Battery charger

• US 4,564,800 A
• Filed: 06/01/1984
• Issued: 01/14/1986
• Est. Priority Date: 06/01/1984
• Status: Expired due to Fees

• Current Assignee: Jetronic Industries, Inc. (New Bastion Development, Inc.)
• Original Assignee: Jetronic Industries, Inc. (New Bastion Development, Inc.)
• Inventors: Jurjans, Ojars
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Ault, Anita M.
• Application Number:
  US06/616,236
• Time in Patent Office: 592 Days
• Field of Search: 320/15, 320/20, 320/21, 320/35, 320/36, 320/39, 320/56, 363/17, 363/56, 363/98
• US Class Current: 320/145
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: H02J 7/007192 in response to temperature
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters

Abstract

A switch-mode battery charger in which a pair of field effect transistors are operated at a relatively high switching rate. Protection against excessive overload is provided by directly monitoring the pulse trains produced by the transistors rather than the output charging current and reducing the duty cycle of the transistors when an excessive overload is detected. Protection against batteries which cannot take a charge is provided by monitoring the temperature in the vicinity of the transistors and first turning on a fan to cool the transistors and then disabling the transistors if the fan has failed to reduce the temperature an adequate amount.

Claims

1. A battery charger comprising:

means for developing a d-c voltage from an a-c line voltage;

switching means, including a first transformer and a pair of field effect transistors connected in a half-bridge configuration, for chopping said d-c voltage to produce a pair of identical time displaced pulse trains having a variable duty cycle and a frequency substantially higher than the frequency of said a-c line voltage, a first secondary winding of said first transformer connected between the gate and source of one of said field effect transistors and a second secondary winding of said first transformer connected between the gate and source of the other of said field effect transistors;

a step-down transformer for converting said pulse trains from high-voltage low-current pulse trains to low-voltage high-current pulse trains;

rectifying means responsive to said lowvoltage high-current pulse trains for developing an output d-c voltage and a d-c charging current;

output means for coupling said d-c charging current to a battery which is to be charged;

means for supplying an output voltage reference signal representative of a predetermined output volage;

means for supplying an overload voltage reference signal representative of an excessive overload caused by a battery which is to be charged;

and control means connected to a primary winding of said first transformer and (1) responsive to said output voltage and said output voltage reference signal for controlling said transistors to vary said duty cycle of said pulse trains to reduce differences between said output voltage and said predetermined output voltage, and (2) responsive to a sampling signal representative of current flow through a primary winding of said step-down transformer and said overload reference signal for controlling said transistors to reduce said duty cycle of said pulse trains to a predetermined minimum when said current flow through said primary winding of said step-down transformer rises in response to an overload which exceeds said excessive overload represented by said overload reference signal, said control means including a third transformer having a primary winding connected in series with said primary winding of said step-down transformer and a secondary winding for developing said sampling signal representative of current flow through said primary winding of said step-down transformer.

2. A battery charger according to claim 1 wherein said output means include a plurality of output terminals to which a plurality of batteries which are to be charged are connected and a plurality of diodes, one associated with each output terminal, for isolating said output terminals.

3. A battery charger according to claim 2 wherein said means for developing said d-c voltage include:

(a) a voltage doubler responsive to a 115 volt line voltage for doubling said 115 volt line voltage; and

(b) a rectifier responsive to a doubled 115 volt line voltage or a 230 volt line voltage for developing said d-c voltage.

4. A battery charger according to claim 2 further including:

(a) means for sensing the temperature in the vicinity of said transistors and for developing a temperature signal representative of said temperature;

(b) means for supplying a first temperature reference signal representative of a first predetermined temperature;

(c) means responsive to said temperature signal and said first temperature reference signal for developing a fan control signal when said temperature in said vicinity of said transistors exceeds said first predetermined temperature; and

(d) a fan located in said vicinity of said transistors and responsive to said fan control signal for cooling said transistors.

5. A battery charger according to claim 4 further including:

(a) means for supplying a second temperature reference signal representative of a second predetermined temperature greater than said first predetermined temperature;

(b) means responsive to said temperature signal and said second temperature reference signal for developing a shut-off signal when said temperature in said vicinity of said transistors exceeds said second predetermined temperature; and

(c) means responsive to said shut-off signal for disabling said transistors.

6. A battery charger according to claim 5 wherein said output means include a plurality of output terminals to which a plurality of batteries which are to be charged are connected and a plurality of diodes, one associated with each output terminal, for isolating said output terminals.

7. A battery charger according to claim 6 wherein said means for developing said d-c voltage include:

(a) a voltage doubler responsive to a 115 volt line voltage for doubling said 115 volt line voltage; and

(b) a rectifier responsive to a doubled 115 volt line voltage or a 230 volt line voltage for developing said d-c voltage.