Voltage quadrupler comprising a second charging capacitor charged using a first charging capacitor

Description

BACKGROUND

Voltage boosters may be employed in any number of electronic devices, such as desktop computers, laptops, tablets, data storage devices, as well as consumer electronics, such as cell phones, televisions, gaming devices, etc. In a typical application, a voltage booster may be used to boost a supply voltage that is dropping due, for example, to a battery discharging. In another example, a disk drive may use a voltage booster to boost a backup supply during a power failure so that the current access operation can be completed before parking the heads and shutting down safely.

FIG. 1A shows a prior art voltage quadrupler 2 comprising three charging capacitors C1, C2 and C3, an output capacitor Cout, and a number of switches. FIG. 1B shows control circuitry 4 for implementing a state machine that controls the switches of the voltage quadrupler 2 according to the following sequence:

• • 1. connect C1, C2 and C3 in parallel with Vin to charge V_C1=V_in, V_C2=V_in, V_C3=V_in; and
  • 2. connect Cout in parallel with V_C1+V_C2+V_C3+V_in to charge V_Cout=4Vin.
    The above sequence is repeated at a high frequency, transferring energy from C1, C2 and C3 to Cout, thereby generating an output voltage that is quadruple the input voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a prior art voltage quadrupler comprising three charging capacitors.

FIG. 1B shows prior art control circuitry implementing a state machine for charging an output capacitor to four times an input voltage.

FIG. 2A shows a voltage quadrupler according to an embodiment of the present invention comprising two charging capacitors.

FIG. 2B shows control circuitry according to an embodiment of the present invention implementing a state machine for charging an output capacitor to three times an input voltage.

FIG. 2C shows control circuitry according to an embodiment of the present invention implementing a state machine for charging an output capacitor to four times an input voltage.

FIG. 3A shows another embodiment of a voltage quadrupler according to an embodiment of the present invention comprising two charging capacitors.

FIG. 3B shows control circuitry according to an embodiment of the present invention implementing a state machine for charging an output capacitor to three times an input voltage.

FIG. 3C shows control circuitry according to an embodiment of the present invention implementing a state machine for charging an output capacitor to four times an input voltage.

FIG. 4A shows a disk drive according to an embodiment of the present invention comprising a head actuated over a disk, and a voltage booster.

FIG. 4B is a flow diagram according to an embodiment of the present invention wherein the voltage booster boosts a supply voltage by N during normal operation and boosts a backup voltage by M during a power failure.

FIG. 5 is a flow diagram according to an embodiment of the present invention wherein the voltage booster boosts the backup voltage by M after the backup voltage falls below a threshold during the power failure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2A shows a voltage booster 6 according to an embodiment of the present invention comprising an input for receiving an input voltage Vin, a first charging capacitor C1, a second charging capacitor C2, and an output capacitor Cout. The output capacitor Cout is charged to four times Vin by connecting C1 in parallel with Vin to charge C1 to Vin, after charging C1 to Vin, connecting C2 in parallel with Vin plus C1 to charge C2 to twice Vin, after charging C2 to twice Vin, connecting C1 in parallel with Vin to recharge C1 to Vin, and after recharging C1, connecting Cout in parallel with Vin plus C1 plus C2 to charge Cout to four times Vin.

In the embodiment of FIG. 2A, the voltage booster 6 comprises a plurality of switches S1-S7 configured by control circuitry 8 into an on/off state defined by a state machine. FIG. 2C shows a state machine implemented by the control circuitry 8 in order to charge the output capacitor Cout to four times Vin as described above. In this embodiment, all of the switches are turned off after each charging state to implement an anti-cross conduction operation (ANTI-CROSS). The states of the state machine in FIG. 2C are repeated at a frequency related to the size of the capacitors so as to maintain the output voltage V_Cout at substantially four times Vin. In one embodiment, the size of the charging capacitors C1 and C2 and the output capacitor Cout may be selected based on the capacity of the input current and/or the load current supplied by the output voltage V_Cout.

In one embodiment, the voltage booster 6 of FIG. 2A is configurable to charge the output capacitor Cout to three times Vin or to four times Vin. For example, in an embodiment described below, a disk drive may employ the voltage booster in order to boost a supply voltage by three times during normal operation, and operable to boost a backup voltage by four times during a power failure. Referring again to FIG. 2A, the output capacitor Cout may be charged to three times Vin using the state machine shown in FIG. 2B by connecting C1 in parallel with Vin to charge C1 to Vin, connecting C2 in parallel with Vin to charge C2 to Vin, and after charging C1 and C2 to Vin, connecting Cout in parallel with Vin plus C1 plus C2 to charge Cout to three times Vin.

In the embodiment of FIG. 2A, Vin is a voltage with respect to a reference node (ground in this example). When boosting the output voltage by three times Vin, during the first state of the state machine of FIG. 2B a first switch S3 is operable to connect C1 to Vin and a second switch S2 is operable to connect C1 to the reference node. The first switch S3 and a third switch S6 are operable to connect C2 to Vin and a fourth switch S5 is operable to connect C2 to the reference node. Connecting C2 to Vin through two switches (S3 and S6) reduces the efficiency of the voltage booster 6 compared to an embodiment that employs a single switch.

FIG. 3A shows a voltage booster 10 according to an embodiment of the present invention which includes an additional switch S8 compared to the embodiment of FIG. 2A. FIG. 3B shows control circuitry 12 for implementing a state machine for boosting the input voltage by three times Vin, and FIG. 3C shows a state machine for boosting the input voltage by four times Vin. When boosting the input voltage by three times Vin, a single switch S8 connects C2 to Vin, and a single switch S5 connects C2 to the reference node (ground). A single switch S3 connects C1 to Vin, and a single switch S2 connects C1 to the reference node. This embodiment is more efficient than the embodiment of FIG. 2A since charging capacitor C2 is connected through a single switch S8 to Vin during the first state of the state machine of FIG. 3B.

FIG. 4A shows a disk drive according to an embodiment of the present invention comprising a head 14 actuated over a disk 16, and a voltage booster 18 configurable into a first mode to boost a supply voltage (SV) by N and configurable into a second mode to boost a backup voltage (BV) by M greater than N. The disk drive further comprises control circuitry 20 operable to execute the flow diagram of FIG. 4B, wherein the voltage booster 18 is configured into the first mode during normal operation (step 22), and the voltage booster 18 is configured into the second mode (step 26) during a power failure (step 24). In one embodiment, the voltage booster 18 boosts the supply voltage (SV) by three times during normal operation, and boosts the backup voltage (BV) by four times during the power failure. The control circuitry 20 may use the boosted backup voltage to safely perform a shutdown operation, such as finishing the current write operation and parking the heads on a ramp.

The backup voltage (BV) may be generated in any suitable manner. In one embodiment, a backup capacitor may be charged by the supply voltage (SV) during normal operation, wherein the backup voltage (BV) may be generated using the backup capacitor during the power failure. In one embodiment, a back electromotive force (BEMF) voltage generated by a spindle motor that rotates the disk 16 may be used to generate the backup voltage (BV). In one embodiment, the backup capacitor may be charged using the BEMF voltage generated by the spindle motor when the backup voltage (BV) falls below the BEMF voltage.

In another embodiment illustrated in the flow diagram of FIG. 5, the voltage booster 18 may be configured to boost the backup voltage (BV) by N during a first part of the power fail operation (step 28). When the backup voltage (BV) decays below a threshold (step 30) due to a backup capacitor discharging and/or a BEMF voltage of the spindle motor falling, the voltage booster 18 may be configured to boost the backup voltage (BV) by M during the remainder of the power fail operation (step 32).

The control circuitry of the voltage booster in FIGS. 2A and 3A and the control circuitry of the disk drive in FIG. 4A may comprise any suitable circuitry, such as an application specific integrated circuit (ASIC) comprising suitable logic circuitry for implementing the state machines disclosed herein. In another embodiment, the control circuitry of the voltage booster and/or the control circuitry of the disk drive may comprise a microprocessor executing code segments of a control program for implementing the state machines disclosed herein, wherein the control program may be stored on any suitable computer readable storage medium, such as a disk or semiconductor memory.