Author Topic: help me about dc converter  (Read 686 times)

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Offline kimeraTopic starter

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help me about dc converter
« on: January 14, 2025, 02:29:27 am »
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.

« Last Edit: January 14, 2025, 03:29:04 am by kimera »
 

Offline Konkedout

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Re: help me about dc converter
« Reply #1 on: January 14, 2025, 03:44:16 am »
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.

 

Offline inse

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Re: help me about dc converter
« Reply #2 on: January 14, 2025, 04:45:21 am »
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
« Last Edit: January 14, 2025, 06:02:03 am by inse »
 

Online squadchannel

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Offline kimeraTopic starter

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Re: help me about dc converter
« Reply #4 on: January 14, 2025, 05:53:04 am »
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.
operates as a floating highside switch
 

Offline Konkedout

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Re: help me about dc converter
« Reply #5 on: January 14, 2025, 06:04:18 am »
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.
operates as a floating highside switch

In 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.
 

Offline kimeraTopic starter

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Re: help me about dc converter
« Reply #6 on: January 14, 2025, 07:35:24 am »
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.
operates as a floating highside switch

In 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.

If you have other circuits that use commonly available ICs, please advise me. My problem is input 18-65V Output 12V1A.

thanks
 

Offline inse

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Re: help me about dc converter
« Reply #7 on: January 14, 2025, 07:49:22 am »
For example LM2575HV
https://www.ti.com/product/LM2575HV
Or even better the proposed successor which covers 65V:
https://www.ti.com/product/LMR36510
Btw the design you proposed is 48..60V
« Last Edit: January 14, 2025, 07:52:24 am by inse »
 

Offline MrAl

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Re: help me about dc converter
« Reply #8 on: January 14, 2025, 09:39:28 am »
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.



Normally 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.
 

Offline Zero999

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Re: help me about dc converter
« Reply #9 on: January 14, 2025, 09:51:33 am »
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.
 

Offline inse

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Re: help me about dc converter
« Reply #10 on: January 14, 2025, 09:54:14 am »
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…
 

Offline Zero999

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Re: help me about dc converter
« Reply #11 on: January 14, 2025, 10:44:58 am »
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…
In 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
 

Offline CaptDon

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Re: help me about dc converter
« Reply #12 on: January 14, 2025, 02:01:11 pm »
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".
Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 

Offline inse

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Re: help me about dc converter
« Reply #13 on: January 14, 2025, 02:26:18 pm »
A good old crowbar should never be disregarded
« Last Edit: January 14, 2025, 02:28:19 pm by inse »
 


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