Hard disk drive (HDD) electrical over voltage stress (EOS) systems and methods

The present invention relates to a hard disk drive system having overvoltage protection circuits for various types of overvoltage conditions. For example, the system comprises one or more hard disk drive integrated circuit chips residing on a board and a hard disk drive power plug receptacle residing on the board having two different value power supply ports associated therewith. The receptacle is operable to receive a power plug therein, wherein when the power plug is inserted therein in a proper orientation the two different value voltages are properly supplied to the one or more hard disk drive integrated circuit chips, and wherein when the power plug is inserted therein in an improper orientation the two different value voltages are switched with respect to their intended values. The system comprises a reverse power plug orientation protection circuit coupled between the hard disk drive power plug receptacle and at least one of the one or more hard disk drive integrated circuit chips. The protection circuit is operable to detect an improper orientation of the power plug when inserted into the hard disk drive power plug receptacle and reduce a larger of the two different voltage values, thereby preventing an electrical over voltage stress of the at least one hard disk drive integrated circuit chip.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described with respect to the accompanying drawings in which like numbered elements represent like parts. The present invention relates to a system and circuitry for preventing overvoltage conditions on a hard disk drive printed circuit board. Turning now to the figures, FIG. 3 is a combined block level and schematic diagram illustrating an electrical over stress protection system 100 according to one exemplary aspect of the present invention. The system 100 may reside on a hard disk drive printed circuit board (PCB) which includes a hard disk drive power plug receptacle or socket 102 . According to one exemplary aspect of the present invention, the non-portable PC industry standard receptacle or socket 102 is a four pin male type adapter having a pin for a high, first supply voltage value (e.g., about 12V), two pins for circuit ground potential value, and a pin for the second, low supply voltage value (e.g., about 5V), respectively. Regulator circuitry 104 may be coupled to a fourth pin 106 of the adapter 102 to provide voltage regulation for the other supply voltages used within the PCB. A reverse plug orientation protection circuit 108 is coupled between the adapter 102 and other hard disk drive board components (e.g., integrated circuit chips) via one or more supply voltage traces 110 . The protection circuit, according to one exemplary aspect of the present invention, is also coupled to the first supply voltage value via a first pin 112 of the adapter 102 . According to an exemplary aspect of the present invention, the protection circuit 108 is operable to detect an improper orientation of a power plug when inserted into the receptacle or socket adapter 102 and then reduce a voltage value at the one or more traces 110 in response to the detection. For example, the protection circuit 108 may comprise a variable resistor circuit which is operable to adjust a resistance value associated therewith based on the orientation of a power plug in the power plug socket 102 . Under normal operating conditions when the power plug is properly oriented in the socket 102 , the variable resistance circuit exhibits substantially no resistance and approximates a short circuit to pass the second supply voltage value to the trace 110 without a substantial voltage drop thereacross. Under other conditions, however, when the power plug is reversed and plugged into the socket 102 in an improper orientation, the variable resistance circuit exhibits a substantial resistance, thereby causing a voltage drop thereacross to thereby prevent an undesirable high voltage value form appearing on the one or more traces 110 . Any type of circuitry which may provide the above functionality may be utilized as the protection circuit 108 , and such variations are contemplated as falling within the scope of the present invention. For example, according to one aspect of the present invention, the protection circuit 108 comprises a transistor such as an NMOS transistor 114 as illustrated in FIG. 3 . In operation, the transistor works as follows, as illustrated in FIG. 4 a and 4 b , respectively. In FIG. 4 a , the power plug is inserted into the socket 102 in the proper orientation such that the first supply voltage value is provided to the first pin 112 (e.g., 12V) and the second supply voltage value is provided to the fourth pin 106 (e.g., 5V), respectively. As seen in FIG. 4 a , this results in 12V being applied to a control terminal (e.g., a gate) of the transistor 114 , causing it to substantially turn on (e.g., full conductance). In such a state, the transistor 114 approximates a short circuit and almost all of the 5V is passed from the fourth pin 106 of the socket 102 to the one or more traces 110 . Alternatively, when the power plug is inserted into the socket 102 in an improper orientation, the first and second supply voltage values are switched on the pins 106 and 112 , as illustrated in FIG. 4 b . That is, the higher voltage (e.g., 12V) now appears on the fourth pin 106 and without the help of the transistor 114 , would result in a high and potentially damaging voltage appearing on the one or more traces 110 which go to various circuit components on the board. However, according to the present invention, the transistor 114 now has the lower voltage value (e.g., 5V) on its gate terminal, thus causing the conductance thereof to be substantially diminished. That is, the resistance associated with the transistor 114 is substantial and therefore a significant voltage drop (&Dgr;V>0V) will occur across the transistor 114 , thereby reducing the voltage on the one or more traces 110 (e.g., &Dgr;V is equal to about 7-8V, thus leaving about 4V at the trace 110 .). According to another aspect of the present invention, a reverse plug orientation and an overvoltage protection circuit is disclosed, as illustrated in FIG. 5 and designated at reference numeral 150 . The overvoltage protection circuit 150 is operable to reduce the voltage at the 5V board trace 110 under system conditions when the 5V supply voltage exceeds its rated voltage (e.g., increasing substantially above 5V) due to, for example, an unregulated or defective 5V supply. According to one exemplary aspect of the present invention, the overvoltage protection circuit 150 comprises a voltage detection circuit 152 and a voltage reduction circuit 154 , respectively. The voltage detection circuit 152 is operable to detect a circuit condition in which the potential of a 5V supply 156 exceeds a predetermined level, for example, some value greater than 5V. Upon detection of such a circuit condition, the voltage detection circuit 152 provides an activation signal to the voltage reduction circuit 154 which is operable to reduce the voltage associated with the 5V supply 156 at the trace 110 which supplies the supply potential to at least one of the various integrated circuit chips on the hard disk drive printed circuit board. In accordance with one exemplary aspect of the present invention, the voltage detection circuit 152 may comprise a zener diode 158 in series with a resistor 160 . In operation, under normal conditions when the supply voltage is about 5V, the voltage across the zener diode 158 is reverse biased and the diode 158 is nonconducting. Under an overvoltage condition, however, where the potential of the 5V supply 156 exceeds substantially its rated voltage, the zener diode is reverse biased and breaks down (e.g., by setting the zener breakdown voltage at about the predetermined level which is greater than 5V) and current conducts therethrough. Based upon the breakdown current, the resistor 160 develops a voltage thereacross which serves as an activation signal that an overvoltage condition has been detected. Although the zener diode and resistor combination has been illustrated and described as one type of voltage detection circuit, other types of circuits may be employed to provide similar voltage detection functionality and such alternative circuitry is contemplated as falling within the scope of the present invention. In accordance with another exemplary aspect of the present invention, the voltage reduction circuit 154 may comprise a transistor 162 such as an NPN type bipolar transistor having a control terminal coupled to the voltage detection circuit 152 . The voltage reduction circuit 154 also may include a resistor 164 coupled in series between another, higher value voltage supply 165 (e.g., a 12V supply) and a control terminal of another transistor 166 , for example, an NMOS transistor. Under normal operating conditions, no activation signal is provided by the voltage detection circuit 152 to the voltage reduction circuit 154 , and thus the NPN transistor 162 is off. With no current conduction through transistor 162 , the resistor 164 conducts substantially no current and passes effectively the voltage potential of the supply 165 to the gate of the transistor 166 . With the gate of the transistor 166 being high, the transistor 166 is conducting and the 5V supply potential is transmitted substantially to the trace(s) 110 . Under a detected overvoltage condition, however, the voltage detection circuit 152 provides an activation signal to the base of the transistor 162 , thus turning the transistor 162 on and initiating current conduction therethrough. As current conducts through the NPN transistor base 162 , a voltage drop occurs across the resistor 164 due to the current conduction therethrough, thus causing the gate voltage of the NMOS transistor 166 to decrease, resulting in decreased current conduction through the transistor 166 . As the NMOS transistor 166 becomes more resistive, a voltage drop occurs thereacross, thereby decreasing the voltage supplied by the 5V supply 156 to the trace(s) 110 . In the above manner, the voltage reduction circuit 152 operates to reduce the voltage at the trace(s) 110 when an overvoltage condition at the supply 156 is detected. Although FIG. 5 illustrates one exemplary voltage reduction circuit, various types of other circuit components and configurations may be employed to provide such functionality and such alternative circuits are contemplated as falling within the scope of the present invention. According to yet another aspect of the present invention, an overvoltage protection circuit is disclosed for protecting against an overvoltage condition associated with the high voltage supply (e.g., 12V supply), as illustrated in FIG. 6 and designated at reference numeral 200 . According to one exemplary aspect of the present invention, the overvoltage protection circuit 200 advantageously utilizes a pass FET 202 which already exists on the hard disk drive printed circuit board, however, use of such pass FET 202 is not required, and other switching components or circuits may be utilized and are contemplated as falling within the scope of the present invention. The overvoltage reduction circuit 200 in FIG. 6 is operable to reduce the board motor voltage to the servo IC 204 , the servo driver FETs 206 and the servo IC motor voltage 208 under system conditions when the 12V supply voltage 210 exceeds its rated voltage (e.g., increasing slightly above 12V). According to one exemplary aspect of the present invention, the overvoltage protection circuit 200 comprises a voltage detection circuit 220 and a voltage reduction circuit 222 , respectively. The voltage detection circuit 200 is operable to detect a circuit condition in which the potential of the 12V supply 210 exceeds a predetermined level, for example, some value greater than 12V. Upon detection of such a circuit condition, the voltage detection circuit 220 provides an activation signal to the voltage reduction circuit 222 which is operable to reduce the voltage associated with the 12V supply 210 at the traces 204 , 206 and 208 , respectively, which supplies the supply potential to at least one of the various integrated circuit chips on the hard disk drive printed circuit board. In accordance with one exemplary aspect of the present invention, the voltage detection circuit 220 may comprise a zener diode 230 in series with a resistor 232 . In operation, under normal conditions (the supply 210 properly supplying 12V) the voltage across the zener diode 230 is reverse biased and nonconducting. Under an overvoltage condition, however, where the potential of the 12V supply 210 exceeds its rated voltage, the zener diode 230 is reverse biased and breaks down (e.g., by setting the zener breakdown voltage at about the predetermined level which is slightly greater than 12V, for example, about 13V) and current conducts therethrough. Based upon the breakdown current, the resistor 232 develops a voltage thereacross which serves as an activation signal that an overvoltage condition has been detected. Although the zener and resistor combination has been illustrated and described as one type of voltage detection circuit, other types of circuits may be employed to provide similar voltage detection functionality and any such circuitry is contemplated as falling within the scope of the present invention. In accordance with another exemplary aspect of the present invention, the voltage reduction circuit 222 may comprise a transistor 240 such as an NPN type bipolar transistor having a control terminal coupled to the voltage detection circuit 220 . The voltage reduction circuit 222 also includes the pass FET 202 having a control terminal coupled to the NPN transistor 240 . The control terminal of the pass FET 202 is also coupled to supply disconnect sense circuit 250 which is operable to detect a system condition where the 12V supply has been disconnected from the hard disk drive system. Under such conditions, the sense circuit 250 turns off the pass FET 202 to enable the back EMF of the motor (not shown) to be used as a power source to park the head into its proper landing zone via the servo IC 204 in the absence of the 12V supply voltage. The overvoltage circuit 200 operates in the following exemplary manner. Under normal operating conditions, no activation signal is provided by the voltage detection circuit 220 to the voltage reduction circuit 222 , and thus the NPN transistor 240 is off. With no current conduction through transistor 240 , the pass FET 202 remains conducting via the sense circuit 250 (when the sense circuit 250 does not detect an absence of the 12V supply). With the gate of the pass FET 202 high, the transistor 202 is conducting and the 12V supply potential is transmitted substantially to the trace(s) 204 , 206 and 208 , respectively. Under a detected overvoltage condition, however, the voltage detection circuit 220 provides an activation signal to the base of the transistor 240 , thus turning the transistor 240 on and pulling the gate of the pass FET 202 low. As the gate voltage of the pass FET 202 decreases, the pass FET 202 becomes more resistive, and a voltage drop occurs thereacross, thereby decreasing the voltage supplied by the 12V supply 210 to the trace(s) 206 and 208 . The resistor 281 serves to limit power dissipation and voltage to other PCB components. In the above manner, the voltage reduction circuit 222 operates to reduce the voltage at the trace(s) 206 and 208 when an overvoltage condition at the 12V supply 210 is detected. Although FIG. 6 illustrates one exemplary voltage reduction circuit, various types of other circuit components and configurations may be employed to provide such functionality and such alternative circuits are contemplated as falling within the scope of the present invention. In accordance with another aspect of the present invention, the overvoltage protection circuit 200 further comprises a reset circuit 260 which is operable to output a reset signal in response to a detected 12V supply overvoltage condition. According to one exemplary aspect of the present invention, the reset circuit 260 comprises a transistor 262 , for example, an NPN type bipolar transistor having a control terminal coupled to the voltage detection circuit 220 . When the voltage detection circuit 220 detects an overvoltage condition associated with the 12V supply 210 , the activation signal (e.g., the voltage across the resistor 232 ) is output to the reset circuit 260 . The activation signal is operable to turn the transistor 262 on and pull an output 264 thereof, labeled RESETZ down to a circuit ground potential. According to an exemplary aspect of the present invention, RESETZ is a reset signal that goes to the hard disk drive microprocessor or ASIC controller (not shown), depending on the hard disk drive system configuration being employed, which turns off the servo motor and parks the head in its appropriate landing zone. The microprocessor or controller will then re-initiate the hard disk drive system start-up process using any one of various well known initialization procedures. Although the above reset circuit 260 is described in conjunction with a transistor 262 , other circuits providing similar functionality may be employed and such alternatives are contemplated as falling within the scope of the present invention. In the above example, the circuit 200 operates well when the 12V supply 210 experiences an overvoltage condition which is not substantially greater than the rated supply voltage of about 12V. In cases where the 12V supply potential greatly exceeds its rated voltage (e.g., about 30V), the circuit 200 has some potential limitations. For example, the diode (not shown) which is implicit in the pass FET 202 (the backgate diode) will tend to conduct when the voltage from the supply 210 is greater than the board motor voltage VM 206 . Consequently, the voltage at the traces 206 and 208 will get clamped at about a backgate diode drop (e.g., about 1V) below the supply potential 210 . For supply potentials not substantially greater than 12V (e.g., about 13-15V) such protection may be acceptable, however, for supply voltages substantially greater, large potentially undesirable voltages may still appear on the traces 206 and 208 , respectively. According to still another aspect of the present invention, a circuit for protecting against substantial overvoltage conditions on the high voltage supply is disclosed in FIG. 7 , and designated at reference numeral 280 . The overvoltage protection circuit 280 is similar in many respects to the circuit 200 of FIG. 6 , however, the circuit 280 of FIG. 7 has a voltage reduction circuit 290 that differs from the voltage protection circuit 222 of FIG. 6 . The voltage protection circuit 290 has a second transistor 292 , for example, an NMOS transistor, in series with the pass FET 202 such that their backgate diodes are coupled together in a back-to-back series fashion (e.g., cathode to cathode). In the above manner, when the 12V supply voltage 210 increases substantially above its rated voltage, although the backgate diode associated with the pass FET 202 becomes forward biased, the second backgate diode associated with the transistor 292 is reverse biased and no current conducts therethrough. Consequently, a substantial portion of the voltage is dropped across the reverse biased backgate diode of transistor 292 , thus protecting the traces 206 and 208 from experiencing a potentially undesirable high voltage thereat. Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the term “includes” is used in either the detailed description and the claims, such term is intended to be inclusive in a manner similar to the term “comprising.”