What is a voltage regulator?

[NewToElectronics]

Thanks!
Mike

 

[ante1]

Hi Mike,

There are many kinds of voltage regulators, can you be more specific?
I assume you understand the general term (voltage regulator)?

 

[NewToElectronics]

Yes, the more general term. Say you have an input voltage that is higher than what you need. E.g. 9V. What if you wanted to reduce that voltage to 3.7V without any power losses (to maximize power efficiency). I understand that in order to do this I could make a dc to dc converter that basically switches a 9V source on 3.7V/9V = 41% of the time and 59% off to produce a sinusoidal a/c source that can be fed through a 1:1 transformer and then be "rectified" into a 3.7V.
Is this what a voltage regulator does?

 

[audioguru2]

Most voltage regulators are a "series linear" design and they waste the extra voltage as heat. The 78xx series and the LM317 are series linear regulators. They need an input voltage at least 2.5V higher than their regulated output voltage for their internal circuit to work properly.

Switching regulators are much more efficient because they pulse and store power in an inductor or a capacitor with a certain on-off ratio to determine their output voltage.

You don't want to use a 9V battery through a regulator to power a cell phone. It doesn't have enough power and if it works, it wouldn't last long.

 

[ante1]

If you’re going to power a cell phone which normally has a 3.7V pack there is some headroom. The phone probably switch of or give low battery warning around 3.2V and a topped of 3.7V pack can carry 4.65V so, between 3.2 and 4.65V will work. You might run it of 3 alkalines.

 

[indulis]

I don't see NewToElectronics mentioning/asking anywhere about powering a cell phone, but anyway...

Say you have an input voltage that is higher than what you need. E.g. 9V. What if you wanted to reduce that voltage to 3.7V without any power losses (to maximize power efficiency). I understand that in order to do this I could make a dc to dc converter that basically switches a 9V source on 3.7V/9V = 41% of the time and 59% off to produce a sinusoidal a/c source that can be fed through a 1:1 transformer and then be "rectified" into a 3.7V.

First, a DC-DC converter works by "chopping" the input DC voltage into a square wave, it's not a "sinusoidal a/c source".

There are a few things to consider when doing "this" with a DC-DC converter. The most basic is... does the ouput voltage need to be isolated or not. If not, you don't need a transformer, it can be done with a "buck converter", whose major components are a power switch, feeding a LC filter with a flywheel diode, to keep the current flowing during the power switch off time. You are correct in how the duty cycle is calculated in a "ideal" circuit, but in the real world you have to figure out your losses as those will make your duty cycle a bit larger. That's it... it comes out DC you don't need any additional circuitry.

 

[ante1]

I don't see NewToElectronics mentioning/asking anywhere about powering a cell phone, but anyway...

Summing the inputs from this and another tread took me to that conclusion my dear Watson!

 

[NewToElectronics]

Thanks for all you guy's inputs. What a great forum board!

I guess I have a some options:
1. Possibly using 3 "AA" batteries (I need to check the topped off voltage of my rechargeable battery).
2. Using a "series linear" voltage regulator to step a 9V source to a 3.7V source.
3. Using a switching regulator for a more efficient way of stepping down/up a voltage to 3.7V source.

From this forum, I gathered this much about Switching Voltage Regulators...
A switching DC regulator works by "pulsing" the input DC signal and then adding that pulsed signal into a steady DC signal by averaging the signal in real-time.
Question:
Wouldn't you need a transformer in the loop if you were going to step up the signal. E.g., my example of 3V to 3.7V?

 

[ante1]

You don’t need any transformer to switch up or down the voltage just an inductor or some caps. In case you like to galvanicaly isolate the input from the output a transformer would help though.
A linear regulator would waste most of the power in a case like this.