| 摘要 |
Operating circuit for at least one LED, in which a supply voltage for at least one LED is provided by a clocked switch (S1), wherein when the switch (S1) is switched on, energy is buffer-stored in a coil (L1), which energy is discharged when the switch (S1) is switched off via at least one LED, and an open-loop/closed-loop control unit (SR) actuates the switch (S1) in such a way that the LED current (iLED) is regulated to a predetermined value and, in order to adjust the brightness of the LED, in each case low-frequency PWM packets of adjustable width are generated, characterized in that, during a low-frequency PWM packet, the switch-on time of the switch (S1) after a plurality of pulses of an adjustable switch-on time is altered to the next higher or lower adjustable switch-on time, and the remaining pulses are output with this altered switch-on time, with the result that the number of pulses with the two adjusted switch-on times assume a specific ratio and an averaged value for the current through the LED results, which value corresponds to the preset by a setpoint value and, in the event of a specific brightness value and therefore a specific width of the low-frequency PWM packet being undershot, individual pulses of the one adjusted switch-on time are omitted, and therefore the ratio of the number of pulses with the two adjusted switch-on times deviates in comparison with the operation with the same LED current during a low-frequency PWM packet with a greater width. |
