Low voltage alert circuit

• US 4,829,290 A
• Filed: 01/04/1988
• Issued: 05/09/1989
• Est. Priority Date: 01/04/1988
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Ford, Robert B.
• Primary Examiner(s): Orsino, Joseph A.
• Assistant Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US07/140,520
• Time in Patent Office: 491 Days
• Field of Search: 340/663, 340/657, 340/660, 340/636, 320/40, 320/48, 324/72
• US Class Current: 340/663
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G08B 29/181 due to failing power supply
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits

Abstract

The alert circuit includes a minimum number of inexpensive descrete electronic components to provide a flashing alert when battery voltage drops below a predetermined trigger voltage. A single unijunction transistor circuit functions as a combination low voltage detector and oscillator to output periodic pulses to an LED annunciator circuit when battery voltage is low.

Claims

1. A low voltage alert circuit having first and second input terminals, comprising in combination:

a three terminal relaxation device;

a Zener diode coupled between the first and second input terminals of said low voltage alert circuit;

a first resistor coupled between said Zener diode and a first terminal of said relaxation device;

a capacitor coupled between said first terminal of said relaxation device and said second input terminal of the low voltage alert circuit;

a second diode coupled between said first input terminal and a second terminal of said relaxation device; and

a second resistor coupled between a third terminal of said relaxation device and an output terminal of said low voltage alert circuit.

2. The low voltage alert circuit of claim 1, further comprising:

a transistor having a first terminal coupled to said output terminal and a second terminal coupled to said second input terminal;

a light emitting diode having a first terminal coupled to said first input terminal and to a third terminal of said transistor; and

a switch coupled between a second terminal of said light emitting diode and said second input terminal.

3. The low voltage alert circuit of claim 1, in which a light emitting diode is operatively coupled to said output of the low alert circuit.

4. A low voltage alert circuit having first and second input terminal, comprising in combination;

a programmable unijunction transistor;

a Zener diode having a first terminal coupled to said second input termina;

a first resistor coupled between said Zener diode and the anode of said unijunction transistor;

a capacitor coupled between said anode of said unijunction transistor and said second input terminal;

a second transistor having a first terminal coupled to said second input terminal;

a second resistor coupled between the cathode of said unijunction transistor and a second terminal of said second transistor;

a second diode having a first terminal coupled to an input terminal of said alert circuit;

a third resistor coupled between a second terminal of said second diode and the gate of said unijunction transistor;

a fourth resistor coupled between said second terminal of said second diode and said second input terminal;

a fifth resistor coupled between a second terminal of said Zener diode and said input terminal;

a light emitting diode having a first terminal coupled to a third terminal of said second transistor;

a sixth resistor coupled between said first terminal of said light emitting diode and said input terminal; and

a switch coupled between a second terminal of said light emitting diode and second input terminal.