what is the point of 7805s?

Why do they still exist? If you can't go from 12v to 5v without burning a hole in the sun, I don't see the point? I mean, come on, what's up with THAT?

Is there any advantage between a 7805 over a switching regulator? they both seem to cost about the same.....

Noise. Linear regulators create almost no noise. In a purely digital application I suppose it probably doesn't matter as long as you bypass everything well. If you are trying to do some precision conversion, it matters a lot.

A 7805 is about the same cost as what switching regulator? Maybe something like the MC33063A, about the cheapest one you can get. They're great. But they don't work without a bunch of external components including a sense resistor, a big capacitor, a decently large inductor, and a switching diode. Not nearly the same price or board space once you factor all that in.

I use these (for low current draw parts). Good luck beating the price.

http://www.ebay.com/itm/100Pcs-AMS1117-3-3-LM1117-3-3V-1A-SOT-223-Voltage-Regulator-Module-Replace-Parts-/201387715646
http://www.ebay.com/itm/100PCS-AMS1117-LM1117-1117-5V-1A-Voltage-Regulator-/250887897406

Switch mode supplies are only suitable for digital or power circuits, not demanding analog electronics, due
to the massive amount of noise on the output (0.2V peak to peak is common, which is
completely useless when measuring or amplifiying microvolt signals). A good linear regulator
into big smoothing capacitor can put you near the thermal limit for noise (nano volts per square-root Hz).

The difference is many orders of magnitude. The hybrid approach is to drop most of the voltage
with switch mode, then filter and linearly regulate down to get a clean(er) analog rail.

[ Of course no-one actually uses actual 7805's in new designs because there are so many newer
better linear regulator chips available with lower drop out, less quiescent current drawn, higher
bandwidth etc etc ]

Well, everyone, +1s all around. So, noise is the problem...

Is this only a problem of your doing something with audio or inside of a meter (a dmm)?

What kinds of things (real world examples) would it affect?

Qdeathstar:
What kinds of things (real world examples) would it affect?

Audio or radio circuits.

Any precision analog circuitry, typical sensors, thermocouple, strain guage/load cell, photometry, audio amp,
ultrasound sensor, rf signal generation for transmitters, lab measuring equipment, signal generator, altimeter,
signal/spectrum analysers, seismometers, RFID sensor, millions of things.

Hmm, so i use a switching regulator on one of my circuits to drop from 12v (for LED strips) to 5v (for an RF rx and teensy 3.1) On an RX, noise isn't a problem?

Also, lets say that the TX is running at 12v, and you run a switching regulator off the 12v rail to get 5 volts for a microcontroller... Will the switching regulator put noise on the 12v rail, or just the 5 volt output?

MarkT:
[ Of course no-one actually uses actual 7805's in new designs because there are so many newer
better linear regulator chips available with lower drop out, less quiescent current drawn, higher
bandwidth etc etc ]

You're talking about commercial designs and not hobby stuff, right? Right?
I use them since they're easy to use, cheap and always available in my local poorly stocked electronics shop.

Qdeathstar:
On an RX, noise isn't a problem?

Noise certainly is a problem for receivers as it limits the sensitivity. However the noise produced by a switching regulator is different to thermal noise in that it has a spectrum consisting of a number of discrete frequencies. You may be lucky in that the signal you wish to receive falls between those frequencies. On the other hand . . .

Russell.

Why do they still exist?

One reason they "exist" is because when they were introduced (maybe 30 or 40 years ago?), there were no "simple" switching regulator chips. A switching regulator or power supply was difficult to design & build, requiring maybe 50 or 100 components, making it expensive and almost impossible for a hobbyist to build. It's still difficult for a hobbyist to build a switching supply (running from 120/240VAC), partly because of special transformer required.

I've probably used about 100 78xx & 79xx regulators in my lifetime and so far I've never made a switching regulator. It's just easier and cheaper to "throw-in" a simple linear regulator. I have purchased switching supplies, and with the modern switching regulator chips it is getting fairly simple to build one, so I'll probably use one at some future time.

Switch mode supplies are only suitable for digital or power circuits, not demanding analog electronics...

EVERY "high power" car stereo has a switching supply. With a 12V power supply, a single-ended output, and an 8 Ohm speaker you can get about 2 Watts. If you go with a bridge output an a 4 Ohm speaker you can get about 9 Watts. Any more than that and you need more voltage.

The switching frequency is usually above the audible frequency range and the power supply output is filtered. Class D amplifiers have switching audio outputs (a kind of PWM) which is also above the audible range.

A lot of modern home amplifiers & receivers also have switching power supplies and Class D outputs. The electronics are more complex, but because of lower power/heat requirements it can be cheaper to build it that way.

MarkT:
Any precision analog circuitry ............... RFID sensor

My engineers believed this as well. I got one of them to try our design with a switch mode regulator in place of the normal linear ones. There was not a jot of difference in the range of reading between the two.

Why are we bothered about dissipating a little heat? The RF receiver and teensy are probably drawing less than 50mA. Even if left powered up all year, the dissipation from the 7805 would be less than 3 kWhr. Only a portion of that would be wasted; during the winter it would help heat the house!

If you were a manufacturer you would choose to use a linear regulator like the 7805 for this sort of application. There’s no need for a bulky inductor or large decoupling capacitors. You would not be bothered at all about the tiny increase in annual electricity cost to the user. Of course if the item is to be battery powered, a switching regulator is more attractive.

Last week a used a L78105 linear regulator to get 5V from 12V. Being a TO-92 package, like a small-signal transistor, it made more sense than constructing a switching regulator or buying in a module.

To answer the OP's question - these device exist because there is still a demand for them. And there is still a demand for them because of the COST. Forget distributors catalogues or eBay these thing cost pennies in bulk. Switching modules cost pounds.

They are littered about complex designs to insure clean decoupled power distribution.

DVDdoug:
A switching regulator or power supply was difficult to design & build, requiring maybe 50 or 100 components, making it expensive and almost impossible for a hobbyist to build.

It's not that complicated. When I was working for Philips in the early 1970s I designed a switching regulator for a miniature battery operated TV set using just three transistors and a small handful of passive components. The efficiency wasn't very high by today's standards but it was much better than a linear regulator and gave a better battery life.

Russell