| 摘要 |
Means for producing a periodic sequence of square-wave pulses at a specific frequency and at an adjustable duty ratio are provided in an electrical circuit arrangement for controlling a direct current, especially for brightness control of the dashboard illumination of vehicles, the frequency and duty ratio being independent of one another, and power switching means, which are driven by the square-wave pulses, are provided in a lamp circuit. In order to minimise the power loss, which occurs in circuit arrangements which control brightness, in the form of energy which is converted into heat, at a very low circuit cost, it is proposed to provide two timing stages (timers) (IC1, IC2), which are coupled via a differentiating element (Tr), as the means for producing a periodic sequence of square-wave pulses at a specific frequency and at an adjustable duty ratio, the first timing stage (IC1) being constructed as part of a freewheeling square-wave generator (III) at a specific frequency and at a specific duty ratio, whose square-wave pulses, which are converted via the differentiating element (IV) into needle-shaped pulses, trigger the second timing stage (IC2) which, for its part, supplies a periodic sequence of square-wave pulses at a specific frequency (70 Hz) and, by means of circuitry, at a duty ratio (0.2 to 0.95) which can be adjusted using a pulse-width control network (P1, P2, R8, C7), and to use a power MOS field-effect transistor (TR2) as the power switching means. <IMAGE>
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