From dkemppai:
" Show me a single SMPS with a 12volt INPUT used for car audio that uses a topology other than push-pull. Please, I'd actually like to see one. Even just one.
At 100 amps input, and a RDS on of .01Ohms, that's 100Watts conduction losses. You would double that with any full bridge topology! That kills efficientcy by around 10% (that's roughly figuring 12volts in, 1000 watts output, at 90% max dutycycle for the power switches with an Rds on of .01 Ohms. )
-Dan "
Apparently we're not communicating, and I believe I'm to blame. My previous responses were quite vague and general, including power supplies as low as 1.5 watts. After re-reading the whole thread, I see that high power is under discussion, so I'll now limit my discussion to such.
As far as car audio power supplies go, the power levels involved lend themselves to push-pull, which is the most highly recommended topology from 200 to 500 watts. The 200 and 500 watt figures are not cast in concrete. Depending on the exact voltage, and current, those may be adjusted. This is why push-pull is the topology of choice for 12 V powered audio supplies. In that power range, my choice has always been push-pull. So far, I'll bet that you and I agree. As far as the reason why 12 V car stereo not using full bridge is concerned, the power requirements are not high enough to justify the added complexity and expense of the full bridge. The following is where we seem to part company.
At 12 volts (actually 13.5 V from alternator ), and 100 amps (1200 to 1350 watts) the push-pull becomes less attractive, and the full bridge becomes more attractive. Consider the following.
The voltage range in auto industry is 9 to 16 volts. For a push-pull converter, each of the two MOSFETs must withstand double the supply, or 32 V max. A MOSFET with a minimum of 40 volts drain to source is required. With a full bridge, only 16 volts max is present, so a 20 volt drain to source MOSFET can be used. Full bridge does require 4 parts vs. 2 for push-pull. The IRF6601 (Intl Rectif) is the premium 20 V part from IR, rated at 3.8 milliohm Rdson. The premium 40 volt part is the IRF1104, rated at 9.1 milliohm Rdson, more than twice. At 100 amps, the conduction loss of each FET in the push-pull circuit is 91 watts. For the full bridge, each FET conduction loss is 38 W. Multiplying by 2 gives 76 W vs. 91 W, still smaller. THe full bridge clearly wins at these power levels.
Another consideration is junction temperature. With push-pull each FET must dissipate 91 W. If the ambient temperature is 70 deg C, and the temp limit of the junction is 150 deg C, the thermal temp coefficient needed is 80 deg C / 91 W or 0.88 deg C per watt. Not impossible, but requires much heat sinking. With full bridge, each device, in an identical package size only need dissipate 38 W. Thermal temp coefficient becomes 80 / 38 or 2.1 deg C per watt, much more managable. Also, since each device runs cooler, the 20 volt parts in the full bridge will exhibit even lower Rdson since Rdson increases with temperature.
Your position that the full bridge will dissipate twice the power due to more FETs present, and exhibit lower efficiency, is based on using identical FETs for both converters. The newest FETs with superb performance are being offered in low voltages down to 12 volts. The advantage to the full bridge lies in the fact that FETs with half the voltage rating can be used, offering lower Rdson. At 200 to 500 watts the tradeoff favors push-pull, due to its reduced parts count and simplicity. At large power levels, above 500 W, the full bridge clearly offers higher efficiency. These are ballpark figures, the exact figures should be determined on a case by case basis.
The purpose of my reply is to simply state that all available choices should be evaluated. Consider all tradeoffs, what the desired objectives are, and compute the pros and cons of each topology. Personally, I really really like push-pull. I like its simplicity, lower parts count, etc., but if I needed 100 amps at 12 volts, I'd feel much better with the full bridge. Nonetheless, a well designed push-pull should work well.
I don't expect everyone to agree with me. I just want to convey to those reading this thread, that there are tradeoffs to consider, and one topology does not provide better performance in all applications. Best regards.
" Show me a single SMPS with a 12volt INPUT used for car audio that uses a topology other than push-pull. Please, I'd actually like to see one. Even just one.
At 100 amps input, and a RDS on of .01Ohms, that's 100Watts conduction losses. You would double that with any full bridge topology! That kills efficientcy by around 10% (that's roughly figuring 12volts in, 1000 watts output, at 90% max dutycycle for the power switches with an Rds on of .01 Ohms. )
-Dan "
Apparently we're not communicating, and I believe I'm to blame. My previous responses were quite vague and general, including power supplies as low as 1.5 watts. After re-reading the whole thread, I see that high power is under discussion, so I'll now limit my discussion to such.
As far as car audio power supplies go, the power levels involved lend themselves to push-pull, which is the most highly recommended topology from 200 to 500 watts. The 200 and 500 watt figures are not cast in concrete. Depending on the exact voltage, and current, those may be adjusted. This is why push-pull is the topology of choice for 12 V powered audio supplies. In that power range, my choice has always been push-pull. So far, I'll bet that you and I agree. As far as the reason why 12 V car stereo not using full bridge is concerned, the power requirements are not high enough to justify the added complexity and expense of the full bridge. The following is where we seem to part company.
At 12 volts (actually 13.5 V from alternator ), and 100 amps (1200 to 1350 watts) the push-pull becomes less attractive, and the full bridge becomes more attractive. Consider the following.
The voltage range in auto industry is 9 to 16 volts. For a push-pull converter, each of the two MOSFETs must withstand double the supply, or 32 V max. A MOSFET with a minimum of 40 volts drain to source is required. With a full bridge, only 16 volts max is present, so a 20 volt drain to source MOSFET can be used. Full bridge does require 4 parts vs. 2 for push-pull. The IRF6601 (Intl Rectif) is the premium 20 V part from IR, rated at 3.8 milliohm Rdson. The premium 40 volt part is the IRF1104, rated at 9.1 milliohm Rdson, more than twice. At 100 amps, the conduction loss of each FET in the push-pull circuit is 91 watts. For the full bridge, each FET conduction loss is 38 W. Multiplying by 2 gives 76 W vs. 91 W, still smaller. THe full bridge clearly wins at these power levels.
Another consideration is junction temperature. With push-pull each FET must dissipate 91 W. If the ambient temperature is 70 deg C, and the temp limit of the junction is 150 deg C, the thermal temp coefficient needed is 80 deg C / 91 W or 0.88 deg C per watt. Not impossible, but requires much heat sinking. With full bridge, each device, in an identical package size only need dissipate 38 W. Thermal temp coefficient becomes 80 / 38 or 2.1 deg C per watt, much more managable. Also, since each device runs cooler, the 20 volt parts in the full bridge will exhibit even lower Rdson since Rdson increases with temperature.
Your position that the full bridge will dissipate twice the power due to more FETs present, and exhibit lower efficiency, is based on using identical FETs for both converters. The newest FETs with superb performance are being offered in low voltages down to 12 volts. The advantage to the full bridge lies in the fact that FETs with half the voltage rating can be used, offering lower Rdson. At 200 to 500 watts the tradeoff favors push-pull, due to its reduced parts count and simplicity. At large power levels, above 500 W, the full bridge clearly offers higher efficiency. These are ballpark figures, the exact figures should be determined on a case by case basis.
The purpose of my reply is to simply state that all available choices should be evaluated. Consider all tradeoffs, what the desired objectives are, and compute the pros and cons of each topology. Personally, I really really like push-pull. I like its simplicity, lower parts count, etc., but if I needed 100 amps at 12 volts, I'd feel much better with the full bridge. Nonetheless, a well designed push-pull should work well.
I don't expect everyone to agree with me. I just want to convey to those reading this thread, that there are tradeoffs to consider, and one topology does not provide better performance in all applications. Best regards.
Claude Abraham said:
Ahhh, I see we're on the same page now! I would agree that at higher power levels the bridge configuration starts to become more attractive. However, I think that there are a few things that will need consideration also.
I have not done the numbers, but think that we should look paralleling the the four fets needed in the bridge, into two pairs used as power switches for the push-pull supply. By using four fets in each design, I'd be willing to bet the efficiency cross over point would shift to higher wattage than previously determined.
Even then, the circuit is still much simpler.
Also, the terminal voltage across the input of the amplifier may easily fall to 9 volts when the power switches are conducting (12 volts is ideal, but never happens! Even with the alternatior at 13.8 volts!). The average voltage may still read 11 volts, when the switches pull it down to 9 for conduction periods. In this case, the output power is made up with more current, and again the push-pull looks more attractive. That 25% loss in voltage will mean 25% increas in current, and increased conduction losses. (I have actually measured this on production car stereo amps with power levels from 1200 to 2500W RMS.)
Also, something that I don't know about is how switching transients affect mosfets in an H-Bridge design when using slightly less than a 50% PWM dutycycle. With push-pull, the transients add to the battery voltage, and therefore you can easily need more than double the input voltage rating of each mosfet.
Can you shed some light on this for the Bridge design? (I've never really thought about it before)
Glad to see we're on the same page now!
-Dan
FerroxCube Cores
fr0st-
The only FerroxCube core I have used is the 3622-sized POT core. 90W @ 20kHz (extrapolate this power figure for higher switching frequency).
The cores I recommend and have used with great success are the powdered-iron and ferrite cores from Amidon Associates. They have a great website and catalogue and quick datasheet for picking your patricular poison.
My favorite ones are the ferrite toroids of the #77-material (u=2000). The FT-114-77 (1.14" o.d.) is good up to 120W @50kHz. The FT-140-77 (1.40" o.d.) is good up to 200W @ 50kHz. Their FT-240-77 (2.40" o.d.) is a BIG honkin' toroid good for about 1.2-1.5kW @ 50kHz.
If you need more power than one FT-140 can pass, and don't have the board space for a '240, then YES, you can stack cores. My 350W DC-DC switycher (11-16V in and +/-35V & +/-45V out) stacks THREE FT-114 cores with great results- I had little board space, and still needed the power.
I just bought a digital camera, and if I ever figure out how to do low-resolution pics (l.t. 100kB), I will post some of my switching power supplies on this thread.
There are many good ideas being exchanged here, so let's keep this thread going. How's this for some food-for-thought? Anyone consider a car amps fot the upcominf 42V standard? (full-bridge -v- half-bridge -v- push-pull).
All the best to all posting here!
'73,
Steve, N8XO
fr0st-
The only FerroxCube core I have used is the 3622-sized POT core. 90W @ 20kHz (extrapolate this power figure for higher switching frequency).
The cores I recommend and have used with great success are the powdered-iron and ferrite cores from Amidon Associates. They have a great website and catalogue and quick datasheet for picking your patricular poison.
My favorite ones are the ferrite toroids of the #77-material (u=2000). The FT-114-77 (1.14" o.d.) is good up to 120W @50kHz. The FT-140-77 (1.40" o.d.) is good up to 200W @ 50kHz. Their FT-240-77 (2.40" o.d.) is a BIG honkin' toroid good for about 1.2-1.5kW @ 50kHz.
If you need more power than one FT-140 can pass, and don't have the board space for a '240, then YES, you can stack cores. My 350W DC-DC switycher (11-16V in and +/-35V & +/-45V out) stacks THREE FT-114 cores with great results- I had little board space, and still needed the power.
I just bought a digital camera, and if I ever figure out how to do low-resolution pics (l.t. 100kB), I will post some of my switching power supplies on this thread.
There are many good ideas being exchanged here, so let's keep this thread going. How's this for some food-for-thought? Anyone consider a car amps fot the upcominf 42V standard? (full-bridge -v- half-bridge -v- push-pull).
All the best to all posting here!
'73,
Steve, N8XO
Re: FerroxCube Cores
Full Bridge would be the only way to go, if you really want to use a DC-DC converter. I think that Claude would agree with this statement also! Any advantages with efficiency that the push-pull may have had will be lost by the three fold increase in voltage and reduction in current.
A bridge type audio amp head unit with no SMPS could push several hundred watts with the 42 volts. I really think the car audio market will change with the new 42 volt standard. We may see very few amps with SMPS included. Only the really grossly huge amps will have them. And they will become really really big, I think!
My 2 cents!
-Dan
N-Channel said:
Full Bridge would be the only way to go, if you really want to use a DC-DC converter. I think that Claude would agree with this statement also!
Any advantages with efficiency that the push-pull may have had will be lost by the three fold increase in voltage and reduction in current. A bridge type audio amp head unit with no SMPS could push several hundred watts with the 42 volts. I really think the car audio market will change with the new 42 volt standard. We may see very few amps with SMPS included. Only the really grossly huge amps will have them. And they will become really really big, I think!
My 2 cents!
-Dan
All Things 42V.......
They're slowin' it down a bit, but those of us in the military (and civilian DoD community) are still going full-speed ahead with it. Military vehicle electrical systems need more power than commercial ones do, and this is a golden opportunity to FINALLY achieve some compatibility between both. Since the Big 2-1/2 have backed away from 42V (for now) this puts the Army in the driver's seat (pardon the pun ) in determining the direction the 42V path will take.
Wow! Imagine: a Head Unit with a REAL 100W/CH (x 4 channels)into 4-ohm load! No more oversized stupid boot-strapping capacitors at the chip-amp to provide only a few milliseconds extended output power. Now, we can really draw some juice with this set-up!
I will be out of touch for the next four days, But i eagerly await any other thoughts on this!!!!!
They're slowin' it down a bit, but those of us in the military (and civilian DoD community) are still going full-speed ahead with it. Military vehicle electrical systems need more power than commercial ones do, and this is a golden opportunity to FINALLY achieve some compatibility between both. Since the Big 2-1/2 have backed away from 42V (for now) this puts the Army in the driver's seat (pardon the pun
) in determining the direction the 42V path will take.Wow! Imagine: a Head Unit with a REAL 100W/CH (x 4 channels)into 4-ohm load! No more oversized stupid boot-strapping capacitors at the chip-amp to provide only a few milliseconds extended output power. Now, we can really draw some juice with this set-up!
I will be out of touch for the next four days, But i eagerly await any other thoughts on this!!!!!
In respect to cores, what features make it a good core (high power handling)?
The ferroxcube core comes in 3 grades.
170nH Al & 125u
7390nH Al & 5500u
11400 nH Al & 8500u
Out of these which is the most suited to the application?
42v car systems are gradually coming into high end cars but most of them have a 12v system aswell. It'll be a long change over time fo sure.
When it does happen it'll be good for us Less current draw and less loss
The ferroxcube core comes in 3 grades.
170nH Al & 125u
7390nH Al & 5500u
11400 nH Al & 8500u
Out of these which is the most suited to the application?
42v car systems are gradually coming into high end cars but most of them have a 12v system aswell. It'll be a long change over time fo sure.
When it does happen it'll be good for us
Less current draw and less loss
These are still 37mm torroids, I'm guessing they will have a little bit of extra power handling over a ones I have (same size but no core info, I'd assume there quite low grade due to the price of them).
I've spoken to some car audio guys that use earthquake amps (d2 & d3). One of them blew up a few FETs so I got him to check the size of the toroids in there, Its using dual 2.5inch's (abouts). Definately nasty stuff
I've spoken to some car audio guys that use earthquake amps (d2 & d3). One of them blew up a few FETs so I got him to check the size of the toroids in there, Its using dual 2.5inch's (abouts). Definately nasty stuff
karma said:
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DIRT®
Re: 2.5 in. Toroids!
but I think thats mainly from the car audio guys burping them at 1 ohm and 1/2 ohm loads 
this amp was a PH-D3, its rated at about 3000Wrms from memory.
I've got no idea of the switching frequency. Noones ever measured I don't think.
You reccomended Amidon Associates before and I had a look at there 2.4" toroids and they look very temping, would they ship to australia? how much did they cost you per core?
I filled out there contact form asking but sofar no response
I know there use a toroid for each supply but there notorious smoking themselvesN-Channel said:2.5" o.d. Cores??? WOW!
but I think thats mainly from the car audio guys burping them at 1 ohm and 1/2 ohm loads this amp was a PH-D3, its rated at about 3000Wrms from memory.
I've got no idea of the switching frequency. Noones ever measured I don't think.
You reccomended Amidon Associates before and I had a look at there 2.4" toroids and they look very temping, would they ship to australia? how much did they cost you per core?
I filled out there contact form asking but sofar no response
your asking alot when building such a huge power source off your vehicle or power source....the pro`s have 8 plus batteries and 150 amp alternators that are custom wound.....some use dual alternators.....I had to rebuild mine once a year with a modest setup and dual batteries.....not refraining you guys but words of experience
DIRT®
DIRT®
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