# adding an AC level (~1V 3KHz Sinus) on a DC level (30 to 100 V) line

Discussion in 'Electronic Design' started by jsmith, Apr 19, 2007.

1. ### jsmithGuest

hi

AC
level (~1V 3KHz Sinus) on a DC level (30 to 100 V) line.

2. ### D from BCGuest

Possibilities are:
1) A transistor common emitter amplifier
2) resistor network
3) transformer
4) RC circuit
5) summing amplifier

D from BC

3. ### John FieldsGuest

---
Assuming you mean "add" as in "algebraic summation":,
view in Courier:

..DC>---[L]--+----->DC+AC
.. |
.. [C]
.. |
..AC>--------+

4. ### petrus bitbyterGuest

What impedances are you talking about? Or you'd better tell something about
the application. Crucial for a usefull advice.

petrus bitbyter

piezo driver

6. ### EeyoreGuest

What impedance is the DC line ?

Graham

7. ### Michael A. TerrellGuest

Transformer couple the signal to the DC voltage. AKA "Modulation
transformer".

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

8. ### Don BoweyGuest

The most easy approach will be to use audio transformers having a split line
side. Put a non-polarized cap (1 or 2 mFd.) across the line-split leads of
the transformers (usually called the A and B leads). Put the dc voltage on
the A and B leads at one end of the line. Put the 3 kHz signal on the
primary of the transformer. At the other end of the line receive the dc on
the A and B leads, and the 3 kHz signal ar the transformer secondary.

Don

9. ### John PopelishGuest

It may be a megohm at DC, but I'll bet a dollar it is lower
at 3kHz. What is the capacitance of the piezo device?

10. ### jsmithGuest

I should measure capacitance of output long cabel and piezo, but it
will be less than 1uF

11. ### Phil AllisonGuest

"jsmith"

** Better not apply 100 volts DC direct to a piezo driver - it will blow
it up.

........ Phil

12. ### jsmithGuest

it is a piezo valve and its work range is up to 100V

13. ### Jan PanteltjeGuest

Small transformer secondary in series.

On its primary for example a 807 tube amp or a trans-sister.

14. ### petrus bitbyterGuest

Ah, a piezo valve ranging 30-100Vdc and a "impedance" of about 1M. That's an
important piece of information. But, all piezo elements I'm aware of have a
capacitance too. That capacitance needs to be charged/discharged when
switching on/off *and* it is much lower an impedance then 1M for a 3kHz
sine. The line will have some impedance (mostly capacitive) too, highly
depending on the type and length of the wiring used. On the other side of
the line you will have a 30-100Vdc power source which also has an impedance.
Depending on the type it might even be a shortcut for the 3kHz sine. (Some
47uF smoothing capacitor for instance). That 3kHz sine source will also have
some (output) impedance I guess. So I still can't give an appropriate answer

petrus bitbyter

15. ### John PopelishGuest

It had better be. If the total capacitance were 1 uF, the
impedance at 3 kHz would be 53 ohms. It will make a lot of
difference to the driver if the total capacitance is 100 pF
or 1000 pF.