Battery charger systems and methods

• US 5,488,284 A
• Filed: 09/30/1992
• Issued: 01/30/1996
• Est. Priority Date: 09/30/1992
• Status: Expired due to Fees

• Current Assignee: Dallas Semiconductor Corporation (Analog Devices, Inc.)
• Original Assignee: Dallas Semiconductor Corporation (Analog Devices, Inc.)
• Inventors: Dias, Donald R., Mumper, Eric W.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): NAPPI, ROBERT E
• Application Number:
  US07/953,906
• Time in Patent Office: 1,217 Days
• Field of Search: 320/20, 320/31, 320/32, 320/39, 320/40
• US Class Current: 320/162
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0032 disconnection of loads if battery is not under charge, e.g. in vehicle if engine is not running
• CPC Class Codes: H02J 7/0036 using connection detecting circuits H02J7/0034 takes precedence

Abstract

A battery charger with varying applied voltage and varying series resistance invoked in response to battery charge level provides an optimizable multipart load line for charging. The multipart load line may be programmed into a memory within the battery charger, and thereby common design battery chargers may be configured with optimized multipart load lines for diverse batteries. Programming access can be over the charge current output terminal for both one-wire communication and programming high voltage for EPROM programming.

Claims

1. A battery charging system, comprising:

(a) a charging current output terminal having a voltage;

(b) a variable-voltage generator with an output node;

(c) a variable resistor; and

(d) a controller electrically coupled to said variable-voltage generator, to said variable resistor, and to said charging current output terminal, said controller comprising at least one memory for storing (V₁, R₁, BP₁), (V₂, R₂, BP₂), . . . (V_N, R_N, BP_N) where V_j is an output voltage, R_j is a resistance, and BP_j is a breakpoint voltage, wherein j is an index between 1 and n;

(e) wherein said controller can compare said voltage at said charging current output terminal to said BP_j s and when said voltage at said charging current output terminal lies between BP_j-1 and BP_j, said controller can drive said variable-voltage generator to provide said output voltage of V_j at said output node and can drive said variable resistor to provide said resistance of R_j between said output node and said charging current output terminal.

2. The battery charging system of claim 1, further comprising:

(a) a timer, wherein said timer can periodically drive said controller to compare the voltage at said Charging current output terminal to said BP_j s.

3. The battery charging system of claim 2, wherein:

(a) when driven by said timer said controller successively reads said codes for (V_j, R_j, BP_j) and compares said voltage at said charging current output terminal to BP_j for j equal to n, n-1, . . . , 1 until said voltage at said charging current output terminal is greater than BP_j and then said controller drives said variable voltage generator to provide a voltage of V_j and drives said variable resistor to provide a resistance of R_j.

4. The battery charging system of claim 2, wherein:

(a) said controller comprises a comparator with one input electrically coupled to said charging current output terminal and with another input electrically coupled to a digital-to-analog converter, said controller providing said BP_j s to said digital-to-analog converter.

5. The battery charging system of claim 4, further comprising:

(a) a disconnected-battery detector electrically coupled to said controller, said disconnected-battery detector comprising a second comparator with a first input electrically coupled to said charging current output terminal and a second input electrically coupled to said output node, said second comparator having an offset so that equal voltages at said first and second inputs yield a second comparator output indication of a higher voltage at said first input than at said second input.

6. The battery charging system of claim 1, wherein:

(a) said variable-voltage generator comprises an operational amplifier and a first voltage divider resistor and a second voltage divider resistor, with a first input of said operational amplifier electrically coupled to a reference voltage, said first voltage divider resistor electrically coupled between a second input of said operational amplifier and a ground node, and said second voltage divider resistor electrically coupled between said second input and said output node, said operational amplifier having an output and a gain;

(b) said first voltage divider resistor is comprised of a fixed resistor in series with a first trim resistor; and

(c) said second voltage divider resistor is comprised of a second variable resistor in series with a second trim resistor, wherein V_j applied to said variable resistor sets said gain of said operational amplifier to provide V_j at said output node.

7. The battery charging system of claim 6, wherein:

(a) said first trim resistor having a first resistance and said second trim resistor having a second resistance, further wherein said first resistance and said second resistance combine to form a sum of resistance;

(b) said memory stores a trim T, said trim T applied to said first trim resistor and said second trim resistor to adjust the first resistance of said first voltage divider resistor and said second resistance of said second voltage divider resistor while keeping said sum of resistances remaining constant.

8. The battery charging system of claim 6, wherein:

(a) the output of said operational amplifier drives a gate of a field effect transistor electrically coupled between a power supply and said output node.

9. The battery charging system of claim 8, wherein:

(a) said variable resistor is comprised of at least one component grouping with each of said at least one component grouping comprising

(1) at least one resistor electrically coupled between said charging current output terminal and a first node and

(2) at least one field effect transistor electrically coupled between said power supply and said first node, each of said at least one field effect transistor having a corresponding gate;

(b) wherein R_j applied to said variable resistor couples one or more of said at least one component groupings to said variable-voltage generator with said output of said operational amplifier electrically coupled to said corresponding gate of said at least one field effect transistor of said at least one field effect transistor and with the output node electrically coupled to said first node.

10. The battery charging system of claim 9, wherein:

(a) said variable resistor includes an adder and a decoder;

(b) said memory stores code for a component grouping trim S, wherein said adder adds said code for a component grouping trim S to said code for R_j to yield a selection sum for said component grouping, and said decoder decodes said selection sum to couple said one or more of said component groupings to said variable-voltage generator.

20. The battery charging system of Claim 1, wherein said system charges a NiCad battery.

11. A programmable battery charging system, comprising:

(a) a charging current output terminal;

(b) a voltage generator, said voltage generator with an output node at voltage V selectable from a set of voltages V₁, V₂, . . . V_N ;

(c) a resistor electrically coupled between said output node and said charging current output terminal, said resistor with a resistance, R, selectable from a set of resistances R₁, R₂, . . . R_M ;

(d) a comparator with one input electrically coupled to said charging current output terminal and one input coupled to a breakpoint generator, said breakpoint generator with an output breakpoint voltage BP selectable from a set of breakpoint voltages BP₁, BP₂, . . . BP_K ;

(e) a controller comprising a memory, said memory programmable to store a plurality of triples (V_j, R_j, BP_j) where V_j is selected from V₁, V₂, . . . V_N, R_j is selected from R₁, R₂, . . . R_M, and BP_j is selected from BP₁, BP₂, . . . BP_K ;

(f) said controller is electrically coupled to said voltage generator, to said resistor, to said comparator, and to said breakpoint generator, wherein said controller can

(1) determine BP_j, said BP_j is the smallest BP_j stored in said memory and which is greater than the voltage at said charging current output terminal, by providing stored BP_j s to said breakpoint generator and sensing the output of said comparator, and wherein said controller can

(2) adjust said output breakpoint voltage and said resistance by providing V_j and R_j to said voltage generator and said resistor, respectively.

12. The programmable battery charging system of claim 11, wherein:

(a) said memory is an erasable programmable read only memory; and

(b) said plurality of triples (V_j, R_j, BP_j) are stored in said erasable programmable read only memory in coded form.

13. The programmable battery charging system of claim 11, wherein:

(a) said memory can be programmed by access at said output terminal, said output terminal also provides for one-wire communication.

14. The programmable battery charging system of claim 11, wherein:

(a) said voltage generator is comprised of an operational amplifier and first and second voltage divider resistors, with a first input of said operational amplifier electrically coupled to a reference voltage, said first voltage divider resistor electrically coupled between a second input of said operational amplifier and a ground node, and said second voltage divider resistor electrically coupled between said second input and said output node;

(b) said first voltage divider resistor is comprised of a fixed resistor in series with a first trim resistor;

(c) said second voltage divider resistor is comprised of a variable resistor in series with a second trim resistor, wherein V_j applied to said variable resistor sets a gain of said operational amplifier to provide V_j at said output node; and

(d) said memory programmable to store a trim T, said trim T applied to said first and second trim resistors adjusts resistances of said first and second trim resistors with the sum of the resistances remaining constant.

15. The programmable battery charging system of claim 14, wherein:

(a) said second voltage divider resistor is comprised of at least one component grouping with each of said at least one component grouping comprising

(1) at least one feedback resistor electrically coupled between said charging current output terminal and a first node and

(2) at least one field effect transistor electrically coupled between a power supply and said first node, each at least one field effect transistor having a corresponding gate;

(b) wherein R_j configures said second voltage divider resistor by coupling one or more of said at least one component groupings to said voltage generator with the output of said operational amplifier electrically coupled to said corresponding gate of said at least one field effect transistor and with said output node electrically coupled to said first node.

16. The programmable battery charging system of claim 15, wherein:

(a) said feedback resistor is comprised of an adder and a decoder;

(b) said memory programmable to store code for a component grouping trim S, wherein said adder adds said code for a component grouping trim S to R_j to yield a component grouping selection sum, and said decoder decodes said component grouping selection sum to couple said one or more of said at least one component grouping to said voltage generator.

17. A method of battery charging, comprising the steps of:

(a) providing a plurality of (V_j, R_j, BP_j) where V_j is a charging voltage for j, R_j is a series resistance for j, and BP_j is a breakpoint voltage for j, wherein j is an index number in a series of said index numbers, so that j+1 is the next index number in said series of said index numbers;

(b) sensing a voltage on a battery;

(c) applying said voltage V_j in series with said series resistance R_j to said battery when said voltage on said battery lies between BP_j and BP_j+1.

18. The method of battery charging of Claim 17, further comprising the step of (d) repeating steps (b)-(c) with (V_j, R_j, BP_j) until said voltage on said battery is above BP_j+1.

19. The method of battery charging of claim 17, wherein said battery is NiCd.