GB1529052A - Circuit arrangement for obtaining a sawtooth current in a coil - Google Patents

Abstract

1529052 Sawtooth current generator INDESIT INDUSTRIA ELETTRODOMESTICI ITALIANA SpA 1 Feb 1977 [14 May 1976 (2)] 04083/77 Heading H3T A circuit arrangement to produce a periodic sawtooth current in a deflection coil 10 gives a controllable switching device 16 a long recovery time relative to the sawtooth period. In operation the first part of the stroke current passes through diode 13, while diode 15 and the SCR16 are off and capacitor 34 charged. At some time in this first part, a sync pulse is applied to fire the SCR16. The capacitor 34 resonantly discharges through the coil 33 and the SCR. When the current in diode 13 has fallen to zero, the stroke current is supplied via the choke 12 and via the diode 15, and initially via SCR16 also. After a half cycle, the current in capacitor 34 and coil 34 reverses, turning off the SCR, and is taken through the two diodes 15, 13 while the stroke current continues. The second half-cycle in the series circuit 33, 34 finishes and the reversal of current cuts off diode 13. The SCR has the whole of this second half-cycle to recover to the fully cut-off condition. There is now no low impedance conductive path in parallel with coil 20 and fly back commences resonantly with capacitor 14. Some current continues to flow in diode 15 until the voltage on capacitor 14 has become such as to cut off this diode sometime before the end of flyback. Flyback finishes and the cycle then repeats. Capacitor 35 is the usual S-correction capacitor. In a second embodiment (Fig. 4 not shown) a series RC (46, 47) suppresses parasitic oscillations in the SCR circuit and an additional series tuned circuit (41, 42) resonant at the sawtooth frequency forms a coupling between the SCR and the coil.