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Build a variable power supply

nghiep

Mar 26, 2022
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Hi ,

I'm a beginner in electronic field . I want to build a DC DC variable power supply with input 3.3V, 12V and 24V , while ouput is vary from 0-25 V. Here how i think about the design:
- First I will make a buck and boost converter and add a current limiter to limit current affect load.
- I decide to use switch DC DC (IC ) converter instead of linear converter (IC) .
I had check the internet and have i look at MC34063. I think it only become step up or step down depend on the re arrange of the component (not have Buck and Boost mode change depend on apply voltage ) .

Question :

1/ What IC do you guy recommend me to use ?
2/ Do my idea correct ?


Furthermore, i have look at this link on internet. He design a step up converter but can get a 9V input to 8.5 V .8.5 V happen in minute 4:20 of video.
Question :

1/ Could it due to lose in wire?

Here is the link:
https://circuitdigest.com/electroni...tput-dc-to-dc-converter-circuit-using-mc34063
 

kellys_eye

Jun 25, 2010
4,878
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Jun 25, 2010
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4,878
I want to build a DC DC variable power supply with input 3.3V, 12V and 24V
Why those input voltages? Presumably those DC 'source' voltages will come from some sort of AC-derived supply in the first place so why not just use an AC source to get the variable DC output(s) you need anyway?

A simple ex-laptop adapter with a buck/boost circuit would do everything you need. Indeed there are ready-built modules with the relevant buck/boost built-in along with digital displays, adjustment and limiting - all for under $20.
 

nghiep

Mar 26, 2022
3
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Mar 26, 2022
Messages
3
Why those input voltages? Presumably those DC 'source' voltages will come from some sort of AC-derived supply in the first place so why not just use an AC source to get the variable DC output(s) you need anyway?

A simple ex-laptop adapter with a buck/boost circuit would do everything you need. Indeed there are ready-built modules with the relevant buck/boost built-in along with digital displays, adjustment and limiting - all for under $20.


Currently i have DC supply with fixed outputs (3.3V ,12 and 24 V ) . However some of my device use 7V or 8V DC. I know there are cheap converter , but I think this is a opportunity to design a circuit , hence i want to create a converter for my power supply.Just a hobby project
 

kellys_eye

Jun 25, 2010
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Put the 12V source into a 7808 device to get 8V at 1A. Three components (one IC and two capacitors)
 

Simon mugo

Mar 27, 2022
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Mar 27, 2022
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Why should you have the 3V3, 12 and 24 DC voltages which will be very expensive to acquire from an AC source? The best way is just rectifying and regulating AC to get DC voltage of 25 V. To get the 25VDC I would propose you use the 7825 voltage regulator for the positive DC and the 7925 voltage regulator for the negative DC. It all depends on the type of DC that you really want.
Thank you!
 

kellys_eye

Jun 25, 2010
4,878
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You can put a diode in series with the LM78** ground lead to increase the output by 0.6-0.7V (two or more if necessary) to achieve 'intermediate' voltages.

I'd recommend the LM317 anyway.......
 
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