On Thu, 16 Nov 2000, averroes wrote:
> Hi,
>
> I had a question about ultrasonic (polaroid)sensors.
> Because they behave like a capacitive load it's
> difficult to make an amplifier for the signals you
> send to these sensors. The signals must be of a
> frequency between 45kHz and 55KHz, so I have to make
> an amplifier that can produce voltages in these
> frequency area, and the voltages have to reach
> voltages of -150 to 150V, perhaps more. These voltages
> make the sensor able to vibrate and send ultasonic
> signals.
> . . .

> Sincerely, ABDALLAH, student design-engineer


Several companies make integrated or hybrid high-voltage
operational amplifiers. For example:
http://www.apexmicrotech.com/products/pages/op_amps/pa44.html

If you select a high-voltage amplifier that will drive up to
+-150V, you also have to check if it is capable of
delivering enough current to charge-discharge the sensor
capacitance at the driving frequency.

In your example, assuming sinosoidal drive of +-150V @
55kHz, the requisite peak-to-peak load current would be
+-50mA per 1nF of load capacitance. The load current is
proportional to capacitance.

You will probably have to mount the amplifier on a heat
sink, and keep one hand in your pocket while working on the
circuit...


Dr. Mike Mladejovsky,
Univ of Utah