Lighting controllers

1. An electronic ballast for a gas discharge lamp, comprising:

a first dc-to-dc switching power supply stage having a dc voltage input, a dc voltage output, and a storage capacitor coupled to said dc voltage output;

a second dc-to-ac switching power supply stage having a dc voltage input coupled to said dc voltage output of said dc-to-dc switching power supply stage and an ac voltage output for driving said lamp;

wherein said electronic ballast includes a single controlled active switch shared between said dc-to-dc switching power supply stage and said dc-to-ac switching power supply stage; and

wherein said first dc-to-dc switching power supply stage includes a coupling capacitor coupled in series between said dc voltage input of said dc-to-dc switching power supply stage and said storage capacitor, said coupling capacitor having a capacitance of less than half a capacitance of said storage capacitor.

2. An electronic ballast as claimed in claim 1 wherein said coupling capacitor has a capacitance of less than a tenth of a capacitance of said storage capacitor.

3. An electronic ballast as claimed in claim 1 wherein said controllable active switch is configured for control by a voltage referenced to a ground of said dc voltage input of said dc-to-dc switching power supply stage.

4. An electronic ballast as claimed in claim 1 wherein said controllable active switch comprises a transistor with one terminal substantially at a ground potential of said dc voltage input of said dc-to-dc switching power supply stage.

5. A mains power fluorescent lamp driver comprising the electronic ballast of claim 1 , and including a rectifier circuit to provide a dc voltage for said dc-to-dc switching power supply stage from a rectified mains voltage.

6. A lighting controller for a gas discharge lamp, the lighting controller comprising:

a mains power supply input;

a mains rectifier circuit coupled to said mains power supply input and having a rectified mains voltage output;

a first inductor having an input side coupled to said rectified mains voltage output and an output side;

a controllable switch coupled in parallel between said output side of said first inductor and a ground connection of said rectified mains voltage output;

a coupling capacitor having an input side coupled to said output side of said first inductor and having an output side;

a second inductor coupled in parallel between said output side of said coupling capacitor and said ground connection;

a first rectifier coupled between said output side of said coupling capacitor and a storage capacitor to provide a dc voltage supply; and

a pair of inductive elements each having a first connection coupled to said dc voltage supply and each having a second connection coupled to a respective rectifier; and an ac output circuit to drive said lamp coupled to said pair of inductive elements; and

wherein a first of said respective rectifiers is coupled to said ground connection and a second of said respective rectifiers is coupled to said controllable switch.

7. A lighting controller as claimed in claim 6 wherein said first of said respective rectifiers is coupled to said ground connection via a second controllable switch.

8. A lighting controller as claimed in claim 6 further comprising a second rectifier coupled between said controllable switch and said coupling capacitor.

9. A light controller as claimed in claim 6 further comprising a controller coupled to said controllable switch and configured to provide a variable frequency oscillatory drive signal to control said controllable switch.

10. A light controller as claimed in claim 6 wherein said controllable switch comprises a bipolar transistor.