Patent ID: 7034582

Claim:
An electronic circuit for supplying a capacitive load, such as an electroluminescent lamp, with an alternating high voltage from a lower voltage DC supply, the circuit comprising: an H-bridge having two parallel limbs, each limb having a first switch element in series with a second switching element and a node between the first and second switching elements, the capacitive load being connected, in use, between the respective nodes of the limbs; a converter powered by the low voltage DC supply and arranged to supply current to the H-bridge to charge the capacitive load to a voltage which is higher than the DC supply voltage; and a diode arranged in series between the converter and the H-bridge to prevent current flowing back from the charged capacitive load; and a capacitor provided downstream from the diode in parallel with the H-bridge, wherein the switching elements of the H-bridge are controlled alternately such that in a first condition the first switching elements of one limb and the second switching elements of the other limb conduct to supply current from the converter to the capacitive load in one direction, and in a second condition the other two switching elements of the limbs conduct to supply current from the converter to the capacitive load in the opposite direction, and the total capacitance provided in parallel with the H-bridge downstream of the diode is less than 50% of the capacitance of the capacitive load.