High voltage protection using SCRs

In an integrated circuit having a plurality of terminals including a power supply terminal, a method for protecting a first circuit path from damage due to electrostatic discharge between two of the terminals, comprising the steps of:

• providing a discharge path different from the first circuit path for conducting the electrostatic discharge between the two terminals, said discharge path requiring a first level of threshold voltage to effect conduction between the two terminals when power is not applied to the power supply terminal;
• and
• increasing the threshold voltage to a second level when power is applied to the power supply terminal to prevent conduction through the discharge path when the voltage between the two terminals is less than the second level.

In an integrated circuit having a plurality of terminals including a supply terminal and a second terminal wherein the supply terminal is of equal potential or is positively biased with respect to the second terminal during circuit operation, a discharge current path for protecting the integrated circuit from damage which could otherwise result from an electrostatic discharge between the supply terminal and the second terminal, comprising:

• an SCR structure having four regions of adjoining semiconductor material of alternating conductivity type, said structure including a first p-type region connected to the supply terminal, a first n-type region connected to the second terminal, a second p-type region and a second n-type region adjoining one another and intermediate to the first p-region and the first n-region, the second n-region adjoining the first p-region and the second p-region adjoining the first n-region;
• said SCR structure providing a discharge current path between the supply terminal and the second terminal when a positive transient voltage is applied between the supply terminal and the second terminal.

In an integrated circuit having a plurality of terminals including a supply terminal and a second terminal wherein the supply terminal is of equal potential or is negatively biased with respect to the second terminal during circuit operation, a discharge current path for protecting the integrated circuit from damage which could otherwise result from an electrostatic discharge between the supply terminal and the second terminal, comprising:

• an SCR structure having four regions of adjoining semiconductor material of alternating conductivity type, said structure including a first n-type region connected to the supply terminal, a first p-type region connected to the second terminal, a second n-type region and a second p-type region adjoining one another and intermediate to the first n-region and the first p-region, the second p-region adjoining the first n-region and the second n-region adjoining the first p-region;
• said SCR structure providing a discharge current path between the supply terminal and the second terminal when a negative transient voltage is applied between the supply terminal and the second terminal.

A protection circuit, for a first circuit which has a plurality of terminals including positive and negative supply terminals, comprising:

• breakdown means connected to said plurality of terminals of the first circuit for providing a low impedance current path between any two of said terminals when a voltage between said two terminals exceeds a threshold value.

A protection circuit, for a first circuit which has a plurality of terminals including positive and negative supply terminals, comprising:

• breakdown means connected to said plurality of terminals of the first circuit for providing a low voltage-low impedance current path between two of said terminals when a voltage between said two terminals exceeds a low threshold value with power removed from said supply terminals.

A method of providing overvoltage protection for a first terminal in a circuit connected to a source of power in which a breakdown means is connected between the first terminal and the source of power, the method comprising the steps of:

• providing a path for a current from the first terminal to the source of power, the path having a first threshold value for effecting conduction therethrough when power is not supplied by the source of power and a second, higher threshold value when power is supplied by the source of power;
• increasing the threshold of the breakdown means to said second threshold value when power is supplied by the source of power to prevent conduction through the path when the voltage between the first terminal and the source of power is less than said second threshold value.