MULTIRANGE LOAD DETECTION CIRCUITRY

• US 20110068819A1
• Filed: 09/24/2009
• Published: 03/24/2011
• Est. Priority Date: 09/24/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Sims, Nicholas A., Terlizzi, Jeffrey J.
• Granted Patent: US 8,575,917 B2
• Time in Patent Office: Days
• US Class Current: 324/764.01
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: H02J 9/007 Detection of the absence of a load
• CPC Class Codes: H02J 9/06 with automatic change-over , e.g. UPS systems

Abstract

Load detection circuitry is provided that may be used to monitor an output line. The load detection circuitry may include one or more current sensing resistors. A monitor circuit can measure voltages across the current sensing resistors to determine whether current is flowing through a load connected to the output line. In configurations with multiple different current sensing resistors, the monitor circuit can determine the amount of current that is flowing through the load based on the measured voltages. A switch may be interposed between the current sensing resistor and the output line. A current-limited voltage regulator may supply a voltage to the output line. The monitor circuit may periodically open the switch and monitor resulting voltage changes on the output line to determine whether an electronic device or other load is attached. Opening of the switch may be inhibited whenever current is sensed through a current sensing resistor.

Claims

1. Load detection circuitry that monitors current in an output line to which a load may be connected, comprising:

a current sensing resistor coupled in series with the output line;

a switch coupled between the current sensing resistor and the output line; and

monitor circuitry that measures voltages across the current sensing resistor and that controls the switch to monitor currents through the output line.

2. The load detection circuitry defined in claim 1 wherein the monitor circuitry is configured to periodically open the switch.

3. The load detection circuitry defined in claim 1 further comprising a current-limited voltage regulator that supplies a voltage to the output line.

4. The load detection circuitry defined in claim 1 wherein the monitor circuitry is configured to measure voltages on the output line when the switch is opened to determine whether the load is attached to the output line.

5. The load detection circuitry defined in claim 4 wherein the monitor circuitry is configured to inhibit opening of the switch when the voltages measured across the current sensing resistor by the monitor circuitry indicate that the load is attached to the output line.

6. The load detection circuitry defined in claim 1 wherein the current sensing resistor is coupled to a source of voltage at a nominal output level, the load detection circuitry further comprising:

a current-limited voltage regulator that supplies a voltage that is different than the nominal output level to the output line, wherein the monitor circuitry is configured to measure voltages on the output line when the switch is opened to determine whether the load is attached to the output line.

7. The load detection circuitry defined in claim 1 further comprising at least one additional current sensing resistor that is coupled in parallel with the current sensing resistor, wherein the monitor circuitry is configured to measure voltages across the additional current sensing resistor.

8. The load detection circuitry defined in claim 7 wherein the additional current sensing resistor is more than ten times greater in resistance than the current sensing resistor.

9. The load detection circuitry defined in claim 7 further comprising at least one transistor that is controlled by the monitor circuitry to adjust current routing though the current sensing resistor and the additional current sensing resistor.

10. The load detection circuitry defined in claim 1 further comprising first and second additional current sensing resistors that are each coupled in parallel with the current sensing resistor, wherein the monitor circuitry is configured to independently measure voltages across the first and second additional current sensing resistors.

11. The load detection circuitry defined in claim 10 further comprising at least two transistors that are controlled by the monitor circuitry to adjust current routing though the current sensing resistor and the first and second additional current sensing resistors.

12. A method for making load current detection measurements in a system in which a load current detection circuit may be coupled to a load through an output line, comprising:

with at least one current sensing resistor in the load detection circuit, measuring how much current is flowing through the output line; and

if the amount of measured current flowing through the output line is less than a given amount, opening a switch that is interposed between the current sensing resistor and the output line and measuring a resulting change in voltage on the output line to determine whether the load is attached to the output line; and

if the amount of measured current flowing through the output line is more than the given amount, maintaining the switch in the closed position.

13. The method defined in claim 12 wherein the load detection circuit comprises a monitor circuit and wherein measuring how much current is flowing through the output line comprises measuring voltages across the at least one current sensing resistor using the monitor circuit.

14. The method defined in claim 12 wherein the load detection circuit comprises at least one additional current sensing resistor of a resistance greater than that of the at least one current sensing resistor, wherein the at least one additional current sensing resistor is coupled in parallel with the at least one current sensing resistor, and wherein measuring how much current is flowing through the output line comprises using the additional current sensing resistor to measure how much current is flowing through the output line after the at least one current sensing resistor has been used to measure how much current is flowing through the output line and before the switch has been opened.

15. An alternating-current (AC) to direct-current (DC) power converter to which an electronic device may be connected when it is desired to power the electronic device with the power converter, the power converter comprising:

a power converter circuit that produces a DC voltage from an AC voltage;

an output line to which the electronic device may be connected;

a current sensing resistor coupled in series with the output line;

a switch coupled between the current sensing resistor and the output line; and

monitor circuitry that measures voltages across the current sensing resistor and that controls the switch to determine whether the electronic device is attached to the output line.

16. The power converter defined in claim 15 wherein the monitor circuitry is configured to measure voltages on the output line when the switch is opened to determine whether the load is attached to the output line.

17. The power converter defined in claim 15 wherein the power converter circuit comprises a control circuit and wherein the monitor circuitry is configured to direct the control circuit to place the power converter circuit in a standby mode upon determining that the electronic device has been detached from the output line.

18. The power converter circuitry defined in claim 15 further comprising a current-limited voltage regulator that supplies a voltage to the output line.

19. The power converter defined in claim 15 further comprising an energy storage element that stores energy for powering the monitor circuitry when the power converter circuit is in a standby mode, wherein the monitor circuitry is configured to direct the control circuit to momentarily place the power converter circuit in an active mode instead of the standby mode when the monitor determines that the energy storage element is to be replenished.

20. The power converter defined in claim 15 wherein the monitor circuitry is configured to make a load current measurement with the current sensing resistor to determine whether current is flowing through the electronic device and is configured to open the switch to determine whether the electronic device is attached to the output line only when the load current measurement does not indicate that there is current flowing through the electronic device.

21. An alternating-current (AC) to direct-current (DC) power converter to which an electronic device may be connected when it is desired to power the electronic device with the power converter, the power converter comprising:

a power converter circuit that produces a DC voltage from an AC voltage;

an output line to which the electronic device may be connected;

a first current sensing resistor coupled in series with the output line;

a second current sensing resistor coupled in series with the output line and coupled in parallel with the first current sensing resistor;

at least one transistor; and

monitor circuitry that controls the at least one transistor to adjust current routing though the first and second current sensing resistors and that measures voltages across the first and current sensing resistors to monitor whether the electronic device is attached to the power converter.