GB2624678A

GB2624678A - Visual alarm device

Info

Publication number: GB2624678A
Application number: GB2217700.0A
Authority: GB
Inventors: David Knight Robert
Original assignee: Apollo Fire Detectors Ltd
Current assignee: Apollo Fire Detectors Ltd
Priority date: 2022-11-25
Filing date: 2022-11-25
Publication date: 2024-05-29
Also published as: GB202217700D0

Abstract

A visual alarm device (VAD) comprises a constant current source 302; a regulator 305 to regulate a front end voltage; a storage capacitor 307 arranged to be charged from the front end voltage; logic 306 configured to, in response to a drop in supply voltage level, provide a reduced front end voltage level, and switch from regulating the front end voltage to regulating a voltage across the constant current source 302, based at least in part on a voltage headroom of the constant current source 302. The front end voltage may be regulated by maintaining a voltage on an input capacitor 304 and reduced by discharging the input capacitor 304. A switching converter 308, such as a buck or boost converter, may be provided for transferring charge to the storage capacitor 307 from the input capacitor 304. The front end voltage may be regulated by a fixed voltage clamp. A variable voltage clamp may be further provided upstream of the fixed voltage clamp and arranged to reduce the front end voltage. The alarm device may be communicatively coupled to a network using a communication protocol having pulses.

Description

Visual Alarm Device

Field of Disclosure

[0001] Aspects of the present disclosure relate to visual alarm devices (VADs) and more specifically methods and apparatus for improving VAD efficiency.

Background

[0002] A fire alarm system typically consists of a central fire panel connected to a number of 'loops' -long cables that extend around the building and return to the panel. A loop is normally two wires and carries both power and a communications protocol to fire alarm peripherals. The fire alarm peripherals are mainly detectors, manual call points, sounders and visual alarm devices (VADs), although more specialised devices are available.

[0003] Owing to the long length of the loop wires, power available to fire alarm peripherals is limited. On loops where the communications protocol uses current signalling, it is particularly difficult to keep the peripheral device efficiency high without affecting the communications. High efficiency is vital for devices such as sounders and VADs which use much more current than other devices.

[0004] A common method of communication by fire alarm systems is by voltage pulses superimposed on a supply voltage from a control panel to communicate with loop devices. The loop devices communicate with the panel using pulses of current superimposed on their supply current. The pulses are small in relation to a maximum loop load and are easily lost if there are other sources of current variation on the loop. For this reason, all loop devices incorporate a constant current power supply so that the current pulses may be easily recovered.

[0005] The constant current characteristic has to be maintained even under fault conditions, where the device supply voltage drops well below the rated voltage range for the device. In low power devices, it is normal practice to make a lower voltage part of an operating range of the constant current power supply, thereby ensuring the power supply still continues to operate in constant current mode during fault.

However, for high power devices this limits the power available from the power supply, which keeps the efficiency low.

[0006] VADs are a type of flashing beacon that periodically emits a very bright flash designed to attract attention of the hearing impaired during an alarm. The energy for the flash is accumulated in a storage capacitor during a flash interval. The power available from a constant current power supply is proportional to the voltage behind it, so if the capacitor is charged directly from the supply the efficiency is reduced as more voltage is dropped across the power supply as the capacitor charges. Therefore, there is a need for a VAD that can maintain a high voltage behind a constant current power supply whilst maintaining sufficient headroom for maintaining the constant current characteristic, and that efficiently uses stored charge to drive the visual element.

Summary of Invention

100071 In accordance with the present invention, there is provided a method of operating an electronic alarm device in accordance with claim 1 and an electronic alarm device in accordance with claim 13 Other aspects of the invention are set out in the dependent claims.

[0008] In a preferred embodiment there is provided a method of operating an electronic alarm device comprising: providing a constant current from a constant current source; charging a storage capacitor from a front end voltage while regulating a level of the front end voltage, reducing the level of the front end voltage to provide a reduced front end voltage in response to a drop in a supply voltage level, and; switching from regulating the front end voltage to regulating a voltage across the constant current source, regulating the voltage across the current source being based at least in part on a voltage headroom of the constant current source.

[0009] Advantageously, this method of operating an alarm device is able to maintain as high a voltage as possible behind a constant current power supply whilst maintaining sufficient headroom for maintaining the constant current characteristic.

[0010] In some embodiments, the front end voltage is regulated by maintaining a voltage on an input capacitor.

[0011] In some embodiments, the front end voltage is reduced by discharging the input capacitor.

100121 In some embodiments, the storage capacitor is limited to discharge to the front end voltage level when driving a load [0013] In some embodiments, the voltage on the input capacitor and the voltage across the current source are regulated by comparators.

100141 In some embodiments, the storage capacitor is indirectly charged from the input capacitor.

100151 In some embodiments, charge is transferred to the storage capacitor via a switching converter.

[0016] In some embodiments, the front end voltage is regulated by a fixed voltage clamp.

[0017] In some embodiments, the front end voltage is reduced by a variable voltage clamp positioned upstream of the fixed voltage clamp 100181 In some embodiments, the electronic alarm device is communicatively coupled to a network using a communication protocol having protocol pulses.

100191 In some embodiments, the method further comprises engaging a protocol pulse extender based on the supply voltage drop.

[0020] In some embodiments, the storage capacitor drives an audio/visual, A/V, component.

[0021] In another preferred embodiment there is provided an electronic alarm device comprising: a constant current source operable to provide a constant current; a regulator to regulate a front end voltage; a storage capacitor configured to be charged from the front end voltage; logic configured to, in response to a drop in a supply voltage level: provide a reduced front end voltage level, and; switch from regulating the front end voltage to regulating a voltage across the constant current source, wherein regulating the voltage across the current source is based at least in part on a voltage headroom of the constant current source [0022] In some embodiments, the front end voltage is regulated by maintaining a voltage on an input capacitor.

[0023] In some embodiments, the front end voltage is reduced by discharging the input capacitor.

[0024] In some embodiments, the storage capacitor drives an audio/visual, A/V, component.

[0025] In some embodiments, the electronic alarm device further comprises a switching converter for transferring charge to the storage capacitor from the input capacitor, wherein the switching converter is a buck converter or a boost converter.

[0026[ In some embodiments, the electronic alarm device further comprises comparators operable to regulate the voltage on the input capacitor and the voltage across the current source.

[0027] In some embodiments, the electronic alarm device further comprises, when the converter is a boost converter, a comparator configured to limit the storage capacitor to discharge to the front end voltage level when driving the A/V component, or; when the converter is a buck converter, a comparator configured to stop driving the A/V component when the storage capacitor is depleted of charge.

[0028] In some embodiments, the electronic alarm device further comprises logic configured to enable the switching converter based at least in part on: a voltage on the input capacitor reaching a threshold voltage, or; a voltage across the current source dropping below a threshold voltage.

[0029] In some embodiments, the electronic alarm device further comprises a fixed voltage clamp, wherein the front end voltage is regulated by the fixed voltage clamp.

[0030] In some embodiments, the electronic alarm device further comprises a variable voltage clamp upstream of the fixed voltage clamp and configured to reduce the front end voltage [0031] In some embodiments, the electronic alarm device is communicatively coupled to a network using a communication protocol having protocol pulses.

[0032] In some embodiments, the electronic alarm device further comprises a protocol pulse extender, wherein the protocol pulse extender is engaged based on the supply voltage drop [0033] In some embodiments, the storage capacitor drives an audio/visual, A/V, component.

[0034] The foregoing provides a simplified summary of one or more embodiments and aspects to provide a basic understanding of those embodiments and aspects, and is not intended to identify key elements of all of the embodiments and aspects nor to provide an extensive overview of all embodiments and aspects. Various embodiments and aspects of the present invention are described without limitation below, with reference to the accompanying figures.

Brief Description of the Drawings

[0035] The features, objects, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numerals refer to similar elements.

[0036] Fig 1 depicts a known visual alarm device.

[0037] Fig. 2 depicts graphs showing various parameters inherent in common visual alarm device designs.

[0038] Fig. 3 depicts a front end voltage monitor and headroom monitor circuit in

accordance with aspects of the present disclosure.

[0039] Fig. 4 depicts a flash latch circuit in accordance with aspects of the present

disclosure.

Detailed Description

[0040] The present disclosure relates to apparatus and methods to maximise efficiency and automatically adjust alarm system operating conditions while ensuring that there is no disturbance to a current signalling mechanism of the communications protocol.

[0041] By regulating a voltage behind the constant current power supply to a high value, while still maintaining the constant current over the rated voltage range, the above mentioned problems may be alleviated. It is preferred that the voltage behind the constant current power supply is regulated to as high a value as possible while still maintaining the constant current over the rated voltage range. Under fault conditions, the voltage is reduced to maintain the constant current characteristic and the circuit automatically adjusts to operate with reduced performance. The automatically adjusting circuitry ensures that outside of the rated voltage range there is a graceful reduction of performance rather than a sudden failure. It also makes for a more reliable design as the current from the power supply is the only critical parameter to control.

[0042] A 30-50% reduction in the supply current (i.e. current from the power supply) may be achieved compared to existing VADs, which may have the highest current consumption of all devices on a loop.

[0043] This improvement in efficiency leads to further advantages. For example, the efficiency allows one or more of the following: more devices may be connected to a loop; the loop may be longer; thinner, cheaper cable may be used; fewer loops may be required to cover a building, less cable, less installation, cheaper control panel; and enhanced reliability and operation under fault conditions. Aspects of the present disclosure are also applicable to systems that do not use current signalling but still require the performance of the system to be deterministic and easily predictable.

[0044] Fig. 1 depicts a known visual alarm device (VAD) 100, also known as a loop powered VAD (LPV). An LPV uses a constant current source 101 to charge up a reservoir, or input capacitor 102. The input capacitor 102 charges until the voltage reaches that of a Zener clamp (also referred to herein as a Zener, Zener diode and a clamping Zener) 103. The charge on the input capacitor 102 is used to drive a switching converter 106, in this case a buck LED driver, also known as a buck converter, which drives LED 107. Voltage source 104 controls pulse length switch 105 with a flash rate of, for example, 0 5Hz [0045] Fig. 2 highlights that the afore mentioned mechanism of charging a capacitor (e.g. input capacitor 102 shown in Fig. 1) from a current source (e.g. current source 101 shown in Fig. 1) is inherently inefficient, as the energy received is proportional to the voltage on the capacitor.

[0046] A front end voltage is the voltage at which the components in the VAD operate. The front end voltage may be within a range having a maximum value accounting for headroom to allow for the constant current characteristic of constant current source as described previously, and a minimum value at which the VAD 100 can still achieve rated performance. The purpose of Zener clamp 103 is to limit the front end voltage so that there is sufficient headroom for the constant current characteristic of constant current source 101 to be maintained but, by selecting a Zener clamp voltage that ensures operation under fault conditions, the available energy is limited and the efficiency of the circuit is compromised.

[0047] As stated above, the charging of a capacitor 102 from a current source 101 is inherently inefficient because the energy received is proportional to the voltage on the capacitor 102 [0048] The lost energy 203 because of the increased voltage drop across the current source during charging is an unavoidable feature of the LPV topology and cannot be eliminated.

[0049] Since any power dissipated 202 in the Zener clamp 103 is also wasted, it is advantageous to minimize the period during which this is conducting.

[0050] Under normal conditions the input capacitor 102 charges up to the Zener clamp voltage before the next flash of the VAD To minimize the wasted energy, the component values would be chosen such that the Zener clamp 103 just starts to conduct by the time the next flash is due.

100511 If the input capacitor 102 does not reach the Zener clamp voltage, the area under the charging curve 201 is reduced -less energy has been received during the charge cycle Despite this, owing to the fixed drive width, the switching converter attempts to take out the same amount of energy on every flash.

[0052] If the energy received is less than the energy required to drive the LED 107, the end of charge voltage will get progressively lower on each cycle until there is no longer enough energy in the input capacitor 102 to drive the LED 107 for the full flash duration. The circuit has transitioned from regulating on the Zener clamp 103 to regulating on the drop out voltage of the switching converter 106, and it will not recover without a power cycle. Although the VAD still works, the LED pulse width is much shorter than could be achieved with the available energy, and the coverage volume specification is no longer met.

[0053] This failure may be triggered by a momentary supply interruption or brownout. Minimizing the wasted power in the Zener clamp 103 to improve the VAD efficiency makes the VAD more susceptible to the failure, to the point where even normal component tolerances can be enough to cause spontaneous failure. Increasing the Zener voltage results in the loss of constant current characteristics very early into a power supply drop.

[0054] The constant current source is an unavoidable feature of the connection to the loop, and this must remain in compliance to prevent current variations on the loop. The current source 101 must have good transient response in order to reject the voltage pulses on the loop and whatever variations are happening behind it. The DC accuracy is less important provided it is accurate enough to provide enough current to run the VAD reliably.

[0055] In a known VAD, the normal operating voltage range of loop devices is 17V to 35V, but the constant current characteristic must be maintained down to a minimum value, e.g. 14V. In lower power devices this is easily accomplished by simply making the device operate from 14V. Allowing for some headroom, this means the voltage behind the current source will be even lower (e.g. around 12V) which is suitable for most applications.

[0056] For most AV devices however, achieving the rated performance from a minimum voltage (e.g. 14V) upwards compromises the efficiency over the normal range For AV devices, rated performance must be achieved at, for example, 17V, but a reduced performance is permitted below this.

[0057] For efficiency, the voltage available behind the current source needs to be as high as possible. In accordance with aspects of the present disclosure, the required headroom could be reduced to e.g. 0.5V or less, giving a front end voltage of around 16.W. This gives over 35% more power available compared to a device with only 12V behind the source.

[0058] This works over the normal range, but if the voltage falls below 17V the current source drops out and the constant current characteristic is lost. Further aspects of the present disclosure provide for reducing the front end voltage under these conditions such that the headroom for current source is maintained and the constant current performance preserved.

[0059] A higher voltage could be used on the front end if aspects of the present disclosure are employed to preserve the current source headroom However, if the rated performance must be achieved at, for example, 17V there is nothing useful that may be done with the extra energy available at higher voltages. Also, for sudden voltage drops, the mechanism employed may not be able to restore the current source headroom instantaneously, giving a brief loss of the constant current characteristic. Sudden voltage drops in the normal voltage range are expected, and any loss in the constant current characteristic over this range is not permitted.

[0060] Sudden voltage drops below 17V, as used in the above example, would only occur under fault conditions, and in this case a brief loss of the constant current characteristic is acceptable as the fault would be likely to cause a loss of protocol data anyway. Ideally the constant current characteristic should be restored within 50ms to ensure only one protocol frame is lost.

[0061] The higher front end voltage as provided by aspects of the present disclosure may be used to provide power to a sounder circuitry directly. This voltage is also reduced under fault conditions, allowing a graceful degradation of performance.

Efficient capacitor charging 100621 As stated earlier, charging the storage capacitor 307 directly from the current source as in the known VAD of Fig. 1 is inefficient because power is dissipated in the source as it charges (see e.g. Fig. 2, area 203). For best efficiency, aspects of the present disclosure provide a method to charge the storage capacitor 307 that maintains the front end voltage at the maximum possible value.

[0063] This also has the effect that it eliminates sudden voltage changes behind the current source, making it easier for the source to regulate the current, and completely decoupling the downstream circuitry from the loop.

[0064] It is important to note that current source is not expected to be perfect.

The current will vary to some degree due to protocol pulses (i.e. the signalling of the communications protocol), but insignificantly since the current variation is synchronous to the communication protocol and dwarfed by the current required to charge and discharge the cable capacitance. Small current variations owing to voltage changes behind the current source are more significant, as these may be caused by the VAD & sounder circuitry. These circuits are synchronized across the loop, so the variations are cumulative, and being asynchronous to the protocol may occur at the right point to cause protocol corruption. Keeping the voltage behind the current source constant not only ensures the best efficiency but also eliminates any possibility of protocol corruption.

Adequate storage [0065] In known LPV designs the Zener clamp across the storage capacitor 307 is an inescapable feature of the current source capacitor charging topology. In known designs, 25% of the total energy has to be dissipated in this component to ensure reliable operation.

[0066] In accordance with aspects of the present disclosure, by ensuring adequate storage capacity the capacitor storage never becomes full, and all the energy 11.

accumulated over a storage interval is used on every flash. No energy is wasted in a Zener clamp. The supply current is adjusted to give the desired margin on the coverage volume at audit [0067] In contrast, when employing a known LPV circuit design there must be allowance for the margin for audit, then add another margin on top to ensure the power supply is reliable The compounding of safety margins like this reduces the efficiency of operation [0068] If a mechanism of maximizing the front end voltage is employed, wasting any power in a limiting clamp is an indication that the capacitor does not have enough storage capacity. If there is excess energy available, it should be used as a safety margin elsewhere rather than being dissipated e.g. through the Zener clamp. A use of this extra energy is to put it into the VAD LED for increased margin at audit.

Use all the available energy on every flash [0069] In known loop powered VAD designs the flash energy is constant, with the pulse width set by a microcontroller and the LED current set by resistors around the LED driver. As described previously, this works until the energy coming into the circuit is less than that required to drive the LED, whereupon the circuit fails, delivering a pulse width that is much shorter than could be achieved with the amount of energy available.

[0070] In each flash it is only possible to deliver the energy that has been harvested during the charging cycle. Attempting to do anything else will lead to failure of the circuit.

[0071] Aspects of the present disclosure achieve this by altering the pulse width fed to the LED driver. The microcontroller may start the flash pulse in the normal way and the pulse may be ended once all the harvested energy on the storage capacitor 307 has depleted.

[0072] This not only provides a fail-safe method of driving the LED, but it also gives an easy way for the performance to be reduced once the supply voltage drops out of the normal operating range.

[0073] It becomes unnecessary to tune and tolerance the supply circuitry to meet the demand. No microcontroller involvement is required, and there is nothing to get wrong such as the limits for and characteristics of a 'limp home mode' as has been suggested in other designs.

[0074] Unlike the difficult to measure Zener conduction time in the known LPV design, the health of the circuit is easily monitored in production by measuring the VAD pulse width. Once the lens is proven, a pulse width and single intensity measurement is all that is required to ensure the coverage volume specification has been met.

[0075] Turning to Fig. 3, there is provided a circuit 300 having a supply voltage 301 and a current source 302 comprising a front end voltage monitor which may include a comparator 305, a logic 306, and a switching converter 308 (e.g. a buck converter or a boost converter) and headroom protection mechanism which may include the comparator 303, the logic 306, and the switching converter 308.

[0076] In an aspect of the present disclosure, the front end voltage monitor comprises a comparator 305 that regulates the voltage on the input capacitor 304. When the voltage is low, the input capacitor 304 is allowed to charge from the current source 302. When the voltage on the input capacitor 304 gets high enough, the switching converter 308 is enabled removing charge from the input capacitor 304 and transferring it to the storage capacitor 307. In this arrangement, the front end voltage is set by maintaining the voltage on the input capacitor 304. The front end voltage can be reduced by discharging the input capacitor 304.

[0077] The comparator 305 has hysteresis to ensure the switching converter 308 operates for a set period. In an example, the upper threshold is around 16.5V to ensure the current source 302 can still regulate when the loop voltage is at 17V. The lower threshold is selected to be as high as possible while still allowing the switching converter 308 to operate for enough time when enabled.

[0078] Note that even though the input capacitor 304 charges from the current source 302, the efficiency remains high because the voltage is maintained around 16V. Because the front end voltage is substantially constant, the current source 302 has only to compensate for the voltage pulses on the loop and the rest of the circuitry is completely decoupled. The constant voltage also allows this to be used to drive the sounder circuitry and supplement a power supply of the microcontroller [0079] In other words, the front end voltage monitor mechanism maintains a high voltage behind the current source to keep the efficiency high, and this is achieved by comparator 305 regulating the voltage on the input capacitor 304 [0080] Hysteresis is provided to ensure the switching converter 308 is enabled for a reasonable pulse width The switching converter pulse width is a function of the hysteresis voltage, the size of the input capacitor 304 and the switching converter current.

[0081] In another aspect of the present disclosure the headroom protection mechanism may comprise comparator 303 which monitors the voltage across a pass element of the current source 302. If the voltage gets too low, the front end voltage is reduced to provide a reduced front end voltage. This maintains enough voltage across the pass element to ensure the current source 302 stays in compliance. In this way, there is a switch from regulating the front end voltage to regulating a voltage across the constant current source.

[0082] The comparator 303 outputs a square wave when the voltage is too low because there are protocol pulses on the loop. To ensure a constant enable signal to the switching converter 308, a pulse extender may be employed in some embodiments sufficient to bridge the gap of the longest protocol pulses (i.e. circuitry to extend the duration of a pulse).

[0083] This headroom protection mechanism will operate only when the loop drops below 17V, and the front end voltage will be reduced to ensure the constant current characteristic is maintained. The reduced front end voltage will reduce the power available for the device and the rest of the circuitry is designed to operate reliably under these conditions, giving a graceful reduction in the performance.

[0084] For sudden voltage drops below 17V it may take some time for the headroom monitor to discharge the capacitor 304 and restore the constant current characteristic. These excursions will only occur under fault conditions which are likely to cause protocol corruption anyway. The time required is short enough that the constant current characteristic is restored by the time the next protocol frame is due [0085] This compromise allows the device to operate with a nominal by front end voltage as opposed to 13V as it would if the constant current characteristic had to be maintained continuously from 14V This gives a 23% increase in the available power.

[0086] It is noted that although Fig 3 shows an implementation using a boost converter as the switching converter, other embodiments may employ, for example, a buck converter.

[0087] The headroom protection mechanism may be implemented using the front end voltage monitor to set, maintain and reduce the front end voltage, or may be implemented by other means to set, maintain and reduce the front end voltage. In a non-limiting example described below, the headroom protection mechanism may be implemented using a fixed and a variable voltage clamp.

[0088] Accordingly, in some examples the front end voltage is set by maintaining a voltage on an input capacitor 304. The voltage on the input capacitor 304 may be maintained at a substantially constant level by charging and discharging the input capacitor 304 by using a comparator e.g. as previously described by the front end voltage monitor. In this arrangement, the front end voltage can be reduced by discharging the input capacitor 304. For example, if the voltage across the pass element of the current source gets too low, the switching converter 308 is enabled via logic 306, pulling charge out of the input capacitor 304.

[0089] In some examples, the headroom protection mechanism comprises a variable voltage clamp and a fixed voltage clamp that are configured to set the front end voltage. Under normal operating conditions the fixed voltage clamp maintains the front end voltage at a predetermined level. When the voltage across the pass element of the current source gets too low, the variable voltage clamp, located upstream of the fixed voltage clamp, responds by lowering the front end voltage thereby keeping the current source in compliance. Under both normal and low voltage conditions, the storage capacitor 307 charges up to the voltage available behind the current source. The variable voltage clamp is able to respond instantly to a low headroom condition (i.e. when the voltage across the pass element of the current source gets too low). In some examples, the variable voltage clamp is a transistorised clamp, and/or the fixed voltage clamp is a Zener diode.

[0090] Turning to Fig. 4 depicting yet another aspect of the present disclosure, there is provided an electronic alarm device 400 comprising a flash latch. The flash latch is a mechanism to ensure the LED driver 405 only uses the energy stored over the last charging period to flash the LED 406. If the LED driver 405 operates for too long it will not only discharge the storage capacitor 401 (equivalent to storage capacitor 307) down to the front end voltage, it will also then discharge the input capacitor 304 via the diode in the switching converter 308. Dropping the front end voltage in this way reduces the efficiency of the device and makes it vulnerable to the same failure as known LPV designs.

[0091] A latch 404 is set by a rising edge of a strobe signal 403 from the microcontroller, enabling the LED driver 405. The latch 404 is reset (via comparator 402) by the voltage on the storage capacitor 401 falling to the front end voltage.

[0092] Under low voltage conditions the storage capacitor 401 will not attain the normal voltage during the charge period. The VAD will continue to work but the flash pulse width will be shorter, giving a smaller coverage volume. Even under these conditions, the efficiency remains high.

[0093] The flash latch 404 may be a transistor latch, or may be implemented in hardware or firmware, and the latch 404 may be resistant to transients to ensure it starts in the correct state. On a rising edge of the strobe signal 403 the latch is set. The LED driver 405 is then enabled and it starts to deplete the charge in the storage capacitor 401.

[0094] As the voltage on the storage capacitor 401 drops, the comparator 402 switches when it reaches the voltage on the input capacitor 304. The comparator 402 has some hysteresis to ensure a long enough pulse width to reset the latch 404 reliably.

[0095] In the event of a fault, the LED driver 405 may not deplete the storage capacitor 401 and the latch 404 may never be reset. To combat this there is a provision (not shown) to reset the latch 404 on a falling edge of the strobe signal If this is implemented, the strobe signal must be longer than the longest expected LED pulse capable by the hardware.

[0096] Many other variants and embodiments will be apparent to the skilled reader, all of which are intended to fall within the scope of the invention whether or not covered by the claims as filed. Protection is sought for any and all novel subject matter and combinations thereof disclosed herein.

Claims

Claims A method of operating an electronic alarm device comprising: providing a constant current from a constant current source; charging a storage capacitor from a front end voltage while regulating a level of the front end voltage; reducing the level of the front end voltage to provide a reduced front end voltage in response to a drop in a supply voltage level; and switching from regulating the front end voltage to regulating a voltage across the constant current source, wherein regulating the voltage across the current source is based at least in part on a voltage headroom of the constant current source.
2. The method of claim 1, wherein the front end voltage is regulated by maintaining a voltage on an input capacitor.
3. The method of claim 2, wherein the front end voltage is reduced by discharging the input capacitor.
4. The method of claims 2 or 3, wherein the storage capacitor is limited to discharge to the front end voltage level when driving a load
5. The method of any of claims 2 to 4, wherein the voltage on the input capacitor and the voltage across the current source are regulated by comparators
6. The method of any of claims 2 to 5, wherein the storage capacitor is indirectly charged from the input capacitor.
7. The method of any of claims 2 to 6, wherein charge is transferred to the storage capacitor via a switching converter.
8. The method of claim 1, wherein the front end voltage is regulated by a fixed voltage clamp
9. The method of claim 8, wherein the front end voltage is reduced by a variable voltage clamp positioned upstream of the fixed voltage clamp
10. The method of any preceding claim, wherein the electronic alarm device is communicatively coupled to a network using a communication protocol having protocol pulses
11. The method of claim 10, further comprising engaging a protocol pulse extender based on the supply voltage drop.
12. The method of any preceding claim, wherein the storage capacitor drives an audio/visual, A/V, component.
13. An electronic alarm device comprising: a constant current source operable to provide a constant current; a regulator to regulate a front end voltage; a storage capacitor configured to be charged from the front end voltage; logic configured to, in response to a drop in a supply voltage level: provide a reduced front end voltage level; and switch from regulating the front end voltage to regulating a voltage across the constant current source, the regulating the voltage across the current source based at least in part on a voltage headroom of the constant current source.
14. The electronic alarm device of claim 13, wherein the front end voltage is regulated by maintaining a voltage on an input capacitor.
15. The electronic alarm device of claim 14, wherein the front end voltage is reduced by discharging the input capacitor.
16. The electronic alarm device of claim 14 or 15, further comprising a switching converter for transferring charge to the storage capacitor from the input capacitor, wherein the switching converter is a buck converter or a boost converter.
17. The electronic alarm device of any of claims 14 to 16, further comprising comparators operable to regulate the voltage on the input capacitor and the voltage across the current source.
18. The electronic alarm device of claim 16 further comprising: when the converter is a boost converter, a comparator configured to limit the storage capacitor to discharge to the front end voltage level when driving the A/V component, or; when the converter is a buck converter, a comparator configured to stop driving the AN component when the storage capacitor is depleted of charge.
19. The electronic alarm device of claim 18, further comprising logic configured to enable the converter based at least in part on: a voltage on the input capacitor reaching a threshold voltage, or; a voltage across the current source dropping below a threshold voltage.
20. The electronic alarm device of claim 13, further comprising a fixed voltage clamp, wherein the front end voltage is regulated by the fixed voltage clamp.
21. The electronic alarm device of claim 20, further comprising a variable voltage clamp upstream of the fixed voltage clamp and configured to reduce the front end voltage.
22. The electronic alarm device of any of claims 13 to 21, wherein the electronic alarm device is communicatively coupled to a network using a communication protocol having protocol pulses
23. The electronic alarm device of claim 22, further comprising a protocol pulse extender, wherein the protocol pulse extender is engaged based on the supply voltage drop.
24. The electronic alarm device of any of claims 13 to 23, wherein the storage capacitor drives an audio/visual, A/V, component.