Chat_Ghosty's PSU

[KrisBlueNZ]

You can learn a lot from failing when part of your circuit doesn't work as you expected. But you won't learn anything from a circuit that doesn't work at all because a small fault completely prevents all of it from doing anything useful, or which blows MOSFETs constantly.

You also need to learn a LOT before your circuit even approaches something you can actually MAKE. There are no component values indicated, except for the ICs. There are no details of the transformers and inductors. These things make or break a switching power supply.

I very strongly recommend that you start with something more straightforward, where sections of the design can be diagnosed separately, and where each small mistake doesn't result in a shower of sparks and hours of rework, with no identifiable lesson learnt.

 

[Chat_Ghosty]

Lets start a bit simpler.

The Cap Values should be 0.33uf and 0.1 uf.

WIll this work?

 

[davenn]

Dave. Why am I thinking that the Line on the Diode is the Negative side?

Are you thinking Electron or Conventional Theory.?

Conventional .... always think conventional, if you try swapping between the 2 all the time you will end up in strife as in that circuit
There are only rare times you need to consider electron flow direction, this isnt one of them

Dave

 

[davenn]

Lets start a bit simpler.

WIll this work?

ummm
.... for a start your schematic shows far fewer components than the PCB layout
the schematic and PCB layout must match

you havent shown the fuse in your schematic
what are those 2 other 3 terminal devices on the PCB that are not shown in the schematic ?

The Cap Values should be 0.33uf and 0.1 uf.

why would say that ?
the schematic clearly shows 470uF in the input to the regulator chip, but yet another mismatch the PCB layout shows 4700uF ??
in reality it should be ~ 1000uF on the input since the regulator is capable of supplying up to 1 Amp

Dave

 

[Chat_Ghosty]

I forgot to add the fuse in the PCB.

The Data sheet said to use 0.33 and 0.1 for this VR.
I did not add the Two Digital Voltage Displays in the Schematic.

Why do I need a 1,000uf Cap when using a battery?
I tought the 1,000uf : 1amp was for Smoothing when using a Bridge Rectifier.
I did mess up on the cap values. Honestly I have no idea when to and how to calculate the values. This I took off the data sheets and added a few parts I needed.

Any books I can read?

 

[KrisBlueNZ]

You're right that you don't need 1000 uF on the input if you're powering it from a source that's already DC. The actual value is not that important. You could just as easily use a 0.1 uF, the same as the capacitor on the output.

Those capacitors are needed by the regulator, to ensure stability. They should be placed close to the regulator and connected to the regulator leads with connections that are as short as possible.

You should be a lot more careful that what you post is correct. Mistakes are unavoidable, but when we see a schematic and a PCB that have more differences than similarities, with no explanation along with the posting (or even if there IS an explanation), it's hard to know where to start when writing a response!

 

[davenn]

Ahhh battery supply OK fair enough on those values
Sorry was glossing over the battery on the input ... am so used to using them off a bridge rectifier

Dave

 

[Chat_Ghosty]

I was meaning for you to only look at the Schematic. My fault for not saying.
The data sheet said to use a 0.33uf.
Why does the caps need to be places as close as possible?

Does the Schematic work?
If so ill post a more complex one. And try and work up to SMPS if you guys have the time.

 

[(*steve*)]

Why does the caps need to be places as close as possible?

To prevent instability (oscillation).

Does the Schematic work?

The schematic doesn't do anything. You have ti build it (on a breadboard perhaps).

Have you?

 

[davenn]

I was meaning for you to only look at the Schematic. My fault for not saying.
The data sheet said to use a 0.33uf.
Why does the caps need to be places as close as possible?

the caps are there, as Kris said, to stop oscillations within the regulator chip
placing the bypass caps close insures that the legs of the chip dont start becoming inductors at certain frequencies

normally in a rectifier supplied regulator, you would use a 0.1uF on input and output
and you would also use a 1000uF on the input and a ~ 10uF on the output

a

Does the Schematic work?
fter that PSU is up and working. And try and work up to SMPS if you guys have the time.

that schematic will work
working up to a SMPS will be a very long time down the track
you would be better off building a linear PSU using a mains transformer to a lower AC voltage and rectifying that

a bit bulkier and heavier but a worthwhile learning experience and you will end up with a good PSU for workshop experimental use
After that PSU is up and working, you could then up the learning/circuit complexity by adding current limiting etc

Dave

 

[Chat_Ghosty]

I see, Ill try and get some of the parts and try and build it.

 

[Harald Kapp]

@Jaclksons : This is an old thread from 2013!. Unfortunately Kris is no longer among us. I'll close this thread.