Help with my Regulated Power Supply Pls..

Status
Not open for further replies.
S

sv_clintrace999

New Member
Hi to all!

I have made this 13.8V Regulated Power Supply of mine which I used for my portable vhf transceiver so that i can get rid of using it`s battery pack when i'm at home. But this power supply produces a humming sound output for the receivers which is very annoying to hear, my fellow Ham said i should put a lot of high valued electrolytic capacitors to the output but seems nothing had happened. The transformer that i used was a 3amp. 12vac and now i am asking for your help so that i can get rid of that annoying sound when i listen to another portable radio, Did i missed something perhaps a components for the schematics or there`s another schematics for removing that hum? I guess there`s somebody which is a Ham here or knows about tansceivers please help.

Salamat,

Clint
 

Attachments

  • Regulated PS.PNG
    7.3 KB · Views: 295
Last edited:
Did you put 3,300u electrolytic on the front-end?

Do you have a bridge rectifier?

What is the voltage on the front-end of the circuit?

These are things we need to know before we can go any further.
 
hi colin!

Yup i have put a much higher value of capacitors in the unregulated part but seems the humming sound won`t disappear, The unregulated part of the schematic is using a 12vac and the unregulated part is 16vdc when it went through the bridge rectifier.
 
Did you put the electrolytics between the bridge and the input of the 3-terminal regulator?

What value? Are they new? How physically big are they? Are they getting hot?
What is their working voltage?

Don't forget, the 2N3055 passes a lot of hum because it has very little separation between its input and output.
The 3-terminal regulator has about 1,000:1 The 2N3055 has about 20:1

This is somthing that no-one has ever mentioned before.
 
Last edited:
Yes i put about a 4,700uf capacitor, another friend of mine told me that there`s no way i can eliminate that annoying sound of humming but to use a 15-0-15 transformer instead of 12-0-12 but what i have is 12-0-12 and i find him seems right because i made another 12-0-12 regulated power supply using a simple regulator LM7812 but still a humming sound was heared. The thing that bothers me for not using a 15-0-15 is that i am afraid if a regulator would be damaged and that 15vac when converted to dc will become more or less 19-20vdc and therefore if will short to the damaged regulator will go directly to the transceiver which cannot hold up to 20vdc thus resulting to damaging the transceiver.
 
Last edited:
If you are using 12 - 0 - 12 You have 2 diodes.
Are the diodes getting hot?

How much current does the transceiver take?

If it takes about 1 amp. try removing the 2N3055 for an instant and listen to the hum
 
Yes you are right i just used only 2 diodes but it is quiet a bigger diode (6amps maybe) and i attached it to a heatsink too, the transceiver can manage 1 amp from a 5watts transmission. I remembered i opened a zebra Porta10 1amp and it is using a 15vac transformer but when the transceiver is transmitting a power output of 5watts, excessive heat from the transformer occurs and a loud humming too that`s why i made a 3amps regulated power supply but it was only 12vac transformer that i used. I haven`t tried using a 15-0-15 yet because i don`t have it in the first place.
 
Last edited:
in your first post you mentioned...
"and now i am asking for your help so that i can get rid of that annoying sound when i listen to another portable radio, "
i did not understand this-does your power supply generates RF ?it can not.so how come you get hum in other radios?
By the way check one of the diode (which you might have..but once more)for short-may it be new -but might have damaged in experimenting .
We were using 10000 micro farads when i was a ham.but 4700 is OK.
also confirm the current rating of all the components as well as the load(the transceiver)
73s
prash.
 
You're passing the ripple right through to the output. National Semi has application notes on how to do this properly.
The cap only needs to be big enough to prevent the regulator from dropping out, and if it's too big you need to raise your rectifier's I squared T rating.
 
That will work but it won't be very good.

The emitter follower's output will drop as the load increases, totally ruining the good regulator provided by the LM317.

See the National Semiconductor datasheet as already suggested.
 
Hero999 said:
That will work but it won't be very good.

The emitter follower's output will drop as the load increases, totally ruining the good regulator provided by the LM317.

See the National Semiconductor datasheet as already suggested.
Click to expand...

Hero was right, i noticed that when my transceiver is transmitting the 5watts power, the voltage drops by almost 1 volt ++, i`m not really good in electronic theories it`s just that i made this power supply from a very simple schematics for transceivers.

@ Prash

Thanks fellow ham for explaining but as what i have said i just followed this schematics and i don`t know what was missing.

Here is the full schematics of what i have made. Please comment on this..
 

Attachments

  • Regulated PS.jpg
    21.1 KB · Views: 321
Last edited:
i guess the humming appears when the voltage is dropping, can anyone suggest of a fixed voltage regulated power supply that doesn`t drop or a steady volt perhaps for a 3amps 12vac transformer?

Any suggestions or chematics are hghly appreciated.

Salamat,

Clint
 
When the hum is being produced, what is the voltage on the input of the 3-terminal regulator and the voltage on the output of the 3-terminal regulator.
 
colin55 said:
When the hum is being produced, what is the voltage on the input of the 3-terminal regulator and the voltage on the output of the 3-terminal regulator.
Click to expand...

Hi colin55!

The voltage before it was regulated normally went up to 16vdc and to the output of the regulator i set it up to 13.8vdc through a pot where the transceiver normally operates in that voltage.
 
That's your problem


The input voltage is 16v and the output is 13.8v But the output of the regulator is 13.8v + 0.7v = 14.5v The difference between 16v and 14.5v is 1.5v This is not enough to provide regulation.

The regulator needs at least 2.5v to 3v absolute MINIMUM.

There’s your problem.
 
oh great!

so does this means that the transformer should be higher than 12vac so that i can produce let`s say 18-20vdc in the input of the regulator? May i know where is this 0.7v came from because i set the voltage to 13.8vdc. Can you suggest of a diagram of a steady regulated voltage or perhaps an additional components of what i have done so that i can eliminate those hum anymore...

Thank you very much Sir!
 
If the output voltage is 13.8v, the output of the regulator must be 0.7v higher than this as the 2N3055 is connected as an emitter-follower and the base is always 0.7v higher than the emitter.
 
The only thing I can suggest at the moment is to put a bridge on the output of the transformer, by connecting the two outer leads to the AC points on the bridge. The 0v wire (the centre-tap) goes no-where.
Try this for a few minutes and see if it cures the problem. This will create additional heat in the 2N3055 but will be ok for 30 seconds.
 
If the above works, I have the next solution.

Get a length of enamelled wire the same gauge as the secondary winding and wind 6 - 9 turns as an over-wind on the bobbin by feeding the wire through the gap between the winding and the core of the transfomer. Do this again as a separate winding.
Now connect one of the 12v leads to one end of the 9 turns and the other 12v lead to the other 9 turn winding.
Measure the output of the new system. You will have added about 1v to each winding. If you have subtracted 1v, reverse the winding.
This will give you an added volt and the output will be just enough to provide 13.8v output.
 
Last edited:
Status
Not open for further replies.

Similar threads

E
  • Question
Help with my project please
Replies
13
Views
3K
danadak
  • Question
Bench Power Supply
2
Replies
20
Views
2K
Tony Stewart
F
Handy Bench Power Supply
Replies
8
Views
2K
schmitt trigger
S
F
A Simple Power Supply Project
Replies
1
Views
1K
Tony Stewart
G
  • Question
My son need help with his circuit design!!!
Replies
14
Views
1K
ZipZapOuch
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…