Electric tool
First Claim
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1. A hand-held power tool comprising:
- a motor;
a pulse width modulator for producing a pulse width modulated signal for operating the motor;
a device for modulating a carrier frequency of the pulse width modulated signal with a noise signal or a pseudorandom signal, thereby reducing EMC interference emitted by the power tool; and
a clock-pulse generator for producing a clock-pulse signal, the pulse width modulated signal being derived from the clock-pulse signal;
wherein a counter register is provided for counting the elapsed clock cycles of the clock signal, a fold-back value register and an overflow value register are provided, and the pulse width modulatoremits a first signal level if the value of the counter register is less than a fold-back value,emits a second signal level if the value of the counter register is equal to or greater than the fold-back value,sets the counter to a starting value if the value of the counter is equal to an overflow value,sets the fold-back value and overflow value to random new values if the value of the counter is equal to a previous overflow value, with the ratio of the new fold-back value to the new overflow value being essentially equal to the ratio of a previous fold-back value to the previous overflow value.
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Abstract
The invention relates to a hand-guided electric tool having a motor and a pulse width modulator for generating a pulse width modulated signal for operating the motor. A unit is provided for reducing the EMC interferences emitted by the electric tool.
25 Citations
6 Claims
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1. A hand-held power tool comprising:
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a motor; a pulse width modulator for producing a pulse width modulated signal for operating the motor; a device for modulating a carrier frequency of the pulse width modulated signal with a noise signal or a pseudorandom signal, thereby reducing EMC interference emitted by the power tool; and a clock-pulse generator for producing a clock-pulse signal, the pulse width modulated signal being derived from the clock-pulse signal; wherein a counter register is provided for counting the elapsed clock cycles of the clock signal, a fold-back value register and an overflow value register are provided, and the pulse width modulator emits a first signal level if the value of the counter register is less than a fold-back value, emits a second signal level if the value of the counter register is equal to or greater than the fold-back value, sets the counter to a starting value if the value of the counter is equal to an overflow value, sets the fold-back value and overflow value to random new values if the value of the counter is equal to a previous overflow value, with the ratio of the new fold-back value to the new overflow value being essentially equal to the ratio of a previous fold-back value to the previous overflow value. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification
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Current AssigneeRobert Bosch GmbH
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Original AssigneeRobert Bosch GmbH
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InventorsBosch, Volker
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Primary Examiner(s)Smith, Scott A.
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Application NumberUS12/746,704Publication NumberTime in Patent Office1,672 DaysField of Search173/2, 173/4, 173/5, 173/11, 173/176, 173/217, 814/67, 814/69, 388/930, 388/937, 388/804, 318/432, 318/434, 318/139, 318/254US Class Current173/2CPC Class CodesH02M 1/44 Circuits or arrangements fo...
