Switching Regulator Control Circuit Using Timer-Based On-Time Adjustment
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Solution Overview
Problem
Existing switching regulators face challenges in controlling the peak of coil current with high precision due to delays in peak current detection, leading to erroneous detection and variations in output voltage stabilization.
Innovation Solution
A control circuit with a timer circuit that generates an off signal based on a measured on-time, rather than voltage comparison, allowing for precise control of the coil current peak by adjusting the on-time based on the difference between the input and output voltages, thereby maintaining a constant peak current even with variations in voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a peak current detector using voltage comparison is used to control the switching transistor, then the control circuit can detect the peak current, but the detection delay causes erroneous detection and reduces measurement precision
Solution Approach 1:
The patent replaces the voltage comparison method (analog/electrical system) with a timing-based control method. Instead of using a peak current detector that compares voltages and suffers from detection delays, the invention uses a timer circuit to generate an off signal at a predetermined time after the on signal, eliminating the detection delay issue inherent in voltage comparison methods.
Solution Approach 2:
The patent introduces a timer circuit as an intermediary between the on signal generation and the off signal generation. This timer circuit acts as a mediator that precisely controls the switching transistor's on-time based on the voltage difference between input and output, rather than relying on delayed voltage comparison feedback.
2Reliability
If the on-time is fixed, then the control circuit is simple to operate, but the peak current varies with voltage changes reducing stability
Solution Approach 1:
The patent makes the on-time dynamic by adjusting it according to the voltage difference between input and output. The timer circuit's charging current is determined by this voltage difference, causing the on-time to automatically adapt to voltage changes. This dynamic adjustment maintains constant peak current and stable output voltage without requiring complex feedback control circuits.
Solution Approach 2:
The patent changes the timing parameter (on-time) based on the voltage difference parameter. By making the on-time proportional to the inverse of the voltage difference (VDD-VOUT), the circuit maintains constant peak current across varying voltage conditions. This parameter adjustment is achieved through the timer circuit's charging mechanism rather than complex control logic.
3Productivity
If voltage comparison is used to determine switching timing, then the control method is straightforward, but delays in comparison reduce productivity
Solution Approach 1:
The patent performs preliminary action by pre-determining the off-time based on the voltage difference before the switching cycle begins. The timer circuit is configured with charging characteristics that correspond to the required on-time, so when the on signal is generated, the off signal is already determined to occur at the correct time, eliminating comparison delays during the switching operation.
Data Source
AI summary
A control circuit for controlling a switching transistor and a synchronous rectifying transistor of a switching regulator includes: a bottom detection comparator configured to assert an on signal; a timer circuit configured to generate an off signal; a zero current detector configured to assert a zero current detection signal; and a driving circuit configured to receive the on signal, the off signal and the zero current detection signal, and (i) turn on the switching transistor and turn off the synchronous rectifying transistor when the on signal is asserted, (ii) turn off the switching transistor and turn on the synchronous rectifying transistor when the off signal is asserted, and (iii) turn off the switching transistor and the synchronous rectifying transistor when the zero current detection signal is asserted.