Constant current source and battery charger

• US 4,829,259 A
• Filed: 12/02/1987
• Issued: 05/09/1989
• 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:
  US07/127,745
• Time in Patent Office: 524 Days
• Field of Search: 323/282, 323/289, 320/21, 320/31, 320/32, 320/39, 320/40, 320/35, 320/36
• US Class Current: 320/112
• 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 battery charger comprising:

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

means for monitoring current flow to said battery;

trigger means including a Schmitt trigger arrangement coupled between said monitoring means and said power switch transistor introducing delay for controlling the conduction duty cycle of said power swtich transistor by controlling the frequency and duty cycle of said pulse width modulation means in response to said monitoring means;

temperature sensing means for monitoring the temperature of said battery; and

means for changing said monitoring means to reduce current flow to said battery when a predetermined battery temperature is reached.

2. A batther charger comprising:

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

means for monitoring current flow to said battery;

trigger means including a Schmitt trigger arrangement coupled between said monitoring means and said power switch transistor for introducing delay for controlling the duty cycle of said power switch transistor for controlling the frequency and duty cycle of said pulse width modulation means in response to said monitoring means; and

temperature sensing means for monitoring the temperature of said battery and means for changing said monitoring means to reduce current flow to said battery when a predetermined battery temperature is reached.

3. 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 ot 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; and

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.

4. A battery charger comprising:

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

means for monitoring current flow to said battery;

trigger means including a Schmitt trigger arrangement coupled between said monitoring means and said power switch transistor for introducing delay for controlling the duty cycle of said power switch transistor for controlling the frequency and duty cycle of said pulse width modulation means in response to said monitoring means;

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

temperature sensing means for monitoring the temperature of said battery and means for changing said monitoring means to reduce current flow to said battery when a predetermined battery temperature is reached.

5. In combination:

a single-ended source of DC voltage;

a load circuit;

a switch transistor having an emitter-collector circuit connected between said voltage source and said load circuit;

a trigger transistor for controlling turn on of said switch transistor in response to a control voltage, said trigger transistor having a load resistor connected in series with the base-emitter circuit of said switch transistor;

an integrating circuit including a capacitor;

a shorting transistor coupled across the base-emitter junction of said switch transistor and being coupled to said trigger transistor through said integrating circuit; and

a diode for permitting the capacitor in said integrating circuit to charge upon turn on of said trigger transistor and to rapidly discharge through said shorting transistor upon turn off of said trigger transistor.