24V to 500-1000V, 20W floating DC-DC converter...

[Edward Lee]

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

 

[Chris]

On 09/09/20 13:21, Edward Lee wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

Only problem with that is that the base drive current of the power
transistor may be greater than the 431 can handle. May need to
use a darlington on the output, which would also improve the
gain around the 431. Or, perhass replace the transistor with a
power mosfet.

Depending on required precision, you could do that with a single zener,
resistor and power transistor. Drop the 431 altogether...

Chris

 

[legg]

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
<edward.ming.lee@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

For 12V, you\'d need to recalculate your voltage divider, regardless
of the regulation method intended.

A 60W shunt regulator? Don\'t forget a collector resistor to
soak up some of that power loss. Silicon resistors, loosely
applied, are expensive and prone to failure.

The only apps in your reference that used pnp power devices
were for a crowbar circuit and for a switching converter; chaotic
after an extra inversion.

RL

 

[legg]

On Wed, 09 Sep 2020 09:03:01 -0400, legg <legg@nospam.magma.ca> wrote:

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward.ming.lee@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

For 12V, you\'d need to recalculate your voltage divider, regardless
of the regulation method intended.

A 60W shunt regulator? Don\'t forget a collector resistor to
soak up some of that power loss. Silicon resistors, loosely
applied, are expensive and prone to failure.

The only apps in your reference that used pnp power devices
were for a crowbar circuit and for a switching converter; chaotic
after an extra inversion.

Ach - figure 19.

At 12V, you\'re TL431 will likely overheat for a normal bipolar
pnp - supplying 250mA of base current.

You\'d get better thermals and reliability with a zener and nmosfet.

RL

 

[Jan Panteltje]

On a sunny day (Wed, 9 Sep 2020 05:21:42 -0700 (PDT)) it happened Edward Lee
<edward.ming.lee@gmail.com> wrote in
<cea1e1a3-9f20-4cce-bdba-0995a0730ba5n@googlegroups.com>:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So,
i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

Other suggestions are good.
But in these days of green looking politicians I think the question:
\'Cannot you use a 12V switcher controlled supply for efficiency\" is justified.
After all California is already warming up to the extreme.
So maybe it would help the world if you told us what you are trying to load\' so much.
Of course if it is US DOD top secret but then I won\'t help anyways.
Not with this precedent.

 

[John Larkin]

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
<edward.ming.lee@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

You could fry the TL431 at 5 amps out, from too much PNP base current.
A p-channel mosfet would help there, instead of the PNP.

But the answer could be 5K either way.


--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Lasse Langwadt Christensen]

onsdag den 9. september 2020 kl. 16.28.15 UTC+2 skrev John Larkin:

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward.ming.lee@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?

You could fry the TL431 at 5 amps out, from too much PNP base current.
A p-channel mosfet would help there, instead of the PNP.

or compound pair, if power npn/nchannel is preferable

 

[Edward Lee]

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

> A p-channel mosfet would help there, instead of the PNP.

OK.

> But the answer could be 5K either way.

OK, thanks.

 

[Edward Lee]

On Wednesday, September 9, 2020 at 5:57:17 AM UTC-7, legg wrote:

On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
For 12V, you\'d need to recalculate your voltage divider, regardless
of the regulation method intended.

It\'s for overcharging protection of the batteries. Once triggered, divider ratio will get lower, until the load shift to another one in the serial chain.

A 60W shunt regulator? Don\'t forget a collector resistor to
soak up some of that power loss. Silicon resistors, loosely
applied, are expensive and prone to failure.

Yes, good idea.

 

[Edward Lee]

On Wednesday, September 9, 2020 at 8:52:19 AM UTC-7, Edward Lee wrote:

On Wednesday, September 9, 2020 at 5:57:17 AM UTC-7, legg wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
For 12V, you\'d need to recalculate your voltage divider, regardless
of the regulation method intended.
It\'s for overcharging protection of the batteries. Once triggered, divider ratio will get lower, until the load shift to another one in the serial chain.
A 60W shunt regulator? Don\'t forget a collector resistor to
soak up some of that power loss. Silicon resistors, loosely
applied, are expensive and prone to failure.
Yes, good idea.

Actually, i only need to drop it couple of volts, to stop charging. So, emitter resistor (5 ohms, 10W?) might work.

 

[John Larkin]

On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
<edward.ming.lee@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.

Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.


--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Edward Lee]

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:

On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.

 

[John Larkin]

On Wed, 9 Sep 2020 10:26:14 -0700 (PDT), Edward Lee
<edward.ming.lee@gmail.com> wrote:

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.

Or consider a collector resistor. That\'s easier to think about.




--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[legg]

On Wed, 09 Sep 2020 10:14:16 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward.ming.lee@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.

Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

It\'s still advisable for any npn running over it\'s Vce
range at the temperature limit.

Germaniums were both leaky and more temperature-sensitive -
typical BE resistor <200R.

You\'d normally want to keep the TL431 in linear operation.
Minimum spec is Ik >= 1mA for bog standard TL431. There\'s
no spec for Ik, out of regulation.

Maximum Ik at 11V is about 30mA, before you\'d get overheating.

RL

 

[legg]

On Wed, 9 Sep 2020 10:26:14 -0700 (PDT), Edward Lee
<edward.ming.lee@gmail.com> wrote:

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.

Check your battery spec. A float voltage will seldom
be 12V.

You\'re looking for a series cell ballancing circuit . . ?

RL

 

[John Larkin]

On Wed, 09 Sep 2020 14:09:45 -0400, legg <legg@nospam.magma.ca> wrote:

On Wed, 09 Sep 2020 10:14:16 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward.ming.lee@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.

Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

It\'s still advisable for any npn running over it\'s Vce
range at the temperature limit.

Why?


--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Edward Lee]

On Wednesday, September 9, 2020 at 11:04:00 AM UTC-7, legg wrote:

On Wed, 09 Sep 2020 10:14:16 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:

On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.

Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.
It\'s still advisable for any npn running over it\'s Vce
range at the temperature limit.

Yes, i will use a 5 ohm emitter resistor to limit both base and collector current.

Germaniums were both leaky and more temperature-sensitive -
typical BE resistor <200R.

You\'d normally want to keep the TL431 in linear operation.
Minimum spec is Ik >= 1mA for bog standard TL431. There\'s
no spec for Ik, out of regulation.

Maximum Ik at 11V is about 30mA, before you\'d get overheating.

It will be much less than 11V for the TL431. I think it can handle 100mA.

 

[Edward Lee]

On Wednesday, September 9, 2020 at 11:08:08 AM UTC-7, legg wrote:

On Wed, 9 Sep 2020 10:26:14 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.
Check your battery spec. A float voltage will seldom be 12V.

Maximum is 12.6V for lithium battery.

> You\'re looking for a series cell ballancing circuit . . ?

Yes. each 12V module (3x 4.2V) has it\'s own BMS ballancing circuit. I just need to limit external voltage to 12V. 4 modules for 48V. 8 modules for 96V.

 

[Lasse Langwadt Christensen]

onsdag den 9. september 2020 kl. 20.17.40 UTC+2 skrev Edward Lee:

On Wednesday, September 9, 2020 at 11:08:08 AM UTC-7, legg wrote:
On Wed, 9 Sep 2020 10:26:14 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.
Check your battery spec. A float voltage will seldom be 12V.

Maximum is 12.6V for lithium battery.

You\'re looking for a series cell ballancing circuit . . ?

Yes. each 12V module (3x 4.2V) has it\'s own BMS ballancing circuit. I just need to limit external voltage to 12V. 4 modules for 48V. 8 modules for 96V.

sure you need the 12V limit? wouldn\'t it already be limited by the individual BMSs?

 

[Edward Lee]

On Wednesday, September 9, 2020 at 12:15:51 PM UTC-7, lang...@fonz.dk wrote:

onsdag den 9. september 2020 kl. 20.17.40 UTC+2 skrev Edward Lee:
On Wednesday, September 9, 2020 at 11:08:08 AM UTC-7, legg wrote:
On Wed, 9 Sep 2020 10:26:14 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:

On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee
edward....@gmail.com> wrote:
I can\'t figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question:

For isolated application, the feedback divider has to be secondary side only
and a TL431 used for error amp, into an opto, in the usual way.

I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7

https://www.onsemi.com/pub/Collateral/TL431-D.PDF

I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?
You could fry the TL431 at 5 amps out, from too much PNP base current.

5A max for the AWG22 wires. Actual current may be couple of As for an instant.

A p-channel mosfet would help there, instead of the PNP.

OK.

But the answer could be 5K either way.

OK, thanks.
Actually, with the PNP, it doesn\'t need a b-e resistor. Once, about 60
years ago, people used leaky germanium transistors, so using b-e
resistors became folklore.

OK, i\'ll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that\'s fine.
Check your battery spec. A float voltage will seldom be 12V.

Maximum is 12.6V for lithium battery.

You\'re looking for a series cell ballancing circuit . . ?

Yes. each 12V module (3x 4.2V) has it\'s own BMS ballancing circuit. I just need to limit external voltage to 12V. 4 modules for 48V. 8 modules for 96V.
sure you need the 12V limit? wouldn\'t it already be limited by the individual BMSs?

Yes, the BMS will cut-off over 12.6V, which would break the serial chain. I need to shunt it slightly below. This is only for charging.