Pulse Width Modulator Delay Control Circuit for PFM to CCM Transitions
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Solution Overview
Problem
Switching power supplies face challenges in transitioning from pulse frequency modulation (PFM) to fixed frequency continuous conduction mode (CCM) due to undesirable transients in output voltage, caused by variations in control voltage and voltage ramp affected by input and output voltages, temperature, and semiconductor manufacturing processes.
Innovation Solution
A pulse width modulator circuit with a delay control circuit and amplifier circuit that generates a control voltage to set the propagation delay, using a configurable delay circuit with multiple delay cells and a voltage reference circuit to compensate for temperature and process variations, ensuring accurate pulse width control during mode transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching power supply transitions from PFM to CCM mode using conventional control methods, then the mode transition can be implemented, but undesirable transients appear in the output voltage due to variations in control voltage and voltage ramp affected by input and output voltages, temperature, and manufacturing processes
Solution Approach 1:
The delay circuit proactively compensates for the inherent delay in the pulse width modulator by adding an equalizing delay to the feedback signal path. This preliminary action ensures that both signals arrive at the comparator simultaneously, preventing output voltage transients during PFM to CCM mode transitions before they can occur.
Solution Approach 2:
The delay circuit acts as an intermediary element inserted into the feedback signal path. It mediates the timing discrepancy between the feedback signal and the voltage ramp signal, allowing both signals to be properly synchronized at the comparator input, thereby eliminating harmful transients during mode transitions.
2Measurement precision
If a delay circuit is added to compensate for pulse width modulator delay, then accurate pulse width control is achieved, but the circuit complexity increases
Solution Approach 1:
The delay circuit utilizes controllable delay elements whose delay parameter can be adjusted based on operating conditions. By dynamically changing the delay parameter to match the pulse width modulator's delay characteristics, accurate pulse width control is achieved without requiring a permanently complex circuit structure.
Solution Approach 2:
The delay control circuit automatically adjusts the delay circuit's delay characteristic based on feedback about the pulse width modulator's operating state. This self-service mechanism eliminates the need for external manual calibration or complex additional control logic, achieving accurate compensation while minimizing overall circuit complexity.
Data Source
AI summary
A switching power supply controller includes a pulse width modulator circuit. The pulse width modulator circuit includes a delay circuit and a delay control circuit coupled to the delay circuit. The delay control circuit includes an amplifier circuit. The amplifier circuit includes a first input terminal, a second input terminal, and an output terminal. The first input terminal is coupled to a first voltage reference terminal. The second input terminal is coupled to the second voltage reference terminal. The output terminal is coupled to a control terminal of the delay circuit.