Power regulator having current and voltage modes

#Power supplies for powering digital and analog circuits are typically voltage regulated ones. When large surges of current are to be drawn at unpredictable times by an analog component (e.g., a laser diode), a predetermined voltage level of a voltage regulated power supply is typically applied to a relatively large charge storage capacitor, current surges are drawn from that large capacitor at the respective unpredictable times and then the voltage of the voltage regulated power supply is re-applied to thus replenish the capacitor by recharging it to the predetermined voltage level.

#In accordance with one aspect of the present disclosure, a dual mode regulated power supply is provided where the dual mode power supply has the ability to rapidly switch (e.g., at unpredictable times) from a voltage regulating mode to a current regulating mode in response to detection of an above threshold amount of current being drawn by a current consuming component.

#In one embodiment, the current consuming component is one whose behavior varies significantly as a function of change in voltage and/or temperature but less so as a function of change in drive current. Thus it is desirable to drive such a voltage and/or temperature sensitive component (e.g., laser diode and/or other semiconductive device) in a current regulated mode rather than in a voltage regulated mode so as to more accurately control the behavior of the voltage/temperature sensitive component. The embodiment however, has other components that preferably operate on a voltage regulated basis. A dual mode regulated power supply is used to provide both voltage regulated power and current regulated power. Switching from the voltage regulating mode to the current regulating mode has to be performed with extreme rapidity because precise timing of activation of the current consuming component (e.g., laser diode) is important to the operability of the system (e.g., a TOF sub-system). A unique circuit arrangement is provided which allows a dual mode power regulator to rapidly switch from a voltage regulating mode to a current regulating mode. More specifically, in one embodiment, a high power insulated gate switching device (e.g., MOSFET) episodically draws larges surges of current (e.g., 0.5 Ampere surges, hereafter also 0.5 A pulses) from a nearby capacitor and uses the drawn current to drive relatively large surges of pulsed power through a semiconductive laser emitter of a Time of Flight (TOF) determining system. The capacitor is replenished with charge from a dual mode power supply that is at the time of current draw, rapidly switched into operating in current regulating mode. Use of the current regulating mode causes the capacitor to automatically converge on a voltage level corresponding to the then present temperature and the then supplied rate of replenishing charge. In other words, the capacitor automatically discovers the temperature appropriate voltage for itself without need for a temperature compensating circuit. In one embodiment, the insulated gate switching device (e.g., MOSFET) and light emitter (e.g., laser diode) are closely mounted to one another on a printed circuit board having further closely packed other components. Waveforms of pulse trains that control the insulated gate switching device (e.g., power MOSFET) are programmably defined to occur at time sensitive moments and may include pulse durations that cause substantial changes of local temperature. A method of sensing the moments when charge draw is needed and of rapidly switching into a current regulating mode is provided. Accordingly, irrespective of how temperature changes, an appropriate current level is automatically applied to the semiconductive light emitter for thereby outputting a desired luminance level or a desired luminance power value.

#FIG. 1A depicts a see-through head mounted display device (HMD) embodiment having a TOF sub-system embedded therein for enabling distance determination for real objects in a field of view seen by a user wearing the see-through HMD.

#FIG. 1B is a schematic diagram organized to show a signal propagation race through physical space between signals used to drive the light emitters of FIG. 1A and signals used to gate light sensors of FIG. 1A.

#FIG. 2A is a schematic diagram of a first circuit for turning on and off high powered components and in which turn-off time may be unduly lengthened.

#One example of a circuit where large surges of current are episodically drawn (that is, at unpredictable times for the view point of the corresponding power supply) is a Time of Photonic Flight determining sub-system (also referred to as a TOF sub-system or LIDAR sub-system). In such a system, one or more light emitters (e.g., laser diodes) are used to episodically emit pulses of high intensity light for illuminating real objects in a user occupied space. TOF sub-systems may be used for example as part of a three-dimensional (3D) augmented reality system. In one variation, a pulsed photonic energy waveform corresponding to certain repetition frequencies and phases is produced as a series of time-bound bundles of photons with each bundle being output for example in the form of a short duration yet high intensity and substantially rectangular pulse of light preferably having steep rising and falling edges as well as a relatively narrow pulse width. More specifically, the per pulse, peak plateau width may desirably be on the order of about 50 nanoseconds (ns) or less as an example while the leading and trailing pulse edges of the pulse each desirably occupy no more than about 10 ns. The time it takes for the output pulses of photons to leave their emitter, travel through air to a reflective target and return to an appropriately sensitized sensor is referred to as the Time of Flight (TOF). Distance between the emitter/sensor pair and the target can be calculated as being TOF*C′/2 where C′ is the speed of light in the transmission medium (e.g., air). Because high powered components are used for producing the pulses, local temperatures may rise and behavior characteristics (e.g., I-V characteristics) of temperature sensitive parts may vary. In particular, the behavior of semiconductive light emitters when driven by a fixed value drive voltage may vary significantly in response to temperature change. Also, the behavior of such semiconductive light emitters may vary significantly in response to voltage change. Measurement accuracy and/or resolution of the TOF sub-system may suffer if component behavior fluctuates as a result of temperature change or voltage change.

#As briefly introduced in the Background section, power supplies for digital and analog circuits are typically voltage regulated ones. However, high power semiconductive light emitters such as laser diodes tend to have luminance versus drive behaviors that are more so voltage and temperature sensitive than they are current sensitive. In other words, a small change (e.g., 1%) in either voltage or temperature can substantially change luminance output. Variation of output luminance is much less if the semiconductive light emitter is driven by a constant current source. However, in cases where the semiconductive light emitter has to be rapidly switched on and off at unpredictable times (unpredictable from the point of view of the power supply), in other words, between a high current mode and a zero current mode, the use of a constant current source is problematic. For example it can be extremely wasteful of energy if the constant current output of a constant current source were to be shunted around rather than through the light emitter each time the emitter is to be shut off. Energy efficiency is much better when a capacitor is charged to an appropriate voltage and then is episodically discharged through the semiconductive light emitter when a pulse of light is to be output. However, a problem with the capacitor discharge configuration is that the voltage needs to be changed in response to temperature changes if relatively constant luminance is to be provided. Use of temperature detection and compensating circuitry has its own set of problems. It would be advantageous if reliance on direct temperature detection could be avoided.

#When a consistently fast turn on of a semiconductive light emitter is desired, there can be a minimum voltage that is needed (e.g., a floor voltage greater than 5 volts) for quickly charging RC or RLC circuits associated with switching elements (e.g., an in-series high power insulated gate switching device such as a power MOSFET) that are used for rapidly turning on the corresponding light emitter (e.g., laser diode). Thus a power regulator should be provided that, on one hand provides the minimal floor voltage (e.g., greater than 5V, and in one embodiment, greater than 7V) and yet on the other hand, overcomes the voltage and temperature sensitivity problems of semiconductive light emitters (and/or other semiconductive loads) in order to produce photonic pulses with steep leading edges and consistency for the desired light intensity.