| 摘要 |
The ballast includes a fused (43) mains input (A',A") which includes filters (38,39,40,41) to minimise waveform distortion and an overcurrent limiter (42) for switch-in surges. The rectified supply (33) is applied across two bridge-connected transistors (5,7). Oscillation begins when their associated capacitors (13,15), charging through resistances (19,16,14), reach a threshold voltage, and is maintained as the transistors are cyclically switched by the secondaries (17b,17c) of a control transformer (17). A low-value capacitor (4) eliminates commutation spikes.The HF oscillator output is delivered, via an inductance (27), to the main transformer (28), which has two secondaries (28b, 28c) supplying the lamp filaments (B',B";C',C"), and a third (28d) energising a thyristor shut-down circuit (22,23,24,30), effective on lamp failure. A further rectifier bridge (35,36), closing the HF transformer primary circuit (31,32), provides power factor compensation.
|
