US 2004/0169547 A1Published application

Electronic circuits

AssigneePelikon Limited

InventorsPhillip Matthew Jones, Christopher James Newton Fryer

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Abstract

A high voltage AC power supply circuit for a capacitive load CL, such as an electroluminescent lamp, includes a low voltage DC supply, an inductor L and a FET S in series. The FET S can be pulsed so that the inductor L generates a voltage to charge the capacitive load CL via an H-bridge H, which is in parallel with the FET S. A diode D prevents current discharging from the capacitive load CL while the FET S is closed. The total capacitance downstream of the diode D and in parallel with the capacitive load CL is less than the capacitive load CL, so that when the polarity of the H-bridge is reversed, the voltage across the H-bridge collapses to earth and the capacitive load CL is discharged via the low voltage DC supply. The circuits which a employ a large smoothing capacitor in parallel with the H-bridge.

Claims4

Dependent claims

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 switching 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, 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 the capacitance of the capacitive load.

3 more elements

Dependencies are inferred from the claim text.