C-multipliers and simple circuit to measure npn beta.

[Winfield Hill]

AntonF wrote...

On Saturday, May 25, 2019 at 3:33:21 PM UTC+3, Winfield Hill wrote:
I'd use a high-beta, low r'bb part like
an NPN ZTX618 or FMMT618. Run it at 20mA
with a 33-ohm PNP base-emitter resistor,
and a PNP power transistor of your choice.

Thank you, Win!
Did you mean something like this?
https://drive.google.com/open?id=1xbp9A59eMNZbZcFTIS5PwegBfwh7ubsB
It gives <-56dB up to 1MHz:
https://drive.google.com/open?id=10QwlsbBWgaJkC6s4F61njGKoCUKS0Za6
Is it possible to make it work at higher frequencies?

I thought the idea was to go to higher currents.
Reducing the 33-ohms might help. Do you have a
lot of high-freq noise to deal with? High-freq
noise is easily dealt with, using R L and C parts
and ferrite beads.


--
Thanks,
- Win

 

[George Herold]

On Friday, May 24, 2019 at 11:49:50 AM UTC-4, George Herold wrote:

On Thursday, May 23, 2019 at 5:35:41 PM UTC-4, Phil Hobbs wrote:
On 5/23/19 4:30 PM, George Herold wrote:
On Thursday, May 23, 2019 at 4:01:25 PM UTC-4, George Herold wrote:
Hi all, We make this low noise power supply. (~ +/- 12V up to ~100mA)
A voltage regulator followed by a cap-multiplier. The first bunch I made had an output noise of ~>1.5 nV/rtHz.
So I wrote a spec of 2nV/rtHz. Then a new batch of transistors (2N4401)
and the noise was worse... ~3.5 nV/rtHz. I had a bag of the older npn's
and just put those in. Now I've run low and ordered a bunch of them (200)
from several different suppliers. These are in now and some of them
test just fine. (transistors from the same batch seem to be very similar)
And I was wondering if the difference in noise is related to a difference in
Beta. (Can I do a DC measurement and ID the good ones?) So I'm looking for
a simple circuit to measure transistor beta. This looks like a good
start,
https://electronicsarea.com/circuit-measuring-beta-of-transistor/

The noise is highest at the highest currents, so I'd like the current source
to ~100 mA. I guess that's simple enough.

Other ideas? Thoughts? Thanks.

George H.

Something like this?
https://www.dropbox.com/s/ozao49go305ik8q/Beta.JPG?dl=0

GH


You also have to worry about the extrinsic base resistance, Rbb'. I use
a lot of 2SD2704K's for cap multipliers of about that power level, but
they only come in SOT23. AOE3 lists a bunch of low noise BJTs on P.
501. You might look at the ZXT851, which is a fave of theirs.

OK I'm going to order some of the ZXT851/ 951 (not a lot of stock at DK)
and the ZXT450/550, I'll report back with results.

The ZTX450 are nice, output noise ~1.5 nV/rtHz. For what ever reason the
ZTX851's filtered less noise than the 2n4401's.

George H.

Thanks everyone.
George H.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 5/30/19 10:14 AM, George Herold wrote:

On Friday, May 24, 2019 at 11:49:50 AM UTC-4, George Herold wrote:
On Thursday, May 23, 2019 at 5:35:41 PM UTC-4, Phil Hobbs wrote:
On 5/23/19 4:30 PM, George Herold wrote:
On Thursday, May 23, 2019 at 4:01:25 PM UTC-4, George Herold wrote:
Hi all, We make this low noise power supply. (~ +/- 12V up to ~100mA)
A voltage regulator followed by a cap-multiplier. The first bunch I made had an output noise of ~>1.5 nV/rtHz.
So I wrote a spec of 2nV/rtHz. Then a new batch of transistors (2N4401)
and the noise was worse... ~3.5 nV/rtHz. I had a bag of the older npn's
and just put those in. Now I've run low and ordered a bunch of them (200)
from several different suppliers. These are in now and some of them
test just fine. (transistors from the same batch seem to be very similar)
And I was wondering if the difference in noise is related to a difference in
Beta. (Can I do a DC measurement and ID the good ones?) So I'm looking for
a simple circuit to measure transistor beta. This looks like a good
start,
https://electronicsarea.com/circuit-measuring-beta-of-transistor/

The noise is highest at the highest currents, so I'd like the current source
to ~100 mA. I guess that's simple enough.

Other ideas? Thoughts? Thanks.

George H.

Something like this?
https://www.dropbox.com/s/ozao49go305ik8q/Beta.JPG?dl=0

GH


You also have to worry about the extrinsic base resistance, Rbb'. I use
a lot of 2SD2704K's for cap multipliers of about that power level, but
they only come in SOT23. AOE3 lists a bunch of low noise BJTs on P.
501. You might look at the ZXT851, which is a fave of theirs.

OK I'm going to order some of the ZXT851/ 951 (not a lot of stock at DK)
and the ZXT450/550, I'll report back with results.


The ZTX450 are nice, output noise ~1.5 nV/rtHz. For what ever reason the
ZTX851's filtered less noise than the 2n4401's.

Maybe higher C-B capacitance. I often use an RC in the collector as
well, like 1 ohm and 10 uF. With a low-V_CEsat transistor, that doesn't
cost any dropout voltage.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[AntonF]

Does ZTX851 have SMD version (SOT-23 prefered)?

 

[George Herold]

On Thursday, May 30, 2019 at 4:39:23 PM UTC-4, Phil Hobbs wrote:

On 5/30/19 10:14 AM, George Herold wrote:
On Friday, May 24, 2019 at 11:49:50 AM UTC-4, George Herold wrote:
On Thursday, May 23, 2019 at 5:35:41 PM UTC-4, Phil Hobbs wrote:
On 5/23/19 4:30 PM, George Herold wrote:
On Thursday, May 23, 2019 at 4:01:25 PM UTC-4, George Herold wrote:
Hi all, We make this low noise power supply. (~ +/- 12V up to ~100mA)
A voltage regulator followed by a cap-multiplier. The first bunch I made had an output noise of ~>1.5 nV/rtHz.
So I wrote a spec of 2nV/rtHz. Then a new batch of transistors (2N4401)
and the noise was worse... ~3.5 nV/rtHz. I had a bag of the older npn's
and just put those in. Now I've run low and ordered a bunch of them (200)
from several different suppliers. These are in now and some of them
test just fine. (transistors from the same batch seem to be very similar)
And I was wondering if the difference in noise is related to a difference in
Beta. (Can I do a DC measurement and ID the good ones?) So I'm looking for
a simple circuit to measure transistor beta. This looks like a good
start,
https://electronicsarea.com/circuit-measuring-beta-of-transistor/

The noise is highest at the highest currents, so I'd like the current source
to ~100 mA. I guess that's simple enough.

Other ideas? Thoughts? Thanks.

George H.

Something like this?
https://www.dropbox.com/s/ozao49go305ik8q/Beta.JPG?dl=0

GH


You also have to worry about the extrinsic base resistance, Rbb'. I use
a lot of 2SD2704K's for cap multipliers of about that power level, but
they only come in SOT23. AOE3 lists a bunch of low noise BJTs on P.
501. You might look at the ZXT851, which is a fave of theirs.

OK I'm going to order some of the ZXT851/ 951 (not a lot of stock at DK)
and the ZXT450/550, I'll report back with results.


The ZTX450 are nice, output noise ~1.5 nV/rtHz. For what ever reason the
ZTX851's filtered less noise than the 2n4401's.


Maybe higher C-B capacitance. I often use an RC in the collector as
well, like 1 ohm and 10 uF. With a low-V_CEsat transistor, that doesn't
cost any dropout voltage.

Cheers

Phil Hobbs

Driving home I was thinking I should describe the circuit.
From the voltage ref. I've got two series 500 ohm R's
and two 100 uF Al. electros to gnd. Between the base
and the last C/R junction I've got ten ohms and a ferrite bead,
Lower r_bb' can only help down to the ten ohm level.
(bead and R_b added to stop oscillations.)

George H.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 5/30/19 8:14 PM, George Herold wrote:

On Thursday, May 30, 2019 at 4:39:23 PM UTC-4, Phil Hobbs wrote:
On 5/30/19 10:14 AM, George Herold wrote:
On Friday, May 24, 2019 at 11:49:50 AM UTC-4, George Herold wrote:
On Thursday, May 23, 2019 at 5:35:41 PM UTC-4, Phil Hobbs wrote:
On 5/23/19 4:30 PM, George Herold wrote:
On Thursday, May 23, 2019 at 4:01:25 PM UTC-4, George Herold wrote:
Hi all, We make this low noise power supply. (~ +/- 12V up to ~100mA)
A voltage regulator followed by a cap-multiplier. The first bunch I made had an output noise of ~>1.5 nV/rtHz.
So I wrote a spec of 2nV/rtHz. Then a new batch of transistors (2N4401)
and the noise was worse... ~3.5 nV/rtHz. I had a bag of the older npn's
and just put those in. Now I've run low and ordered a bunch of them (200)
from several different suppliers. These are in now and some of them
test just fine. (transistors from the same batch seem to be very similar)
And I was wondering if the difference in noise is related to a difference in
Beta. (Can I do a DC measurement and ID the good ones?) So I'm looking for
a simple circuit to measure transistor beta. This looks like a good
start,
https://electronicsarea.com/circuit-measuring-beta-of-transistor/

The noise is highest at the highest currents, so I'd like the current source
to ~100 mA. I guess that's simple enough.

Other ideas? Thoughts? Thanks.

George H.

Something like this?
https://www.dropbox.com/s/ozao49go305ik8q/Beta.JPG?dl=0

GH


You also have to worry about the extrinsic base resistance, Rbb'. I use
a lot of 2SD2704K's for cap multipliers of about that power level, but
they only come in SOT23. AOE3 lists a bunch of low noise BJTs on P.
501. You might look at the ZXT851, which is a fave of theirs.

OK I'm going to order some of the ZXT851/ 951 (not a lot of stock at DK)
and the ZXT450/550, I'll report back with results.


The ZTX450 are nice, output noise ~1.5 nV/rtHz. For what ever reason the
ZTX851's filtered less noise than the 2n4401's.


Maybe higher C-B capacitance. I often use an RC in the collector as
well, like 1 ohm and 10 uF. With a low-V_CEsat transistor, that doesn't
cost any dropout voltage.

Cheers

Phil Hobbs


Driving home I was thinking I should describe the circuit.
From the voltage ref. I've got two series 500 ohm R's
and two 100 uF Al. electros to gnd. Between the base
and the last C/R junction I've got ten ohms and a ferrite bead,
Lower r_bb' can only help down to the ten ohm level.
(bead and R_b added to stop oscillations.)

I use that approach too, though I put in a single 0603 in the base,
which starts out as a jumper and gets hacked if necessary. (I've only
seen one or maybe two cap multipliers oscillate.) The electros probably
have tens to hundreds of milliohms ESR, so a 1-uF MLCC can help.

A bead to prevent oscillation plus another big cap on the emitter will
get rid of the residual noise pretty well.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[AntonF]

On Tuesday, May 28, 2019 at 11:56:28 PM UTC+3, Winfield Hill wrote:

I thought the idea was to go to higher currents.
Reducing the 33-ohms might help. Do you have a
lot of high-freq noise to deal with? High-freq
noise is easily dealt with, using R L and C parts
and ferrite beads.

Yes, it is not even ripple problem. We have very thin spikes from Traco Power's isolated dc-dc converter. And those spikes are really wideband and difficult to suppress. They leaks through Murata BLMs and capacitors somehow.... I'm considering to replace Traco with isolated push-pull converter built around LT1683 (which is slew rate controlled). But it costs a lot of PCB space and some time to understand adum3190 compensation...

I simulated cap mult with single FMMT620 transistor (without PNP) at 500mA load in LTSpice. Behaves very good. Especially in Phil's "5-Pole 2-Stage Capacitance Multiplier" setup. May be FMMT620's model is too optimistic. Have to test on bench.