Boost Converter Control Loop With Quantized Duty-Cycle Skipping
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Solution Overview
Problem
Conventional DC-DC boost converters face inefficiencies due to parasitic ringing and require additional circuitry for duty-cycle modulation, which can be complex and prone to process, voltage, and temperature variations, especially when driving MEMS mirror devices.
Innovation Solution
A DC-DC boost converter design incorporating an inductor, diode, output capacitor, and a control loop circuit with an error amplifier, quantizer, and drive voltage generation circuit that uses a thermometer code to adjust the duty cycle of the drive signal, allowing operation in both normal and skip modes to minimize power loss and reduce complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a body diode is used to prevent voltage from falling below threshold, then ringing is reduced, but power loss increases and efficiency decreases
Solution Approach 1:
The patent extracts the harmful body diode from the circuit by using an external NMOS switch instead. The body diode is completely removed from its function of preventing voltage from falling below threshold, eliminating both the ringing it was meant to prevent and the power loss it caused.
Solution Approach 2:
The patent introduces an external NMOS switch as an intermediary component between the inductor and ground. This switch acts as a mediator that provides a controlled path for inductor current without the parasitic effects of a body diode, allowing precise control of when current flows to ground while minimizing power loss.
2Ease of operation
If conventional duty-cycle modulation circuitry is used, then control is achieved, but device complexity increases and sensitivity to PVT variations worsens
Solution Approach 1:
The patent implements self-service by using the inductor current itself as the feedback signal for duty-cycle modulation. The controller directly monitors the inductor current and adjusts the switch duty cycle accordingly, eliminating the need for separate sensing circuitry, error amplifiers, and complex control loops that would increase device complexity and PVT sensitivity.
Solution Approach 2:
The controller performs multiple functions: it generates the drive signal for the NMOS switch, monitors the inductor current, determines when voltage falls below threshold, and adjusts duty cycle based on all these inputs. This multi-functional approach consolidates what would otherwise require separate dedicated circuits into a single integrated controller.
3Loss of energy
If Schottky diode is used in parallel with switch, then power loss is reduced, but manufacturing complexity increases due to discrete component requirements
Solution Approach 1:
The patent merges the functions of the Schottky diode and the NMOS switch into a single NMOS switch. By properly configuring the switch's source and drain connections and using its intrinsic body diode in reverse, the circuit achieves the low forward voltage drop of a Schottky diode while maintaining full integrability in standard CMOS processes.
Solution Approach 2:
The patent inverts the conventional approach by using the NMOS switch's body diode in reverse orientation compared to its normal operation. The source and drain are connected such that the body diode conducts during the off-state, providing the Schottky-like behavior, while the channel conducts during the on-state with minimal resistance.
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 enhances efficiency by minimizing power loss and simplifying the control loop, making it less sensitive to PVT variations and eliminating the need for trimming, while maintaining stable output voltage across varying loads.
Implementation Method 1
the inductor current L falls, and the strength of the magnetic field collapses as the stored energy is converted to current to attempt to maintain the current output from the inductor L
Implementation Method 2
a parasitic resonating LC circuit is formed between the inductor L and the parasitic capacitance Cp across the switch Sw, resulting in voltage and current ringing during a third time period
Implementation Method 3
this body diode D2 prevents the voltage Vsw from falling below the threshold of the body diode D2, helping to reduce the ringing at node Nn
Data Source
AI summary
A DC-DC boost converter includes an inductor coupled between an input voltage and an input node, a diode coupled between the input node and an output node, and an output capacitor coupled between the output node and ground such that an output voltage is formed across the output capacitor. A switch selectively couples the input node to ground in response to a drive signal. Control loop circuitry includes an error amplifier to generate an analog error voltage based upon a comparison of a feedback voltage to a reference voltage, the feedback voltage being indicative of the output voltage, a quantizer to quantize the analog error voltage to produce a digital error signal, and a drive voltage generation circuit to generate the drive signal as having a duty cycle based upon the digital error signal.