Bi-directional control of power adapter and load

A system comprises a computer and an external power adapter configured to be connected to the computer to provide power to the computer. The computer comprises a computer control circuit that generates a computer control signal that is provided to the external power adapter and causes a change in an output voltage of the external power adapter. The external power adapter comprises an adapter control circuit that generates an adapter control signal that is provided to the computer and causes the computer to change its power draw. The computer and adapter control circuits generate the control signals on a common conductor interconnecting the computer and the external power adapter.

BACKGROUND

Some computers, such as notebook computers, have an external power adapter that converts alternating current (AC) voltage to direct current (DC) voltage for consumption by the computer. The DC voltage provided to the computer can be used to operate the logic circuits in the computer as well as to charge a battery. Different voltages may be required for battery charging as opposed to operating the computer's logic circuits. Additionally, a computer may be able to draw more current than the power adapter is rated to provide.

NOTATION AND NOMENCLATURE

DETAILED DESCRIPTION

FIG. 1illustrates an embodiment comprising an AC power adapter10coupled to a load20via an electrical cable15. The AC power adapter10is external to the load, at least in the embodiment shown inFIG. 1, and converts AC voltage (e.g., 120 VAC) to one or more suitable DC voltages (14 VDC, 19 VDC, etc.) for operating the load20. The load20may comprise any type of electrical system. In some embodiments, the load20comprises a computer (e.g., a notebook computer). In the examples ofFIGS. 2 and 3provided below, the load20is referred to as a notebook computer, but the load could comprise systems other than notebook computers. In some embodiments, the load20is battery-operated and comprises a rechargeable battery that is recharged by power provided the AC power adapter10(hereinafter “power adapter”) via cable15.

In accordance with at least some embodiments, the power adapter10and load20comprise circuitry that enables each such device to control the other. The power adapter10causes the load20to change (e.g., reduce) its power draw as the power draw from the power adapter10nears and/or exceeds the power rating, or other threshold, of the power adapter. That is, if the load20begins to draw more power than the power adapter10can safely provide, the power adapter provides a control signal to the load to reduce its power consumption. The load20responds to the signal initiated by the power adapter10by reducing its power consumption. This reduction can be in accordance with any of a variety of power-reducing techniques. Examples comprise dimming a display of the load, throttling back a processor of the load, spinning down a rotatable storage medium (e.g., hard disk drive), ceasing battery charging, etc. The power adapter10also permits the load20to increase its power draw if the load's power draw is not at or in excess of the power adapter's threshold.

The load20is also able to control the power adapter10. In at least some embodiments, the load20comprises host logic (e.g., processor, memory, etc.) as well as a rechargeable battery. The voltage used to recharge the load's battery may be a different voltage level than the voltage used to power the load's host logic. While some loads may comprise battery charging circuitry to generate the appropriate battery charging voltage, the load20of various embodiments does not necessarily comprise battery charging circuitry. In such embodiments, the power adapter10provides the voltage necessary to charge the load's rechargeable battery. Moreover, the power adapter10selectively provides at least two different voltages to the load20. One voltage level is suitable for operating the host logic in the load20and another voltage level is suitable for charging the load's battery. The load20causes a control signal to be generated between the power adapter10and load20which, in turn, causes the output voltage provided by the power adapter10to the load20to change, for example, to increase if the load20requires a higher voltage or to decrease if the load20is operable with a lower voltage.

The cable15connecting the power adapter10to the load20comprises at least three conductors in various embodiments. In the embodiment ofFIG. 1, the cable comprises conductors16,17, and18. Conductor16is used to provide the power adapter's output voltage (Vout) to the load20and conductor17is a return (ground). In accordance with various embodiments, the power adapter10and load20cause control signals to be provided between the power adapter and load to enable one such device to control the other as described above. Such control signals are provided between the power adapter10and load20on a common conductor18. Thus, the power adapter10and load20, at least in part, control each other via control signals provided therebetween on a common conductor.

The control principle is illustrated inFIG. 2. Vout16is set to the desired voltage by regulating the voltage at the regulation feedback node19. While the power adapter10is not commanding a decrease in load current, the decrease load command current signal80is zero. While the notebook20is not requesting an increase in adapter voltage, the increase supply voltage request current signal85is zero. In this state, the voltage at regulation feedback node19is lower than the zener voltage of zener diode72in the notebook computer, so zener72is not conducting, and the voltage across resistor71is zero. Likewise diode48is not conducting, so the only current through resistor45is that drawn by the feedback for regulation of Vout16. The notebook20may request an increase in adapter voltage, by increasing current signal85. This current flows through resistor45and diode48, resulting in an increase in Vout16. Alternately, the adapter10may command a decrease in load current drawn by the notebook20, by increasing current signal80. Current80then flows through zener diode72and resistor71, causing a voltage across resistor71, which commands the notebook20to decrease, or throttle, its power draw. Should the load decrease command current80occur while current signal85is flowing, the signal80simply subtracts from the signal85, thus reducing the effect of the increase supply voltage request signal85. The difference between them is used to control power adapter voltage16. This is a seamless transition, requiring no switching or additional control signals. No logic is required to separately control or modify the signals80and85to assert one signal while holding the other signal inactive—both signals can co-exist simultaneously and on the same conductor18. By design, the maximum level of the decrease load command current80is greater than the maximum level of the increase supply voltage request signal85, so the adapter can overcome any request to increase voltage and still decrease load, as prevention of overload is higher priority than increasing power adapter voltage.

FIG. 3shows illustrative circuitry in the power adapter10and load20(e.g., notebook computer). The circuitry to the left of dashed dividing line30represents at least some of the circuitry provided in the power adapter10, while circuitry to the right of the dashed dividing line30represents at least some of the circuitry provided in the notebook computer20.

The circuitry of the power adapter10comprises an adapter voltage adjust circuit40coupled to an adapter control circuit50. The adapter voltage adjust circuit comprises operational amplifier41, capacitor42, resistors43and45-47, and zener diode44. Adapter control circuit50comprises operational amplifier51, resistors53-54, and56-59, capacitor52, zener diode55, and transistor56. A diode48is provided coupling the adapter voltage adjust circuit40to the adapter control circuit50.

The notebook computer circuitry shown inFIG. 3comprises a computer control circuit60coupled to a computer power draw adjust circuit70. The computer control circuit60comprises an operational amplifier61, resistor64, transistor63, and potentiometer62. The computer power draw adjust circuit70comprises an operational amplifier70, resistors71and73and zener diode72.

The component values listed inFIG. 3are illustrative of an embodiment. The component values can be different from that shown.

As described above, the power adapter10causes the notebook computer20to change (e.g., reduce) its power draw as the power draw from the power adapter10nears and/or exceeds the power rating, or other threshold, of the power adapter. The circuitry that performs this functionality comprises circuitry in both the power adapter10and the notebook computer20, namely the adapter control circuit50working in concert with the computer power draw adjust circuit70.

Current from the power adapter10(Iout) flows through conductor16and to the notebook computer20, and returns via ground conductor17. Resistor54comprises a sense resistor, that is, a resistor with a low resistance value (e.g., 0.01 ohms). The resistance is low enough so as not to disturb the operation of the circuit. The voltage across the resistor is proportional to the output current of the power adapter10. The zener diode55comprises, for example, a 50 millivolt (mV) voltage reference. The voltage generated across sense resistor54is provided, in part via the zener diode55to the non-inverting (+) and inverting (−) terminals of operational amplifier51. The zener diode voltage is applied to the non-inverting terminal. If the voltage across sense resistor54is less than 50 mV, the output of operational amplifier51goes high. When the current Iout is high enough so as to generate a voltage across sense resistor54in excess of 50 mV, the voltage applied to the inverting terminal of operational amplifier51will be greater than the 50 mV voltage applied to the non-inverting terminal via zener diode55. When the inverting terminal voltage becomes greater than the non-inverting terminal, the output of operational amplifier51goes low.

The values of the zener diode55(e.g., 50 mV) and the sense resistor (0.01 ohms) is chosen so that the output voltage of operational amplifier decreases when the power adapter's output current Iout begins to near or exceed a rating associated with the power adapter. Thus, a low voltage at the output of the operational amplifier51indicates that the power adapter10is being driven, or about to be driven, past its maximum current rating.

In the embodiment ofFIG. 3, the transistor56comprises a PNP transistor. A PNP transistor is turned on (i.e., conducts current from its collect to emitter) upon application of low base-to-emitter voltage and is turned off upon application of a high base-to-emitter voltage (i.e., lower or higher than a threshold voltage). When the power adapter's output current Iout is less than the adapter's rating, the current through sense resistor54is low enough relative to the voltage of zener diode55so that the output voltage of the operational amplifier51is high. The operational amplifier's high output voltage forces the PNP transistor56to be off.

However, if the current through the sense resistor54is high (relative to the zener diode's voltage), the output voltage of the operational amplifier51decreases which drives the PNP transistor56to turn on. While on, current80flows through resistor57, transistor56, across conductor18, and through zener diode72and resistor71in the computer power draw adjust circuit70. The magnitude of the current80is proportional to the difference between the power adapter's output current Iout and the rating threshold.

In some embodiments, a sawtooth waveform is generated (via circuitry not shown inFIG. 3) and provided to the non-inverting input terminal of comparator74. In the example shown inFIG. 3, the minimum voltage of the sawtooth waveform is 1.2V and the maximum voltage is 2.5V. The voltage across resistor71is provided to the comparator's inverting terminal. The output voltage of the comparator74is high if the voltage on the non-inverting terminal exceeds the voltage on the inverting terminal, and low otherwise. When current flows through transistor56and conductor18, the current80has a magnitude that is such that the voltage generated across resistor71is greater than 1.2V. The voltage across resistor71is proportional to the magnitude of current80and thus increases as the current80increases and, indirectly, as the adapter's output current Iout increases. The output voltage from comparator74comprises a pulse train (i.e., series of digital pulses) whose duty cycle is controlled by the magnitude of the voltage across resistor71(and thus current80and the power adapter's output current Iout).

The pulse train output of comparator74comprise a pulse-width modulated (PWM) signal controlled indirectly by the power adapter's output current lout. The PWM signal from comparator74is used by the computer power draw adjust circuit70to cause the notebook computer20to adjust its power draw (e.g., throttling the clock speed of a processor, dimming a display, etc.). The smaller the pulse width, the lower the power draw. This results in a controlled reduction in power draw; it is a regulation process.

The zener diode72in the computer power draw adjust circuit70comprises a current blocking device that prevents the computer power draw adjust circuit from generating the PWM signal unless the voltage on conductor18through which current80flows has a voltage greater than a threshold voltage associated with the zener diode72(e.g., 6.8V).

As the notebook computer20reduces its power draw, the output current Iout provided by the power adapter will reduce to the point at which the voltage across sense resistor54is less than the threshold voltage of zener diode55. At that point, the PNP transistor56starts to turn off, decreasing current80through the resistor71of the computer power draw adjust70. When PNP transistor56turns off completely, the output voltage of comparator74becomes a constant high voltage which signals to the notebook computer that it no longer need actively reduce its power draw.

The combination of capacitor52and resistor53in the adapter control circuit50acts as an integrator that slows down the changes in current80to thereby slow down the notebook computer's attempts to alter its power consumption, and thereby stabilizes the control loop that controls power draw.

As described above, the notebook computer20causes a control signal to be generated between the power adapter10and load20which, in turn, causes the output voltage provided by the power adapter10to the notebook computer20to change, for example, to increase if the notebook computer20requires a higher voltage or to decrease if the notebook computer20is operable with a lower voltage. The circuitry that performs this functionality comprises circuitry in both the power adapter10and the notebook computer20, namely the computer control circuit60working in concert with the adapter voltage adjust circuit40.

The operational amplifier41in the adapter voltage adjust circuit40is configured as an error amplifier in the embodiment ofFIG. 3. A voltage reference is provided to the non-inverting terminal of operational amplifier41. Resistors45-47are connected in series to form a voltage divider network. The voltage across resistor47is coupled to the inverting terminal of the operational amplifier41. The adapter voltage adjust circuit40generally functions to regulate the output voltage Vout of the power adapter10. Current flows downward through the series combination of resistors45-47. The values of resistors45-47are selected so that, at a nominal value of the adapter's output voltage Vout (e.g., 14 V), the voltage across resistor47is substantially equal to the reference voltage of zener diode44, which is 2.5 V in the example ofFIG. 3. If the power adapter's output voltage Vout deviates from its nominal voltage, the voltage across the resistor47will also change. Amplifier41amplifies the difference between the voltage across resistor47and the zener diode's reference voltage. This output error signal from operational amplifier41is provided to power circuitry (not specifically shown) in the power adapter10to adjust (e.g., increase or decrease) the power adapter's output voltage so as to reduce the error signal back to zero. If the output voltage from operational amplifier41decreases, the power adapter reacts by decreasing Vout. If the output voltage from operational amplifier41increases, the power adapter reacts by increasing Vout.

In some situations (e.g., for battery charging), the notebook computer20may require a different output voltage Vout from the power adapter10. Logic in the computer control circuit60is used by the notebook computer20to cause the adapter voltage adjust circuit in the power adapter10to adjusts the output voltage of the adapter accordingly. Such logic may, for example, comprise the notebook computer's processor or analog circuitry. Such logic in the notebook computer20adjusts the potentiometer62, which may comprise a digital potentiometer in some embodiments. The output voltage of the operational amplifier61equals or is proportional to the voltage provided on the operational amplifier's non-inverting terminal from the potentiometer62.

As the logic in the notebook computer20adjusts potentiometer62, transistor63(which comprises an NPN transistor) is turned on and a control signal current85flows through resistor45in the adapter voltage adjust circuit40, through diode48, through transistor63and resistor64. Current85, in addition to the current already flowing through resistors45-47, increases the voltage drop across resistor45. As a result, the voltage across resistor47decreases and the operational amplifier41generates a positive output voltage proportional to the difference between the voltage reference (zener diode44) and the voltage across resistor47. The adapter voltage adjust circuit40thereby causes the power adapter10to re-adjust (increase) its output voltage until the voltage across resistor47equals the zener diode's reference voltage. Current85causes the adapter voltage adjust circuit40to cause the adapter10to re-adjust the output voltage Vout. As the control current85decreases, the output voltage from operational amplifier41also decreases. Thus, logic in the notebook computer20can control the potentiometer62to thereby cause the power adapter10to increase or decrease its output voltage to the notebook computer20.

The diode48in the power adapter10comprises signal blocking device disposed between the adapter control circuit50and the adapter voltage adjust circuit40to block the adapter control signal (current80) from being received by the adapter voltage control adjust circuit40. That is, the diode48precludes the current80from flowing to the adapter voltage adjust circuit40, which otherwise would result in an unintended change to the power adapter's output voltage Vout when the adapter control circuit50was attempting to cause the notebook computer10to change its power draw.

In the event the adapter is requesting a decrease in load, while the notebook is requesting an increase in adapter voltage Vout, the current80sourced by adapter control circuit50is shared with current85that is drawn by computer control circuit60. This tends to cancel out the effect of each request. As a result, the currents80and85are increased by their respective control circuits, until one reaches its maximum level, and is overdriven by the other. By design, the adapter control circuit50can drive current80to a higher level than the maximum of current85from computer control circuit60. This way, overload of power adapter10is prevented. In this manner, the control circuits are able to operate simultaneously, and transition seamlessly between operating modes, without switching in new control logic or signals.