# Ultrasonic generator - a couple of questions

Here is the ultrasonic generator circuit I'm trying to understand:

It is powered by USB and it produces 100V at 100kHz on the piezoelectric speaker BQ1.

Two mutually inverted PWM signals go from the micro-controller to the transformer T1.

Questions:

1) Is this the simplest, cheapest circuit of the ultrasonic generator with similar output?

2) Why do we need C1-C2 capacitors?

3) Center tapped transformer T1 is used here, but is it ok to replace T1 with a transformer without center tap and to use single PWM signal as input?

Edit:

4) Why C1?

5) If I'm powering the circuit from a separate power supply which is able to deliver several amps do I need R1, C1, C2?

• R2/R1=10 and R1 limits current. T1 must be symmetrical centre tap to eliminate DC flux and N=step-up >20, Caps provide low ESR for low ripple V on supply due to high ripple current. Mar 28 '17 at 21:05

Yes, this is the simplest way to do it.

C1 and C2 are needed for supplying current to the transformer as it switches, as its supply is decoupled from the main +5V by a 100Ω resistor. This is done to avoid ripple coming from the transducer circuit leak into the main +5V.

The center-tapped transformer is needed to keep it simple, as you cannot deliver a DC component to the transformer core. Which you would if you used only one transistor. If you don't have a center-tapped transformer, you need a H-Bridge of four transistors, and correct triggering.