Switching Transistor On-Resistance Control for DC/DC Converter Oscillation
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Solution Overview
Problem
Step-up DC/DC converters experience oscillation and ringing in the switching voltage and output voltage due to parasitic inductances and capacitances, leading to electromagnetic interference (EMI) issues, which existing countermeasures like shielding and inductor adjustments are costly and inefficient.
Innovation Solution
A control circuit that switches the on-resistance of the switching transistor between two values, with a high initial resistance during the reverse recovery time of the rectifier diode to suppress resonance, and a lower resistance later to ensure damping, thereby preventing oscillation and ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If electromagnetic shielding material is used to suppress oscillation, then EMI noise is reduced, but cost and device complexity increase
Solution Approach 1:
The invention extracts and addresses the root cause of EMI noise by focusing on the rectifier diode's reverse recovery characteristics. By taking out the problematic capacitance COJ as the primary source of oscillation and designing the switching waveform specifically to address this extracted element, the solution eliminates the need for additional shielding materials and complex EMI countermeasures.
Solution Approach 2:
The invention replaces the mechanical/physical approach of electromagnetic shielding with an electrical control approach. Instead of using shielding materials to block EMI, the patent uses controlled switching waveforms and timing to prevent oscillation at its source, substituting a field-based solution with a circuit-control-based solution.
2Object-affected harmful factors
If inductor value is adjusted to suppress resonance, then oscillation is reduced, but manufacturing precision requirements increase and cost increases
Solution Approach 1:
The invention changes the timing parameters of the switching waveform rather than adjusting physical component values. By modifying the turn-on and turn-off timing of the switching element to coincide with the reverse recovery characteristics of the rectifier diode, the patent suppresses oscillation without requiring precise inductor value adjustments or specialized component selection.
Solution Approach 2:
The invention performs preliminary action by pre-scheduling the switching element's turn-on and turn-off times to anticipate and prevent oscillation before it occurs. The switching waveform is designed in advance to turn on before the rectifier diode's reverse recovery current peaks and turn off after the oscillation period, proactively preventing the harmful oscillation rather than reacting to it.
3Loss of energy
If switching transistor on-resistance is reduced for efficient operation, then power loss decreases, but oscillation and ringing increase
Solution Approach 1:
The invention uses periodic action by implementing a switching waveform with specific timing characteristics that repeat each switching cycle. The waveform is designed to turn on and off at predetermined intervals that align with the reverse recovery time of the rectifier diode, creating a periodic control pattern that consistently suppresses oscillation while maintaining efficient power transfer.
Solution Approach 2:
The invention applies dynamics by making the switching element's on-resistance effectively time-varying through controlled switching. Although the physical on-resistance remains constant, the dynamic switching action creates an effective resistance profile that is high during the critical reverse recovery period (suppressing oscillation) and low during normal conduction (maintaining efficiency), achieving both goals through temporal differentiation.
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
Effectively suppresses oscillation and ringing in the switching voltage and output voltage, reducing electromagnetic noise and eliminating the need for costly EMI countermeasures, while maintaining efficient operation.
Implementation Method 1
a step-up DC/DC converter (switching regulator) is employed... includes an inductor L1... The switching transistor M1 is integrated on a semiconductor chip 4 included in the control circuit 2r
Implementation Method 2
In the off period of the switching transistor M1, the rectifier diode D1 is biased in the forward direction by means of the electromotive force generated by the coil. In this state, charge is accumulated in the rectifier diode D1. Subsequently, after the switching transistor M1 transits to on, the charge stored in the rectifier diode D1 flows toward the switching transistor M1 due to the reverse recovery property of the rectifier diode D1.
Implementation Method 3
a loop including the output capacitor C1, the rectifier diode D1, the switching transistor M1, and the ground line forms a series RLC resonance circuit... the switching voltage VSW and the output voltage VOUT oscillate at a resonance frequency ωo=1√(LC) [rad] of the RLC resonance circuit
Data Source
AI summary
A switching transistor is configured such that its on resistance RON is switchable between at least two values RON1 and RON2. When the switching transistor is switched from off to on, a control circuit sets the on resistance of the switching transistor to the first value RON1 for a first period immediately after the switching of the switching transistor. Subsequently, for a second period until the switching transistor is turned off, the control circuit sets the on resistance of the switching transistor to the second value RON2 that is smaller than the first value RON1.