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dc to dc converter

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chopper

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Hi everyone, i have a DC 11V ,100mA= 1.1W, is there any way to convert it to 5V 230mA=1.1W?? is this achievable using a 7805 voltage regulator?

if not, please tell me how.thanks for your reply
 
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Hi everyone, i have a DC 11V ,100mA= 1.1W, is there any way to convert it to 5V 230mA=1.1W?? is this achievable using a 7805 voltage regulator?

if not, please tell me how.thanks for your reply

Hi,

You need a buck converter to do that but you will not get exact 1.1W as the efficiency of the converters matters. With 7805 impossible it will dissipate more than buck converter .
 
hi dark, thanks for the reply. can i use a 5v zener diode to act as voltage regulator and achieve the 5V 0.23A??
 
hi dark, thanks for the reply. can i use a 5v zener diode to act as voltage regulator and achieve the 5V 0.23A??

Hi,

In that case regulation will be a concern . what are you trying to power with this supply?
 
im trying to use this power to charge a cell phone and 5V 0.23 is sufficient enough to do it

have alook at the following links ;
12V to 5V DC converter using Zener diode and transistor : simple electronics

dc-dc converter by 555 : simple electronics

you might require slight modifications also do consider the charging rate for the celphone battery . Even if you loose some current as conversion losses it will just take more time to charge your battery. There are dedicated buck converters out there ,if you need for hobby purpose the above links looks good to me .
 
Hi everyone, i have a DC 11V ,100mA= 1.1W, is there any way to convert it to 5V 230mA=1.1W?? is this achievable using a 7805 voltage regulator?
if not, please tell me how.thanks for your reply

refer to the datasheet of LM7805.
Electrical Characteristics (MC7805/LM7805)
(Refer to test circuit ,0°C < TJ < 125°C, IO = 500mA, VI = 10V, CI= 0.33μF, CO= 0.1μF, unless otherwise specified)
The max output current is 500 mA, as stated. The current can be limited using a resistor in series with the output.
 
Let's start with the basics: 1.1W at 5V is 220mA, not 230.

Sorry, this is worse than a 7805 because the series resistor wastes as much as the 7805 plus zener diode bypasses additional current. It can only supply 5V 100mA or less from 11V 100mA.

Would work if the value of Rb is adjusted for 11V. (I would start playing with 18k.) It's unregulated so it passes any variations from the incoming 11V. It would probably be around 60% efficient (11V 100mA in, 5V 132mA out) at best, because it uses the NPN in emitter follower configuration. The choice of diode D is critical to efficient operation, but none is recommended. It runs at about 20kHz so a fast schottky diode is a pretty good idea. 1N4001 is a poor choice. Coil isn't specified either.

(This switcher actually might be better without the transistor or diode D. Just connect pin 3 to the inductor L. Needs more study, it's too late for me to build or simulate tonight. Inductor L would need to be chosen carefully, not just a few turns wound on some antenna rod.)

you might require slight modifications also do consider the charging rate for the celphone battery . Even if you loose some current as conversion losses it will just take more time to charge your battery. There are dedicated buck converters out there ,if you need for hobby purpose the above links looks good to me .
 
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OK, couldn't sleep. Haven't built it but this works in simulation: Both diodes can be 1N4148, it only needs to catch brief spikes. Another diode from Pin 3 to 11V is a good idea; I see spikes in simulation that I don't expect on the bench. Pin 3 is connected to L, there's no transistor. Rb becomes 24k. L needs to be between 250 and 500 microhenries. (This is not a few turns on a piece of ferrite.)

555 needs to be the bipolar (NE555, LM555, etc.), not CMOS.

Regulation is nonexistent, it varies with input and load.
 
I'll want to build it before I post a new schematic just in case I forgot something that simulation doesn't reveal. It's the same as the second posted schematic with changes as I noted.

I knew I forgot something; your two-transistor SMPS is better than either 555 attempt.
 
I haven't posted a schematic, stayed away from the forums all day to limit my frustration. For a while it was working in IE, now some pages sort of work in Firefox.

Meanwhile, the design I was promoting was marginal, achieving barely 60% efficiency. While this site stabilizes, 'dark's second link dc-dc converter by 555 : simple electronics with these changes:
Pin 3 is connected to L, there's no transistor. Rb becomes 24k. L needs to be between 250 and 500 microhenries.
That said, the Black Regulator is better than any of the suggestions, mine included.
 
Yep the new forum is slow as crap, I'm glad it's not just me that noticed it.

Some of it works in IE6 but it won't display the thread dates right and some panels are "squishy", in Mozilla it just plain sluggy and the viewed page locks up while non-selected pages are loading in the background! That's just criminal. If it doesn't get fixed I will probably find somewhere else to browse because this is painful. The AllAboutCircuits forum still works nice and fast.

Thanks for the mention of the Black regulator, its a small fast minimalist convenient thing (unlike the new forum) :eek: :D

(edit) And those new emoticons are awful too! They are tiny and just don't have personality like the old ones did.
 
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