Patent Application
20080266739
The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to produce over-voltage and voltage transient protection circuits that could be used to protect various types of devices such as voltage regulators. These over-voltage and voltage transient protection circuits generally included a linear regulator that used a pass transistor and an operational amplifier to control an output voltage. During a transient or over-voltage event, the over-voltage protection circuit generally disabled the linear regulator and prevented regulation until the transient or over-voltage condition was eliminated. Because the linear regulator was disabled, the recovery time after the linear regulator was re-enabled usually was very long which caused variations in the output voltage. Additionally, the circuitry usually reacted slowly to the voltage transient which caused the output voltage to overshoot prior to the regulator being disabled. One example of such a transient protection circuit is described in U.S. Pat. No. 4,008,418 that issued on Feb. 15, 1997 that issued to Howard E. Murphy.
Accordingly, it is desirable to have a protection circuit that more accurately regulates the output voltage, that minimizes overshoots during a transient, avoids disabling the regulator, and that has a faster reaction time.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action.
For the embodiment of circuit 20 that is illustrated in
During the operation of circuit 20, it is possible that the value of the voltage received on input 18 could rapidly increase as illustrated by plot 61 at time T1. For example, a battery charger may be connected to battery 23 in order to charge battery 23. The voltage from the battery charger generally would be greater than the voltage from battery 23 and would rapidly increase the value of the voltage on input 18. Alternately, battery 23 may be replaced by a line adapter which may have a fault that causes the voltage on input 18 to quickly increase. If the value of the input voltage causes the intermediate voltage on output 33 to increase to a value that is greater than a first value, represented by the threshold voltage of transistor 45, threshold detector 42 enables the voltage reduction circuit of diodes 54 and 55 to decrease the value of the output voltage on output 21. Typically, the first value is greater than the upper limit of the values within the range of values of the desired value. Those skilled in the art will appreciate that amplifier 31 has a finite reaction time. Consequently, the increase in the input voltage may be coupled through transistor 32 to output 33, and the voltage on output 33 may temporarily increase above the first value for a period time before amplifier 31 can react. Threshold detector 42 is configured to detect the intermediate voltage on output 33 increasing to no greater than the first value and to responsively disable the current flow path around diodes 53 and 54 thereby coupling diodes 53 and 54 in series between output 33 and output 21. As the value of the voltage on output 33 increases to the first value, the voltage on node 38 increases to the threshold voltage of transistor 45 thereby enabling transistor 45. Enabling transistor 45 pulls the gate of transistor 49 low thereby enabling transistor 49 which couples node 44 and the gate of transistor 52 to a voltage substantially equal to the voltage on output 33. This disables transistor 52 which enables the voltage reduction circuit by terminating the current flow path around diodes 53 and 54 thereby connecting diodes 53 and 54 between transistor 32 and output 21. Connecting diodes 53 and 54 in series with transistor 32 subtracts the voltage drop across diodes 53 and 54 from the intermediate voltage and reduces the value of the output voltage on output 21 as illustrated by plot 63 after time T1. Preferably, transistors 45, 49, and 52 are formed to be small geometry transistors so that transistors 45, 49, and 52 can switch very rapidly and disable transistor 52 much more quickly than the response time of amplifier 31. Preferably, transistors 45, 49, and 52 are close to or at the minimum geometry for the technology used to produce transistors 45, 49, and 52. Generally, the change in the input voltage is much greater than the desired value on the intermediate voltage. The clamp circuit of diode 41 is configured to detect the intermediate voltage increasing to a second value that is greater than the first value and to substantially clamp output 33 to the second value. The zener voltage of diode 41, generally is greater than the first value as illustrated by plot 62 at time T2. For large increases in the input voltage, zener diode 41 may have to conduct large currents which may force the second value to be greater than the zener voltage of diode 41.
The control loop of regulator section 25 remains operating during and after the increase of the input voltage. However, the rapid increase in the input voltage may cause section 25 to loose regulation for a short time period as illustrated between times T1 and T2. After the input voltage increases, such as at time T2, the regulation loop of section 25 begins to recover and again regulate the value of the voltage on output 33 as illustrated by plot 62 between time T2 and T3. Transistor 52 remains disabled as long as the input voltage keeps the value of the intermediate voltage on output 33 greater than the first value. If the input voltage reduces and the value of the intermediate voltage on output 33 reduces below the first value, transistor 45 again becomes disabled and transistor 52 is enabled to again form the current flow path around diodes 53 and 54. Those skilled in the art will appreciate that if the input voltage decreases below the desired value of the intermediate voltage on output 33, that section 25 no longer regulates the intermediate voltage and the value of the intermediate voltage will follow the input voltage.
In one example embodiment, the value of the voltage on input 18 was at least approximately five volts (5 V) and the desired value of the voltage on output 33 was approximately 3.5 volts. For this example, the zener voltage of diode 41 was formed to be approximately 5.5 V, the voltage divider of resistors 35, 37, and 39 is formed to provide the threshold voltage of transistor 45 at node 38 when the value of the voltage on output 33 was approximately four volts (4.0 V), and each of diodes 53 and 54 are formed to have a forward voltage of approximately 0.7 volts. When the value of the input voltage increased to approximately 5.5 V, threshold detector 42 quickly disabled transistor 52 which dropped the voltage on output 21. As the input voltage increases forced the intermediate voltage on output 33 to increase above four volts, diode 41 clamped the voltage on output 33 to about 5.5 volts so the voltage drop of diodes 53 and 54 formed the output voltage to be about 4.1 volts. Without threshold detector 42, the output voltage on output 21 would increase to approximately 5.5 V and remain there until section 25 can recover to again regulate the output voltage.
In order to facilitate this functionality for circuit 20, reference 28 and error amplifier 31 are connected to receive operating power between input 18 and return 19. The output of reference 28 is connected to an inverting input of amplifier 31. A non-inverting input of amplifier 31 is connected to node 36, and the output of amplifier 31 is connected to a gate of transistor 32. A source of transistor 32 is connected to input 18 and a drain is connected to output 33 of section 25. A first terminal of resistor 35 is connected to output 33 and a second terminal is commonly connected to node 36 and a first terminal of resistor 37. A Second terminal of resistor 37 is commonly connected to node 38, a gate of transistor 45, and a first terminal of resistor 39. A second terminal of resistor 39 is connected to return 19. A cathode of diode 41 is connected to output 33 and an anode is connected to return 19. A first terminal of resistor 43 is connected to output 33 and a second terminal is commonly connected to a gate of transistor 49 and a drain of transistor 45. A source of transistor 45 is connected to return 19. A source of transistor 49 is commonly connected to an anode of diode 53, a source of transistor 52, and output 33. A drain of transistor 49 is commonly connected to node 44, a gate of transistor 52, and a first terminal of resistor 50. A second terminal of resistor 50 is connected to return 19. A drain of transistor 52 is connected to output 21 and a cathode of diode 54. An anode of diode 54 is connected to a cathode of diode 53.
Resistors 35, 36, and 37 are selected to form the desired value of the intermediate voltage at a value that forms the sense signal on node 38 to be greater than the threshold voltage of transistor 45. In operation, if the input voltage is greater than the desired value the input voltage on input 18 is regulated to form a regulated voltage on output 33. The input voltage has to be greater than the desired value by at least the voltage dropped by transistor 32. For the embodiment illustrated in
If the value of the input voltage decreases below the first value that causes the sense signal to decrease below the threshold voltage of transistor 45, transistor 45 becomes disabled and transistor 52 becomes enabled to form a current flow path around diodes 53 and 54 and form the output voltage to be substantially equal to the value of the intermediate voltage. For the embodiment illustrated in
For example, battery 23 may be charged to a voltage such as a voltage that is greater than five volts (5 V) and section 25 may regulate the intermediate voltage on output 33 to substantially five volts (5 V). Resistors 35, 37, and 39 may be selected to form the sense voltage to be no less than the threshold voltage of transistor 45 for values of the intermediate voltage that are no less than about four volts (4 V). Thus, for the input voltage value that is greater than the voltage that forms the sense signal to be no less than the threshold voltage of detector 42, transistor 45 is enabled and transistor 52 is disabled, thus, diodes 53 and 54 drop some of the intermediate voltage and form the output voltage to be less than the intermediate voltage. If battery 23 discharges down to a value that causes the sense voltage to reduce to less than the threshold voltage of transistor 45, transistor 45 becomes disabled and transistor 52 is enabled, thus, diodes 53 and 54 are shorted and the output voltage is formed to be substantially equal to the intermediate voltage. Since the input voltage has decreased below the value that is to be regulated by section 25, section 25 does not regulate the intermediate voltage and the intermediate voltage follows the input voltage.
However, if the input voltage quickly increases to a third value that is greater than the first value, such as the zener voltage of diode 41, diode 41 clamps output 33 to a value that is greater than the intermediate voltage. For example, the zener voltage of diode 41 may be 5.5 volts. If the input voltage increases past the zener voltage, diode 41 begins to conduct and clamps output 33 to the zener voltage. As stated hereinbefore, the input voltage may quickly increase to a value that is much greater than the zener voltage which may force diode 41 to conduct a large current thereby allowing the intermediate voltage to increase. However, after section 25 has sufficient time to recover, section 25 will regulate the intermediate voltage back down to the first value.
In view of all of the above, it is evident that a novel device and method is disclosed. Included, among other features, is forming a protection circuit that does not disable the linear regulator section during a voltage transient of the input voltage. Additional, selectively enabling a voltage reduction responsively to the intermediate voltage being no less than the first value minimizes the increase in the output voltage.
While the subject matter of the invention is described with specific preferred embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the semiconductor arts. For example, the voltage reduction circuit of diodes 53 and 54 may have more or fewer diode as required to provide a proper voltage drop between output 33 and output 21. Although circuit 20 is illustrated and described as providing power to a switching voltage regulator, circuit 20 may be used to provide the protect voltage to a variety of circuits that could use such a protected voltage such as a charge pump circuit, or any logic circuit. Also, the clamp circuit that is illustrated by diode 41 may be replaced with any type of circuit that provides a clamping type of function. Additionally, the word “connected” is used throughout for clarity of the description, however, it is intended to have the same meaning as the word “coupled”. Accordingly, “connected” should be interpreted as including either a direct connection or an indirect connection.
