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I have recently bought a voltage regulator (link, specs, and datasheet below) and I am regulating a AC-to-DC 9v power supply into 5v with as little components as possible. In the datasheet, all of the diagrams use capacitors, and I don't have any on hand, nor do I have the desire to use them if I can. I have seen people create phone chargers with Altoids cans with only a voltage regulator, two wire, 9v battery, and 2 resistors (from 5v to to both of the data lines), so I don't know if it is just providing additional circuits for different uses.


Basic Information:

LM7805 L7805 7805 Voltage Regulator IC 5V 1.5A

Manufacturer: STMicroelectronics - SGS THOMSON
Manufacturer Part No: L7805CV
Package / Case: TO-220
RoHS: Yes

Specifications
Product Category: Linear Voltage Regulators - Standard
Polarity: Positive
Number of Outputs: Single 
Output Type: Fixed
Output Voltage: 5 V
Output Current: 1.5 A
Line Regulation: 50 mV
Load Regulation: 100 mV
Dropout Voltage (Max): 2.5 V @ 1A
Maximum Operating Temperature: 150 C
Minimum Operating Temperature: 0 C
Mounting Style: Through Hole

From eBay descripiton.

Datasheet


P.S. This is not a duplicate of Proper use of a voltage regulator because that one is not about the schematics, it is talking about if it is needed in the first place.

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From the Datasheet (Figure 17, Standard Regulator Circuit):

2. Although no output capacitor is need for stability, it does improve transient response.

3. Required if regulator is locate an appreciable distance from power supply filter.

Both can be omitted if you arn't too concerned with how clean the regulation is. If you are using it for a cell phone charger, you would want the caps. If you have a load that switches between low and high current often, you would want the caps. Also depends on how dirty/noisy the ac adaptor is. But if all you are doing is adding a few leds with resistors and nothing else, you don't really need that clean of a line.

The input cap is to filter noise while the output is to keep the line steady during certain times. The "appreciable distance" is wire length, in less than 10 inches.

That said, you could get those caps from dead electronics. 0.1uf is common, and you could use the same size on the input cap as well.

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  • \$\begingroup\$ Thanks for your quick reply. I should probably tell you what I am doing. I am adding an external power supply to a USB hub I bought. Following this Instructable: instructables.com/id/… but I can only get 9v power supplies using parts at my house and I have one of the voltage regulators laying around. Since things like that can be fussy, I guess I need a cap, right? \$\endgroup\$ – Anonymous Penguin Feb 18 '13 at 20:03
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    \$\begingroup\$ @AnnonomusPerson I would, especially for a usb hub. Find a dead vcr or similar, and you should find the right capacitors. Or even Radioshack or something. \$\endgroup\$ – Passerby Feb 18 '13 at 20:09
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    \$\begingroup\$ You can use 0.1 uf (MicroFarad) on both sides (recommended). And 'long way' means that the cable from your power adaptor is more than a few 5~10 inches long. \$\endgroup\$ – Passerby Feb 18 '13 at 21:30
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    \$\begingroup\$ The 0.33 uf would be better, but it's really just a suggested value for typical circuits. You could use three 0.1uf in parallel to make 0.3uf even. But 0.1uf on both sides works just fine for most uses. \$\endgroup\$ – Passerby Feb 18 '13 at 21:58
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    \$\begingroup\$ I'm not certain which would be best. 0.15 is close enough to 0.1 that it doesn't make a difference. You are just looking for something in that range, think 0.05 to 0.5 uf. 100 nf = 0.1 uf. They should have a five dollar multipack in store, that might have caps in that range. Should, but might not. \$\endgroup\$ – Passerby Feb 21 '13 at 22:04
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Caps are not required but you should not ignore them! From the datasheet the caps are not required but improve transient response:

enter image description here

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Input and output caps are needed for fast and stable operation. If you need a reliable voltage regulator - add caps.

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  • \$\begingroup\$ Thanks for your quick reply too. I just posted my comment on "Passerby"'s answer because it was on the top when I posted the comment. \$\endgroup\$ – Anonymous Penguin Feb 18 '13 at 20:05
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You must use cap's with regulators, they make a very bad ripple after they regulate it, otherwise any sensitive electronics could be effected by the ripple, it will also reduce electrical noise.

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