Frequency modulation device and switching mode power supply using the same
First Claim
1. A frequency modulation device comprising:
- a counter for using a first clock signal having a predetermined cycle and generating at least one first signal having a cycle of an integer times the cycle of the first clock signal;
a latch unit for detecting the first signal at a predetermined time and generating a second signal corresponding to a level of the first signal;
a reference signal generator for generating a first reference signal having at least two different levels according to the second signal; and
a pulse width modulation (PWM) oscillator for generating an oscillator signal that increases with a first slope and decreases with a second slope between the first reference signal and a second reference signal, wherein the second reference signal has a level that is different from that of the first reference signal.
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Abstract
The present invention relates to a frequency modulation device and a switching mode power supply using the frequency modulation device. To prevent electromagnetic interference (EMI), it is required to slightly vary a switching operation frequency in an SMPS operation. In some embodiments, at least one first signal having a predetermined cycle is generated, a second signal corresponding to a level of a first signal is generated at a turn-off time of a switch, a first reference voltage having at least two different levels is generated according to the second signal, and an oscillator signal for increasing along a first slope during a first period and decreasing along a second slope during a second period between the first reference voltage and a second reference voltage having a level that is different from the first reference voltage is generated.
61 Citations
26 Claims
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1. A frequency modulation device comprising:
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a counter for using a first clock signal having a predetermined cycle and generating at least one first signal having a cycle of an integer times the cycle of the first clock signal; a latch unit for detecting the first signal at a predetermined time and generating a second signal corresponding to a level of the first signal; a reference signal generator for generating a first reference signal having at least two different levels according to the second signal; and a pulse width modulation (PWM) oscillator for generating an oscillator signal that increases with a first slope and decreases with a second slope between the first reference signal and a second reference signal, wherein the second reference signal has a level that is different from that of the first reference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A switching mode power supply (SMPS) comprising a transformer and a main switch coupled to a primary coil of the transformer, for supplying power to a secondary coil of the transformer according to a switching operation of the main switch, the SMPS comprising:
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a frequency modulation device for generating an oscillator signal having a first cycle; and a switch controller for generating a gate control signal for controlling the main switch by using a pulse width modulation (PWM) clock signal having a second cycle corresponding to the first cycle, a feedback signal corresponding to a voltage of the secondary coil of the transformer, and a detection signal corresponding to a current flowing through the main switch, wherein the frequency modulation device is configured to generate at least one first signal having a predetermined cycle, a second signal corresponding to a level of the first signal at a reference time when a level of the gate control signal is changed, a first reference signal having at least two different levels according to the second signal, and an oscillator signal that increases along a first slope during a first period and decreases along a second slope during a second period between the first reference signal and a second reference signal having a level that is different from that of the first reference signal, and the first cycle corresponds to a sum of the first and second periods. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification