Strange SMPS configuration. Can some decipher it for me.

T

The Real Andy

Guest
This schematic is hard to read, but you can get a reasonable picture
from it.
http://www.irf.com/technical-info/refdesigns/iradk10.pdf

The SMPS controller appears to be on a floating ground. The mosfet
switches power from the DC Bus through an 8.2 ohm resistor to the
floating ground. The inductor is connected to this floating ground.
Now I understand the purpose of the resistor is to provide current
feedback, but thats about where it stops. I can kind of see how it
works, and i like it, the whole controller sits between the inductor
and the DCBus.

I tried to google for app notes on this but without sucess. I take it
if I were to use this same configuration with a different controller,
then I would be wise to clamp the voltage across the controller
itself?

Regards:

Andy
 
On Sat, 20 Aug 2005 10:36:14 +1000, The Real Andy
<will_get_back_to_you_on_This> wrote:

This schematic is hard to read, but you can get a reasonable picture
from it.
http://www.irf.com/technical-info/refdesigns/iradk10.pdf

The SMPS controller appears to be on a floating ground. The mosfet
switches power from the DC Bus through an 8.2 ohm resistor to the
floating ground. The inductor is connected to this floating ground.
Now I understand the purpose of the resistor is to provide current
feedback, but thats about where it stops. I can kind of see how it
works, and i like it, the whole controller sits between the inductor
and the DCBus.

I tried to google for app notes on this but without sucess. I take it
if I were to use this same configuration with a different controller,
then I would be wise to clamp the voltage across the controller
itself?
Click to expand...
The pdf file's schematic is illegible.

Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing line
definition).

It's not worth guessing about.

Suggest you inquire re hard copy - it may come with the kit.

The main power semiconductor datasheet is at-

http://www.irf.com/product-info/datasheets/data/irams10up60b.pdf

- which may assist in determining the actual power train connections.

RL
 
On Sat, 20 Aug 2005 06:42:08 GMT, legg <legg@nospam.magma.ca> wrote:

On Sat, 20 Aug 2005 10:36:14 +1000, The Real Andy
will_get_back_to_you_on_This> wrote:

This schematic is hard to read, but you can get a reasonable picture
from it.
http://www.irf.com/technical-info/refdesigns/iradk10.pdf

The SMPS controller appears to be on a floating ground. The mosfet
switches power from the DC Bus through an 8.2 ohm resistor to the
floating ground. The inductor is connected to this floating ground.
Now I understand the purpose of the resistor is to provide current
feedback, but thats about where it stops. I can kind of see how it
works, and i like it, the whole controller sits between the inductor
and the DCBus.

I tried to google for app notes on this but without sucess. I take it
if I were to use this same configuration with a different controller,
then I would be wise to clamp the voltage across the controller
itself?


The pdf file's schematic is illegible.

Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing line
definition).

It's not worth guessing about.

Suggest you inquire re hard copy - it may come with the kit.

The main power semiconductor datasheet is at-

http://www.irf.com/product-info/datasheets/data/irams10up60b.pdf

- which may assist in determining the actual power train connections.

RL
Click to expand...
I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.
 
The Real Andy wrote...
Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.
Click to expand...
Good idea.


--
Thanks,
- Win
 
On 20 Aug 2005 09:59:00 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

The Real Andy wrote...

Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.

Good idea.
Click to expand...
Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE
 
The Real Andy wrote:
On 20 Aug 2005 09:59:00 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:


The Real Andy wrote...

Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.

Good idea.


Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE
Click to expand...
Its a buck converter. What they have done is float the entire
peak-current-mode controller with the N-channel MOSFET. The start-up
behaviour would be tricky to get exactly right, but nothing very funny
here. Thanks for the nice pic :)

Cheers
Terry
 
On Sun, 21 Aug 2005 15:03:04 +1200, Terry Given <my_name@ieee.org>
wrote:

The Real Andy wrote:
On 20 Aug 2005 09:59:00 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:


The Real Andy wrote...

Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.

Good idea.


Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE

Its a buck converter. What they have done is float the entire
peak-current-mode controller with the N-channel MOSFET. The start-up
behaviour would be tricky to get exactly right, but nothing very funny
here. Thanks for the nice pic :)

Cheers
Terry
Click to expand...
What is the advantages of doing it this way over say fixing it to
ground? The only advantage that I can see so far is by not having to
put a resistor between ground and the load for current measuremnt,
which I assume would be an advantage in the situation at hand.

Thanks,

Andy
 
The Real Andy wrote:
On Sun, 21 Aug 2005 15:03:04 +1200, Terry Given <my_name@ieee.org
wrote:


The Real Andy wrote:

On 20 Aug 2005 09:59:00 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:



The Real Andy wrote...


Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.

Good idea.


Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE

Its a buck converter. What they have done is float the entire
peak-current-mode controller with the N-channel MOSFET. The start-up
behaviour would be tricky to get exactly right, but nothing very funny
here. Thanks for the nice pic :)

Cheers
Terry


What is the advantages of doing it this way over say fixing it to
ground? The only advantage that I can see so far is by not having to
put a resistor between ground and the load for current measuremnt,
which I assume would be an advantage in the situation at hand.

Thanks,

Andy
Click to expand...
lack of a level-shifted gatedrive is probably the biggest benefit.

a "conventional" buck would use a P-ch (or PNP) switching element, with
a ground-referred voltage-mode controller.

The current sensing resistor senses switch current, not load current
(although when the switch is on, the two are related), but yes, this is
a real PITA with a "conventional" buck converter.

they would have to be careful to ensure it starts up properly, but the
UC3842 has an UVLO, so it ought to survive regardless of how shonky the
supply is. DCM would be an issue - D8 keeps the 3842 supply "pumped"
every time the FET turns off and inductor current commutates to D13,
pulling U5-8,U5-9 to a schottky drop below 0V. During DCM, this can be
quite a short interval.


Cheers
Terry
 
On Sun, 21 Aug 2005 17:29:26 +1200, Terry Given <my_name@ieee.org>
wrote:

The Real Andy wrote:
On Sun, 21 Aug 2005 15:03:04 +1200, Terry Given <my_name@ieee.org
wrote:


The Real Andy wrote:

On 20 Aug 2005 09:59:00 -0700, Winfield Hill
Winfield_member@newsguy.com> wrote:



The Real Andy wrote...


Someone has republished a 15-page document in 11 pages, without
regarding its actual contents (ie index page numbering or drawing
line definition).

I emailed IR and got a decent copy. I was trying to find it but I must
have deleted the email. I do have a printed copy. If helps any, i will
scan the print I have and post it to ABSE or on my website.

Good idea.


Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE

Its a buck converter. What they have done is float the entire
peak-current-mode controller with the N-channel MOSFET. The start-up
behaviour would be tricky to get exactly right, but nothing very funny
here. Thanks for the nice pic :)

Cheers
Terry


What is the advantages of doing it this way over say fixing it to
ground? The only advantage that I can see so far is by not having to
put a resistor between ground and the load for current measuremnt,
which I assume would be an advantage in the situation at hand.

Thanks,

Andy

lack of a level-shifted gatedrive is probably the biggest benefit.

a "conventional" buck would use a P-ch (or PNP) switching element, with
a ground-referred voltage-mode controller.

The current sensing resistor senses switch current, not load current
(although when the switch is on, the two are related), but yes, this is
a real PITA with a "conventional" buck converter.

they would have to be careful to ensure it starts up properly, but the
UC3842 has an UVLO, so it ought to survive regardless of how shonky the
supply is. DCM would be an issue - D8 keeps the 3842 supply "pumped"
every time the FET turns off and inductor current commutates to D13,
pulling U5-8,U5-9 to a schottky drop below 0V. During DCM, this can be
quite a short interval.


OK, getting this now. I was going to attempt a similar concept with a
Click to expand...
TL494 (easy to get at local hobby shops) but now I am thinking this
may be a bad idea. I can see many areas where the TL494 wont cut it
now. I think I am left with using the same controller used in the IR
dev kit or going with a different concept with the TL494.

Sooo, the next question is, how best to sense switching current or
load current with a conventional buck converter without lifting the
ground? Am I going in the wrong direction?

Can you point me to a good app note on the former topology using the
3842 or similar?

Many thanks for the help, tis appreciated. To have even got a working
circuit so far amazes me considering I am a former digital person who
now only does software.

Regards:

Andy
 
In article <931jg15o7mc1ms2papd7269g390ctrlo7u@4ax.com>,
The Real Andy <will_get_back_to_you_on_This> wrote:
[...]
Sooo, the next question is, how best to sense switching current or
load current with a conventional buck converter without lifting the
ground? Am I going in the wrong direction?
Click to expand...
There are two places that allow you to get at the switch current without
having to have a large common mode AC voltage. You can sense at the input
side of the switch or at the load side of the inductor.

Input side of switch:

Linear and several others make chips for this purpose. You can also make
a do-it-yourself current mirror for the job.

Inductor output side:

If you are doing a roll-your-own switcher controller out of an LM339, this
is the way to go. You modify the normal control circuit like this:

Rsense
--+-/\/\-+--
Vout Vref ! !
! ! \ \
/ / /R1 / R2
\ \ \ \
/ / ! !
\ \ +-------------!-\ !
! ! ! ! ! >-+---
+--/\/\/--!!-+ \ +------!+/ !
! ! /R3 ! ---
! ! \ \ ---
+----!-\ ! ! / R4 !
! ! >--+-+--------- \
/ --!+/ ! !
\ ! --- GND
/ Vref ---
\ !
! GND
GND

This provides a foldback current limit of the switch current. You may get
foldback of the load current too depending on other circuit
characteristics. Adding a resistor from the "off time one shot" capacitor
to the output voltage will give you foldback of the load current.

R1,2,3,4 are unbalanced enough that the switch certain to be held off
when there is zero load.
--
--
kensmith@rahul.net forging knowledge
 
On Mon, 22 Aug 2005 14:34:58 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <931jg15o7mc1ms2papd7269g390ctrlo7u@4ax.com>,
The Real Andy <will_get_back_to_you_on_This> wrote:
[...]
Sooo, the next question is, how best to sense switching current or
load current with a conventional buck converter without lifting the
ground? Am I going in the wrong direction?

There are two places that allow you to get at the switch current without
having to have a large common mode AC voltage. You can sense at the input
side of the switch or at the load side of the inductor.

Input side of switch:

Linear and several others make chips for this purpose. You can also make
a do-it-yourself current mirror for the job.

Inductor output side:

If you are doing a roll-your-own switcher controller out of an LM339, this
is the way to go. You modify the normal control circuit like this:

Rsense
--+-/\/\-+--
Vout Vref ! !
! ! \ \
/ / /R1 / R2
\ \ \ \
/ / ! !
\ \ +-------------!-\ !
! ! ! ! ! >-+---
+--/\/\/--!!-+ \ +------!+/ !
! ! /R3 ! ---
! ! \ \ ---
+----!-\ ! ! / R4 !
! ! >--+-+--------- \
/ --!+/ ! !
\ ! --- GND
/ Vref ---
\ !
! GND
GND

This provides a foldback current limit of the switch current. You may get
foldback of the load current too depending on other circuit
characteristics. Adding a resistor from the "off time one shot" capacitor
to the output voltage will give you foldback of the load current.

R1,2,3,4 are unbalanced enough that the switch certain to be held off
when there is zero load.
--
Click to expand...
Thanks Ken. After much reading (On Semi and Philips have a great
selection of SMPS app notes) I have decided to follow the current mode
path. In the application I am using it (same as the pic provided) i
think the current mode controller has significant advantages over
voltage mode. I am really warming to the IR design, just got to go
find some app notes on that method now :). As an added bonus, the
UC3842 is about half the price of the TL494, so the hobbiest who build
this will be even happier!

Thanks all, rest assured i will be back with more questions :)

Andy
 
On Tue, 23 Aug 2005 10:57:44 +1000, The Real Andy
<will_get_back_to_you_on_This> wrote:

snip
Click to expand...
One more question, why chose the N-Channel Fet? A few quick serches of
online suppliers seems to suggest the the P-Channel breed is cheaper.
I did notice that there where less P-Channel parts available, perhaps
this is the reason? I did notice however, for a search of 600V P
devices, no results, 500V, about 3....

Andy
 
In article <79tkg1lu1v1b1hg1k3vvs863ked4rqtr8f@4ax.com>,
The Real Andy <will_get_back_to_you_on_This> wrote:
[...]
One more question, why chose the N-Channel Fet? A few quick serches of
online suppliers seems to suggest the the P-Channel breed is cheaper.
I did notice that there where less P-Channel parts available, perhaps
this is the reason? I did notice however, for a search of 600V P
devices, no results, 500V, about 3....
Click to expand...
Pound for pound, a N channel FET has a lower RDS(ON) than a P channel FET
of the same voltage rating. To fairly compare prices you need to compare
ones with equal RDS(ON) and voltage ratings.

I've run into the problem of there being no 600V P-channels out there and
solved it in a very ugly way. I made the whole controller chip etc fly up
and down with the source of the N channel FET. This works well but is
very nasty to trouble shoot when it doesn't. You have to put a psudo
ground plane under the switcher chip and stuff so you end up with a fairly
large Cstray to deal with. This is not a circuit you want to try to do at
2MHz.

--
--
kensmith@rahul.net forging knowledge
 
The Real Andy wrote:
On Mon, 22 Aug 2005 14:34:58 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:


In article <931jg15o7mc1ms2papd7269g390ctrlo7u@4ax.com>,
The Real Andy <will_get_back_to_you_on_This> wrote:
[...]

Sooo, the next question is, how best to sense switching current or
load current with a conventional buck converter without lifting the
ground? Am I going in the wrong direction?

There are two places that allow you to get at the switch current without
having to have a large common mode AC voltage. You can sense at the input
side of the switch or at the load side of the inductor.

Input side of switch:

Linear and several others make chips for this purpose. You can also make
a do-it-yourself current mirror for the job.

Inductor output side:

If you are doing a roll-your-own switcher controller out of an LM339, this
is the way to go. You modify the normal control circuit like this:

Rsense
--+-/\/\-+--
Vout Vref ! !
! ! \ \
/ / /R1 / R2
\ \ \ \
/ / ! !
\ \ +-------------!-\ !
! ! ! ! ! >-+---
+--/\/\/--!!-+ \ +------!+/ !
! ! /R3 ! ---
! ! \ \ ---
+----!-\ ! ! / R4 !
! ! >--+-+--------- \
/ --!+/ ! !
\ ! --- GND
/ Vref ---
\ !
! GND
GND

This provides a foldback current limit of the switch current. You may get
foldback of the load current too depending on other circuit
characteristics. Adding a resistor from the "off time one shot" capacitor
to the output voltage will give you foldback of the load current.

R1,2,3,4 are unbalanced enough that the switch certain to be held off
when there is zero load.
--


Thanks Ken. After much reading (On Semi and Philips have a great
selection of SMPS app notes) I have decided to follow the current mode
path. In the application I am using it (same as the pic provided) i
think the current mode controller has significant advantages over
voltage mode. I am really warming to the IR design, just got to go
find some app notes on that method now :). As an added bonus, the
UC3842 is about half the price of the TL494, so the hobbiest who build
this will be even happier!

Thanks all, rest assured i will be back with more questions :)

Andy
Click to expand...
current mode is the best IMO. A well-designed smps should happily run
with a dead short on the output.

Cheers
Terry
 
Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE
Click to expand...
For US$40 you can download and register PMView for 'doze or OS2-eCS.
Excellent viewer as well as image format converter.

http://www.pmview.com/

Scan20002 .png 101,682
Scan20002 .tif 1,088,064

Scan20001 .png 279,289
Scan20001 .tif 4,352,434

The PNG format is about as good as it gets for b/w images or ones with a
few colours. JPG is best for colour photos.

Ted
 
On Tue, 23 Aug 2005 21:50:35 GMT, Ted Edwards
<Ted_Espamless@telus.net> wrote:

Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE

For US$40 you can download and register PMView for 'doze or OS2-eCS.
Excellent viewer as well as image format converter.

http://www.pmview.com/

Scan20002 .png 101,682
Scan20002 .tif 1,088,064

Scan20001 .png 279,289
Scan20001 .tif 4,352,434

The PNG format is about as good as it gets for b/w images or ones with a
few colours. JPG is best for colour photos.

Ted
Click to expand...
I "printed" Scan20001.tif to a 300dpi PDF via Acrobat... 130kB, very
readable, zooms quite nicely.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Tue, 23 Aug 2005 15:03:07 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Tue, 23 Aug 2005 21:50:35 GMT, Ted Edwards
Ted_Espamless@telus.net> wrote:

Ok, can be found at www.wayit.com.au/images/Scan20001.tif for 600dpi
version

or www.wayit.com.au/images/Scan20002.tif for the 300dpi version.

Be warned, the big one is about 4mb. The smaller is quite visible and
is about 1Mb. Sorry I cant get them smaller, i lack the tools on the
computer. LEt me know if you want it on ABSE

For US$40 you can download and register PMView for 'doze or OS2-eCS.
Excellent viewer as well as image format converter.

http://www.pmview.com/

Scan20002 .png 101,682
Scan20002 .tif 1,088,064

Scan20001 .png 279,289
Scan20001 .tif 4,352,434

The PNG format is about as good as it gets for b/w images or ones with a
few colours. JPG is best for colour photos.

Ted

I "printed" Scan20001.tif to a 300dpi PDF via Acrobat... 130kB, very
readable, zooms quite nicely.

...Jim Thompson
Click to expand...
Cheers guys, will keep that in mind. I didn't have a pdf converter at
hand at that time but I think that too would have been my preffered
method.
 
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