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"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message
news:llrkq5$hr4$1@news.albasani.net...
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
That bridge configuration will in theory charge the caps to 1.41 times
the RMS voltage of the transformer secondary, because a sine wave has
a peak voltage 1.41x its RMS.
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly something
I'd like to avoid. Back to the Googling board!
Search under "active ripple cancelling" - pretty much just an emitter
follower with some bias and a not quite as huge electrolytic as you'd need
on its own.
That doesn't help when you're building a power supply. You may as well
just connect the rectifier caps to the main linear regulator. That's
better, actually; a ripple canceler ahead of the regulator makes
things worse.
The issue is energy storage. 120 times a second, the transformer
output goes to zero volts. If you want to keep powering the load then,
the energy has to come from somewhere, and in this case it's the
filter caps.
I never said don't use reservoir caps - an unregulated emitter follower with
a heavily decoupled base does its best to follow the insignificant ripple on
its base.
Nah, that's a capacitance multiplier. As long as you don't let itOn Sun, 25 May 2014 18:33:16 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message
news:llrkq5$hr4$1@news.albasani.net...
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
That bridge configuration will in theory charge the caps to 1.41 times
the RMS voltage of the transformer secondary, because a sine wave has
a peak voltage 1.41x its RMS.
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly something
I'd like to avoid. Back to the Googling board!
Search under "active ripple cancelling" - pretty much just an emitter
follower with some bias and a not quite as huge electrolytic as you'd need
on its own.
That doesn't help when you're building a power supply. You may as well
just connect the rectifier caps to the main linear regulator. That's
better, actually; a ripple canceler ahead of the regulator makes
things worse.
The issue is energy storage. 120 times a second, the transformer
output goes to zero volts. If you want to keep powering the load then,
the energy has to come from somewhere, and in this case it's the
filter caps.
I never said don't use reservoir caps - an unregulated emitter follower with
a heavily decoupled base does its best to follow the insignificant ripple on
its base.
Problem is, it will also follow the significant ripple on its
collector.
There is no amount of caps you can add that will remove the ripple 100%
and expect to be able to get full use of the supply..
---
Sure there is.
All you have to do is make sure that the ripple valleys are high
enough to give the regulator the headroom it needs to provide a
ripple-free output at the supply's rated output current.
---
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly
something I'd like to avoid.
On Monday, May 26, 2014 1:54:51 PM UTC-7, John Fields wrote:
The real problem lies in not letting the magic smoke out of the
rectifiers during turn-on, and that's easily side-stepped by sizing
(overrating) the rectifiers properly.
It doesn't help that rectifier ratings are by average current passed
through a whole cycle. A nominal '1A' rectifier (1N4003) will be OK
with 10A (nonrepetitive) during startup, and 2A output current in
a fullwave bridge (because it has only 50% duty cycle) and that
amounts to 1A average, but is also 2.8 A peak, and 1.4A RMS.
Then there's the problem of overrated components (low ESR capacitors
and low series resistance rectifiers and oversize copper windings) causing
excessive startup currents. You might need to add NTC or other resistive
elements if your capacitors, windings, and rectifiers have been overrated
improperly. I shudder to recollect some of the attempts of
golden-eared audiophiles to redo power supply components according
to vague ideas like 'properly overrating'.
In article <hp97o9hv1tvf0g01h68huuh6scoh01moba@4ax.com>,
jfields@austininstruments.com says...
There is no amount of caps you can add that will remove the ripple 100%
and expect to be able to get full use of the supply..
---
Sure there is.
All you have to do is make sure that the ripple valleys are high
enough to give the regulator the headroom it needs to provide a
ripple-free output at the supply's rated output current.
---
That still does not remove the ripple from the caps,
On Monday, May 26, 2014 1:54:51 PM UTC-7, John Fields wrote:
The real problem lies in not letting the magic smoke out of the
rectifiers during turn-on, and that's easily side-stepped by sizing
(overrating) the rectifiers properly.
It doesn't help that rectifier ratings are by average current passed
through a whole cycle. A nominal '1A' rectifier (1N4003) will be OK
with 10A (nonrepetitive) during startup, and 2A output current in
a fullwave bridge (because it has only 50% duty cycle) and that
amounts to 1A average, but is also 2.8 A peak, and 1.4A RMS.
Then there's the problem of overrated components (low ESR capacitors
and low series resistance rectifiers and oversize copper windings) causing
excessive startup currents. You might need to add NTC or other resistive
elements if your capacitors, windings, and rectifiers have been overrated
improperly. I shudder to recollect some of the attempts of
golden-eared audiophiles to redo power supply components according
to vague ideas like 'properly overrating'.
"whit3rd" <whit3rd@gmail.com> wrote in message
news:30ec191b-ff90-47fd-954d-b95bc3c0ef04@googlegroups.com...
On Monday, May 26, 2014 1:54:51 PM UTC-7, John Fields wrote:
The real problem lies in not letting the magic smoke out of the
rectifiers during turn-on, and that's easily side-stepped by sizing
(overrating) the rectifiers properly.
It doesn't help that rectifier ratings are by average current passed
through a whole cycle. A nominal '1A' rectifier (1N4003) will be OK
with 10A (nonrepetitive) during startup, and 2A output current in
a fullwave bridge (because it has only 50% duty cycle) and that
amounts to 1A average, but is also 2.8 A peak, and 1.4A RMS.
Then there's the problem of overrated components (low ESR capacitors
and low series resistance rectifiers and oversize copper windings) causing
excessive startup currents. You might need to add NTC or other resistive
elements if your capacitors, windings, and rectifiers have been overrated
improperly. I shudder to recollect some of the attempts of
golden-eared audiophiles to redo power supply components according
to vague ideas like 'properly overrating'.
So far I don't recall ever having seen a PTC in front of a transformer PSU.
"whit3rd" <whit3rd@gmail.com> wrote in message
news:30ec191b-ff90-47fd-954d-b95bc3c0ef04@googlegroups.com...
On Monday, May 26, 2014 1:54:51 PM UTC-7, John Fields wrote:
The real problem lies in not letting the magic smoke out of the
rectifiers during turn-on, and that's easily side-stepped by sizing
(overrating) the rectifiers properly.
It doesn't help that rectifier ratings are by average current passed
through a whole cycle. A nominal '1A' rectifier (1N4003) will be OK
with 10A (nonrepetitive) during startup, and 2A output current in
a fullwave bridge (because it has only 50% duty cycle) and that
amounts to 1A average, but is also 2.8 A peak, and 1.4A RMS.
Then there's the problem of overrated components (low ESR capacitors
and low series resistance rectifiers and oversize copper windings)
causing
excessive startup currents. You might need to add NTC or other resistive
elements if your capacitors, windings, and rectifiers have been overrated
improperly. I shudder to recollect some of the attempts of
golden-eared audiophiles to redo power supply components according
to vague ideas like 'properly overrating'.
So far I don't recall ever having seen a PTC in front of a transformer
PSU.
On 5/26/2014 9:33 PM, John Larkin wrote:
On Sun, 25 May 2014 18:33:16 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message
news:llrkq5$hr4$1@news.albasani.net...
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
That bridge configuration will in theory charge the caps to 1.41 times
the RMS voltage of the transformer secondary, because a sine wave has
a peak voltage 1.41x its RMS.
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly something
I'd like to avoid. Back to the Googling board!
Search under "active ripple cancelling" - pretty much just an emitter
follower with some bias and a not quite as huge electrolytic as you'd need
on its own.
That doesn't help when you're building a power supply. You may as well
just connect the rectifier caps to the main linear regulator. That's
better, actually; a ripple canceler ahead of the regulator makes
things worse.
The issue is energy storage. 120 times a second, the transformer
output goes to zero volts. If you want to keep powering the load then,
the energy has to come from somewhere, and in this case it's the
filter caps.
I never said don't use reservoir caps - an unregulated emitter follower with
a heavily decoupled base does its best to follow the insignificant ripple on
its base.
Problem is, it will also follow the significant ripple on its
collector.
Nah, that's a capacitance multiplier. As long as you don't let it
saturate, it's the bomb for supply rejection.
Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly
something I'd like to avoid.
Quick version: I am almost certain John is talking about the DC *on C1
and C2*, not the DC at the output of the supply.
Long version...
There will *always* be some ripple "before" the LM317 - across C1 and
C2 in the diagram you posted.* If you had a transformer with a 24 V AC
secondary, and you were drawing 1 A (DC) from the output of the power
supply, and you put an oscilloscope probe across C2, you'd see a DC
voltage varying between about 30 V and 32 V DC. The variation would
be at 120 Hz. You can reduce the amount of this ripple by making C1 and
C2 bigger, but you can never get it to go away completely.
(* From "Getting Started in Electronics" by Forrest Mims, I think.)
There will be *much less* ripple "after" the LM317 - across C3 - as long
as you have R1 adjusted to give an output voltage less than about 27 V
(in this example). If you put an oscilloscope probe across C3, you'd
see a DC voltage varying between (say) 27.000 V and 27.005 V. You can
reduce this ripple a little by putting another capacitor across R1 - see
the LM317 data sheet. A lot of things you would run from this power
supply won't care about this. Audio stuff might care a little (you
might hear a 120 Hz hum in the audio), depending on the audio voltage
levels you are using.
The main reason you have to care about the ripple "before" the LM317 is
that it effectively sets the highest output voltage you can get from
the supply. There will always be a couple of volts of drop "through"
the LM317 - in other words, even if you set the ADJ pin for maximum
output, the OUT pin will always be a couple of volts less than the IN
pin.
If the voltage on C1 and C2 is rippling between 30 V and 32 V, and you
set R1 for 27 V output or less, then there is always at least 3 V
available to lose in the LM317, and the output will be stable at 27 V.
If you tried to turn up R1 to get 29 V on the output, there would only
be between 1 and 3 V available to lose in the LM317. 1 V isn't enough
for the LM317, so part of the time, you wouldn't get the full 29 V on
the output.
There is an article by Don Lancaster on how to pick the filter capacitor
size on PDF page 104 of http://www.tinaja.com/glib/hackar1.pdf . In
that article, Figure 1-B is you, the capacitor is the combination of
C1 and C2 in your schematic, and the resistor represents your LM317 and
everything "after" it.
Matt Roberds
Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly
something I'd like to avoid.
Quick version: I am almost certain John is talking about the DC *on C1
and C2*, not the DC at the output of the supply.
Long version...
There will *always* be some ripple "before" the LM317 - across C1 and
C2 in the diagram you posted.* If you had a transformer with a 24 V AC
secondary, and you were drawing 1 A (DC) from the output of the power
supply, and you put an oscilloscope probe across C2, you'd see a DC
voltage varying between about 30 V and 32 V DC. The variation would
be at 120 Hz. You can reduce the amount of this ripple by making C1 and
C2 bigger, but you can never get it to go away completely.
(* From "Getting Started in Electronics" by Forrest Mims, I think.)
There will be *much less* ripple "after" the LM317 - across C3 - as long
as you have R1 adjusted to give an output voltage less than about 27 V
(in this example). If you put an oscilloscope probe across C3, you'd
see a DC voltage varying between (say) 27.000 V and 27.005 V. You can
reduce this ripple a little by putting another capacitor across R1 - see
the LM317 data sheet. A lot of things you would run from this power
supply won't care about this. Audio stuff might care a little (you
might hear a 120 Hz hum in the audio), depending on the audio voltage
levels you are using.
The main reason you have to care about the ripple "before" the LM317 is
that it effectively sets the highest output voltage you can get from
the supply. There will always be a couple of volts of drop "through"
the LM317 - in other words, even if you set the ADJ pin for maximum
output, the OUT pin will always be a couple of volts less than the IN
pin.
If the voltage on C1 and C2 is rippling between 30 V and 32 V, and you
set R1 for 27 V output or less, then there is always at least 3 V
available to lose in the LM317, and the output will be stable at 27 V.
If you tried to turn up R1 to get 29 V on the output, there would only
be between 1 and 3 V available to lose in the LM317. 1 V isn't enough
for the LM317, so part of the time, you wouldn't get the full 29 V on
the output.
There is an article by Don Lancaster on how to pick the filter capacitor
size on PDF page 104 of http://www.tinaja.com/glib/hackar1.pdf . In
that article, Figure 1-B is you, the capacitor is the combination of
C1 and C2 in your schematic, and the resistor represents your LM317 and
everything "after" it.
Matt Roberds
On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:
On 5/26/2014 9:33 PM, John Larkin wrote:
On Sun, 25 May 2014 18:33:16 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message
news:llrkq5$hr4$1@news.albasani.net...
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
That bridge configuration will in theory charge the caps to 1.41 times
the RMS voltage of the transformer secondary, because a sine wave has
a peak voltage 1.41x its RMS.
In real life you'd typically get more DC than that at light loads and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly something
I'd like to avoid. Back to the Googling board!
Search under "active ripple cancelling" - pretty much just an emitter
follower with some bias and a not quite as huge electrolytic as you'd need
on its own.
That doesn't help when you're building a power supply. You may as well
just connect the rectifier caps to the main linear regulator. That's
better, actually; a ripple canceler ahead of the regulator makes
things worse.
The issue is energy storage. 120 times a second, the transformer
output goes to zero volts. If you want to keep powering the load then,
the energy has to come from somewhere, and in this case it's the
filter caps.
I never said don't use reservoir caps - an unregulated emitter follower with
a heavily decoupled base does its best to follow the insignificant ripple on
its base.
Problem is, it will also follow the significant ripple on its
collector.
Nah, that's a capacitance multiplier. As long as you don't let it
saturate, it's the bomb for supply rejection.
Sure, as long as the input ripple is small, a few tenths p-p. But the
suggestion was to put the c-multiplier between the bridge+filter caps
and the main linear regulator, where one might expect amps of current
and volts of ripple.
On 5/27/2014 7:21 PM, John Larkin wrote:
On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A. You can adjust that
to lop off the ripple if you like, though of course it isn't as
efficient as using a huge cap.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
On 05/28/2014 10:24 AM, George Herold wrote:
On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote:
On 5/27/2014 7:21 PM, John Larkin wrote
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A. You can adjust that
to lop off the ripple if you like, though of course it isn't as
efficient as using a huge cap.
That's interesting, the Exar is "best" because it has the least noise to start with?
The Exar is quieter and has a lower minimum cathode current.
Nice, I like that you've got the cap multiplier inside the feedback path.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A.
The Exar is quieter and has a lower minimum cathode current.
On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote:
On 5/27/2014 7:21 PM, John Larkin wrote:
On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A. You can adjust that
to lop off the ripple if you like, though of course it isn't as
efficient as using a huge cap.
That's interesting, the Exar is "best" because it has the least noise to start with?
As you've said, the reference/regulator can be the noisiest part of a design.
I've got an LT3080 in an instrument. (cap multiplier after it.)
And I've regretted it. Much better to just make your own,
(reference->opamp->transistor)
George H.
On 05/28/2014 10:24 AM, George Herold wrote:
On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote:
On 5/27/2014 7:21 PM, John Larkin wrote:
On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A. You can adjust that
to lop off the ripple if you like, though of course it isn't as
efficient as using a huge cap.
That's interesting, the Exar is "best" because it has the least noise to start with?
As you've said, the reference/regulator can be the noisiest part of a design.
I've got an LT3080 in an instrument. (cap multiplier after it.)
And I've regretted it. Much better to just make your own,
(reference->opamp->transistor)
George H.
The Exar is quieter and has a lower minimum cathode current.
0-------*---------RRRR---*---* *-*----------0
| | \ / |
R | \ A |
R | ------ |
R CCC | |
R CCC R |
| | R R
| GND R R
| R R
| | R
| | |
*---RRRR---*--RRRR------* |
| | | |
| | | |
CCC /---/ CCC |
CCC / \---* CCC *--RRRR--*
| --- | | | |
GND | | GND | GND
| | |
GND *-------------*
Cheers
Phil Hobbs
On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:
On 5/26/2014 9:33 PM, John Larkin wrote:
On Sun, 25 May 2014 18:33:16 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in
message
news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message
news:llrkq5$hr4$1@news.albasani.net...
On 5/24/2014 8:48 PM, John Larkin wrote:
On Sat, 24 May 2014 20:06:45 -0500, Jurd
That bridge configuration will in theory charge the caps to 1.41
times
the RMS voltage of the transformer secondary, because a sine wave
has
a peak voltage 1.41x its RMS.
In real life you'd typically get more DC than that at light loads
and
less at heavy loads. And the "DC" will have ripple, which makes the
voltage dip at 120 Hz (100 Hz in the hinterlands).
Ah thanks. Good to know about the ripple, as that's certainly
something
I'd like to avoid. Back to the Googling board!
Search under "active ripple cancelling" - pretty much just an emitter
follower with some bias and a not quite as huge electrolytic as you'd
need
on its own.
That doesn't help when you're building a power supply. You may as well
just connect the rectifier caps to the main linear regulator. That's
better, actually; a ripple canceler ahead of the regulator makes
things worse.
The issue is energy storage. 120 times a second, the transformer
output goes to zero volts. If you want to keep powering the load then,
the energy has to come from somewhere, and in this case it's the
filter caps.
I never said don't use reservoir caps - an unregulated emitter follower
with
a heavily decoupled base does its best to follow the insignificant
ripple on
its base.
Problem is, it will also follow the significant ripple on its
collector.
Nah, that's a capacitance multiplier. As long as you don't let it
saturate, it's the bomb for supply rejection.
Sure, as long as the input ripple is small, a few tenths p-p. But the
suggestion was to put the c-multiplier between the bridge+filter caps
On Wednesday, May 28, 2014 10:05:31 AM UTC-7, Phil Hobbs wrote:
Lately I've been using shunt regulators on the base string of cap
multipliers. AFAICT the best is the Exar SPX431A.
The Exar is quieter and has a lower minimum cathode current.
It's possible to get lower (SPX431A wants over 400 uA, and TLV431
wants over 50 uA) but there's some cathode-voltage-range issues, too.
Have you considered direct shunt regulation?
0--------*---RRRR---*-----*----------0
| | |
R | |
R | *-----*
R CCC R |
R CCC R C
| | R |
| | *-----*
*--RRRR----* |
| | |
| /---/ |
CCC / \----*
CCC --- |
| | R
| | R
GND | |
GND GND