Lahat ng questions related sa Switched-Mode Power Supply (SMPS)

[glutnix_neo]

Ok mga bro, i know you're going to have a lot of questions and marami din sa atin ang bago pa lang sa field ng Power Electronics so I decided to have a structured lecture sa thread para in case na may mga bagong pumapasok at may tanong na naitanong na before eh madali nating mairerefer sa past lectures natin.

I'll try my best na magprovide ng isang discussion for a topic every day, I will try to make it as simple as possible. You may ask question or we can discuss the topic on the thread para mas masaya,hehe,

Below are my initial topics na pwede kong idiscuss,

1. Introduction
   What is Power Electronics
   Some history of SMPS
   Applications


2. Why there's a need for power supply? (Can't we just use a voltage divider?)
   effects of changing input voltage
   effects of changing load resistance

3. types of power supply and operation
   zener
   linear
   SMPS

4. Category of SMPS topologies
   non-isolated
   isolated


5. Buck Converter
   operation

   issues in buck converter design
      high side switching

6. Boost Converter

7. Forward

8. Flyback
   
9. Self Oscillating Flyback

10. Control of SMPS

Please let me know if you have comments or suggestions. Or anything that you'd like to say

[glutnix_neo]

Lesson 1.0    Introduction to Power Electronics   20080213

Some Introduction...
Hi guys, gusto ko sana maging spontaneous sa aking mga lectures kaya I 'll just use taglish and I'll do my best to
present the topic as simple as I can that even a store keeper could understand (hopefully, hehe).

I supposed you're now thinking why I am explaining Power Electronics and what is its relation to Switched-Mode
Power Supplies(SMPS)? Well to answer that briefly, I can say that SMPS are the foundations of modern Power Electronics.
Because of the industry's demand for efficient conversion of power from source nagkaroon ng application ang SMPS
sa field ng Power Electronics and, oftentimes, the word Power Electronics could refer to SMPS through it is not
limited to it.

What is Power electronics?...
Wikipedia has a nice definition of Power Electronics, it states that...
"Power electronics is the technology associated with the efficient conversion, control and conditioning of electric
power by static means from its available input form into the desired electrical output form"

Take note of the word "efficient conversion", this is probably the main reason why Power Electronics often refer to
SMPS. SMPS are the most efficient power supply for high power applications, its efficientcy ranges from 65% - 93%
depending on the output power( the higher the output power, the greater the efficiency ) as compared to their
Linear Power supply counterpart which are only about 30%-60% on their efficiency, never technologies claimed they
can achieved higher than 80%. But, as I have said SMPS is far more superior in terms of efficiency than Linear Power Supply and
the theory of how they operate explains why.

Control and conditioning are also equally important elements of Power Electronics.

History of SMPS...
The SMPS technology is not so new technology. The theory of its operation has been around since the early 1950's
however, due to the complexity of its operation which boils down to high cost in production limited its
application. Early devices (vacuum tubes pa noon at kaiimbento pa lang ng transistors) are not sufficient to meet
the switching speed requirements of early SMPS.

As the technology of transistors matures, the SMPS technology also matured along with it. SMPS can be found on few
electronic appliances as early as 1970's  and it was extensively used on early PC during the early 80's because of
its size.

On the 90's, the age where mobile devices started to appear, the smaller the better became the trend on technology
and so SMPS became widely used for chargers/adapters for every mobile devices during the late 90's because they can comply with the size and weight demand of mobile markets.

At present, people became aware(conscious) of environmental problems especially on global warming and energy
problems that laws are passed (see "energy star") requiring a highly efficient power conversion that made SMPS the
only choice for most consumer products. The demand for industrial applications became another driving force that
encouraged the development of SMPS technologies.

Conclusion...
The two major qualities of SMPS are its efficiency and size. Application of it ranges from a small battery chargers, UPS, ATX Power Supply, Electronic Ballast, Electronic Appliances, Motor drives (washing machine and for industrial application) and many others that are too many to mention.?


Karagdagang Babasahin...
http://en.wikipedia.org/wiki/Power_electronics
http://en.wikipedia.org/wiki/Switched-mode_power_supply
www.g3src.org.uk/downloads/G4FDN-psu.pdf

[subzer0]

sir glutnix,gagawa po ako ng proto,buck converter,gagamit ako ng UC3842 sa PWM.
Tapos po 5V output,5A,input cguro 12 to 24,ok lang po as a starter?

[glutnix_neo]

OK lang icefire, ang medyo complikado lang sa UC3842 eh current mode controller xa, try to read the application note of 3842 regarding current mode control.

Kung for experiment lang muna, pwede mo rin itry open loop using LM555 (check mo net sa configuration ng LM555 na adjustable duty).

Another difficulty na pwede mo maencounter is yung problem ng MOSFET on high side switching, common sa buck at buck-boost yun.

[motion55]

Another difficulty na pwede mo maencounter is yung problem ng MOSFET on high side switching, common sa buck at buck-boost yun.

I am interested in this topic specially about MOSFET driver circuits.

[glutnix_neo]

Brief Explaination lang ng problem sa high side switching, common to hindi lang sa power electronics kundi sa mga VLSI na rin.

 High-side switching means the MOSFET is operated on a high side or there's a high impedance between the source and the ground(opposite: low side, source is connected to ground)

Usually the problem appears when the gate drive voltage is equal to the drain voltage with respect to ground (or (Vg - Vd)  < Vth).
Remember that there's a requied Vgs voltage(Vth) to fully turn on the MOSFET.

Let's have an example, ang gate drive voltage is 12V, supply ng buck is 12V, Vth required is 5V,
Before mag-turn on ang FET sa buck usually ang diode ay nakaforward bias, so may drop yun na -0.7 wrt ground.
Magsusupply ng 12V ang gate drive and syempre magtuturn-on ang FET because Vgs = 12-0.7 > Vth (5V),

but what happens if nagturn-on na ang FET? Drain would be shorted to Source and Vd would be equal to Vs wrt Ground.
At this point hindi na nasatisfy yung condition para magturn-on ang FET kasi Vgs would be equal to 0 that is < Vth.

Sa high side switching hindi marereach ang turn-on condition dahil magstop na magincrease bias the moment na Vgs becomes < Vth.

May mga technique para makapagswitch sa high side, (search nyo sa net ibat-ibang ways para dito)

[kamote]

Eto po share ko nice article kung paano pagpili ng inductor, capacitor, diode at fet na gagamitin sa buck converter

http://powerelectronics.com/mag/606PET25.pdf

informative to.  salamat.

hehehe.  allergic ako sa analog design, pang digital lang talaga utak ko.  kung may tanong ako puede bang abusihin ka nang tanong in the future? 

[glutnix_neo]

hehehe.  allergic ako sa analog design, pang digital lang talaga utak ko.  kung may tanong ako puede bang abusihin ka nang tanong in the future? 

Well, consider mo na lang ang SMPS as digital power supply kasi switch lang  naman ang operation ng transistor,hehehe

 ???OK lang magtanong kayo, sasabihin ko naman kung di ko alam ang sagot eh, ;Dhehe

[motion55]

@glutnix_neo

I design motor drivers (stepper motor drivers in particular) as part of my job. One of my projects is a high current rated type that uses an H-bridge configuration. That is, a pair of stacked N-channel MOSFETs. As you can see it needs a high side driver as well as a low side one. I think your expertise can be helpful to me.



How come there so many different high side drivers available from like IR or Telcom (now part of Microchip)? Do they have to be matched to the MOSFET it will be used for. What are the selection criteria? What are the typical failure modes of MOSFETs in your designs and their causes?

[0b00000111]

@glutnix_neo

any recommended ebooks/reading materials for SMPS?

[0b00000111]

may power electronics ebook nga pala ako by Muhammad Rashid. anyone interested? upload ko bukas kung may interested...

[paranz]

i also have "SwitchMode Power Supply Handbook" by Keith H. Billings

oki ba book na ito?

[glutnix_neo]

@glutnix_neo



How come there so many different high side drivers available from like IR or Telcom (now part of Microchip)? Do they have to be matched to the MOSFET it will be used for. What are the selection criteria? What are the typical failure modes of MOSFETs in your designs and their causes?

Nice to know madami interested sa power electronics dito, to be honest I not much experienced on high side switching circuit, yun kasi yung iniiwasan namin sa design kasi malaking added cost kung magdadagdag ng pyesa, but there's one practical solution jan.

You can use a choke and form it like a transformer where on the primary andun yung gate drive na nakaground and on secondary nakaconnect sa Gate and Source ng FET, Yun nga lang, I dont think its applicable sa stepper kasi may time na hindi continous ang pulse, magsasaturate ang core, sa SMPS OK tong technique na to.

Would you like to consider using a stepper motor driver IC's? sa tingin ko mas makakatipid ka dun kasi wala ng FET yun, diretso na, L293 yata yung pwede.

For the criteria of selecting a driver, I think slew rate/speed is a major factor at yung driving current na rin. Although voltage driven xa may mga FET na mataas yung g-s capacitance kaya iba-iba din driver, Low side switching I dont think magkakaproblema ka dun, pwede ka gumamit ng simple transistor buffer(for high speed use a totem pole).

[glutnix_neo]

may power electronics ebook nga pala ako by Muhammad Rashid. anyone interested? upload ko bukas kung may interested...

Books? OK yung book ni sir Pranz, bilings

Kung theory yung kay Ned Mohan nakabili ako sa goodwill sa glorieta dati ok din yun at saka yung kay abraham pressman

Kung practical guide naman sa design eh yung "Power Supply Cookbook" ni Marty Brown, kaso nawawala yung book ko na to.

[glutnix_neo]

Lesson 2.0    Why is There a Need for Power Supply   20080213

Introduction...

I am often asked by a question and even I asked it when I was a student, "Why do we need power supply?"...
That question is often followed by another question, "Can't we just use a voltage divider?"

Those are very good questions for beginners. Well, explaining why we can't use a voltage divider to have a stable

voltage source also explains why we need power supplies (because there's no other alternatives, hehehe).

In theory, if the voltage supplied by the input or the current drawn by the load does not vary with time,

definitely, a voltage divider computed for that specific load and input voltage is sufficient to keep the output

voltage fix on that level. But, in real applications the input voltage from battery and worst from AC line varies

with time. Switching loads such as micrcontrollers and digital circuits draws different amount of current from time

to time. Thus, the need for power supply arise.

What is a voltage divider anyway?...

It is a circuit commonly composed of two resistors in series that produces an output that is a fraction of its

input.


the relationship of input and output becomes

Vout = vin * R2 / (R1 + R2)            eq. 2.1

I don't need to explain the derivation in detail but in case you're interested, you may refer to Mr. Wiki on the

link below

On the formula, R2 could represent a load (the effective resistance of the component supplied by the voltage

divider) or if you need to add load to it just compute the effective resistance of it and place them in parallel to

R2.


Very Simple Example...
Suppose we have a circuit that draws 5A and needs to be powered by 5V but our Vin is 10V, how are we going to have

this using a voltage divider?

Given are:
Vout = 5V
Vin = 10V
Iout = 5A

The effective resistance of the load (R2) can be calculated using Ohm's law (I = V/R) or R = V/I

R2 = 5V / 5A = 1 Ohm

Required is :
the resistance of R1 to form a voltage divider

Rearranging equation 2.1 we get

R1 = R2 * (Vin - Vout)  / Vout

R1 = 1 Ohm * ( 10V - 5V ) / 5V

R1 = 1 Ohm

Therefore 1 Ohm is the required series resistance to have a 5V output.

Effects if changing voltage on the voltage divider...

Supposed we are using the same circuit as mentioned on our "very simple example" and the voltage increased from 10V

to 20V, will our output remain the same?

Given:
Vin = 20V
R1 = 1 Ohm
R2 = 1 Ohm

Required:
V2 = ?

Again, using equation 2.1 we get

Vout = 20V * 1 Ohm / ( 1 Ohm + 1 Ohm )

Vout = 10V <<< Lumake!!!!

From the example we can conclude that in a voltage divider

1. As we increase the input voltage, the output voltage also increases
2. As we decrease the input voltage, the output voltage also decreases

Effects of loading a voltage divider...

Supposed we are using the same circuit as mentioned on our "very simple example" and two paralled 1 Ohm resistor

are used in place of R2 (same as increasing the load), will our output remain the same?

Given:
Vout = 10V
R1 = 1 Ohm
R2 = 1 Ohm // 1 Ohm = 0.5 Ohms

Required:
V2 = ?

Again, using equation 2.1 we get

Vout = 10V * 0.5 Ohms / (0.5 ohms + 1 Ohm)

Vout = 3.33333333333333333333333333333333333333333333V        <<< Lumiit!!!

From the example we can conclude that in a voltage divider

1. As we increase the input voltage, the output voltage decreases
2. As we decrease the input voltage, the output voltage increases

Conclusion...

Because of the limitations of the voltage divider on maintaining the output at a constant level on varying loads

and input voltages, the need for a better regulator became a necessity.

Karagdagang Babasahin...

http://en.wikipedia.org/wiki/Voltage_divider

[glutnix_neo]

sorry dun sa last post ko, ipinoformat ko pa lang eh napasend na, double space tuloy,hehe

[motion55]

Nice to know madami interested sa power electronics dito, to be honest I not much experienced on high side switching circuit, yun kasi yung iniiwasan namin sa design kasi malaking added cost kung magdadagdag ng pyesa, but there's one practical solution jan.

You can use a choke and form it like a transformer where on the primary andun yung gate drive na nakaground and on secondary nakaconnect sa Gate and Source ng FET, Yun nga lang, I dont think its applicable sa stepper kasi may time na hindi continous ang pulse, magsasaturate ang core, sa SMPS OK tong technique na to.

Would you like to consider using a stepper motor driver IC's? sa tingin ko mas makakatipid ka dun kasi wala ng FET yun, diretso na, L293 yata yung pwede.

For the criteria of selecting a driver, I think slew rate/speed is a major factor at yung driving current na rin. Although voltage driven xa may mga FET na mataas yung g-s capacitance kaya iba-iba din driver, Low side switching I dont think magkakaproblema ka dun, pwede ka gumamit ng simple transistor buffer(for high speed use a totem pole).

I need to design a microstep driver that is rated 8A. I have an existing 3A rated design using the ST-Micro L6203 H-bridge. This design is already close to 10-years old. I have made minor updates but the end user is quite content with the original.

One time, I was considering using transformer to level shift the pulse. I use PWM control and duty seldom goes to 100%. That happens when the motor is running and the H-bridge is commutating anyway and so it is possible to use a transformer. I have studied lots of sample drivers from other vendors but they don't use a transformer.

I have been making prototypes of 8A rated drivers through the years but they suffer from reliability problems. Overheating isn't a problem since I use relatively over rated 25A and up MOSFET. The MOSFETs run quite cool. They MOSFET occasionaly fail on power-ON or accidental shorting of the output. I think transients cause the ratings to be exceeded and the MOSFETs suffer from catastrophic failure when this happens. Supply rail voltages range from 24V-75V.

In motor driver designs, we can afford more expensive devices compared to your business where competition is very stiff and cost is a huge factor. I have used various high-side+low-side drivers from Telcom, IR and others.

For SMPS designs, I use L4978, LM2576S or LM2676S devices for buck converters. These are used to supply +5V and other DC voltages for my controller designs. Linear regulators are seldom found in a modern appliance like a DSL modem or router.

[glutnix_neo]

I have been making prototypes of 8A rated drivers through the years but they suffer from reliability problems. Overheating isn't a problem since I use relatively over rated 25A and up MOSFET. The MOSFETs run quite cool. They MOSFET occasionaly fail on power-ON or accidental shorting of the output. I think transients cause the ratings to be exceeded and the MOSFETs suffer from catastrophic failure when this happens. Supply rail voltages range from 24V-75V.

Interesting yan work nyo sir ah,

All I can say po eh, sa shorting definitely the FET will fail unless we include protection circuit na ishashut-down nya mga FETs if over current.

Problems on turn-on, hindi ako maxado familiar sa turn-on sequence ng stepper, all I know eh malaki current na nadodraw nya at start up, using soft start (min duty muna) would lessen the transient, not sure lang kung kaya nya patakbuhin motor nun,hehe,

On bridge circuit, one thing na pwede nating iwatchout is yung nagsasabay na naka-on mga FETs (hindi pa fully turn-off yung FET eh nagon na yung other rail), This problem is can be resolved using dead time sa alternation ng mga driving pulses

Sana nakatulong po sir,?

[motion55]

Interesting yan work nyo sir ah,

All I can say po eh, sa shorting definitely the FET will fail unless we include protection circuit na ishashut-down nya mga FETs if over current.

Problems on turn-on, hindi ako maxado familiar sa turn-on sequence ng stepper, all I know eh malaki current na nadodraw nya at start up, using soft start (min duty muna) would lessen the transient, not sure lang kung kaya nya patakbuhin motor nun,hehe,

On bridge circuit, one thing na pwede nating iwatchout is yung nagsasabay na naka-on mga FETs (hindi pa fully turn-off yung FET eh nagon na yung other rail), This problem is can be resolved using dead time sa alternation ng mga driving pulses

Sana nakatulong po sir,?

May short circuit protection na naka-designed into the circuit. It is similar to the circuit I used in the lower current devices pero it is not enough. Kaya ang nagtatanong anung possibleng mag fail sa MOSFET in case may short sa H-bridge. Karamihan ang nasisira ay yung sa high side. My theory is the short circuit causes the gate-source voltage to exceed the rating.

I use a motor control PIC like the PIC18F4431 with it's PWM control for controlling the current. With it I can also control the soft start.

I am also aware of the shoot-through problem. That is, the two stacked MOSFETs conduct at the same time when switching one ON while switching the other OFF. This is where is becomes confusing. Looking at the catalogue of half-bridge MOSFET driver devices from Telcom, ang daming klase. It gets confusing to pick which one. May built-in dead time control na ang mga motor control PICs. So that adds to the confusion too.

Putting too much dead-time will cause one MOSFET to turn completely OFF before the other one will turn ON. Ordinarily, the MOSFET's intrinsic diode will conduct the current if the MOSFET isn't ON. This is not a good thing because firstly, the diode has a greater resistance than the MOSFET's ON resistance. This will increase the power dissipation. Secondly, once the intrinsic diode conducts, it slows the MOSFET down. At least that is my theory.

[glutnix_neo]

Ok sir seems like aware naman po kayo sa lahat ng pwede mangyari ,
based from my experience sa bridge circuit (although SPMS ang application) the causes of failures are...

ndi ko alam pano magupload pic dito pero labelan na lang natin mga FET as

                  a                     b
                  |----o o o o----|
                  c                    d

1. Rating exceed, V-D or V-G voltage (peak usually when no snubbers used), Id current
2. Thermal runaway dahil hindi totally on FET dahil sa weak/slow drive or may naiiwang charge sa G-S nya, watchout sa D-S voltage nya kung fully on or off ba xa at slew rate na rin. Or thermal runaway dahil mainit talaga
3. Inductive kick kung may charge ang inductor at nag-off ang FET c but FET b is still on, may path ng current sa FET a through its body diode. With this two things can happen pwede magproduce ng malaking peak voltage sa FET c or maexceed current sa dalawang high side FET(Transients lang to at di pangmatagalan)
4. As you mentioned sir, shoot through (vin shorted to ground)
5. Lastly, kung mas ibang FET sa bridge na sira na talaga, pwede madamay iba.

Other than these, isip pa ko.

Sir can i have the link ng websites?tingnan ko na rin po pag may time. Ilang FET po nasisira sa isang failure?