| 摘要 |
<p>1509665 Automatic current control PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 March 1976 [1 April 1975] 12469/76 Heading G3R [Also in Division H1] A discharge lamp with a ballastless supply has two main electrode systems. The current in the lamp is stabilized by an auxiliary circuit which varies the space charge potential drop near one or both the electrode systems in such a way as to oppose changes in the current. The auxiliary circuit switches a second current path to one of the electrode systems so as to change its effective area or temperature. As shown in Fig. 1, a low-pressure sodium vapour discharge lamp 1, nominally rated at 90 watts, has an anode 5 and pre-heatable cathode 7 connected to D.C. supply terminals 2, 3. A resistor 4 and current level detector 4a are connected in parallel between terminal 2 and anode 5. The lamp is initially ignited by high frequency, high voltage pulses, and the relatively low discharge current results in relay contacts 8, 10 being closed, so that a cylindrical auxiliary anode 6 is connected to D.C. terminal 2, and heating current is supplied to the cathode 7. If the lamp current exceeds a given upper level, the detector 4a opens the contacts 8, 10 and the current falls until a lower level is reached, when the contacts will again be closed. The current may thus be maintained between 0À85 and 0À95 amps. In an A.C. embodiment, Fig. 2 (not shown) a single pre-heatable electrode is provided at each end of the lamp. Heating current is supplied by transformers, each of which has a primary winding connected in series with a contact controlled by a current level detector. Another A.C. embodiment, Fig. 3 (not shown), uses non-pre-heatable electrodes surrounded by auxiliary cylindrical electrodes connected through controlled contacts. This arrangement produces increased current in an anode phase and decreased emission during a cathode phase, resulting in an overall current reduction when the auxiliary electrodes are in circuit.</p> |
