SMPS: add 1.5V 100A on TOP of 36V - Page 1
Forum section: electronics / projects

author: elektrinis
author_rank: Regular Contributor
timestamp: February 13, 2018, 09:28:49 am
content: I have a non-standard application, where I have to add 1.5V 100A on top of 36V power source.The requirements are:* 1.5V 100A power supply added in SERIES to 36V source.* The input of this power supply is from the same 36V source, which it is connected to in series.* Max 10W of heatThis is required by some special equipment connected to this 1.5V supply and can not be changed. Please don't offer changes in existing system, It has to be done in such series format.It's like having this type of power supply, but I am only interested in that secondary output:What topology I should go with? Any similar designs already exist?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 13, 2018, 02:15:41 pm
content: What's your project timeline and budget?It may be most economical to chop the converter off a PC motherboard, and use a 36 --> 12V isolated or inverting supply to power it.Otherwise, I would guess either a polyphase buck-boost; or an isolated forward converter (also polyphase, half as many phases are required if fullwave), possibly with acurrent multiplierto improve conversion ratio.Tim

author: elektrinis
author_rank: Regular Contributor
timestamp: February 13, 2018, 03:24:46 pm
content: Thank you for input.BOM cost should be below $45 at 1k quantity.At the moment I have a working prototype built from off the shelf power bricks, two in series: one isolated 36V to 24V and then one non-isolated buck 24V to 1.5V. In the end I get isolated 36V to 1.5V 100A and it is working really well. It is fine for proof of concept, however is way over budget, close to $200.I was also looking at CPU buck controllers and thinking about hacking them to add the voltage on top of existing power rail, instead of referencing it to GND. Maybe some kind of synchronous buck with coupled inductor would do?I have to admit I am bit rusty on SMPS, my knowledge is stuck in 20th century, when TL494 was one of more popular chips. For now I just want to get the basic idea on most suitable topology (of a few) and then ask someone to implement it.Also I am able to pay for (serious) development, so offers are welcome.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 13, 2018, 07:14:28 pm
content: Ah, cool.Yes, the dark ages have passed; voltage mode TL494s are a thing of the past, and current mode (usually slope compensated peak current mode) are abundant and popular. Downside: they're usually single-purpose, so you might find one capable of bucking +36V down to +1.5V single stage, which would do just as well (in a driven-ground bootstrap configuration) as a buck-boost for -1.5V, but which might not be so happy with doing 34.5V out of 36V (duty cycle limits?), or likewise, a bootstrapped 37.5V out of 36V.You have to read a lot of datasheets. The suppliers have quite a lot of fields to select by, but there's just so many more features they can't accommodate that are important in edge cases like this.Incidentally, you can do a buck-boost with tapped inductor, to get a current ratio as well. That can help. With a 50% tap, the switching waveform goes down to 0V and up to VIN + 2*VOUT (rather than being clamped by diode/sync rect. at VIN + VOUT). Tapped inductors are not terribly uncommon these days, though a high current part may be harder to come by.I'm just wrapping up another high current DC-DC module, actually, so if you want to take this to PM/email that'd be great.Tim

author: elektrinis
author_rank: Regular Contributor
timestamp: February 22, 2018, 09:36:00 am
content: Thanks for your help so far, sent a PM.Anyone else have ideas how do I modify a buck converter in to adding some voltage on top of existing power rail? For example, is it powwible to use a 10:1 coupled inductor or a transformer, with minimal losses at 100 amps? I mean, is there an option to make bit simpler/cheaper solution than typical isolated PSU?