When to use which voltage regulator?

[adamthole]

I was just curious if their is a guideline as to when I would be able to use the , for example, 7805L (looks like a transistor) and when I would have to switch to the 7805T (has a heatsink). I am designing a poject right now and didn't know which to use.

If their is a guideline, would it be similar for 7812 also?

Thanks!

 

[Morgen]

It depends on the current requirement of your project. The 7805L is okay if the supply is 100mA or less. The 7805T is good up to 1 to 1.5 amps with a heatsink attached. The rest of the 78xx family is similar. You should use this opportunity to obtain datasheets and get acquainted with them.

 

[leonel]

18V regulator - 3 Amperes

Hi...
Does anybody knows some reference/component of an 18V regulator that supports 3A of current?
Regards

 

[Jay.slovak]

Re: 18V regulator - 3 Amperes

Hi...
Does anybody knows some reference/component of an 18V regulator that supports 3A of current?
Regards

Try LT1085, it's a 3A Adjustable stabilizator.

 

[k7elp60]

Another adjustable regulator that will do the job is a LM338, either the T or the K version will work. Depending on the load current and the input/output differential voltage and heatsink my be required.

 

[Jay.slovak]

Another adjustable regulator that will do the job is a LM338, either the T or the K version will work. Depending on the load current and the input/output differential voltage and heatsink my be required.

LM338K (or T) is also good, I used it in my supply without problems.

 

[Oznog]

It depends on the current requirement of your project. The 7805L is okay if the supply is 100mA or less. The 7805T is good up to 1 to 1.5 amps with a heatsink attached. The rest of the 78xx family is similar. You should use this opportunity to obtain datasheets and get acquainted with them.

Not just current, but the voltage gap is equally important. For example pulling even 100ma continuously with a 30v input voltage means a 5v reg will need to dissipate 2.5 watts, which would require a TO-220 with a heatsink.

 

[Morgen]

Agreed, though a 30V input shouldn't be spec'd for a 5VDC supply design unless it is a necessity due to the other circuitry. I would also imagine a TO-220 could dissipate 2.5W without any additional heatsinking.

 

[leonel]

24V AC

If I have an input 24AC 3Amp and if I need an output of 18V and a maximum output corrent of 250mA, what regulator and bridge should I use? I have a little difficulties choosing components...
Regards.

 

[Nigel Goodwin]

Re: 24V AC

If I have an input 24AC 3Amp and if I need an output of 18V and a maximum output corrent of 250mA, what regulator and bridge should I use? I have a little difficulties choosing components...
Regards.

As the load is only going to draw 250mA, you don't need a bridge rectifier able to handle the 3A capability of the transformer - a 1A bridge would be fine.

Likewise, a 1A regulator would be all that's required, so a 7818 (do they do 18V versions?) should be fine. I would also suggest you check the maximum allowable input voltage, as the output from the bridge will be about 36V DC. This means the regulator will be dropping 18V at 250mA, and dissipating 4.5W - so I would suggest you mount it on a heatsink, to help keep it cool. You could also put a wirewound resistor between the bridge and regulator, this would transfer some of the heat loss from the regulator to the resistor - you can calculate a suitable value with ohms law - but basically every 4 ohms will drop one volt at 250mA.

 

[leonel]

I was thinking using L7818 - this IC has REGULATOR +18V; Voltage regulator typeositive Fixed; Voltage, output:18V; Current, output max:1.5A; Voltage, input max:35V; Temperature, operating (a) min:0°C; Temperature, operating (a) max:150° .
I know that the maximum input is 35V, and we probably have 36V, but I think it´s ok...

 

[Nigel Goodwin]

I was thinking using L7818 - this IC has REGULATOR +18V; Voltage regulator typeositive Fixed; Voltage, output:18V; Current, output max:1.5A; Voltage, input max:35V; Temperature, operating (a) min:0°C; Temperature, operating (a) max:150° .
I know that the maximum input is 35V, and we probably have 36V, but I think it´s ok...

I suspect it probably would be, but adding a wirewound resistor in the feed to the 7818 will drop it anywhere (but only under load!), and also keep it cooler.

I presume you already know?, but you MUST fit two small capacitors from input and output to 0V, as close to the regulator pins as possible. They are to stop it from oscillating, and shouldn't be left out!.

 

[leonel]

Sorry but I'm Portuguese and I don't understand the translation of "wirewound"...
As it concerns to capacitors, I already have.
Regards

 

[Nigel Goodwin]

Sorry but I'm Portuguese and I don't understand the translation of "wirewound"...

If you had your location entered in your profile, we would have known that! - as you don't, we didn't know.

'Wirewound' is a resistor made from resistance wire wrapped around a former, and usually coated in ceramic - it gives a high wattage resistor, far more so than small carbon or metal film resistors.

 

[leonel]

Thanks

Ok... Thanks!

 

[Phasor]

Sorry but I'm Portuguese and I don't understand the translation of "wirewound"...
As it concerns to capacitors, I already have.
Regards

A picture says 1000 words... These are wirewound resistors.

 

[leonel]

Image

Your right!
Thanks

 

[shamikrudra]

I was just curious if their is a guideline as to when I would be able to use the , for example, 7805L (looks like a transistor) and when I would have to switch to the 7805T (has a heatsink). I am designing a poject right now and didn't know which to use.

If their is a guideline, would it be similar for 7812 also?

Thanks!

L stand for 100mA version like this there are many like 500mA and 1A version first read data sheet from any regulater manufacturer like www.onsemi.com