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tictac
Joined: 22 Oct 2006
Posts: 63
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 11 Sep 2008 22:20 getting regulated 5V-dc from variable voltage |
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Hi Dear Friends
I want to design a circuit that has a variable input voltage from 12V to 60V DC.I have a digital section that need regulated 5v-dc that should be acquire from this input voltage. initially I want to use lm7805 to do this. but at high value of input voltage it doesnt work and may be hurt.
please give me some advice.
by regards.
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Sinisa
Joined: 03 Mar 2003
Posts: 300
Helped: 60
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| 11 Sep 2008 22:53 Re: getting regulated 5V-dc from variable voltage |
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| Most efficient way is to use DC/DC switching converter with 12V-60V input range and with power you require. For low power requirement you might get away by building series regulator with NPN transistor or similllar, but with higher current, dissipation and power requirement might be prohibitive.
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tictac
Joined: 22 Oct 2006
Posts: 63
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| 11 Sep 2008 23:18 getting regulated 5V-dc from variable voltage |
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Hi Sinisa
it use low power and I want to use series regulator .
Could you give me some schematic for this?
thank you
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Sinisa
Joined: 03 Mar 2003
Posts: 300
Helped: 60
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| 12 Sep 2008 0:25 Re: getting regulated 5V-dc from variable voltage |
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Circuit bellow should work up to 15mA. It does not have any current protection. To increase curent capability you will need bigger transistor and heatsink for it.
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tictac
Joined: 22 Oct 2006
Posts: 63
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| 12 Sep 2008 10:07 getting regulated 5V-dc from variable voltage |
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Hi I cant See any circuit bellow
Added after 1 minutes:
sorry I See it later
thank you
Added after 1 hours 38 minutes:
hi Sinisa
15mA is too low for my digital unit.it must be suffer up to 1A .
as far as I know about this circuit that the tl431 is fix and I must replace ztx453 with bigger one.Is it correct?
please help me.
by regards
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Sinisa
Joined: 03 Mar 2003
Posts: 300
Helped: 60
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| 12 Sep 2008 14:17 Re: getting regulated 5V-dc from variable voltage |
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If you go linear, dissipation would be 55W! That requires large heatsink and would be, uhm... well just ridiculous to do that.
You can use "Webench" from National Semiconductor to create switcher design:
@ltium file link
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tictac
Joined: 22 Oct 2006
Posts: 63
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| 15 Sep 2008 8:37 getting regulated 5V-dc from variable voltage |
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Hi
thank you Sinisa
Can I use buck converter to make a step down converter for 5v?could you tell me about IC that do this?
Added after 4 minutes:
sorry.I can find it on the site you told me
thank you so much
by regards
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tyassin
Joined: 22 Jul 2004
Posts: 242
Helped: 30
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| 15 Sep 2008 8:39 Re: getting regulated 5V-dc from variable voltage |
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Hi
Yes you can use a Buck-converter(step-down) to your application.
As mention go to National's homepage and use webbench.
This switcher can be used: LM5575.
But check out the homepage.
Regards
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Sinisa
Joined: 03 Mar 2003
Posts: 300
Helped: 60
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| 15 Sep 2008 13:28 Re: getting regulated 5V-dc from variable voltage |
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| Quote: |
| sorry.I can find it on the site you told me |
Just click on blue webench in my previous post.
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tictac
Joined: 22 Oct 2006
Posts: 63
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| 18 Sep 2008 21:28 getting regulated 5V-dc from variable voltage |
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Hi
a buck switch converter such a lm5575 needs a constant dc voltage about 5v to work,
and then convert higher voltage to lower one.
but I want to have a circuit to supply this voltage without need of any regulated voltage.
what can I do?
by regards
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Sinisa
Joined: 03 Mar 2003
Posts: 300
Helped: 60
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| 19 Sep 2008 12:17 Re: getting regulated 5V-dc from variable voltage |
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| Quote: |
a buck switch converter such a lm5575 needs a constant dc voltage about 5v to work,
and then convert higher voltage to lower one. |
Nonsense. Use webench to create design, I don't think it could be any simpler ather than someone doing it for you.
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fsmyth
Joined: 15 Nov 2004
Posts: 54
Helped: 1
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| 22 Sep 2008 9:42 Re: getting regulated 5V-dc from variable voltage |
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Lots of examples:
http://hmin.tripod.com/als/
60V pre-regulator:
http://hmin.tripod.com/als/andysm/pages/analogs6.html#APS619
<als>
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siongboon
Joined: 24 Jan 2006
Posts: 180
Helped: 14
Location: Singapore
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| 05 Oct 2008 15:29 Re: getting regulated 5V-dc from variable voltage |
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Use LM2575 High Voltage version. input 7Vdc to 60Vdc. rated at 1A
It will be able to regulate to the 5V you need.
For 3A version use LM2576.
http://www.siongboon.com/projects/2005-08-07_lm2576_dc-dc_converter/
Best Regards,
Siong Boon
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