DC-DC Converter Burst Mode Control Using Sawtooth Waveform
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Solution Overview
Problem
Conventional hysteretic burst mode converters generate audible noise and increase output voltage ripple due to varying group frequencies, which are within the audible frequency bandwidth and are load-dependent.
Innovation Solution
A converter and driving method that maintain a predetermined group frequency in burst operation using a burst mode controller with a sawtooth waveform signal and a PWM controller to control the main switch's switching operation, independent of load conditions, thereby reducing noise and ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional hysteretic burst mode converter uses a hysteresis comparator to control switching, then the structure remains simple, but the group frequency varies with load and falls within the audible frequency bandwidth, generating audible noise
Solution Approach 1:
The patent changes the control parameter from hysteresis-based to sawtooth waveform-based frequency modulation. The burst mode controller uses a sawtooth waveform signal with a fixed frequency (e.g., 20 kHz) that is intentionally set above the audible range, replacing the hysteresis comparator's variable frequency operation. This parameter change ensures the group frequency remains constant and inaudible regardless of load conditions.
Solution Approach 2:
The patent implements periodic action by using a sawtooth waveform signal that repeats at a fixed frequency to control the burst mode operation. This periodic signal forces the converter to operate at predetermined frequency intervals above the audible range, eliminating the irregular frequency variations that occur with hysteresis control and ensuring consistent noise-free operation.
2Use of energy by moving object
If the group frequency is reduced in a burst mode converter, then power consumption is reduced, but the output voltage ripple is increased
Solution Approach 1:
The patent changes the frequency parameter to a fixed value above the audible range (e.g., 20 kHz) while maintaining burst mode operation. This allows the converter to achieve low power consumption through burst mode while preventing output voltage ripple increase by keeping the frequency sufficiently high, as the fixed frequency ensures consistent filtering performance regardless of load variations.
3Device complexity
If a hysteresis comparator is used to control burst mode switching, then the control mechanism is simple, but the group frequency bandwidth (1 kHz-14 kHz) falls within the audible frequency range, causing user inconvenience
Solution Approach 1:
The patent changes the frequency parameter from the hysteresis-comparator-generated variable frequency (1-14 kHz) to a fixed sawtooth waveform frequency (e.g., 20 kHz) that is intentionally set above the audible range. This parameter change maintains control simplicity while eliminating audible noise by operating in the ultrasonic range.
Solution Approach 2:
The patent introduces a sawtooth waveform generator as an intermediary component between the burst mode controller and the main switch. This intermediary generates the frequency-control signal at a fixed ultrasonic frequency, replacing the direct hysteresis comparator control and thereby mediating the frequency to remain constant and inaudible across all operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively eliminates audible noise and reduces output voltage ripple by maintaining a constant group frequency greater than the audible noise bandwidth, improving converter performance across varying loads.
Implementation Method 1
an oscillator for generating the sawtooth waveform signal
Implementation Method 2
a trans-conductance amplifier for receiving a voltage at a node where the first resistor and the second resistor meet and the reference voltage
Implementation Method 3
a first comparator for receiving the first voltage and the sawtooth waveform signal, comparing the first voltage and the sawtooth waveform signal, and generating the burst mode control signal according to the comparison result
Implementation Method 4
a power supply for generating an output voltage by using an input voltage by a switching operation of the main switch
Data Source
AI summary
The present invention relates to a converter and a driving method thereof. The converter uses an input voltage to generate an output voltage by a main switch's switching and applies power to a load, senses the current flowing to the main switch to generate a sense voltage, uses a first voltage corresponding to the current applied to the load and a sawtooth waveform signal having a first frequency to control a group frequency of the burst mode, controls the main switch's turn-on timing, and uses the first voltage and the sense voltage to determine whether to turn off the main switch, thereby controlling the main switch's switching. The converter determines the start and end of the period for switching according to the result of comparing the first voltage and the sawtooth waveform signal. Therefore, a converter for having a constant group frequency, preventing audible noise, and preventing output voltage ripple, and a driving method thereof, are provided.