Constant current source and battery charger

• US 4,885,522 A
• Filed: 11/16/1988
• Issued: 12/05/1989
• 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): Hickey, R. J.
• Application Number:
  US07/272,142
• Time in Patent Office: 384 Days
• Field of Search: 320/21, 320/31, 320/32, 320/39, 320/40, 323/282, 323/289
• US Class Current: 320/145
• 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 current foldback circuit includes a zener diode coupled to the battery for changing the sensitivity of the switch to substantially reduce charging current when a battery voltage corresponding to a fully charged state is reached.

Claims

1. A battery charger operated from a single-ended power supply comprising:

pulse width modulation means including a transistor power switch, a diode and an inductor for supplying current to a battery;

means for monitoring current flow to said battery;

trigger means for controlling the frequency and duty cycle of said pulse width modulation means responsive to said monitoring means;

a speed up circuit for said switch transistor comprising a shorting transistor coupled across the base-emitter circuit of said switch transistor and means responsive to said trigger means for driving said shorting transistor conductive;

current foldback means including zener diode sensing means for monitoring the voltage of said battery; and

means for changing said monitoring means to substantially reduce current flow to said battery when a battery voltage corresponding to a fully charged state is reached.

2. A charger in accordance with claim 1 wherein said trigger means includes a Schmitt trigger arrangement coupled between said monitoring means and said power switch transistor for introducing a delay in controlling said duty cycle.

3. The battery charger of claim 2 wherein said zener diode sensing means comprises a zener diode in a series resistive path between said battery and said Schmitt trigger.