Variable level periodic excitation circuit for a capacitive load

Claim 1

A predetermined frequency and adjustable level excitation circuit for a capacitive load having a first terminal connected to a first supply voltage, said predetermined frequency and adjustable level excitation circuit comprising: two switches connected in series between a second supply voltage and said first supply voltage, a junction of said two switches being coupled to a second terminal of the load, said two switches not being simultaneously closed; a control circuit for periodically controlling the operation of the two switches, wherein said control circuit comprises: (a) a periodic logic control signal input, (b) a first output controlling a first of the switches in phase with the periodic logic control signal, (c) a second output controlling the other switch in phase opposition to the periodic logic control signal, (d) a high impedance setting input for receiving a high impedance setting signal, (e) means responsive to said high impedance setting signal for causing one of the switches to be opened at least until a next state transition of the control signal, and (f) for each switch, a means for detecting current in the switch and opening the other of said switches if the current exceeds a predetermined value; and regulation means for triggering the control circuit to open said one of the switches when a voltage across the load reaches a predetermined value.

Claim 10

A method of exciting a capacitive load at a predetermined frequency and an adjustable excitation level, comprising the steps of: periodically closing a first switch connected to a supply voltage, and simultaneously opening a second switch connected to ground, to periodically couple the capacitive load to the supply voltage and charge the capacitive load; periodically opening the first switch and simultaneously closing the second, to periodically couple the capacitive load to the ground to discharge the capacitive load; detecting the voltage across the capacitive load; in response to the voltage detection, when the voltage across the capacitive load reaches a predetermined value during discharging of the capacitive load, opening said second switch to reduce discharging of said capacitive load; and adjusting the predetermined value to adjust the excitation level applied to the capacitive load.

Claim 11

A method of exciting a capacitive load at a predetermined frequency and an adjustable excitation level, comprising the steps of: periodically closing a first switch connected to a supply voltage, and simultaneously opening a second switch connected to ground, to periodically couple the capacitive load to the supply voltage and charge the capacitive load; periodically opening the first switch and simultaneously closing the second, to periodically couple the capacitive load to the ground to discharge the capacitive load; detecting the voltage across the capacitive load; in response to the voltage detection, when the voltage across the capacitive load reaches a predetermined value during discharging of the capacitive load, opening said second switch to reduce discharging of said capacitive load; and adjusting the predetermined value to adjust the excitation level applied to the capacitive load.