Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

12 Volts 5A voltage regulator circuit problem

Status
Not open for further replies.

adnan_m_s

New Member
:( Hellow every body,

I need your help on something I need to build a power supply of 220/12 volt regulated with 5 amperes,
I have located some circuits here and there but they all need large heat sinks somethink like 10*200*100 mm aluminum, or can even need a fan for that IC regulator and pass transistors, so does any have a diagram that needs less heat sink spaces,

my real problem is in my country Jordan there aren't any 5A 12 V regulator ICs they use only the known 70812 with pass transistors ?

can any one help me build this power supply with this IC 78012 without having to use so much space in heat sinks?

thank you all
new member
Adnan Samra
 
Unlikely. The 7812 is an old, inefficient part. The 5A delivered to the load has to go through the pass transistor. Each volt of difference between the input voltage to the regulator and the 12V output represents 5 Watts of heat which must be removed. The best way to do that is with surface area and fluid flow, thus the heat sink.

If you wanted to build a switching regulator you would have more of a chance, since they are 80 to 90 percent efficient.
 
what if i used more pass transistors would that divide the load abit?
I mean I have a circuit which has something like 5-6 pass transistors TIP36
and it is used with a 30 A 220/24 v adaptor to give regulated 12 V 30 A with 78012 IC
so what do you think guys?
can i use this circuit with a 5 amperes 19 V to give 5 amperes 12 V regulated
 
No matter how many pass transistors, you will still be dissipating the same amount of heat.

You haven't said what the PSU is for ?
How well regulated does the output need to be ?

I would looking at modifying an old 12V car battery charger - these usually give about 15 volts at around 4 to 6 amps which is ideal for making a 12v PSU. Its cheaper to buy a battery charger than a 50 or 60W transformer. You also get a rectifier and a case.

The other alternative is a switcher, Could you use an PSU from an old computer ? even if you ignore the outputs you dont want (5V, -12V) it may still be relatively compact compared to a linear PSU
 
Guys,
What do you think of the IC LM2679-12 Simple switcher? is it a reliable IC to do a switchable power supply 12 V 5A , what about the heat dissipation ? does it need one , and how should be the size of its' heat sink?
 
adnan_m_s said:
Guys,
What do you think of the IC LM2679-12 Simple switcher? is it a reliable IC to do a switchable power supply 12 V 5A , what about the heat dissipation ? does it need one , and how should be the size of its' heat sink?

Hi,
Looking at hero's link, it says the output current for the LM2679 has to be less that 5Amp.
EDIT: did a re-run, this time it said OK for LM2679????
Whats the input voltage to the LM2679 going to be?

But it does recommend the LM3488 for 12V at 5Amps, use the interactive design option on the website page.

Hope this helps.
**broken link removed**
 
Last edited:
They are 90% efficient so for 60W out the IC or Mosfet heats with only 7W.
 
adnan_m_s,
Do the calculations, as audioguru says it will produce 7W of heat, most of which will be in the MOSFET.

Heatsinks are rated iby their thermal resistance (°C/W), a 1°C/W heat sink will rise by 1W above ambient if the when dissipating 1W or 2°C above ambient when dissipating 2W.

Also take in to account the thermal resistance of the MOSFET juncion to case and any insulators between the case and the heat sink (just add them all together).

You want the MOSFET junction to remain below the maximum operating temperature when dissipating 7W at the highest ambient temperature that you want to operate your design in.
 
GUYS,
I WANTED TO ASK YOU SOMETHING,
I used to assemble Audio amplifiers of different kinds of ICs but I always faced the problem of the 50 Hz noise coming out of the speaker, so does using a regulated power source terminate this 50 Hz noise becasue I know regultor circuits alows only dc current to pass?
 
Most audio amplifiers reject mains hum that is from the power supply so that they don't need a regulator. Mains hum is usually picked up if unshielded input wires are used. Shielded audio cable should always be used for feeding a signal to an amplifier.
 
Also note that if a dual supply is used the hum from positive and negitive rail is 180° and therefore cancels at the output.
 
So do you think that the bridge rectifier is not good for supplying audio circuits and it is better to use a dual (like 2 diodes + a mid point) what is the audio circuit design requires a bridge rectifier, do you think that sheilded input is enough for the deleting the Hum of the public 220 V supply current?
 
adnan_m_s said:
So do you think that the bridge rectifier is not good for supplying audio circuits and it is better to use a dual (like 2 diodes + a mid point) what is the audio circuit design requires a bridge rectifier, do you think that sheilded input is enough for the deleting the Hum of the public 220 V supply current?

A bridge rectifier is the preferred way, although either makes no real difference - your hum problems are almost certainly down to bad layout and construction, with a slight possibility of a particularly badly designed circuit.
 
adnan_m_s said:
so if I use shielded input and put the whole circuit in a thin metal can, would this solve most problems?

It will help, bear in mind you should only connect grounds at ONE point, multiple ground points will tend to cause hum (earth loops). It's really just a case of following good design principles.
 
Short the input snd if the hum goes away then it is probably mains hum picked up by unshielded input wires.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top