# Forum: Analog Circuits DDS output - U channel 100 V, I channel 1 A

 Author: Pavel (Guest) Posted on: 2013-01-02 20:07

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Hi!
I chose AD9850 for my project (sine generator, with frequency 40 to 60
Hz).
What type of output has this dds? (U or I)

I have to make two different channels:
1) Output1 has tunable (with computer) voltage within the limits of 0 -
100 V (current is not important).
2) Output2 has tunable (with computer) current within the limits of 0 -
1 A (voltage is not important).
(for simulation a secondary circuit of the voltage/current transformer)

I have question, how I can become such parameters at output?
I decided to use dds -> active_lowpass_filter -> digital_potentiometer
-> amplifier(e.g. TDA2030) -> transformer (for voltage conversion and
electrical isolation). may be needed to shift the voltage with op amp.

Sine wave must be sufficiently clean with precisely controlled from a
computer amplitude (deviation within 0.1% are allowed)

What do you think about this?

 Author: Raimund Rabe (corvuscorax) Posted on: 2013-01-03 10:43

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A quick view into the datasheet would have brought some light onto that
question and "current output" would be the correct answer.

1): Look for opamp schematics at i.e. Analog Devices, Linear Technology,
Texas Instruments, ..., for applications (so called 'application notes')
that cover designs with opamps extending there output voltage swing by
using additional external circuitry (by using bipolar or MOSFET
transistors, ...).
0...100V means exactly what? 100Vpp, 100Vp, 100Veff, ... ???
2): just like above mentioned - the application notes are (usually)

If an electrical isolation is necessary you might think about to shift
it to the (digital input) of the DDS chip. Otherwise I doubt that you
are able to control an amplitude deviation within the limits of 0.1%
when using an output transformer.

 Author: Pavel (Guest) Posted on: 2013-01-03 12:19

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Thank you for answer, Raimund Rabe!

thanks, but I have not found anything in application notes on my topic.
0...100V means tunable (with computer) voltage within 0 to 200 Vp-p
(peaks -100_100).

I have to try to do this (with output transformer).

 Author: Raimund Rabe (corvuscorax) Posted on: 2013-01-03 16:14

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Okay. So please have a look for instance here:
http://www.analog.com/library/analogDialogue/archi...
Chapter 6 (and in particular Figure 6-174) might be interesting to look
at.
Somewhere I found once an app note like this ready designed for rail
voltages of ±125V which result in a maximum output voltage swing of
±120V at a max. current of 25mA (as far as I remember).
Nevertheless with some component (and value) changes you can fulfill
this task by using this schematic easily.
With Google you might be able to find such things if you know what to
look for, of course. And that would i.e. "voltage boosted opamp".
May I introduce you to sites like this:
http://how-to.wikia.com/wiki/How_to_boost_the_outp...
or even this
www.ti.com/lit/an/snoa600a/snoa600a.pdf

You might figure out that some of the schematics you found are almost
identical.
Have fun.

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