DC-DC Converter Control Loop for Input Ripple PSRR Improvement
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Solution Overview
Problem
Existing DC-DC converters, particularly boost and buck-boost converters, face challenges in effectively suppressing input voltage ripple noise, leading to undesirable variations in output voltage due to poor power supply rejection ratio (PSRR), which disrupts downstream circuitry operation.
Innovation Solution
A control circuit with a voltage control loop and a current control loop is implemented, where the current control loop adjusts the control current inversely proportional to the input voltage, allowing for modulation of both the duty cycle of power transistors and inductor current to compensate for input voltage ripple, thereby improving PSRR without perturbing the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage control loops are used in boost or buck-boost converters, then the circuit structure remains simple, but the power supply rejection ratio (PSRR) is poor and input voltage ripple translates into output voltage variations
Solution Approach 1:
The control circuit is segmented into two independent control loops: a voltage control loop that generates a control voltage based on output voltage feedback, and a current control loop that generates a control current based on the control voltage and modulates it with an input voltage signal. This segmentation allows each loop to specialize in specific functions, with the current control loop specifically addressing PSRR by modulating control current based on input voltage variations.
Solution Approach 2:
The invention transitions from conventional single-loop voltage control to a two-dimensional control approach by introducing both voltage control (affecting duty cycle) and current control (affecting inductor current magnitude). This dual-dimensional control enables independent optimization of voltage regulation and PSRR performance without compromising the other.
2Stability of the object's composition
If the control current is adjusted inversely proportional to input voltage to improve PSRR, then output voltage stability improves, but the control circuit complexity increases
Solution Approach 1:
The voltage control loop provides feedback by comparing the output voltage with a reference voltage and generating a control voltage that reflects output voltage deviations. This feedback mechanism ensures that the control system automatically adjusts to maintain output voltage stability while the current control loop processes this feedback signal along with input voltage information.
Solution Approach 2:
The current control loop performs preliminary action by pre-modulating the control current with an input voltage signal before the power conversion stage. This preliminary modulation anticipates input voltage variations and prepares the control current to compensate for them, thereby improving PSRR before the ripple can affect the output voltage.
3Object-affected harmful factors
If a current control loop is added to modulate inductor current based on input voltage, then PSRR improves by 10-20 dB, but the device complexity increases
Solution Approach 1:
The control current serves as an intermediary between the voltage control loop output and the power stage input. By introducing this intermediate control signal that can be independently modulated with input voltage information, the system achieves improved PSRR without directly complicating the power stage hardware, as the modulation is accomplished through signal processing in the control domain.
Data Source
AI summary
Control circuits for DC-DC power converters. In one example, a control circuit includes a voltage control loop configured to produce a control voltage based on an output voltage of a DC-DC converter and a reference voltage, and a current control loop configured to produce a control current based on the control voltage. The current control loop may be further configured to adjust the control current based on a signal proportional to an input voltage of the DC-DC converter to provide an adjusted control current that is inversely proportional to the input voltage, and to produce, based on the adjusted control current and an inductor current in an inductor of the DC-DC converter, a drive signal to drive one or more power transistors of the DC-DC converter.