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Paul Jackson
Guest
Sun Jan 22, 2012 1:05 pm
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
Paul Jackson
Bill Sloman
Guest
Sun Jan 22, 2012 2:55 pm
On Jan 22, 1:05 pm, pauljack...@thermalux.com (Paul Jackson) wrote:
Quote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
The only kind of transformer that has a hope of offering that kind of
bandwidth is a transmission line transformer.
Impedance goes as the square of the step-ratio, so you are asking for
step-up ratio of 4.47, which is difficult to realise in a transmission-
line transformer - impossible in a low-order transformer
http://home.earthlink.net/~christrask/TraskTLTTutorial.pdf
If you can live with a more accessible impedance transformation ratio,
a transmission line transformer could be perfectly practicable, and
possibly even practical. Some off-the-shelf small pulse transformers
are bifilar wound, which makes them transmission line transformers,
but the characteristic impedance of a twisted pair is around 110R,
which won't suit your set-up.
It should be easy enough to wind something with miniature coax on a
biggish ring core or two.
--
Bill Sloman, Nijmegen
amdx
Guest
Sun Jan 22, 2012 3:01 pm
On 1/22/2012 6:05 AM, Paul Jackson wrote:
Quote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
Paul Jackson
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
Just my thoughts,
Mikek
Jamie
Guest
Sun Jan 22, 2012 4:27 pm
Paul Jackson wrote:
Quote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
Paul Jackson
Being a function generator as the source, I think you better start
thinking of HV amplifiers instead. A DC coupled one to be exact.
2 Mhz isn't much of a problem for non reactive type amps.
Jamie
Joerg
Guest
Sun Jan 22, 2012 5:29 pm
amdx wrote:
Quote:
On 1/22/2012 6:05 AM, Paul Jackson wrote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
As Mike hinted, the math doesn't compute here. 50ohms into 1k is not a
10x voltage step-up.
Quote:
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
Paul Jackson
The transformer has to be of multi-filar winding technique in order to
provide the required bandwidth. Not sure if two of these would work:
http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/Data%20Sheets/BUS_Elx_PM_4301_VERSA_PAC.pdf
One winding, both transformers parallel, for the input. Five plus five
in series on the output side. Should result in 10:1. Three of them could
give 15:1. I've never tried to use them for that but have used them in
switch-mode converters and they behaved very nicely.
You could also check Mini-Ciruits. Rule of thumb: The cumulative
inductance on each side should represent a Z of four times the presented
impedance. It's ok if the "stated impeance" in the datasheet is lower,
then the transformer just has to be listed for much lower frequencies
than 200kHz.
Quote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
--
Regards, Joerg
http://www.analogconsultants.com/
amdx
Guest
Sun Jan 22, 2012 5:56 pm
Quote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
Joerg
Guest
Sun Jan 22, 2012 6:41 pm
amdx wrote:
Quote:
If you want 20 ma at 100 volts, I don't think you generator will
supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
Essentially you can do this using a PNP/NPN follower pair driven by an
opamp, and then a resistor from bases to emitters for the crossover
region. Just make sure the transistors are sufficiently SOA rated. One
of those situation where the old American saying holds, if the
transistors ain't big enough get bigger ones :-)
Much cheaper than trying to obtain some extinct buffer.
--
Regards, Joerg
http://www.analogconsultants.com/
John Larkin
Guest
Sun Jan 22, 2012 6:57 pm
On Sun, 22 Jan 2012 04:55:02 -0800 (PST), Bill Sloman
<bill.sloman_at_ieee.org> wrote:
Quote:
On Jan 22, 1:05 pm, pauljack...@thermalux.com (Paul Jackson) wrote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
The only kind of transformer that has a hope of offering that kind of
bandwidth is a transmission line transformer.
At 2 GHz, yes. But 2 MHz isn't especially fast.
John
John Larkin
Guest
Sun Jan 22, 2012 6:58 pm
On Sun, 22 Jan 2012 08:01:45 -0600, amdx <amdx_at_knologynotthis.net>
wrote:
Quote:
On 1/22/2012 6:05 AM, Paul Jackson wrote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
Paul Jackson
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
200 mA, short-circuit current.
John
Quote:
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
Just my thoughts,
Mikek
John Fields
Guest
Sun Jan 22, 2012 7:11 pm
On Sun, 22 Jan 2012 12:05:59 GMT, pauljackson_at_thermalux.com (Paul
Jackson) wrote:
Quote:
I am looking for an impedance matching transformer that will convert
the 50 Ohm output of my function generator and to a 1K Ohm resistive
load.
That provides a 20x step-up as well, so with losses 10V yields maybe
100V.
---
Voltage (turns) ratio goes as the square root of the impedance ratio,
so instead of a step-up of 20, you'll only get a step-up of 4.47.
That means that if you want 100 volts out you'll need to input about
24 VAC.
---
Quote:
Frequency range is anywhere between 200KHz to 2MHz. Required current,
up to 20mA.
---
If you want to push 20mA through a 1000 ohm load, then the
transformer's output voltage needs to be 20V, not 100.
then, since the step-up is 4.47, the input to the transformer would
need to be 4.47V and the current from the generator would need to be
89.5mA
Quote:
I would definitely prefer a ready-made transformer. Does anyone know
under what application heading one might be found?
---
Wide-band transformers?
BTW, Arnold Engineering had a nice little DOS transformer winding
program called: "MAT 4.1" and they still make reference to it here:
http://www.arnoldmagnetics.com/Search.aspx?searchtext=MAT%204.1&folderid=0&searchfor=all&orderby=id&orderdirection=ascending
Their web site is at:
http://www.arnoldmagnetics.com/
--
JF
Phil Hobbs
Guest
Sun Jan 22, 2012 10:13 pm
amdx wrote:
Quote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
I once had a Wavetek generator die on me when I connected a 50 ohm
termination to its "50 ohm" output. Fried an output transistor.
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Jamie
Guest
Sun Jan 22, 2012 10:29 pm
Phil Hobbs wrote:
Quote:
amdx wrote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
I once had a Wavetek generator die on me when I connected a 50 ohm
termination to its "50 ohm" output. Fried an output transistor.
Cheers
Phil Hobbs
So I assume the warranty must of expired?
Jamie
John Larkin
Guest
Sun Jan 22, 2012 10:46 pm
On Sun, 22 Jan 2012 16:13:16 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:
Quote:
amdx wrote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
I once had a Wavetek generator die on me when I connected a 50 ohm
termination to its "50 ohm" output. Fried an output transistor.
Cheers
Phil Hobbs
The old Waveteks blew up a lot. Fortunately, they were pretty
repairable.
I have a couple of these. Handy gadgets.
https://www.bkprecision.com/products/signal-generators/4003A-4-mhz-sweep-function-generator-with-5-digit-red-led.html
John
Tim Williams
Guest
Sun Jan 22, 2012 10:47 pm
"Phil Hobbs" <pcdhSpamMeSenseless_at_electrooptical.net> wrote in message
news:4F1C7BEC.E3925D87_at_electrooptical.net...
Quote:
I once had a Wavetek generator die on me when I connected a 50 ohm
termination to its "50 ohm" output. Fried an output transistor.
Tell me about it.. I fried mine driving a B-E junction... same idea. How
can something not be made to drive the rated load? Beats me. They used a
weird output stage too, it has an op-amp around it for DC; the fast stuff
is AC coupled, a peculiar complementary buffer.
I replaced the transistors with some TO-126 parts I had on hand, not
nearly as much fT so it hardly does 5MHz from the output proper; I tapped
a jack off a testpoint so I can still use a full-bandwidth signal, though
it doesn't have attenuation or offset on it.
Tim
--
Deep Friar: a very philosophical monk.
Website:
http://webpages.charter.net/dawill/tmoranwms
Phil Hobbs
Guest
Sun Jan 22, 2012 10:47 pm
Jamie wrote:
Quote:
Phil Hobbs wrote:
amdx wrote:
If you want 20 ma at 100 volts, I don't think you generator will supply
the power you need.
If the generator supplies 10V into 50 ohms that is 20 ma.
With a 1 to 10 voltage step up you generator would need to supply
200 ma.
If Paul's generator is too weak to drive loads under 10ohms then he'd
need to find or build a staunch buffer.
I'll add to that, some signal generators have an amplifier with a very
low output impedance and a series 50 ohm resistor. If you have this type
and want to load it at 10 ohms, make sure the 50 ohm resistor is rated
for the wattage needed, especially if you expect continuous use. I have
seen blacked 50 ohm output resistors. I won't name any HP names.
Mikek
I once had a Wavetek generator die on me when I connected a 50 ohm
termination to its "50 ohm" output. Fried an output transistor.
Cheers
Phil Hobbs
So I assume the warranty must of expired?
Jamie
I don't recall. I needed the generator, so I opened it up and put in a
beefier transistor. It slowed down the edges a bit, but didn't blow
up.
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
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
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