I am planning to use the LA4450 12W power amplifier to drive a piezo tweeter . the input to the amplifier is 23Khz square wave .
I am putting a 8 ohm 50 W resistor in parallel with the piezo tweeter to satisfy the amplifier load requirement.
will this setup work ?
I have attached the schematics as jpg file.
Reading on one of the audio boards, you may need an L-pad to properly handle the crossover concerns:
Best to ask such things in a forum that concentrates on knowing such particulars.
Typically, you don't have to do anything special... Just connect the Piezo to to amplifier.
The Piezo presents a capacitive load, and if that's a problem for this amplifier you can put a 4 - 8 Ohm resistor in series with the Piezo (or you can just add the resistor for "insurance"). Since there isn't much current through the Piezo (and the optional series resistor), a 1/4W or 1/2W resistor should be fine, and it should have little or no effect on the sound.
If you need the resistive load in parallel, something like 50 or 100 Ohms will probably work, and won't generate as much heat in the amplifier or resistor so you won't need such a high wattage resistor (Power = Voltage squared/Resistance).
You could probably get away with a much simpler amplifier, a transistor or mosfet would work easily, especially since its a square wave and not an actual analog signal .u
DVDdoug:
Typically, you don't have to do anything special... Just connect the Piezo to to amplifier.The Piezo presents a capacitive load, and if that's a problem for this amplifier you can put a 4 - 8 Ohm resistor in series with the Piezo (or you can just add the resistor for "insurance"). Since there isn't much current through the Piezo (and the optional series resistor), a 1/4W or 1/2W resistor should be fine, and it should have little or no effect on the sound.
If you need the resistive load in parallel, something like 50 or 100 Ohms will probably work, and won't generate as much heat in the amplifier or resistor so you won't need such a high wattage resistor (Power = Voltage squared/Resistance).
Definitely. Typically the treble/bass balance of loadspeakers with piezo tweeters is preset using a 30 ohm
potentiometer IIRC so even 30 ohm in series should be fine.
Piezo elements behave electrically like capacitors of a few nF.
A push-pull MOSFET driver using PNP-NPN BJTs with P and N channel MOSFETs should be able to drive this. There was a circuit in a thread here somewhere that was wired so that the two MOSFETs could never be ON at the same time.
I'm not going to look for hours to find it, so here's the general idea, no part values.
Edit: In case you looked at this before I corrected it, I had the P channel MOSFET upside down before. Corrected now.
Oh, and it isn't good for a piezo to have a DC level on it, so I'd use capacitive coupling to the piezo from that, with a resistor in parallel with the piezo. 100 ohms or so ought to do. It won't take much capacitance at 23kHz. 10uF at 23kHz is less than 1 ohm, be sure to use a low ESR/high frequency capacitor. Output>>10uF>>piezo and 100 ohms in parallel.
edit: Doh! Said series, meant parallel. The resistor is there to drain the 10uF capacitor.