TLV431 maximum ratings

[bitrex]

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf> as
an expample, shows a maximum Ika current rating of +/- 20mA does that
mean it can be run "forward biased" as well as reversed in the usual
Zener-like direction, and source current as well as sink it?

like if you wanted to press it into service in some situation as an
analog to a one-input low voltage op-amp with a large "offset voltage"
where its anode voltage might sometimes be higher than its cathode

 

[Jan Panteltje]

On a sunny day (Sun, 25 Aug 2019 14:15:06 -0400) it happened bitrex
<user@example.net> wrote in <LeA8F.29293$to5.1330@fx04.iad>:

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf> as
an expample, shows a maximum Ika current rating of +/- 20mA does that
mean it can be run "forward biased" as well as reversed in the usual
Zener-like direction, and source current as well as sink it?

like if you wanted to press it into service in some situation as an
analog to a one-input low voltage op-amp with a large "offset voltage"
where its anode voltage might sometimes be higher than its cathode

The standard way to make an uni-directional 'thing' bi-directional is to put it in a bridge rectifier.
But that will always add 2 diode drops each way:
_______________________________
| | |
--- --- |
\ / \ / |
--- --- |
| | +
|-- AC --| thing
| | -
--- --- |
\ / \ / |
--- --- |
|________|____________________|

'thing' can be any-thing here, your TL431, transistor, MOSFET, LED, etc et
c

 

On Sunday, 25 August 2019 19:38:01 UTC+1, Jan Panteltje wrote:

On a sunny day (Sun, 25 Aug 2019 14:15:06 -0400) it happened bitrex
user@example.net> wrote in <LeA8F.29293$to5.1330@fx04.iad>:

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf> as
an expample, shows a maximum Ika current rating of +/- 20mA does that
mean it can be run "forward biased" as well as reversed in the usual
Zener-like direction, and source current as well as sink it?

like if you wanted to press it into service in some situation as an
analog to a one-input low voltage op-amp with a large "offset voltage"
where its anode voltage might sometimes be higher than its cathode

The standard way to make an uni-directional 'thing' bi-directional is to put it in a bridge rectifier.
But that will always add 2 diode drops each way:
_______________________________
| | |
--- --- |
\ / \ / |
--- --- |
| | +
|-- AC --| thing
| | -
--- --- |
\ / \ / |
--- --- |
|________|____________________|

'thing' can be any-thing here, your TL431, transistor, MOSFET, LED, etc et
c

It won't be very accurate once it is inside a bridge rectifier.
However, the TI data sheet gives current/voltage curves and absolute
maximum ratings for positive and negative currents.

John

 

[Winfield Hill]

jrwalliker@gmail.com wrote...

On Sunday, 25 August 2019 19:38:01 UTC+1, Jan Panteltje wrote:
On a sunny day (Sun, 25 Aug 2019 14:15:06 -0400) it happened bitrex
user@example.net> wrote in <LeA8F.29293$to5.1330@fx04.iad>:

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf
as an expample, shows a maximum Ika current rating of +/- 20mA does
that mean it can be run "forward biased" as well as reversed in the
usual Zener-like direction, and source current as well as sink it?

Yes.

The standard way to make an uni-directional 'thing' bi-directional
is to put it in a bridge rectifier.

It won't be very accurate once it is inside a bridge rectifier.

Depending on your needs, it's often good to use two
parts in parallel. For example,a Schottky diode in
parallel with a TLV431, get Vzener in one direction,
and low V_Schottky in the other.

For another example, in my 1MHz 1.2kV amplifier(!),
I needed a 7.5 to 10V zener to protect the output
MOSFET, see Figure 4x.137 in the draft article:
https://www.dropbox.com/s/f4i2hy4j0e048oa/4x.23_HV-amplifier_Draft.pdf?dl=1

But xeners have 55pF of capacitance (compare to 40pF
for the MOSFET) so I used a low-capacitance D1213.
It has only 1pF, but wasn't able to handle 150mA in
the other direction. Solution, use a BAT54 Schottky,
only 5pF at 3V, but conducts 150mA with Vf = 700mV.


--
Thanks,
- Win

 

[Tim Williams]

"Jan Panteltje" <pNaOnStPeAlMtje@yahoo.com> wrote in message
news:qjuki4$vt8$1@dont-email.me...

The standard way to make an uni-directional 'thing' bi-directional is to
put it in a bridge rectifier.
But that will always add 2 diode drops each way:

Easy, wire two back-to-back like you'd make a TRIAC out of SCRs*, then it'll
clamp symmetrically.

(*Except this is a sometimes-repeated lie; to do that properly, you need
reverse diodes to clamp the gates in the reverse direction, and string up
the trigger (a phototriac or what have you) between the gates.)

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[whit3rd]

On Sunday, August 25, 2019 at 1:35:14 PM UTC-7, jrwal...@gmail.com wrote:

On Sunday, 25 August 2019 19:38:01 UTC+1, Jan Panteltje wrote:

The standard way to make an uni-directional 'thing' bi-directional is to put it in a bridge rectifier.
But that will always add 2 diode drops each way:
_______________________________
| | |
--- --- |
\ / \ / |
--- --- |
| | +
|-- AC --| thing
| | -
--- --- |
\ / \ / |
--- --- |
|________|____________________|

'thing' can be any-thing here, your TL431, transistor, MOSFET, LED, etc et
c

It won't be very accurate once it is inside a bridge rectifier.

The alternative is to use a two-terminal current source in the DC path of the
bridge, and feed the AC drive through that bridge, then to a resistor to GND.
While forward voltage isn't necessarily well-controlled, the reverse current leakage
of the bridge rectifier can be very small, while the current source (and its
resistor) are identical for both polarities of the drive (and output).

 

[Jan Panteltje]

On a sunny day (25 Aug 2019 14:25:26 -0700) it happened Winfield Hill
<winfieldhill@yahoo.com> wrote in <qjuuc601ghn@drn.newsguy.com>:

jrwalliker@gmail.com wrote...

On Sunday, 25 August 2019 19:38:01 UTC+1, Jan Panteltje wrote:
On a sunny day (Sun, 25 Aug 2019 14:15:06 -0400) it happened bitrex
user@example.net> wrote in <LeA8F.29293$to5.1330@fx04.iad>:

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf
as an expample, shows a maximum Ika current rating of +/- 20mA does
that mean it can be run "forward biased" as well as reversed in the
usual Zener-like direction, and source current as well as sink it?

Yes.

The standard way to make an uni-directional 'thing' bi-directional
is to put it in a bridge rectifier.

It won't be very accurate once it is inside a bridge rectifier.

Depending on your needs, it's often good to use two
parts in parallel. For example,a Schottky diode in
parallel with a TLV431, get Vzener in one direction,
and low V_Schottky in the other.

For another example, in my 1MHz 1.2kV amplifier(!),
I needed a 7.5 to 10V zener to protect the output
MOSFET, see Figure 4x.137 in the draft article:
https://www.dropbox.com/s/f4i2hy4j0e048oa/4x.23_HV-amplifier_Draft.pdf?dl=1

But xeners have 55pF of capacitance (compare to 40pF
for the MOSFET) so I used a low-capacitance D1213.
It has only 1pF, but wasn't able to handle 150mA in
the other direction. Solution, use a BAT54 Schottky,
only 5pF at 3V, but conducts 150mA with Vf = 700mV.

I am glad to see somebody use a trimmer and trimpot
Component tolerances make it hard to select just the right C,
so trimmers are great here.
Especially when it is just a one time project.

 

[Jan Panteltje]

On a sunny day (Sun, 25 Aug 2019 19:54:40 -0500) it happened "Tim Williams"
<tiwill@seventransistorlabs.com> wrote in <qjvak6$i4u$1@dont-email.me>:

"Jan Panteltje" <pNaOnStPeAlMtje@yahoo.com> wrote in message
news:qjuki4$vt8$1@dont-email.me...

The standard way to make an uni-directional 'thing' bi-directional is to
put it in a bridge rectifier.
But that will always add 2 diode drops each way:

Easy, wire two back-to-back like you'd make a TRIAC out of SCRs*, then it'll
clamp symmetrically.

(*Except this is a sometimes-repeated lie; to do that properly, you need
reverse diodes to clamp the gates in the reverse direction, and string up
the trigger (a phototriac or what have you) between the gates.)

Tim

Yes, then only 1 diode drop.
I see I reversed + and - in the ASCII diagram (oops).

 

[piglet]

On 26/08/2019 08:07, piglet wrote:

On 25/08/2019 19:15, bitrex wrote:
The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf
as an expample, shows a maximum Ika current rating of +/- 20mA does
that mean it can be run "forward biased" as well as reversed in the
usual Zener-like direction, and source current as well as sink it?

like if you wanted to press it into service in some situation as an
analog to a one-input low voltage op-amp with a large "offset voltage"
where its anode voltage might sometimes be higher than its cathode

Yes. Look at the graphs on top of page 5.

When forward biased you get the normal si diode behavior of the chip's
substrate-internal node diodes and a rather sloppy looking knee. When
reverse biased you the designed for functionality and a sharp knee.

Either way 20mA isn't going to create enough heat to damage.

piglet

To add to my previous :>

I meant 20mA forward wouldn't create too much heat, 20mA reverse (as
zener mode) might depending on programmed shunt voltage.

piglet

 

[piglet]

On 25/08/2019 19:15, bitrex wrote:

The TLV431 spec <https://www.diodes.com/assets/Datasheets/TLV431.pdf> as
an expample, shows a maximum Ika current rating of +/- 20mA does that
mean it can be run "forward biased" as well as reversed in the usual
Zener-like direction, and source current as well as sink it?

like if you wanted to press it into service in some situation as an
analog to a one-input low voltage op-amp with a large "offset voltage"
where its anode voltage might sometimes be higher than its cathode

Yes. Look at the graphs on top of page 5.

When forward biased you get the normal si diode behavior of the chip's
substrate-internal node diodes and a rather sloppy looking knee. When
reverse biased you the designed for functionality and a sharp knee.

Either way 20mA isn't going to create enough heat to damage.

piglet