(19)
(11) EP 0 034 401 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
02.09.1981 Bulletin 1981/35

(43) Date of publication A2:
26.08.1981 Bulletin 1981/34

(21) Application number: 81300106

(22) Date of filing: 12.01.1981
(84) Designated Contracting States:
AT CH DE GB IT LI NL

(30) Priority: 08.02.1980 GB 8004226

(71) Applicant: THORN EMI PLC
 ()

(72) Inventor:
  • Pegg, John Cyril
     ()

   


(54) Discharge lamp circuit


(57) Two (or more) gas discharge lamps (10, 110), each in series with a choke ballast (18,118) across A.C. supply terminals (16a, 16b) are started by a single starter circuit (70), the lamps being connected to the starter circuit through respective rectifying diodes (150, 152). The starter circuit (70) operates with rectified half-cycles of the A.C. supply, and resistors (154,156) balance the cathode heating currents between the two lamps. Preferably the starter circuit is rendered ineffective in a failed-lamp condition, and to this end (per DE-OS 28 16 415) it includes a thyristor (26) triggered by a control circuit which includes a capacitor (32) effective to increase the instantaneous applied voltage which is required totriggerthe thyristor with successive cycles of the applied voltage after initial switch-on of the circuit. A Zener diode (30) is in series with the capacitor (32).







Search report