heating of 5V regulator

[nikhilele]

i have variable DC supply from 10.2V to 13V now i want to convert it into 5V.

1>
we can use 7805 directly but this IC is getting hot and its reliability becomer poor.
2>
most desirable option is to used step-down convertor like MC34063 this will lead to switching noise and require inductor which are hard to find on the shelf.
3>
first i convert it to 8V then this 8V to 5V which will divided heat in two IC and IC wont get much hot and can work in realiable manner.

so I would like to disscuss the above points in this forum.

 

[rocky_jan]

i have variable DC supply from 10.2V to 13V now i want to convert it into 5V.

1>
we can use 7805 directly but this IC is getting hot and its reliability becomer poor.
2>
most desirable option is to used step-down convertor like MC34063 this will lead to switching noise and require inductor which are hard to find on the shelf.
3>
first i convert it to 8V then this 8V to 5V which will divided heat in two IC and IC wont get much hot and can work in realiable manner.

so I would like to disscuss the above points in this forum.

1>You can use the regulator straight way if you have allocated a proper heat disipation. You may provide sufficient ground pad to dissipate the heat OR use some metal block for effective dissipation.

If you don't have such means then it is recomended that you go for step 3 what you have mentioned.

2>Switching regulator are very efficient regulators but the layout needs lot of consideration for eliminating the switching freq noise. I don't know what inductor values you are looking for but you can go to TOKO,coilcraft etc. web sites to find the required inductor.It is not necessary to use the inductor value same as calculated one it can be any std. value near to the calculated one.

 

[nikhilele]

what about the second option i would like to listen some comments on that

 

[sisc1525]

you can use a buck regulator

 

[DarkJedi]

nikhilele, the problem there is that you are regulating from 10 to 13 V to 5V, the regulator looses performance when the input voltaje is to high from the output voltage, you loose power on this manner because the power the regulator have to support all the power... try lowering your 10 to 13V to 10 to 8 v it should get better that way.

 

[nikhilele]

DarkJedi
so you are talking about second option.

my current requiremenents are near 500mA.
but my ouput at 7805 is near 4.9 not 5V.

 

[dika]

from my experience 7805 need voltage around 9-10V to produce an exact 5V.
so simply use 13V -- 10V -- 5V
for added stability use a good heatsink to reduce power dissipation

 

[Nimer]

hi
could you chekc how much load current is drown from the regulator and try to lower it bey using difeernt components .

regards

 

[memarian]

Dear,

You Can use one of the LM123 or LM223 or LM323 5V Regulators.

These Linear Regulators Can provide you up to 5V @ 3A and with good Heatsink they can dissipate about 35W.They packaged as a power transistor in TO-3 Package.

Difference between 3 models is in working Temprature.
LM123 -55...+150
LM223 -25...+150
LM323 0...+125

Good Luck.

 

[nikhilele]

1>
I cannot use lm223 or such because i want to use TO220 package
I can use LM7805 or LM317 or similar
2>
as i said previously my dc input changes from 10.3V to 13V
i cannot have 13-10-5 as when input is less than 12V; 10v is not achievable.
instead i was thinking of [10.3V - 13V] ---> 8.3V [using LM317] ----> 5V[7805].
3>
how to lower my current consumption.

 

[DarkJedi]

I think solution 2 is better. Why only 10.3 to 13V input? where does this input comes from?

4.9v isn't as good as 5v? most IC will assume 4.9 as "1" so, what's the bg deal there?

 

[Borber]

You have to dissipate 2.5-4W of power. Current is not a problem.
You can use a 10°C/W heatsink and 7805 (25cm^2 area).
You can use 7808 (LM317) and 7805 with smaller heatsinks.

To help you lowering current consumption give us your schematics.

 

[memarian]

Dear,

Check L200 Regulator From STMicroelectronics.

I think you can use it as a single stage 10.3~13v to 5V converter.

Datasheet Link : eu.st.com/stonline/books/pdf/docs/1318.pdf

This is an adjustable regulator can provide you up to 2A.It also has an current Limmit.

It packaged in Pentawatt Package (similar to TO220,but has 5 Leads).

Good Luck.

 

[nikhilele]

can i use 7805 as single stage 10.3~13v to 5V converter. i have better heat sink then displayed in ml26aa.jpg but smaller then ml73-25p.jpg.

 

[Borber]

What you need is heatsink with no higher thermal resistance then 20°C/W for ambient temperature up to 50°C. For orientation go to http://www.velleman.be/be/en/product/list/?id=343790 and look how those looks like.

 

[ulaska]

Hello,
for example, we have a 12V switching mode power supply, and want to drop it to 5V by a 7805,
does the 7805 heat so much?

or doesnt it make no differences where we connect the 7805, 7805 hets all time, 12v to 5v operation?

thanks.

 

[Borber]

It heats exactly as
P=(12-5)*Iload

 

[louisnells]

Hi
7805 seems to be hotter when either a high input voltage is applied or because of high load current. It can't provide more than 1A peak value. Also try a good heat sink and to expose it very well.

 

[nikhilele]

can we drop few voltages using diode and then suppply that to 7805
for example if my input is 12V after adding two diode it will drop to 10.8V and provide this to 7805 this will decrease the heating of 7805.
this may look funny.
but heat will be divided among 7805 and two diodes.

 

[Borber]

You can play with it as you want. The fact is that for regulation a certain amount of power must be spent for dissipation. You can use 7805 with appropriate heatsink or distribute that power to 7805 and few diodes in series (up to 6 in your case) and use smaller heatsink or in some cases no heatsink. But the dissipated power will be the same.