Patent Publication Number: US-10759163-B2

Title: Printing device

Description:
BACKGROUND 
     Printing devices include circuitry used in ejecting ink from printheads. Application of a current to a printhead of a printing device causes an ink droplet to be ejected by heating a resistive element located within an ink supply in a firing chamber. This resistive heating causes a bubble to form in the ink, and the resultant pressure increase forces an ink droplet from a nozzle fluidly coupled to a firing chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are given merely for illustration, and do not limit the scope of the claims. 
         FIG. 1A  is a diagram of a printing device incorporating a power loss protection circuit, according to one example of the principles described herein. 
         FIG. 1B  is a diagram of a printing device incorporating a power loss protection circuit, according to another example of the principles described herein. 
         FIG. 2  is a diagram of an on-die V DD_ plp generator of the power loss protection circuit of  FIGS. 1A and 1B , according to one example of the principles described herein. 
         FIG. 3  is a diagram of an off-die V DD_ plp generator of the power loss protection circuit of  FIGS. 1A and 1B , according to one example of the principles described herein. 
         FIG. 4  is a graph depicting a printer controlled power down sequence, according to one example of the principles described herein. 
         FIG. 5  is a graph depicting an uncontrolled power down sequence of a printing device without the power loss protection circuits of  FIGS. 2 and 3 , according to one example of the principles described herein. 
         FIG. 6  is a graph depicting an uncontrolled power down sequence of a printing device with the power loss protection circuits of  FIGS. 2 and 3 , according to one example of the principles described herein. 
         FIG. 7  is a flowchart showing a method of operating a printing device during a power loss event, according to one example of the principles described herein. 
     
    
    
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
     DETAILED DESCRIPTION 
     The resistive elements located within the ink supply in a firing chamber may be destroyed or otherwise rendered inoperable if too much current is applied to the resistive elements. Therefore, a loss in control of a number of circuits in the printing device through an unexpected or uncontrolled loss in power to the printing device may destroy the resistive elements used to eject ink from the printheads. 
     Examples described herein provide circuit topologies that reduce or eliminate the potential for uncontrolled high voltage dissipation within printhead resistive elements and other active devices in a number of high voltage circuits of a printing device that may render the resistors and other active devices inoperable. Application of too much energy in a resistor, including resistors used to eject ink from a printhead, may destroy the resistors. Whether the resistor is made of metal-film, wire, glass, glass-ceramic, or another resistive material, its material may melt due to the application of too high of voltages. The resulting high temperature destroys the resistor material. 
     When power to a printing device is lost unexpectedly, the printing device loses control of a number of low voltage circuits that supply fire control signals to a number of high voltage circuits. The high voltage circuits such as nozzle firing field-effect transistors (FETs) that control the firing of ink from the nozzles of the printhead are enabled and disabled based on the signals from the low voltage circuits. Loss of control signals from the low voltage circuits to the high voltage circuits results in loss of control of the high voltage circuits, which may result in damage to, or destruction of the resistors and other active devices within the printhead. 
     The circuit topologies of the present application utilize a power loss protection V DD  supply referred to herein as “V DD_ plp” to prevent damage to firing resistors and other circuitry within the printhead die in the case were a V DD  supply voltage drops before a high voltage supply (V PP ) or its associated logic line (V PP_ logic) (collectively referred to herein as V PP ) is at a safe level. V DD_ plp represents a V DD  “power loss protected” supply voltage generated by the circuit topologies of the present application, and is provided to circuits within the printing device and the printhead die to prevent V PP  from being switched onto the firing resistors in an uncontrolled state. 
     As used in the present specification and in the appended claims, the terms “power loss,” “uncontrolled power loss,” or similar language is meant to be understood broadly as any loss of power to any number of circuitry within a printing device. 
     Further, as used in the present specification and in the appended claims, the term “a number of” or similar language is meant to be understood broadly as any positive number including 1 to infinity; zero not being a number, but the absence of a number. 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to “an example” or similar language means that a particular feature, structure, or characteristic described in connection with that example is included as described, but may not be included in other examples. 
     Turning now to the figures,  FIG. 1A  is a diagram of a printing device ( 100 ) incorporating a power loss protection circuit, according to one example of the principles described herein. The printing device ( 100 ) includes a number of printheads ( 110 ). Each printhead ( 110 ) includes a number of ink firing elements ( 120 ), and a number of high voltage circuits ( 121 ) to drive the ink firing elements. A high voltage power source (V PP ) ( 122 ) is included in the printing device ( 100 ) to power the high voltage circuits ( 121 ) and ink firing elements ( 120 ). 
     The printing device ( 100 ) further includes a number of low voltage circuits ( 123 ) to provide a number of fire control signals to the high voltage circuits ( 121 ). A final stage fire control signal generation device ( 124 ) is connected to the low voltage circuits ( 123 ). The printing device further includes a low voltage power supply (V DD_ plp) is connected to the low voltage circuits ( 123 ) to provide power to the low voltage circuits. 
     The printing device ( 100 ) further includes a printer power loss protection circuit ( 126 ). The printer power loss protection circuit ( 126 ) includes a power loss protection supply voltage generator ( 127 ) to maintain a power loss protection supply voltage (V DD_ plp) to the final stage fire control signal generation device ( 124 ) until the high voltage power source (V PP ) ( 122 ) drops below a threshold voltage within the high voltage circuitry ( 121 ). V DD_ plp is generated from the high voltage power source (V PP ) ( 122 ). These various elements will now be described in more detail in connection with  FIGS. 1B through 9 . 
       FIG. 1B  is a diagram of a printing device ( 100 ) incorporating a power loss protection circuit ( 112 ), according to another example of the principles described herein. The printing device ( 100 ) may be implemented in an electronic device. The printing device ( 100 ) may be utilized in any data processing scenario including, stand-alone hardware, mobile applications, through a computing network, or combinations thereof. Further, the printing device ( 100 ) may be used in a computing network, a public cloud network, a private cloud network, a hybrid cloud network, other forms of networks, or combinations thereof. 
     In one example, the methods provided by the printing device ( 100 ) are provided as a service over a network by, for example, a third party. In this example, the service may include, for example, the following: a Software as a Service (SaaS) hosting a number of applications; a Platform as a Service (PaaS) hosting a computing platform including, for example, operating systems, hardware, and storage, among others; an Infrastructure as a Service (IaaS) hosting equipment such as, for example, servers, storage components, network, and components, among others; application program interface (API) as a service (APIaaS), other forms of network services, or combinations thereof. The present systems may be implemented on one or multiple hardware platforms, in which the modules in the system can be executed on one or across multiple platforms. Such modules can run on various forms of cloud technologies and hybrid cloud technologies or offered as a SaaS (Software as a service) that can be implemented on or off the cloud. In another example, the methods provided by the printing device ( 100 ) are executed by a local administrator. 
     To achieve its desired functionality, the printing device ( 100 ) includes various hardware components. Among these hardware components may be a number of processors ( 101 ), a number of data storage devices ( 102 ), a number of peripheral device adapters ( 103 ), and a number of network adapters ( 104 ). These hardware components may be interconnected through the use of a number of busses and/or network connections. In one example, the processor ( 101 ), data storage device ( 102 ), peripheral device adapters ( 103 ), and a network adapter ( 104 ) may be communicatively coupled via a bus ( 105 ). 
     The processor ( 101 ) may include the hardware architecture to retrieve executable code from the data storage device ( 102 ) and execute the executable code. The executable code may, when executed by the processor ( 101 ), cause the processor ( 101 ) to implement at least the functionality of detecting an uncontrolled power loss to a number of high voltage devices, and with a power loss protection supply voltage generator coupled to a printhead driving circuit, maintaining a power loss protection supply voltage (V DD_ plp) to the printhead driving circuit until a high voltage supply (V PP ) to the high voltage devices drops below a threshold voltage, according to the methods of the present specification described herein. In the course of executing code, the processor ( 101 ) may receive input from and provide output to a number of the remaining hardware units. 
     The data storage device ( 102 ) may store data such as executable program code that is executed by the processor ( 101 ) or other processing device. As will be discussed, the data storage device ( 102 ) may specifically store computer code representing a number of applications that the processor ( 101 ) executes to implement at least the functionality described herein. 
     The data storage device ( 102 ) may include various types of memory modules, including volatile and nonvolatile memory. For example, the data storage device ( 102 ) of the present example includes Random Access Memory (RAM) ( 106 ) and Read Only Memory (ROM) ( 107 ). Many other types of memory may also be utilized, and the present specification contemplates the use of many varying type(s) of memory in the data storage device ( 102 ) as may suit a particular application of the principles described herein. In certain examples, different types of memory in the data storage device ( 102 ) may be used for different data storage needs. For example, in certain examples the processor ( 101 ) may boot from Read Only Memory (ROM) ( 107 ), and execute program code stored in Random Access Memory (RAM) ( 106 ). 
     The data storage device ( 102 ) may include a computer readable medium, a computer readable storage medium, or a non-transitory computer readable medium, among others. For example, the data storage device ( 102 ) may be, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium may include, for example, the following: an electrical connection having a number of wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store computer usable program code for use by or in connection with an instruction execution system, apparatus, or device. In another example, a computer readable storage medium may be any non-transitory medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     The hardware adapters ( 103 ,  104 ) in the printing device ( 100 ) enable the processor ( 101 ) to interface with various other hardware elements, external and internal to the printing device ( 100 ). For example, the peripheral device adapters ( 103 ) may provide an interface to input/output devices, such as, for example, user interface ( 109 ), a mouse, or a keyboard. The peripheral device adapters ( 103 ) may also provide access to other external devices such as an external storage device, a number of network devices such as, for example, servers, switches, and routers, client devices, other types of computing devices, and combinations thereof. 
     The user interface ( 109 ) may be provided to allow a user of the printing device ( 100 ) to interact with and implement the functionality of the printing device ( 100 ). The peripheral device adapters ( 103 ) may also create an interface between the processor ( 101 ) and the user interface ( 109 ), another printing device, or other media output devices. The network adapter ( 104 ) may provide an interface to other computing devices within, for example, a network, thereby enabling the transmission of data between the printing device ( 100 ) and other devices located within the network. 
     The printing device ( 100 ) may, when executed by the processor ( 101 ), display the number of graphical user interfaces (GUIs) on the user interface ( 109 ) associated with the executable program code representing the number of applications stored on the data storage device ( 102 ). The GUIs may display, for example, a number of user-interactive printing options. 
     The printing device ( 100 ) further includes a number of printheads ( 110 ) used to eject ink onto a print medium. The printheads ( 110 ) operate based on instructions contained within a print job sent from a computing device. The print job contains instructions to print, for example, a document. The processor ( 101 ) interprets the print job, and causes the printheads ( 110 ) to eject ink onto the print medium such that the document contained in the print job is represented on the print medium. 
     Each of the number of printheads ( 110 ) includes a printhead die ( 111 ). A printhead die ( 111 ) may be made from a block of semiconducting material on which the functional circuits described herein are fabricated. In one example, the printhead die ( 111 ) is fabricated on a wafer of electronic-grade silicon (EGS) or other semiconductor through processes such as photolithography. 
     The printing device ( 100 ) further includes a power loss protection circuit ( 112 ) fabricated into the printhead die ( 111 ) of each of the printheads ( 110 ). The power loss protection circuit ( 112 ) may assist the printing device ( 100 ) in controlling a number of circuits in a printhead die ( 111 ) through an unexpected or uncontrolled loss in power to the printing device. As described herein, an unexpected or uncontrolled loss in power to the printing device ( 100 ) may destroy the resistive elements used to eject ink from the printheads ( 110 ) or other elements included within the printhead dice ( 111 ) of the printheads ( 110 ). 
     The power loss protection circuit ( 112 ), in one example, may include a power loss protection, low voltage power (V DD_ plp) generator ( FIG. 2, 208 ). In one example, the V DD_ plp generator ( FIG. 2, 208 ) may continuously provide V DD_ plp to a number of low voltage circuits that control the firing of a number of high voltage circuits before, during, and after a power loss event occurs. In this example, the V DD_ plp generator ( FIG. 2, 208 ) may continually provide V DD_ plp to the low voltage circuits. When an uncontrolled power loss event occurs, the V DD_ plp generator ( FIG. 2, 208 ) generates and maintains V DD_ plp to the low voltage circuits until a high voltage power supply (V PP ) applied to the high voltage circuits or its associated logic line (V PP_ logic) drops below a threshold. 
     In another example, the V DD_ plp generator ( FIG. 2, 208 ) may be instructed by a power loss detection device ( FIG. 2, 208 ) to provide V DD_ plp to the low voltage circuits when an uncontrolled power loss event occurs, while the V DD_ plp generator ( FIG. 2, 208 ) remains inactive until the uncontrolled power loss event occurs. In this example, a V DD  supply voltage is used to power the digital, low voltage control logic until an uncontrolled power loss event occurs. Once instructed by the power loss detection device ( FIG. 2, 208 ), the V DD_ plp generator ( FIG. 2, 208 ) maintains V DD_ plp to the low voltage circuits until V PP  drops below the threshold. 
     In the above examples, the V DD_ plp generator ( FIG. 2, 208 ) obtains and derives the power for V DD_ plp from the V PP  or an associated logic line (V PP_ logic). In this manner, the high voltage circuits are protected from damage by ensuring that the low voltage circuits are powered and control of the high voltage circuits is maintained for at least as long as the high voltage circuits are powered. In one example, the V DD_ plp generator ( FIG. 2, 208 ) maintains V DD_ plp at the same voltage level as V DD . The high voltage circuits include resistive devices located within an ink supply in a firing chamber of the printheads ( 110 ) that cause ink to be ejected from a number of nozzles fluidly coupled to a firing chamber. In the above examples, the power loss detection device ( FIG. 2, 208 ) may detect a power loss event in V PP  either on the printhead die ( 111 ) or off the die printhead die. In one example, the power loss detection device ( 208 ) may be part of the V DD_ plp generator ( FIG. 2, 208 ). In another example, the V DD_ plp generator ( FIG. 2, 208 ) may be located on or off the printhead die ( 111 ). 
     Without the functionality of the present systems and methods, a number of power supplies powering the printheads ( 110 ), if not powered down in a correct sequence, may damage a number of circuits within the printheads ( 110 ) and their respective printhead dice ( 111 ). For example, if the V DD  supply voltage used to power the digital, low voltage control logic is lost, but V PP  and V PP_ logic supply voltages used to fire nozzle circuits are still powered, then the printhead ( 110 ) may enter an uncontrolled firing mode. In this scenario, the resistive devices would likely burn out and become unusable, rendering the printhead defective, and leaving defects in any subsequent prints. Other circuit failures may also render the printhead ( 110 ) unusable. The functionality of the power loss protection circuit ( 112 ) will be described in more detail below. 
     The printing device ( 100 ) further includes a number of modules used in the implementation of the systems and methods described herein and in printing documents. The various modules within the printing device ( 100 ) include executable program code that may be executed separately. In this example, the various modules may be stored as separate computer program products. In another example, the various modules within the printing device ( 100 ) may be combined within a number of computer program products; each computer program product including a number of the modules. The printing device ( 100 ) may include a power loss protection module ( 113 ) to, when executed by the processor ( 101 ), generate and maintain V DD_ plp flow to the low voltage circuits when an uncontrolled power loss event occurs as described herein. 
     The printing device ( 100 ) further includes a power source ( 114 ) to power the printing device ( 100 ) and its various hardware components including the power loss protection circuit ( 112 ). As will be described in more detail below, the power source ( 114 ) may be divided into a number of types of power sources that are used by the power loss protection circuit ( 112 ). 
       FIG. 2  is a diagram of an on-die V DD_ plp generator ( 203 ) of the power loss protection circuit ( 112 ) of  FIGS. 1A and 1B , according to one example of the principles described herein. The power loss protection circuit ( 112 ) may include a number of sub-circuits including a number of input/output (I/O) circuits ( 201 ), a reset signal receiver ( 202 ), a V DD_ plp generator ( 203 ), a reset buffer tree ( 204 ), a number of low voltage circuits ( 205 ), a final stage fire control generation circuit ( 206 ), a number of high voltage circuits ( 207 ), and a power loss detection device ( 208 ). 
     The I/O circuits ( 201 ) provide power to the power loss protection circuit ( 112 ) from a number of power sources. The printing device ( FIGS. 1A  and  1 B,  100 ) may receive electrical power from a main power source and provide the electrical power to the I/O circuits ( 201 ) and the remainder of the power loss protection circuit ( 112 ) to electrically drive the power loss protection circuit ( 112 ). As depicted in  FIG. 2 , a high voltage power supply (V PP ) ( 209 ), a high voltage logic power supply (V PP_ logic) ( 210 ), and a low power voltage supply (V DD ) ( 211 ) may be provided to the I/O circuits ( 201 ). V PP  ( 209 ) is used to power a number of high voltage circuits ( 207 ) including the firing resistors located within a firing chamber of the printheads ( 110 ), power supply pads, signal pads, signal receivers, and other circuits within a printhead die ( 111 ) that use a high voltage power supply. In one example, V PP  ( 209 ) may provide approximately 30V, positive or negative. 
     V PP_ logic ( 210 ) is a second high voltage supply used to switch a number of field-effect transistors (FETs) that connect V PP  ( 209 ) to the firing resistors. In one example, V PP_ logic ( 210 ) may provide approximately the voltage provided by V PP  ( 209 ) minus 2V. In another example V PP_ logic ( 210 ) may provide approximately 28V, positive or negative. Thus, in one example, V PP_ logic ( 210 ) may be set to a slightly different voltage than V PP  ( 209 ). This allows the power loss protection circuit ( 112 ) to account for system parasitics and provides energy regulation to the nozzles so that the same amount of energy is dispersed in a thermal ink jet firing event. 
     V DD  ( 211 ) is used to power a number of low voltage circuits ( 205 ) including digital control logic and analog functions used to transmit nozzle fire control signals to the high voltage circuits ( 207 ) that control the function of the high voltage circuits ( 207 ). In one example, V DD  ( 211 ) may provide approximately 5V, positive or negative. 
     Thus, a printhead, controlled by the power loss protection circuit ( 112 ), has multiple supplies powering it and its various hardware components. However, if V PP  ( 209 ) and V DD  ( 211 ) are not powered down in a correct sequence, elements within the high voltage circuits ( 207 ) may be damaged. For example, if V DD  ( 211 ) is lost, but V PP  ( 209 ) and V PP_ logic ( 210 ) are still powered, then the printhead may enter an uncontrolled firing mode. In this situation, the firing resistors may burn out and become unusable, leaving a defect in any subsequent prints. Other circuit failures may render the printhead unusable. 
     Continuing with the description of  FIG. 2 , the I/O circuits ( 201 ) further provide communication between a processor ( FIG. 1A, 101 ) of the printing device ( FIGS. 1A and 1B, 100 ) and the loss protection circuit ( 112 ) as well as other networked computing devices. For example, data signals ( 212 ) in the form of nozzle firing instructions based on a print job sent to the printing device ( FIGS. 1A and 1B, 100 ) are received by the I/O circuits ( 201 ). The data signals ( 212 ) may be used by the low voltage circuits ( 205 ) and high voltage circuits ( 207 ) to fire a number of nozzles within a number of printheads ( FIGS. 1A and 1B, 110 ) of the printing device ( FIGS. 1A and 1B, 100 ). 
     The I/O circuits ( 201 ) further include a reset receiver ( 202 ) to receive and provide a number of reset signals ( 213 ) to various elements of the power loss protection circuit ( 112 ). The reset signals ( 213 ) cause the all nozzle firing activity within the power loss protection circuit ( 112 ) to cease. However, even with the reset signal ( 201 ) active, if V DD  ( 211 ) is low enough, it cannot be guaranteed that all circuits will remain in a reset state while V PP  ( 209 ) is still high. 
     The reset buffer tree circuitry ( 204 ) receives the reset signals ( 213 ) from the reset receiver ( 202 ) as indicated by arrow  223 , and sends the reset signals ( 223 ) to the low voltage circuits ( 205 ) and the final stage control generation circuit ( 206 ) as indicated by arrows  233  and  243  to reset the firing controls produced by these circuits. The digital circuits including flip-flops, registers, counters, and other digital circuits within the low voltage circuits ( 205 ) and the final stage control generation circuit ( 206 ) may receive the reset signal that sets these circuits to a pre-determined state. In one example, the predetermined state is a state in which the low voltage circuits ( 205 ) and the final stage control generation circuit ( 206 ) are sending instructions for a non-firing state. 
     The reset signals ( 213 ) may be applied after powering on the printing device, before beginning execution of a print job, during a controlled power down sequence within the printing device ( FIGS. 1A and 1B, 100 ), during an uncontrolled power down sequence within the printing device ( FIGS. 1A and 1B, 100 ), other circumstances, or combinations thereof. The reset buffer tree ( 204 ) resets a pair of flip-flops within the reset buffer tree ( 204 ). Resetting these flip-flops drives the reset signal ( 213 ) through the reset buffer tree to the rest of the flip-flops so that a number of circuits such as the low voltage circuits ( 205 ) and the final stage control generation circuit ( 206 ) each receive the reset signal ( 213 ). 
     The power loss protection circuit ( 112 ) may further include low voltage circuits ( 205 ). The low voltage circuits ( 205 ) may receive the data signals ( 212 ) from the I/O circuits ( 201 ) as indicated by arrow  222 , and convert the data signals ( 222 ) into nozzle fire control instructions that control the firing of the nozzles within the high voltage circuits ( 207 ) as described herein. The low voltage circuits ( 205 ) may further receive V DD  ( 211 ) from the I/O circuits ( 201 ) as indicated by arrow  221 . The low voltage circuits ( 205 ) use V DD  ( 211 ) as a power source for operation of the low voltage circuits ( 205 ). 
     The power loss protection circuit ( 112 ) may further include the final stage fire control generation circuit ( 206 ). The final stage fire control generation circuit ( 206 ) generates fire control signals ( 232 ) sent to the high voltage circuits ( 207 ) to control the high voltage circuits ( 207 ) as described herein. 
     The power loss protection circuit ( 112 ) may further include the high voltage circuits ( 207 ) described above. The high voltage circuits ( 207 ) receive a number of the fire control signals ( 232 ), and use the signals to eject ink droplets from the nozzles of the printheads ( FIGS. 1A and 1B, 110 ) according to the data signals ( 222 ) received and processed by the low voltage circuits ( 205 ). Further, power is supplied to the high voltage circuits ( 207 ) from the high voltage power supply (V PP ) ( 209 ) as indicated by arrow  219 . V PP  ( 219 ) represents both V PP  ( 209 ) and the high voltage logic power supply (V PP_ logic) ( 210 ). In one example, V PP  ( 209 ) and V PP_ logic ( 210 ) are transferred over the same electrical transmission line. In another example, V PP  ( 209 ) and V PP_ logic ( 210 ) are transferred over different but associated electrical transmission lines. In still another example, V PP  ( 209 ) and V PP_ logic ( 210 ) are transferred over different, unassociated electrical transmission lines. 
     The power loss protection circuit ( 112 ) further includes a V DD_ plp generator ( 203 ). As described herein, the V DD_ plp generator ( 203 ) generates a V DD  power loss protection supply voltage (V DD_ plp) ( 214 ,  224 ,  234 ). In one example, the V DD_ plp generator ( 208 ) maintains V DD_ plp ( 214 ,  224 ,  234 ) at the same voltage level as V DD  ( 211 ,  221 ). This ensures that circuits that drive the operation of the high voltage circuits ( 207 ) remain powered during an uncontrolled power loss event long enough to allow V PP  to bleed down below a safe, threshold voltage level. 
     The V DD_ plp generator ( 203 ) is connected to the V PP  ( 219 ) line. In one example, the V DD_ plp generator ( 203 ) is connected to V PP  ( 209 ) via the V PP  ( 219 ) line, as opposed to V PP_ logic ( 210 ). In another example, the V DD_ plp generator ( 203 ) is connected to V PP_ logic ( 210 ) via the V PP  ( 219 ) line, as opposed to V PP  ( 209 ). In either example, the V DD_ plp generator ( 203 ) obtains electrical power from the V PP  ( 219 ) line, and produces the power loss protection supply voltage (V DD_ plp) as described herein. The V DD_ plp supply voltage ( 214 ,  224 ,  234 ) is provided to a number of circuits within the power loss protection circuit ( 112 ) to maintain control of the high voltage circuits ( 207 ). 
     In one example, V DD_ plp ( 214 ,  224 ,  234 ) is provided to all circuits used in controlling the high voltage circuits ( 207 ). In this example, the circuits used in controlling the high voltage circuits ( 207 ) include the reset signal receiver ( 202 ), the reset buffer tree ( 204 ), the low voltage circuits ( 205 ), and the final stage fire control generation circuit ( 206 ), among other circuits. In this manner, the power loss protection circuit ( 112 ) provides a power loss protection to all non-high voltage circuits. Although providing V DD_ plp ( 214 ,  224 ,  234 ) to all circuits used in controlling the high voltage circuits ( 207 ) ensures that the power loss protection circuit ( 112 ) continues to function as if no uncontrolled power loss event occurred, doing so may add to the cost of manufacturing the power loss protection circuit ( 112 ). 
     In another example, V DD_ plp ( 214 ,  224 ,  234 ) is provided to an exclusive number of circuits used in controlling the high voltage circuits ( 207 ). In this example, the circuits used in controlling the high voltage circuits ( 207 ) include the reset signal receiver ( 202 ), the reset buffer tree ( 204 ), and the final stage fire control generation circuit ( 206 ). In this manner, the only circuits chosen to be powered by V DD_ plp ( 214 ,  224 ,  234 ) are those circuits that draw little current, and are sufficient to ensure safe power down. This example excludes analog circuits which draw DC current including, for example, nozzle data memory upstream of the final stage fire control generation circuit ( 206 ). This also excludes high-frequency digital switching circuits such as those found in the low voltage circuits ( 205 ). 
     This example of exclusive powering of the reset signal receiver ( 202 ), the reset buffer tree ( 204 ), and the final stage fire control generation circuit ( 206 ) is depicted using the shading of the various circuits and the shading keys ( 250 ,  251 ,  252 ,  253 ). Using the shading keys ( 250 ,  251 ,  252 ,  253 ),  FIG. 2  indicates that the high voltage circuits ( 207 ) are powered by V PP  ( 209 ,  219 ). 
     Shading key ( 251 ) indicates that the low voltage circuits ( 205 ) are powered by V DD  ( 221 ). Thus, in the example described above where V DD_ plp ( 214 ,  224 ,  234 ) is provided to an exclusive number of circuits, the low voltage circuits ( 205 ) are not powered by V DD_ plp ( 214 ,  224 ,  234 ). However, in the example described herein where the V DD_ plp generator ( 203 ) generates V DD_ plp ( 214 ,  224 ,  234 ) to all circuits used in controlling the high voltage circuits ( 207 ) including low voltage circuits ( 205 ), the shading of the low voltage circuits ( 205 ) block may include the shading of shading key ( 253 ). 
     Shading key ( 252 ) indicates that the I/O circuits ( 201 ) and the V DD_ plp generator ( 203 ) are powered by the low power voltage supply (V DD ) ( 211 ) or V PP  ( 209 ,  219 ) as obtained directly or indirectly from the power source ( FIG. 1B, 114 ). The I/O circuits ( 201 ) would be unpowered if an uncontrolled power loss event was to take place in the printing device ( FIGS. 1A and 1B, 100 ). In this situation, the V DD_ plp generator ( 203 ) powers the reset receiver ( 202 ) of the I/O circuits ( 201 ), but the remainder of the I/O circuits ( 201 ) are rendered inoperable. Shading key ( 253 ) indicates that the reset receiver ( 202 ), the reset buffer tree circuitry ( 204 ) and the final stage fire control generation circuit ( 206 ) are powered by V DD__ plp ( 214 ,  224 ,  234 ) generated by the V DD_ plp generator ( 203 ). 
     In continuing with the example of exclusive powering of the reset signal receiver ( 202 ), the reset buffer tree ( 204 ), and the final stage fire control generation circuit ( 206 ), excluding a number of circuits from receiving V DD_ plp ( 214 ,  224 ,  234 ) has several advantages. One advantage is that if V DD_ plp ( 214 ,  224 ,  234 ) is generated on the printhead die ( 111 ), the V DD_ plp generator ( 203 ) may be physically smaller. Area available on the printhead die ( 111 ) of a printhead ( 110 ) may be a significant driver of the manufacturing costs of the printhead. Another advantage of excluding a number of circuits from receiving V DD_ plp ( 214 ,  224 ,  234 ) is that if V DD_ plp ( 214 ,  224 ,  234 ) is generated and maintained off-die, it may be more cost-effective to also implement the exclusive circuits which maintain voltage on V DD_ plp ( 214 ,  224 ,  234 ) off the printhead die ( 111 ) if there is a small load on V DD_ plp ( 214 ,  224 ,  234 ). 
     The power loss protection circuit ( 112 ) further includes a power loss detection device ( 208 ). The power loss detection device ( 208 ) detects a loss of power to the printing device ( FIGS. 1A and 1B, 100 ), a number of circuits within the power loss protection circuit ( 112 ), or combinations thereof. If the power loss detection device ( 208 ) detects a loss of power, the power loss detection device ( 208 ) sends instructions to the V DD_ plp generator ( 203 ) as indicated by arrow  235 . The instructions instruct the V DD_ plp generator ( 203 ) to generate V DD_ plp for a number of the circuits within the power loss protection circuit ( 112 ) as described herein. 
     In an example where V DD_ plp generator ( 203 ) does not continuously provide V DD_ plp to a number of low voltage circuits, but, instead, is active when an uncontrolled power loss event occurs, the V DD_ plp generator ( 203 ) receives the instruction from the power loss detection device ( 208 ), and begins to provide V DD_ plp to a number of low voltage circuits as described herein. In this example, the V DD_ plp generator ( 203 ) remains inactive until an uncontrolled power loss event occurs. In an example where the V DD_ plp generator ( 203 ) continuously provides V DD_ plp to a number of low voltage circuits irrespective of whether an uncontrolled power loss event has occurred, the power loss detection device ( 208 ) may be optional within the power loss protection circuit ( 112 ). 
     In  FIG. 2 , the power loss detection device ( 208 ) is depicted as being coupled to the V PP  ( 219 ) line such that the power loss detection device ( 208 ) may detect power loss to the V PP  ( 219 ) line. However, the power loss detection device ( 208 ) may be coupled to any number of circuits within the power loss protection circuit ( 112 ). Further, in  FIG. 2 , the power loss detection device ( 208 ) is depicted as being located on the printhead die ( 111 ). However, in another example, the power loss detection device ( 208 ) may be located off die. In this off-die example, the power loss detection device ( 208 ) may send instructions to the V DD_ plp generator ( 203 ) via the I/O circuits ( 201 ). 
       FIG. 3  is a diagram of an off-die V DD_ plp generator ( 208 ) of the power loss protection circuit ( 112 ) of  FIGS. 1A and 1B , according to one example of the principles described herein. Similar descriptions and element numbering presented above in connection with  FIG. 2  are applicable to  FIG. 3  and its associated description herein. In  FIG. 3 , the V DD_ plp generator ( 208 ) is located at an off-die location. The printhead die ( 111 ) may include limited area for the inclusion of additional circuits or other hardware. Inclusion of the V DD_ plp generator ( 208 ) on the printhead die ( 111 ) may increase the cost of manufacturing the printhead die, and may result in a relatively more expensive printhead ( 110 ). Therefore, in the example of  FIG. 3 , the V DD_ plp generator ( 208 ) is located at off the printhead die ( 111 ). 
     In the example of  FIG. 3 , the V DD_ plp generator ( 208 ) derives power from the high voltage power supply (V PP ) ( 209 ) or high voltage logic power supply (V PP_ logic) ( 210 ) as described above, but does so at an off-die location. In this manner, the V DD_ plp generator ( 208 ) may obtain sufficient power to generate the V DD  power loss protection supply voltage (V DD_ plp) ( 314 ,  324 ,  334 ), and provide V DD_ plp ( 314 ,  324 ,  334 ) to a number of circuits in the power loss protection circuit ( 112 ) located on the printhead die ( 111 ). 
     The power loss protection circuit ( 112 ) of  FIG. 3  may further include the power loss detection device ( 208 ) described in connection with  FIG. 2  above. In the example of  FIG. 3 , the power loss detection device ( 208 ) is located off the printhead die ( 111 ) along with the V DD_ plp generator ( 208 ). In this manner, the power loss detection device ( 208 ) may detect a power loss within the printing device ( FIGS. 1A and 1B, 100 ) from any circuit within the printing device ( FIGS. 1A and 1B, 100 ) such as, for example, the power loss protection circuit ( 112 ), the power source ( FIG. 1B, 114 ), or other device or circuit that may be effected by a power loss event upstream from the power loss protection circuit ( 112 ). 
     The possibilities associated with controlled or uncontrolled loss of power to the printing device ( FIGS. 1A and 1B, 100 ) and its power loss protection circuit ( 112 ) will now be described in connection with  FIGS. 4 through 6 . The numbers, values, units, curves, lines, or other aspects of  FIGS. 4 through 6  are only examples to be used in describing the processes associated with controlled or uncontrolled loss of power. 
       FIG. 4  is a graph depicting a printer-controlled power down sequence, according to one example of the principles described herein. Printing devices ( FIGS. 1A and 1B, 100 ) are designed to power down the printheads ( FIGS. 1A and 1B, 110 ) and their respective high voltage circuits ( 207 ) in a controlled and safe manor. This controlled power down uses a protocol to power down circuits within the printing device ( FIGS. 1A and 1B, 100 ) including the input/output (I/O) circuits ( 201 ), reset signal receiver ( 202 ), reset buffer tree ( 204 ), low voltage circuits ( 205 ), final stage fire control generation circuit ( 206 ), and high voltage circuits ( 207 ), in a sequence that will not damage the circuits. A controlled power down may occur when a request is made to do so, such as when a user pushes a power button on the printing device ( FIGS. 1A and 1B, 100 ). This sequence may include powering down the multiple power supplies used on a printhead such as V PP  ( FIGS. 2 and 3, 209, 219 ), V PP_ logic ( FIGS. 2 and 3, 210, 219 ), and V DD  ( FIGS. 2 and 3, 211, 221 ) in a particular sequence. 
     In both examples described in connection with  FIGS. 2 and 3 , the V DD_ plp generator&#39;s ( 208 ) derivation of power from the high voltage power supply (V PP ) ( 209 ) or high voltage logic power supply (V PP_ logic) ( 210 ) ensures that the voltages provided to the reset signal receiver ( 202 ), reset buffer tree ( 204 ), and final stage fire control generation circuit ( 206 ), and, in some examples, the low voltage circuits ( 205 ), drop to a safe voltage level after V PP  drops to a safe level. Further, the manner in which the power loss protection circuit ( 112 ) powers down the low voltage circuits ( 205 ) and high voltage circuits ( 207 ) is independent of the architecture of the power supplies within the power loss protection circuit ( 112 ), and independent of firmware sequencing controls provided by, for example, the processor ( FIG. 1B, 101 ) of the printing device ( FIGS. 1A and 1B, 100 ). 
     As depicted in  FIG. 4 , the y-axis represents voltage levels within the power loss protection circuit ( 112 ) of the printing device ( FIGS. 1A and 1B, 100 ). The x-axis represents time. In one example, the time taken to power down the printing device ( FIGS. 1A and 1B, 100 ) and its various circuitry may be on the order of microseconds or milliseconds. However, because the present systems and methods ensure that the V DD_ plp generator ( 203 ) provides V DD_ plp ( 214 ,  224 ,  234 ) until a sufficient bleed down of V PP  ( 209 ,  219 ) as described herein, the x-axis and its indication of time is independent of any required or specified time period. 
     Initially, the printing device ( FIGS. 1A and 1B, 100 ) is operating at normal voltages as indicated by bracket  406 . During this period before the controlled power down sequence begins, V PP  ( 209 ,  219 ) may be at, for example, approximately 30 volts, and V DD  ( 211 ,  221 ) may be at, for example, 5 volts. These are example voltages, and V PP  ( 209 ,  219 ) and V DD  ( 211 ,  221 ) may operate at other voltages or voltage ranges depending on voltage requirements of the circuits within the printing device ( FIGS. 1A and 1B, 100 ). In  FIGS. 4 through 6 , line  402  indicates the voltage level of V PP  ( 209 ,  219 ) before and during the controlled power down, and line  403  indicates the voltage level of V DD  ( 211 ,  221 ) before and during the controlled power down. 
     Line  401  indicates the instance when the printing device ( FIGS. 1A and 1B, 100 ) initiates a controlled power down sequence. When the controlled power down sequence begins at  401 , V PP  ( 209 ,  219 ) begins to bleed down. As the controlled power down sequence occurs, a number of circuit elements such as a number of capacitors within the high voltage circuits ( 207 ) start dissipating their stored energy. During the controlled power down, the printing device ( 100 ) maintains the voltage level of V DD  ( 211 ,  221 ) until V PP  ( 209 ,  219 ) drops below a threshold voltage ( 405 ). This allows the high voltage circuits ( 207 ) to safely bleed down in a controlled manner without damaging circuitry within the high voltage circuits ( 207 ). 
     In one example, the threshold voltage ( 405 ) is approximately 12 volts. In this example, the threshold voltage ( 405 ) is 12 volts because this is a minimum voltage level at which a number of circuits used to switch V PP_ logic ( 210 ) into a firing event of the nozzles within the printheads ( FIGS. 1A and 1B, 110 ) are operable. However, the threshold voltage ( 405 ) required for operation of the circuits used to switch V PP_ logic ( 210 ) may be any voltage level. Once the voltages provided by V PP_ logic ( 210 ) and stored within the high voltage circuits ( 207 ) bleeds below the threshold voltage ( 405 ), the possibility of damage to the high voltage circuits ( 207 ) is mitigated or eliminated. 
     V DD  ( 211 ,  221 ) is maintained at a voltage level sufficient to power a number of circuits used to control the high voltage circuits ( 207 ) including the input/output (I/O) circuits ( 201 ), reset signal receiver ( 202 ), reset buffer tree ( 204 ), low voltage circuits ( 205 ), final stage fire control generation circuit ( 206 ), or combinations thereof. In one example, the voltage level maintained by V DD  ( 211 ,  221 ) is 5 volts. However, the voltage level required for operation of the circuits used to control the high voltage circuits ( 207 ) may be any voltage level. 
     The period at which the printing device ( 100 ) maintains the voltage level of V DD  ( 211 ,  221 ) during a controlled power down sequence is indicated by bracket  406 . The period ( 407 ) of maintaining V DD  ( 211 ,  221 ) at its operating voltage level may end at line  404  where V PP  ( 209 ,  219 ) drops below the threshold voltage ( 405 ). At  404 , V DD  ( 211 ,  221 ) may also bleed down as V PP  ( 209 ,  219 ) continues to bleed down. 
       FIG. 5  is a graph depicting an uncontrolled power down sequence of a printing device ( FIGS. 1A and 1B, 100 ) without the power loss protection circuits ( 112 ) of  FIGS. 2 and 3 , according to one example of the principles described herein. As described above in connection with  FIG. 4 , the printing device ( FIGS. 1A and 1B, 100 ) initially operates at normal voltages as indicated by bracket  406 . An uncontrolled power loss event may occur at line  501  with line  503  indicating the voltage level of V DD  ( 211 ,  221 ) before and during an uncontrolled power down. In the uncontrolled power down sequence of  FIG. 5 , V DD  ( 211 ,  221 ) immediately starts to bleed down. As depicted in  FIG. 5 , V DD  ( 211 ,  221 ) bleeds down at a faster rate than V PP  ( 209 ,  219 ) bleeds down due, in part, to large capacitance within the high voltage circuits ( 207 ). Within the area designated by  502 , even though the printhead die ( FIGS. 2 and 3, 111 ) may have been reset via the application of the reset signals ( FIGS. 2 and 3, 223, 233, 243 ), the low voltage circuits ( 205 ) may be in an unknown state due to a relatively low V DD  ( 211 ,  221 ). This may result in the high voltage circuits ( 207 ) firing uncontrollably, and may result in damage to or destruction of the resistors and other active devices within the high voltage circuits ( 207 ). In order to overcome this potential for damage, the power loss protection circuit ( FIGS. 1, 2 , and  3 ,  112 ) maintains V DD  ( 211 ,  221 ) at an active voltage level until after V PP  ( 209 ,  219 ) falls below the threshold voltage ( 405 ) as will now be described in connection with  FIG. 6 . 
       FIG. 6  is a graph depicting an uncontrolled power down sequence of a printing device ( FIGS. 1A and 1B, 100 ) with the power loss protection circuits ( 112 ) of  FIGS. 2 and 3 , according to one example of the principles described herein. As described in connection with  FIG. 5 , line  503  indicates the voltage level of V DD  ( 211 ,  221 ) before and during an uncontrolled power down. In order to maintain V DD  ( 211 ,  221 ) at an active voltage level until after V PP  ( 209 ,  219 ) falls below the threshold voltage ( 405 ), the V DD_ plp generator ( 203 ) generates V DD_ plp ( FIGS. 2 and 3, 214, 224, 234 ) as indicated by line  601 . In this manner, a number of the non-high voltage circuits are maintained at an active voltage level until after V PP  ( 209 ,  219 ) falls below the threshold voltage ( 405 ) by using the V DD_ plp generator ( 203 ) to generate V DD_ plp ( FIGS. 2 and 3, 214, 224, 234 ) in place of the original V DD  ( 211 ,  221 ). Non-high voltage circuits include the reset signal receiver ( 202 ), reset buffer tree ( 204 ), and final stage fire control generation circuit ( 206 ), and, in some examples, the low voltage circuits ( 205 ). Thus, as described in connection with  FIG. 6 , the V DD_ plp generator ( 203 ) reduces or eliminates the potential for uncontrolled high voltage dissipation within printhead resistive elements and other active devices in a number of high voltage circuits ( FIGS. 2 and 3, 207 ) of the printing device ( FIGS. 1A and 1B, 100 ) that may render the resistors and other active devices inoperable. 
       FIG. 7  is a flowchart showing a method ( 700 ) of operating a printing device ( FIGS. 1A and 1B, 100 ) during a power loss event, according to one example of the principles described herein. The method ( 700 ) of  FIG. 7  may begin by detecting (block  701 ) an uncontrolled power loss event to a number of high voltage devices ( FIGS. 2 and 3, 207 ). Detection (block ( 701 ) of the power loss event may be performed by the power loss detection device ( FIGS. 2 and 3, 208 ). 
     The method ( 700 ) may further include, with a power loss protection supply voltage (V DD_ plp) generator ( FIGS. 2 and 3, 203 ) coupled to a printhead driving circuit ( FIGS. 2 and 3, 205 ), maintaining a power loss protection supply voltage (V DD_ plp) ( FIGS. 2 and 3, 214, 224, 234 ) to the printhead driving circuit ( FIGS. 2 and 3, 205 ) until a high voltage power supply (V PP ) ( 209 ,  219 ) to the high voltage devices ( FIGS. 2 and 3, 207 ) drops below a threshold voltage ( FIGS. 4, 5, and 6, 405 ). In this manner, the high voltage devices ( FIGS. 2 and 3, 207 ) are protected from damage to or destruction of the resistors and other active devices within the high voltage devices ( FIGS. 2 and 3, 207 ). This type of damage may occur if the high voltage devices ( FIGS. 2 and 3, 207 ) were allowed to fire without being controlled by the low voltage circuits ( FIGS. 2 and 3, 205 ) and other circuitry used to control the firing of the high voltage devices ( FIGS. 2 and 3, 207 ). 
     Aspects of the present system and method are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to examples of the principles described herein. Each block of the flowchart illustrations and block diagrams, and combinations of blocks in the flowchart illustrations and block diagrams, may be implemented by computer usable program code. The computer usable program code may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the computer usable program code, when executed via, for example, the processor ( 101 ) of the printing device ( 100 ) or other programmable data processing apparatus, implement the functions or acts specified in the flowchart and/or block diagram block or blocks. In one example, the computer usable program code may be embodied within a computer readable storage medium; the computer readable storage medium being part of the computer program product. In one example, the computer readable storage medium is a non-transitory computer readable medium. 
     The specification and figures describe systems and methods for operating a printing device during a power loss event. The method may include detecting an uncontrolled power loss to a number of high voltage devices. The method may further include, with a power loss protection supply voltage generator coupled to a printhead driving circuit, maintaining a power loss protection supply voltage (V DD_ plp) to the printhead driving circuit until a high voltage power supply (V PP ) to the high voltage devices drops below a threshold voltage. A circuit topology for a printing device may include a number of high voltage devices to power firing of a number of nozzles within a printhead die, and a high voltage power supply connected to the high voltage devices. The circuit topology may further include fire control circuitry connected to the high voltage devices to control the firing of the nozzles. The fire control circuitry may include a final stage fire control signal generation device. The circuit topology may further include a low voltage power supply connected to the fire control logic to supply power to the fire control circuitry, and a power loss protection supply voltage generator to provide a power loss protection supply voltage (V DD_ plp) from the high voltage power supply to the final stage fire control signal generation device. The power loss protection supply voltage (V DD_ plp) may be supplied for a long enough duration after an uncontrolled power loss to the printing device to allow the high voltage power supply to fall below a threshold voltage. 
     This operation of the printing device during a power loss event may have a number of advantages, including: (1) protecting resistors and other circuits within the high voltage circuits from damage resulting from power loss events; (2) reduces the cost of manufacturing the printing device by not requiring extra system-level components and by enabling possible cost reduction of existing power-down circuits; and (3) provides for fully integrated power loss protection circuitry on the printhead die using minimal die area, among other advantages. 
     The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.