Driver circuit and method for controlling a capacitive element
The disclosure pertains to a method of charging or discharging a capacitive element, such as a piezoelectric crystal. The disclosure also pertains to a device that implements charging of a capacitive element according to said method. The device comprises a bipolar buck-boost converter, whereby a capacitive element can be charged with both positive and negative voltages. The discharge of the capacitive element is provided with energy recovery and feedback to the device's power supply.
1. A driver circuit configured to control a capacitive element, comprising
a switched boost regulator circuit and a switched buck regulator circuit;
a plurality of change-over switches;
a transformer comprising at least two windings on a primary side of the transformer and at least one winding on a secondary side of the transformer; and
a tank capacitor on the primary side of the transformer;
wherein the driver circuit has two operative states that are selectable by said change-over switches, wherein a first operative state is a boost regulator and a second operative state is a buck regulator.
2. The driver circuit for controlling a capacitive element according to claim 1 , wherein:
said change-over switches comprise at least four switches, of which a first primary switch and a second primary switch are arranged on a primary side of the transformer, and a first secondary switch and a second secondary switch are arranged on a secondary side of the transformer; and
said operative states are obtained by opening or closing said first primary switch and said second primary switch, as well as said first secondary switch and said second secondary switch, in different configurations.
3. The driver circuit according to claim 1 , wherein said operative states are obtained as follows: by opening the second primary switch and the first secondary switch and connecting the second secondary switch, a positive boost converter is provided which is controlled by the first primary switch for positive charging of the capacitive element; by opening the first primary switch and the second secondary switch and connecting the first secondary switch, a negative boost converter is provided, which is controlled by the second primary switch for negative charging of the capacitive element; by opening the first primary switch and the second primary switch and connecting the second secondary switch, a positive buck converter is provided, which is controlled by the first secondary switch for discharging of the capacitive element and feedback to a tank capacitor.
4. The driver circuit according to claim 2 , wherein the capacitive element is grounded on one side; both secondary switches are placed on one side of the transformer's secondary winding; and a diode is arranged between the second primary switch and the primary transformer winding.
5. The driver circuit according to claim 1 , in which the at least two windings of the transformer constitute as an energy storage element for the driver circuit.
6. The driver circuit according to claim 1 , wherein the driver circuit is configured to controllably supply positive voltages to the capacitive element by controlling the switching of the first primary switch and the second primary switch.
7. The driver circuit according to claim 1 , wherein the driver circuit is configured to controllably supply negative voltages to the capacitive element using the first primary switch or the second primary switch.
8. The driver circuit according to claim 7 , wherein a negative control range to the capacitive element is limited.
9. The driver circuit according to claim 1 , wherein the capacitive element is an actuator element.
10. The driver circuit according to claim 9 , wherein the actuator element is a piezoelectric actuator.
11. The driver circuit according to claim 1 , wherein at least one of the change-over switches is a MOS transistor.