Switching Mode Power Supply Current Limiting Control
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Solution Overview
Problem
Existing switching mode power supplies (SMPS) face challenges in maintaining a uniform maximum limit current across the main switch independent of input voltage levels, leading to increased production costs due to the need for higher-rated circuit elements to account for delay times, which affect the maximum power transmitted to the output terminal.
Innovation Solution
The SMPS design includes a switch configuration with a first transistor and multiple second transistors, where the ratio of currents changes over time, and a resistor coupled to a power source, allowing for a driving control signal to manage the operation and maintain a uniform maximum limit current without additional complex circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a maximum limit current ILIM is set to prevent damage to the main switch, then the main switch is protected from excessive current, but the maximum power transmitted to the output terminal is limited and the rating of circuit elements must be selected according to the highest main switch current which exceeds ILIM due to delay time, leading to increased production cost
Solution Approach 1:
The patent applies preliminary action by detecting the main switch current before it reaches the maximum limit current ILIM, taking into account the delay time caused by different SMPS elements. The control circuit predicts when the current will reach ILIM based on the delayed detection signal and turns off the main switch in advance, preventing current overload without requiring circuit elements with higher ratings than necessary.
2Reliability
If the maximum limit current ILIM is set to protect the main switch, then the main switch is protected, but the delay time causes the actual main switch current to exceed ILIM, requiring higher-rated circuit elements
Solution Approach 1:
The control circuit performs preliminary action by compensating for the delay time in current detection. It turns off the main switch before the current actually reaches ILIM, based on the delayed detection signal, thereby preventing current overload without requiring circuit elements with higher ratings.
Solution Approach 2:
The patent employs feedback by continuously monitoring the main switch current through a detection circuit and using this information to control the main switch operation. The control circuit adjusts the main switch turn-off timing based on the feedback from the current detection, ensuring the current does not exceed ILIM despite detection delays.
3Reliability
If the maximum limit current ILIM is set, then the main switch current is limited, but the delay time causes the maximum main switch current to vary with input voltage, affecting the maximum output power
Solution Approach 1:
The control circuit uses feedback from the current detection circuit to dynamically adjust the main switch operation. By continuously monitoring the actual main switch current and comparing it with the maximum limit current ILIM, the control circuit ensures consistent current limiting across different input voltages, maintaining stable maximum output power.
Solution Approach 2:
The patent applies parameter changes by adjusting the main switch turn-off timing based on the detected current parameters. The control circuit modifies the switching parameters dynamically to compensate for variations caused by different input voltages and delay times, ensuring consistent current limiting and output power.
Data Source
AI summary
A switching mode power supply and a switch thereof are provided. The switch includes a plurality of first transistors, and a second transistor that is turned on/off by a control signal that is equal to that of the plurality of first transistors and in which a second current corresponding to a first current flowing to the plurality of first transistors flows, wherein a ratio of the first current to the second current sequentially changes from a time point at which the second transistor is turned on. Therefore, a switching mode power supply and a switch thereof that can always uniformly sustain a maximum limit current flowing to the switch regardless of a level of an input voltage without including a special additional circuit can be provided.