help me about dc converter  - Page 1
Forum section: electronics / beginners

author: kimera
author_rank: Contributor
timestamp: January 14, 2025, 02:29:27 am
content: I want to try making this circuit. I have a question about L1 pin 7-8. L1 must have 2 coils, right? The 2nd coil is connected to VSS. I am not familiar with this circuit. Please advise. Thank you.

author: Konkedout
author_rank: Frequent Contributor
timestamp: January 14, 2025, 03:44:16 am
content: I am pretty sure that this circuit diagram is screwed up. But it might work as a one-time smoke generator.If you look at recommended UC384X circuits, you will see that the transformer is connected in series with the MOSFET drain and not with the source. I think you ought to refer to circuits in the TI datasheet and website.I believe that you are asking others to explain a circuit which makes no sense.

author: inse
author_rank: Super Contributor
timestamp: January 14, 2025, 04:45:21 am
content: Oops, BS removed.L1 is only a coil, the pins connected to VSS are only for stability, or maybe there is some shielding.It will be hard to copy the design without info about the coil.Isn‘t there a more straightfoward buck converter design that fulfills your needs?TI, ST and Onsemi etc have appnotes with all the necessary formulas and component proposals

author: squadchannel
author_rank: Frequent Contributor
timestamp: January 14, 2025, 04:59:39 am
content: https://www.eevblog.com/forum/beginners/dcdc-48v60v-to-12v-10a/

author: kimera
author_rank: Contributor
timestamp: January 14, 2025, 05:53:04 am
content: Quote from: Konkedout on January 14, 2025, 03:44:16 amoperates as a floating highside switch

author: Konkedout
author_rank: Frequent Contributor
timestamp: January 14, 2025, 06:04:18 am
content: Quote from: kimera on January 14, 2025, 05:53:04 amIn order to do that, I think you need to show us the inductor/transformer more accurately. If you are correct, this is not a "beginner" circuit. Start with the basic stuff.I can point you to some unconventional designs that I have done. But I did forward engineering. Asking others to reverse engineer someone else's weird design based upon incomplete information may not be impossible but it is a tough nut to crack.

author: kimera
author_rank: Contributor
timestamp: January 14, 2025, 07:35:24 am
content: Quote from: Konkedout on January 14, 2025, 06:04:18 amIf you have other circuits that use commonly available ICs, please advise me. My problem is input 18-65V Output 12V1A.thanks

author: inse
author_rank: Super Contributor
timestamp: January 14, 2025, 07:49:22 am
content: For example LM2575HVhttps://www.ti.com/product/LM2575HVOr even better the proposed successor which covers 65V:https://www.ti.com/product/LMR36510Btw the design you proposed is 48..60V

author: MrAl
author_rank: Super Contributor
timestamp: January 14, 2025, 09:39:28 am
content: Quote from: kimera on January 14, 2025, 02:29:27 amNormally you would look at the data sheet for the IC chip being used, and any application notes that go with it. They often show reference designs too.For your question about L1, the basic DC to DC converter uses just one inductor. It's only when you need galvanic isolation that you need a two coil device like a transformer.

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2025, 09:51:33 am
content: A transformer can also be a good when there's a large difference between input and output voltages, especially at higher currents. It means the duty cycle can be increased or a push-pull converter can be used, which results in lower losses and smaller magnetics.What's more questionable is the use of an opto-coupler feedback, which isn't required for a non-isolated design. It will work better without PC817 and TL431.

author: inse
author_rank: Super Contributor
timestamp: January 14, 2025, 09:54:14 am
content: As the UC384x has a floating ground, the feedback needs to be isolated, took me a hit with the wooden hammer to understand the working principle of this design…

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2025, 10:44:58 am
content: Quote from: inse on January 14, 2025, 09:54:14 amIn the circuit attached to the OP yes, but it depends on the application. All the information can be found on the data sheet.https://www.ti.com/lit/ds/symlink/uc3842.pdf

author: CaptDon
author_rank: Super Contributor
timestamp: January 14, 2025, 02:01:11 pm
content: About 99% of the possible failure modes of the O.P.'s design insure that the input voltage will also be the output voltage. "When smoke gets in your eyes".

author: inse
author_rank: Super Contributor
timestamp: January 14, 2025, 02:26:18 pm
content: A good old crowbar should never be disregarded