| 摘要 |
The tube LR is normally powered from the mains supply 2, 3 via a reactor RE, and in the event of mains failure the tube is supplied from a battery powered high frequency oscillator OSC coupled via a winding L3 of a transformer TR1 to a winding L5 connected between a starter GL and a filament G1 of the tube. A capacitor C5 has a high impedance at mains frequency and a lower impedance at the oscillator frequency, the oscillator producing voltage transients so that the tube LR will start even with cold filaments G1, G2. An electromechanical or electronic relay turns the oscillator OSC off if the mains supply is present. Alternatively, the battery charging current may saturate a transformer (TR2), (Fig. 2), in oscillator OSC and also establish a voltage drop to hold a transistor (T1) in the oscillator OSC blocked when the mains supply is present. The transformer TR1 has a further winding L4 having the same number of turns as winding L5 so that when the oscillator is operating points 4 and 5 are at the same potential, whereby if the switch S is closed there is no potential drop across the mains terminals 2, 3 so that the oscillator will not be loaded by any other load connected across 2, 3. The oscillator OSC includes a circuit (D2, C4, T2) to turn it off if excess voltage is produced, eg. if the tube LR is disconnected. <IMAGE> |
