Switch mode power supply, pulse width modulation (PWM) frequency dithering device and method
A switching mode power supply and frequency jittering technology, which is applied in the direction of electrical components, adjusting electrical variables, output power conversion devices, etc., can solve problems such as failure to obtain certification and/or model acceptance
Active Publication Date: 2009-08-05
MICROCHIP TECH INC
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Problems solved by technology
If switch mode power supplies fail to meet these EMI test requirements, they cannot be certified and / or type accepted by the appropriate testing organization and / or government agency
Method used
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[0013] In switch-mode power supplies, power transistors can generate electromagnetic interference (EMI). Therefore, EMI needs to be limited to comply with customer needs and government regulations. Dithering the pulse-width-modulated PWM cycle cleans up EMI over a range of frequencies, reducing peak EMI emissions at any frequency.
[0014] Reference is now made to the drawings, which schematically illustrate details of some example embodiments. In these drawings, the same elements will be represented by the same numbers, and similar elements will be represented by the same numbers with different lowercase letter suffixes.
[0015] refer to figure 1 , which shows a schematic block diagram of an electronic system powered by a switch-mode power supply. An electronic system, generally indicated by the numeral 100 , may include a power supply, such as a switch-mode power supply 102 , which may provide operating voltage and current to an electronic circuit 104 of the electronic s...
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A switch mode power supply has pulse width modulation (PWM) frequency dithering of a PWM clock frequency. The PWM frequency dithering circuit may change the frequency of the PWM clock based upon each of a plurality of frequencies. A PWM time base circuit may comprise a period register containing a PWM period value, a comparator, and a PWM counter, wherein a PWM count value may be incremented in the PWM counter by the variable frequency PWM clock, the comparator may compare the PWM period value with the PWM count value and when the PWM period value and the PWM count value are substantially equal the PWM count value may be reset. The PWM frequency dithering circuit may comprise a roll counter, wherein the roll counter changes a roll count value each time the comparator resets the PWM count value in the PWM counter; a multiplexer having a plurality of inputs and an output, wherein the output is coupled to each one of the plurality of inputs of the multiplexer based upon the roll counter count value; and a plurality of frequency registers, each one of the plurality of frequency registers may be coupled to a respective one of the plurality of inputs of the multiplexer; wherein the output of the multiplexer may be coupled to a frequency control input of the variable frequency PWM clock such that frequency values stored in the plurality of frequency registers may be used in determining the variable frequency PWM clock frequency.
Description
technical field [0001] According to an embodiment, the present invention relates to switching regulator power supplies, and more particularly, to pulse width modulation frequency dithering in switching regulator power supplies. Background technique [0002] When selling switch-mode power supplies, power supply manufacturers must meet government (eg, Federal Communications Commission) and customer electromagnetic interference (EMI) emissions requirements. Switched mode power supplies may use pulse width modulation (PWM) to control switches such as power transistors, power field effect transistors, etc. that charge an inductor to a desired current. The longer the PWM signal is on, the longer the inductor is charged by controlling the switch and a greater current can be supplied from the switch mode power supply. [0003] In larger capacity switch-mode power supplies, power transistors generate electromagnetic interference (EMI). These larger capacity switch mode power suppli...
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IPC IPC(8): H02M1/00H02M3/156
CPCH02M1/12H02M1/44H02M3/156H02M3/155
Inventor 布赖恩·克里斯
Owner MICROCHIP TECH INC