the switching-stage mid-point via the centre conductor of the base drive-transformers and the power-transformer primary is the means by which the power supply circuit is initially started?The SG3524N is entirely on the isolated side of the circuits, and there are NO "housekeeping" or "standby" control supply transformers on these units - one secondary of the base-drive transformer has four 1N4148 diodes connected as a standard bridge-rectifier going back somewhere on the main PCB - I didn't get a chance @ work to trace it out!I've not actually seen a representative schematic of this type of 150-300W SG3524N Half-Bridge PSU, does anyone have a link to one please?Chris Williams

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 24, 2017, 12:15:38 pm
content: Ew...*Well, this should give you some clues, at least:http://www.pavouk.org/hw/en_atxps.htmlTL494, KA7500 and SG3524 are very similar chips, the same functions and outputs, differing in their exact control setups (error amps and pinouts). There's also TL598 and 3525 (totem pole outputs), and UC352x (higher performance TI version).*The fundamental problem is that -- in all commercialized versions I have seen -- it's always a voltage mode control, which is inherently unreliable with respect to transient behavior (input inrush, output transient or short circuit, and dynamic stability). A current mode control can be realized with these chips (which has the benefit of inherently limited output current, no need for protective hacks), but for some reason, never is.The BJT output stage is also kind of ew, mainly just because it's old, inefficient, and not as cost-effective as it used to be. MOSFETs are cheap and efficient, and easier to drive (no transformer required)....You didn't mention what it is you're actually doing here, so, consider this as general information, or perhaps a review of the circuit, extrapolating from what information was given.Tim