Conduction interval timing circuit for transistorised ignition system - uses controlled current sources supplying capacitors and responding to ignition coil currents

摘要

The control circuit for an automotive ignition system comprising an ignition coil (17) connected to a DC supply (B+) through a switching transistor (15) with its drive circuit, has provision to switch the transistor into conduction and a circuit measuring the current in the coil, to ensure minimal energy dissipation over the switching transistor. The driver circuit turns the switching transistor (15) 'on' using a circuit comprising a first current source (3) connected to a first capacitor (C1) the discharge of which is controlled by ignition command pulses. A switching circuit (6) interrupts the first current source (3) when the voltage at the first capacitor terminals reaches a preset level (U1), and simultaneously initiates conduction of the switching transistor (15) and a second current source (8) controlled from the coil current to charge a second capacitor (C2), the voltage of which controls the first current source.