Voltage regulator

Hello! Could you please look on this scheme:

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Is it proper way to connect resistor divider to the positive regulator? (Positive regulator is used for negative output.) Thanks in advance!

Reply to
Vladimir
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Thank you very much!

Reply to
Vladimir

It doesn't look right. The second resistor is connected between ground and ground, and is useless.

I am too lazy to look up the circuit you should use, but I can tell you how to do it.

Use the standard circuit for the positive regulator you use.

Assuming that the input power supply is floating, a transformer connection to the mains, you can then safely ground the positive output from the regulator and use the ground=negative from that regulator circuit as your negative output.

That negative output will be the same as the negative end of the input power supply.

If you want to combine this negative power supply with a positive one, remember to connect their common ground to the positive output of this negative supply, and no other point.

In short, build the circuit just like you would build a positive power supply, then use its outputs as a negative power supply.

--
Roger J.
Reply to
Roger Johansson

I read in sci.electronics.design that Vladimir wrote (in ) about 'Voltage regulator', on Sun, 3 Apr 2005:

No. The resistor on the right is short-circuited.

All you need is a perfectly ordinary circuit. Then you earth the + output terminal. Use Courier font:

____

  • o--------| |-----+---+-o + |____| | | | [R1] Earth Input |_______| | Output [R2] |

- o-----------+-------------o -

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Regards, John Woodgate, OOO - Own Opinions Only.
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Reply to
John Woodgate

Hello! Suppose, i have a required voltage on the output of linear regulator(Vout=6.3), but output current is too high (Iout=7.5). I need Iout=5.5 A. How I can work it out? I think about a follow way. (It is quite possible that it is wrong.)

I should increase output voltage, then choose two appropriate resistors:

|----[ R1 ]----o V=6.3; I=5.5A V>6.3; Iout=7.5 | ----------------| (Output of regulator) | |----[ R2 ]----|[ground] Could you please advise me something about it.

Reply to
Vladimir

Linear regulators usually regulate voltage, not current. The current is then defined by the load, not the regulator.

6.3/5.5 = 1.14 ohms.
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   Robert Monsen
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Reply to
Robert Monsen

If there was no way to modify the linear regulator, you could limit the current with a separate current limiter. This wastes power though. Check out some of these ideas:

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Reply to
Mark Jones

I think you'd need to explain what the problem is rather more clearly.

NT

Reply to
bigcat

First i am sorry for my bad English.

I have this regulator: _________ | Volt. | Output (Vout=+6.3; Iout=7.5A) ____|Regulator|_________ | | |_________| (Adj)| | I can adjust output voltage using resistor divider (from 1.25v to 30v). But i need the other current value. Iout must be equal to 5.5 amperes. Can it be implemented, but without much complexity? Thank you!

Reply to
Vladimir

No problem. It is better than the English of some English-speakers. :-)

I think you misunderstand about voltage, current, and resistance. The voltage is regulated at the set point, yes.

However: the load (what you're supplying power to) will only draw as much current as it needs. The 7.5A spec on the existing regulator means merely that it has the _ability_ to provide that much current. If the load presents a resistance of, say, two ohms, then at 6.3 volts, it will only draw 3.15 amps.

Think of a water faucet. When it's off, you still have full water pressure (which will show on a gauge), but the amount of flow depends on how far the valve is open. Even if the pipe is very big, and has the ability to provide, say, one liter per second, if the valve is open only a little bit, it might provide, say, half a liter per minute, but the available pressure will be the same (except for losses in the system, which are called "internal resistance").

So the supply itself can not control both voltage and current - the load will only take what it needs.

Hope This Helps! Rich

Reply to
Rich Grise

clearly.

30v).

understood.

?

?

?

situation not explained, so cant help. Your english is good, but if you cant tell us what youre doing, what the problem is, what you want to achieve... how are we expected to help? Much too ambiguous.

NT

Reply to
bigcat

That is not the problem, your english is good enough.

But you do not explain a lot of things.

Is this a practical real problem or a theoretical problem?

Give us the data on the regulator/power supply. What are you using this circuit for? What is the load, what is this power supply used to drive?

The method of using resistors to set the output voltage is only acceptable if you need very low current, but you seem to need a lot of current.

Can you change the regulator instead, to give the voltage you need? Have you built the regulator yourself, do you have the schematic for it? Is it the same regulator circuit as the one we talked about a few days ago?

Is the same regulator/power supply used for some other load at the same time as you need this reduced voltage?

What is the real practical problem you are trying to solve? Are you trying to control a motor, or a lamp, or what?

--
Roger J.
Reply to
Roger Johansson

I am designing a circuit of voltage regulator. I've got all required parameters except the current value. It is too high.

The problem is to limit this current.

I'm not familiar with electronics. It is possible that there is no problem in case of a superfluous current (ie 2 amperes) do not affect the load.

Reply to
Vladimir

ha. I'm all for him trying it, its not that hard. I think we all designed things a bit beyond our current abilities once, and look where it got us.

But as he's not wiling to explain, not much way to help.

NT

Reply to
bigcat

If you connect no load at all to your regulator no current will be used.

Every battery or power supply has limits to how much can be used.

If you built your power supply with a standard 1Amp regulator you cannot take out more than 1Amp. If you try to take out more current the regulator will lower the voltage or shut itself down completely, until you remove the load.

You need to study more elementary electronics, like Ohms law, series and parallell connection, current, voltage and resistance, DC circuits analysis. Use these keywords to find information about it on the web.

A link to a free electronics course for beginners:

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You can borrow books about electronics for beginners at your local library.

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Roger J.
Reply to
Roger Johansson

I read in sci.electronics.design that Vladimir wrote (in ) about 'Voltage regulator', on Wed, 6 Apr 2005:

..... but you are designing a voltage regulator?

Will you be doing brain surgery next week?

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Reply to
John Woodgate

"John Woodgate" schreef in bericht news:+ snipped-for-privacy@jmwa.demon.co.uk...

He should be getting it ;) Clearly a troll, carefully avoiding the posts that explain too much.

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Reply to
Frank Bemelman

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