[SOLVED] Single or dual rectifier bridge, safe ? - Page 1
Forum section: electronics / projects

author: Thor-Arne
author_rank: Unknown
timestamp: October 19, 2012, 08:41:39 pm
content: Hi guys.I was wondering if there is any security differences, or any other disadvantages/benefits between these two examples.Thermal relief perhaps, as one can mount the bridges further apart on the heat-sink?The maximum current drawn will be 5A (fused) and the transformer is rated at 2*3,2A.In the example with two rectifiers; if one rectifier fails, both fuses will blow if the current exceeds 3A.

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2012, 06:00:08 am
content: 2 diode bridges has a lower forward drop due to current. This will increase the output voltage by a few hundred millivolfs, and the diodes will run cooler and be more reliable. Use 2 10A bridges in any case, not much higher in price than a 5A unit, and it has a bigger case which in this use can be bolted to a chassis as a heatsink.

author: Thor-Arne
author_rank: Unknown
timestamp: October 20, 2012, 04:06:19 pm
content: Ok, thanks.So it can safely be done with two bridges...I have a bunch of 4A bridges that I'd like to use, guess I'll bolt a couple of those to the heat sink and see how it goes.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: October 20, 2012, 07:07:11 pm
content: quote :- "The maximum current drawn will be 5A (fused) and the transformer is rated at 2*3,2A."Dont forget to derate the transformer current rating if your putting a filter capacitor after the bridge rectifier .A transformer winding rated at 3.2 A rms will only supply 3.2 x 0.61 =1.9 Amps per winding in those circumstances.

author: Thor-Arne
author_rank: Unknown
timestamp: October 20, 2012, 07:28:10 pm
content: Quote from: kevotronic on October 20, 2012, 07:07:11 pmHm, that I didn't know.Thanks for the info.That means I have 3,8A available total. I was thinking I had 6,4A total, bummer.Well, I'll just derate the project to safely within this then. I guess 3,5A max will be safe.I don't want to overload the transformer under no circumstances.

author: Zero999
author_rank: Super Contributor
timestamp: October 20, 2012, 07:50:13 pm
content: Don't forget that the current sharing between the rectifiers won't be perfectly equal.

author: Thor-Arne
author_rank: Unknown
timestamp: October 20, 2012, 08:09:18 pm
content: Quote from: Hero999 on October 20, 2012, 07:50:13 pmThat's why I want to leave a little room for variations.If i draw 1.75A per winding it leaves 150mA margin (7 to 8%), this should be enough I think.

author: ptricks
author_rank: Frequent Contributor
timestamp: October 21, 2012, 03:50:09 pm
content: Most of the time I use a single diode on each secondary wire , then join the DC outputs, with the center taps I join those together and use the center tap as ground. It is also really easy to add on negative voltage output if you need it.

author: Thor-Arne
author_rank: Unknown
timestamp: October 21, 2012, 05:33:03 pm
content: Quote from: ptricks on October 21, 2012, 03:50:09 pmYes, this is one way to do it.This is basically the same as the example with a single bridge rectifier, with exception that this has the windings in series and my example has them in parallel.I doesn't need dual rail in this design, I need power. That's why the windings is in parallel.Also, I want to use bridge rectifiers so I can mount them on the heat sink.