Voltage Regulators in-depth

[BabaYaga]

Hi Guys,
When i studied academically about the voltage regulators, they were devices used to reduce ripple in the output DC voltage with Zener diode forming the reference and operating in reverse bias.i don't know what are the disadvantages of such a regulator but i do know that Band gap is used as voltage reference now-a-days, so here are some queries to address:
1 - How does a Band Gap function as a Voltage Reference
2 - There are several kinds of PMICs like Buck, Boost, Buck-Boost
a - what are they in terms of functioning?
b - when to use them(applications or How to select appropriate one for a given application)?
3 - Linear Regulators vs Switching Regulators

you can take any device as an example like LT1086, PTN04050C etc.,

So, lets a have an interesting discussion and please kindly provide any references to your suggestions or replies since it really helps in the precise understanding of the topic.

Thank You

 

[udhay_cit]

I can answer some of your questions... In practical i am using both linear & switching regulators for automotive applications. I am using Micrel MIC29302 & A5975. Even though both devices are capable to deliver 3A current, micrel get hot for little more then 500mA. But the A5975 is operating cool @ 3A constant current. only the inductor get warm little.
My opinion is linear regulator will give very good DC output without noise, but will get hot for high current & need heat sink(Suitable for low current low noise applications).
Switching regulators are high efficiency, rugged usage, cooler operation, but noisy, required more peripheral components, need more filtering ect... see the attachment of my application....

 

[BradtheRad]

2 - There are several kinds of PMICs like Buck, Boost, Buck-Boost
a - what are they in terms of functioning?
b - when to use them(applications or How to select appropriate one for a given application)?

All use a switched coil to change a supply voltage.

The buck converter reduces voltage.

The boost converter increases voltage.

The buck-boost is versatile. It provides an opposite polarity from the supply voltage. It can be a couple of different levels, depending on where you hook up your leads to.

 

[albert22]

The key point of switching regulators vs linear regulators is efficiency. For example in a 12v to 5 v !A regulator a linear regulator has to dissipate 7 watts which are loosed as heat. Your input is 12w and your output is 5W so the efficiency is around 40%. The same application with a step down or a buck converter can easily have an efficiency of 95% so the looses here are less than 1 w. You save 6w in your energy bill.
Also as switching regulators operate at frequencies much higher than the line voltage ( 60Hz ) the magnetic components are smaller. And use less iron and less copper. Imagine placing a 400W 110v to 12VAC transformer inside a PC power supply. The higher frequency requires smaller values of capacitance for filtering.
So switching power supplies can pack more power per volume.
The disadvantages include complexity, EMI, noise and reduced dynamic regulation. Also the components are subject to more stress.

 

[BabaYaga]

@BradtheRad,
Thank you for the reply, can you please describe how does the switched coil achieve its purpose?
@albert22,
Thank you for the reply, Precise Explanation!, Can you please tell me how does a switching regulator look like internally or its internal functions?

 

[BradtheRad]

@BradtheRad,
Thank you for the reply, can you please describe how does the switched coil achieve its purpose?
@albert22,
Thank you for the reply, Precise Explanation!, Can you please tell me how does a switching regulator look like internally or its internal functions?

Verbal summary of the boost converter:

1. Start sending current through coil.
2. Current builds at speed determined by time constant L/R. Flux field builds.
3. Stop current through coil.
4. Flux field starts to collapse at speed determined by a new time constant L/R (load resistance now being added to total R).
5. Coil generates current.
6. Current must go somewhere. Capacitor and load receive this current.
7. Coil generates however great a voltage is necessary in order to overcome existing charge on capacitor.
8. Voltage builds on capacitor and load.
9. Repeat cycle.

To aid in conceptualizing the action, below is a link to a user-interactive animated simulation. Clicking it will open the falstad.com website, load my custom boost converter schematic, and run it on your computer. (Click Allow to load the Java applet.)

https://tinyurl.com/9hk2teq

Click the switch at left to start the process.

Current is depicted moving through wires at a speed in proportion to amp level.

Click the other switch to apply clock driven pulses to the converter.

Values can be changed at will. Right-click a component to bring up an edit window.

(The buck converter will be explained in a later post.)

 

[BradtheRad]

Buck converter:

Verbal summary, about the same as for boost converter. (See preceding post.)

The supply voltage is not added to what goes through the coil in this configuration.

Link to a user-interactive animated simulation of a buck converter.

https://tinyurl.com/8g8e6q7

You can turn power on and off through the coil manually, or you can watch clock pulses drive the action.

 

[BradtheRad]

Buck-boost converter:

Verbal summary, about the same as for boost converter. The buck-boost inverts the polarity of the supply voltage.

The amplitude can be less than, or greater than, the supply voltage, based on length of the duty cycle.

Two different voltage differentials are simultaneously available, depending on which points you tap for output.

Link to a user-interactive animated simulation of a buck-boost converter.

https://tinyurl.com/9q2snsy

You can turn power on and off through the coil manually, or you can watch clock pulses drive the action.

 

[BabaYaga]

Hi Guys,
Thank you for all the replies, especially @BradtheRad, i'm extremely thankful to you as you took this discussion to a whole new another level.
But my basic doubt and question still remains answered which is about the band gap, i have an inkling about this topic that Band gap has something related to atomic physics,
or based on some molecular or orbital theory, and i would like to definitely know how does band gap function as a voltage reference and how is it physically realized on a chip.

 

[albert22]

The term band gap refers to the solid state theory that describes the internal workings of the semiconductor devices. Voltage references are usually build around a diode (a PN junction). Without going into the physics of a PN junction you can look the characteristic I/V curve (Current/Voltage). With a forward bias a diode has a rather constant voltage drop across its terminals, about 0.7v (for Si). When reverse biased, the diode will not conduct until sufficient voltage is applied. Then the voltage drop on its terminals will remain constant regardless of the current that passes thru it.
https://en.wikipedia.org/w/index.php?title=File:Diode-IV-Curve.svg&page=1
The effects that gives place to this behavior are the zener breakdown or avalanche breakdown.
Diodes designed to take advantage of either effect are called zener diodes.
A voltage reference could be build with just a zener. But temperature compensation and correct biasing improves its performance to obtain a constant voltage with a few ppm of deviation. Integrated voltage references do that and also include an op. amp. to buffer the output.
A simple temp compensation for a zener is to place a forward bias diode in series. But that depends if it is using the zener effect or avalanche effect.
This is a very short explanation. I hope that you can get something clear of it.

 

[BabaYaga]

Thanks @albert22,
I know that in regulators traditionally zener diodes were used as voltage reference in reverse biased breakdown region, but now a days all the regulators have band gap as the voltage reference part replacing the zener diode, i was curious about the band gap thing, especially how a topic(Band Gap) of atomic physics is physically realized on a semiconductor chip.

Thanks for the replies.

 

[marce]

This may be of use:
ww1.microchip.com/downloads/en/AppNotes/01114A.pdf
and this can be somthing to worry about with supply design:
http://www.freeclassnotesonline.com/Miller-Capacitance-Effects.php

 

[HTA]

Hybrid DC/DC Converter:
In mixed analog and digital subsystems there is a combination of Buck-Boost conversion with linear regulation to achieve a split between low noise analog supply and digital supply. Specifically for multiple supply voltages in small subsystem this hybrid architecture is useful. One example of this new architecture as a single chip solution is the iC-DC: https://www.ichaus.biz/product/iC-DC . Similar application is here: **broken link removed** .

Enjoy your design work!

 

[doors666]

can the 78 series of voltage regulators provide higher current than rated for switched applications depending upon the duty cycle?