VOLTAGE SENSING AND SWITCHING CIRCUIT

• US 3,719,859 A
• Filed: 08/31/1971
• Issued: 03/06/1973
• Est. Priority Date: 08/31/1971
• Status: Expired due to Term

• Current Assignee: Cooper Industries, Inc. (Eaton Corporation PLC.)
• Original Assignee: Alton R. Morris, Richard J. Frantz
• Inventors: Frantz, Richard J., Morris, Alton R.
• Primary Examiner(s): Goldberg, Gerald
• Application Number:
  US05/176,587
• Time in Patent Office: 553 Days
• Field of Search: 307/290,23S 323/22T,22SC,24,4,9 317/27,31 328/147
• US Class Current: 361/92
• CPC Class Codes: H02M 7/1557 with automatic control of the output voltage or current

Abstract

A circuit to sense variations in alternating voltage applied to a load and to interrupt power flow to the load on reduction of the applied voltage, including a rectifier to rectify the alternating voltage, a voltage regulator to apply a constant level part of the rectified voltage as the power supply to a Schmitt trigger, part of the rectified voltage controlling conductivity of a transistor that provides the input signal to the Schmitt trigger according to variations in the rectified alternating applied voltage, a Zener diode to reference the Schmitt trigger at a voltage slightly below the voltage applied to the transistor controlling the trigger, a Zener diode at the output of the trigger to control the presence or absence of signals from the Schmitt trigger to a further transistor that controls the gate of a triac connected in the power line to the load, and the triac being gated to a non-conductive state to block power flow to the load upon reduced alternating applied power. Said circuit also can be used to sense variations in direct current voltage applied to a load and to interrupt power flow to the load on reduction of the applied voltage, in which circumstance no rectifier is used and the direct current applied voltage is utilized in the same manner as the rectified voltage when alternating voltage variations are being sensed.

Claims

1. An undervoltage sensing circuit having first and second terminals, comprising:

a Schmitt trigger circuit having an input first transistor and an output second transistor, the emitter of said transistors being connected to one another and to a common emitter resistance;

means for applying a constant level portion of an applied voltage across the first and second terminals as the supply voltage to said Schmitt trigger circuit;

means for deriving a portion of said applied voltage, which portion is variable in proportion to variations in said applied voltage;

means for applying an input signal to said Schmitt trigger of a value determined by said derived variable portion of said applied voltage;

means including a zener diode connected between said Schmitt trigger circuit emitter resistance and said second terminal for referencing said trigger circuit at a voltage level intermediate said derived variable portion of said applied voltage and the voltage at said second terminal to increase the sensitivity of said Schmitt trigger circuit;

said Schmitt trigger circuit providing a high level output signal at a predetermined level of applied voltage across said first and second terminals and providing a low level output signal at a lower level of applied voltage across said first and second terminals.

2. An undervoltage sensing circuit as claimed in claim 1 wherein:

said means for deriving a portion of said applied voltage comprises a voltage dividing resistance means.

3. An undervoltage sensing circuit as recited in claim 1 wherein:

said input signal applying means includes a fourth transistor having its collector connected to said constant level applying means and its emitter connected to the base of said input first transistor of said Schmitt trigger circuit, and a voltage divider and tap for applying said derived variable portion of said applied voltage to the base of said fourth transistor.

4. An undervoltage sensing circuit as recited in claim 1 including:

threshold means coupled to said output second transistor for conducting when said Schmitt trigger produces a high level output signal; and

gate means coupled to said threshold means which is enabled by said threshold means.

5. An undervoltage sensing ciRcuit as recited in claim 4 wherein:

said threshold means includes a third transistor, and a zener diode coupled to the collector of said output second transistor and to the base of said third transistor, and said gate means includes a triac having its gate coupled to the emitter of said third transistor.

6. An undervoltage sensing circuit as recited in claim 5 including:

a leakage resistance connected between the base of said third transistor and said second terminal.