GB1412205A - Capacitor discharge ignition circuit - Google Patents

Abstract

1412205 Capacitor discharge ignition circuits SAFE ELECTRONIC SYSTEMS SA 13 March 1973 [23 June 1972] 12038/73 Heading F1B A capacitor discharge ignition circuit for an internal combustion engine includes a first capacitor C3 connectible to the primary winding of an ignition coil (not shown) a power supply unit in the form of a D.C. to D.C. converter having first and second input terminals 1,2 for connection to respective poles of a D.C. source and an output connected to the first capacitor C3 to supply electrical energy to the first capacitor in use, a gate controlled switching device SCR connected in the circuit in such a way as to prevent discharge of the first capacitor when in one state and to cause discharge of the capacitor when in its other state and control means connected to the gate electrode of the device and adapted to respond to opening of the contact breaker 8 of the ignition distributer so as to effect switching of the device from the one state to the other state. The D.C. to D.C. converter comprises a transformer having magnetically coupled primary, secondary and feedback windings 5, 7, 6 and rectifier means D 1 to D4 coupled between the secondary winding 7 and the output of the converter. The primary winding has an intermediate tapping connected to one of the input terminals 1 through the agency of a first resistor R3 which is shunted by at least one diode D5, D6. A pair of transistors T 1 T 2 are arranged with their emitter collector paths connected between respective ends of the primary winding and the other input terminal 2 and with their bases connected to the respective ends of the feedback winding. A biasing network for the transistors comprises second and third resistors R 2 R 1 connected in series across the input terminals and a second capacitor Cl connected in parallel with the third resistor R1, the feedback winding 6 being connected to the junction between the second and third resistors. The twin ratio between the primary and feedback windings is between 1.6:1 and 2.7:1. The second capacitor has a value between 1 and 8 uF. For transistors of the germanium type the first resistor has a value between 3 and 8 ohms the second resistor has a value between 22 and 56 ohms and the third resistor has a value between 600 and 1200 ohms. For transistors of the silicon type the first resistor has a value between 0.05 and 8 ohms, the second resistor has a value between 10 and 56 ohms and the third resistor has a value between 200 and 1200 ohms. As shown the gate controlled switching device is a silicon controlled rectifier. The control pulse for this silicon controlled rectifier is obtained from the inductive effect of a coil L associated with the contact breaker 8.