Constant current source and battery charger

• US 4,862,013 A
• Filed: 11/16/1988
• Issued: 08/29/1989
• Est. Priority Date: 12/02/1987
• Status: Expired due to Fees

• Current Assignee: Zenith Electronics Corporation (LG Corporation)
• Original Assignee: Zenith Electronics Corporation (LG Corporation)
• Inventors: Konopka, John G.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Thai, Nancy
• Application Number:
  US07/272,194
• Time in Patent Office: 286 Days
• Field of Search: 307/246, 307/270, 307/296 A, 307/297, 307/549, 307/570, 307/571, 307/23, 307/24, 307/48, 307/66, 307/85, 307/86, 307/300, 323/289, 323/282, 320/39, 320/21, 320/31, 320/40, 320/35
• US Class Current: 327/538
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A constant current battery charger includes a bucking regulator comprising a power switch transistor, a diode, an inductor and a voltage sensitive switch with adjustable delay for controlling the power switch transistor. The hysteresis or delay is obtained with a Schmitt trigger and the effect is a stable pulse width modulator in which the duty cycle of the power switch transistor is varied. A temperature sensor adds resistance to change the sensitivity of the switch and reduce charging current when a predetermined battery temperature is reached. A speed up circuit consisting of a shorting transistor is connected across the base-emitter of the switch transistor.

Claims

1. A speed up circuit for a power transistor switch operated from a single-ended power supply comprising:

a switch transistor coupled between said power supply and a load circuit;

control means for controlling the conduction of said switch transistor in response to a control signal;

said control means comprising a shorting transistor connected across the base-emitter junction of said switch transistor and trigger means, including a trigger transistor, for rapidly driving said shorting transistor into conduction in response to said control signal; and

a diode coupled across the base-emitter circuit of said shorting transistor and a resistor and capacitor series circuit connected between said diode and the load circuit of said trigger transistor.

2. The circuit of claim 1 wherein said resistor and capacitor and said diode are connected in parallel with the load circuit of said trigger transistor.

3. The circuit of claim 2 wherein said load circuit of said trigger transistor comprises a resistor.