Analog Switch Circuit with Phase-Reverse Clamp for Motor Drive

The patent introduces a clamp circuit as an intermediary component between the analog switch and the input terminal. This clamp circuit includes a clamp transistor and clamp resistor that work together to limit the voltage at the input terminal, preventing it from exceeding the power supply voltage or falling below ground voltage. The clamp circuit acts as a mediator that protects the main analog switch from voltage excursions without requiring modification to the core switch structure.

The clamp circuit uses simple, low-cost components (clamp transistor, clamp resistor, and control logic) that can be easily integrated into the existing circuit. The control logic uses basic digital signals already present in the system to activate the clamp function only when needed, rather than requiring complex continuous protection mechanisms. This approach provides reliable protection while keeping the added complexity minimal.

The patent applies the clamp circuit only to specific terminals where voltage excursions can cause erroneous operation, rather than protecting all terminals uniformly. The control logic identifies which terminals need protection based on the operational state of the analog switch, and activates clamp functions selectively. This localized approach provides necessary protection while minimizing the number of clamp circuits required, thereby reducing manufacturing cost.

The clamp circuit design uses components that can serve multiple functions. The clamp transistor not only limits voltage but also works in conjunction with the control logic to provide intelligent protection. The control logic itself serves dual purposes by managing both the analog switch operation and the clamp circuit activation. This multi-functionality reduces the need for separate dedicated protection components, lowering overall manufacturing cost.

The patent applies preliminary anti-action by activating the clamp circuit before the erroneous turning-on can occur. The control logic monitors the control voltages applied to the analog switch and proactively activates the clamp function when the switch is in the off state. This preliminary protection prevents voltage excursions at the input terminal from causing the transistor to turn on unexpectedly, maintaining reliable disconnection even when input voltage exceeds normal ranges.

The clamp circuit provides beforehand cushioning by creating a voltage barrier at the input terminal before harmful voltage excursions can affect the analog switch. The clamp transistor and resistor combination acts as a cushion that absorbs and limits voltage spikes, preventing them from reaching levels that would cause erroneous turning-on. This prior protection ensures that the switch maintains its intended off state despite abnormal input voltage conditions.