# Patent

## Title
Cascode configured switching using at least one low breakdown voltage internal, integrated circuit switch to control at least one high breakdown voltage external switch

## Abstract

An electronic system includes a low breakdown voltage (LBV) switch internal to an integrated circuit controller to control conductivity of an external, high breakdown voltage (HBV) switch. In at least one embodiment, the internal LBV switch and a cascode configuration of the LBV and HBV switches allow the controller to control the LBV switch and the HBV switch using an internal (“on-chip”) control signal. In at least one embodiment, the LBV switch and the cascode configuration of the HBV switch also allows the controller to control the LBV and HBV switches with more accuracy and less parasitic losses relative to directly controlling the HBV switch. Thus, in at least one embodiment, the low breakdown voltage switch is fabricated as part of an integrated circuit controller, and the high breakdown voltage switch is fabricated separately and located external to the integrated circuit controller.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to a system and method related to cascode configured switching using at least one low breakdown voltage internal, integrated circuit switch to control at least one high breakdown voltage external switch.
2. Description of the Related Art
Systems often modulate conductivity of one or more semiconductor-based switches to control current through the switches. For example, switching power converters utilize a switch to control conversion of alternating current (AC) voltages to direct current (DC) voltages or DC-to-DC. Switches are also often used to control regulated current devices such as light emitting diodes (LEDs). Semiconductor-based switches can be categorized as low voltage switches and high voltage switches relative to each other. For example, semiconductor-based switches have breakdown voltages. Breakdown occurs when a voltage greater than the breakdown voltage causes avalanche multiplication of carriers in the switch. For example, in at least one embodiment, the breakdown voltage of a complimentary metal oxide semiconductor (CMOS) field effect transistor (FET) refers to a maximum allowable drain-to-source voltage of the CMOS FET beyond which breakdown of the CMOS FET occurs. In at least one embodiment, the breakdown voltage of a bi-polar junction transistor (BJT) refers to a maximum allowable collector-to-emitter voltage of the BJT beyond which breakdown of the BJT occurs.
FIG. 1 represents a power control system 100, which includes switching power converter 102. In at least one embodiment, switching power converter operates in a continuous conduction mode (CCM). Voltage source 101 supplies an alternating current (AC) input voltage VIN to a full bridge diode rectifier 103. The voltage source 101 is, for example, a public utility, and the AC voltage VIN is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe. The rectifier 103 rectifies the input voltage VIN and supplies a rectified, time-varying, line input voltage VX to the switching power converter.
The switching power converter 102 includes at least two switching operations, i.e. controlling field effect transistor (FET) 108 to provide power factor correction and controlling FET 108 to provide regulation of link voltage VLINK. The inductor current iL ramps ‘up’ when FET 108 conducts, i.e. is “ON”. The inductor current iL ramps down when FET 108 is nonconductive, i.e. is “OFF”, and supplies current iL to recharge capacitor 106. The time period during which inductor current iL ramps down is commonly referred to as the “inductor flyback time”. Diode 111 prevents reverse current flow into inductor 110. In at least one embodiment, control signal CS0 is a pulse width modulated signal, and FET 108 is an n-channel FET. In this embodiment, control signal CS0 is a gate voltage of FET 108, and FET 108 conducts when the pulse width of CS0 is high. Thus, the ‘on-time’ of FET 108 is determined by the pulse width of control signal CS0. In at least one embodiment, the switching power converter 102 operates in CCM, i.e. ramp up time of the inductor current iL plus the inductor flyback time is greater than or equal to the period of the control signal CS0.
In at least one embodiment, switching power converter 102 boosts a 110-120 V rectified input voltage VX to a higher link voltage VLINK, such as 200-400V. Accordingly, FET 108 is fabricated to have a breakdown voltage sufficient to accommodate the controlled current iCCT and voltage drops across FET 108 associated with the high input voltage VX and higher link voltage VLINK. FET 108 is a high breakdown voltage device fabricated using a “high” voltage process. In at least one embodiment, FET 108 has a breakdown voltage greater than or equal to 30V and at least sufficient to accommodate operating characteristics of switching power converter 102. In at least one embodiment, power factor correction (PFC) and output voltage controller 114 is an integrated circuit and is fabricated using a low voltage process that is insufficient to fabricate a switch with a sufficiently high breakdown voltage to control the controlled current iCCT. Thus, FET 108 is located external to PFC and output voltage controller 114. As subsequently described in more detail, PFC and output voltage controller 114 generates a pulse width modulated control signal CS0 to control conductivity of FET 108. In at least one embodiment, FET 108 is a FET, and control signal CS0 is a gate voltage.
Switching power converter 102 includes current sense resistor 109. Current sense circuit 109 can be any circuit that senses the switch controlled current iCC. The switch controlled current iCC generates a sense voltage VSEN across current sense resistor 109. The PFC and output voltage controller 114 receives the sense voltage VSEN. The resistance R of sense resistor 109 is known. The sense voltage VSEN is directly related to switch controlled current iCC via Ohm's law, i.e. VSEN=iCC·R. “R” represents a resistance value of sense resistor 109, and the value of R is a matter of design choice. In at least one embodiment, PFC and output voltage controller 114 utilizes the sense voltage VSEN and sensing two signals, namely, the line input voltage VX and the capacitor voltage/output voltage VLINK to generate the pulse width and duty cycle of control signal CS0.
Capacitor 106 supplies stored energy to load 112. The capacitor 106 is sufficiently large so as to maintain a substantially constant output voltage VLINK, as established by a switch state controller 114 (as discussed in more detail below). The output voltage VLINK remains substantially constant during constant load conditions. However, as load conditions change, the output voltage VLINK changes. The switch state controller 114 responds to the changes in VLINK and adjusts the control signal CS0 to restore a substantially constant output voltage as quickly as possible. The switch state controller 114 includes a small capacitor 115 to filter any high frequency signals from the line input voltage VX.
The switch state controller 114 of power control system 100 controls FET 108 and, thus, controls power factor correction (PFC) and regulates output power of the switching power converter 102. The goal of power factor correction technology is to make the switching power converter 102 appear resistive to the voltage source 101. Thus, the switch state controller 114 attempts to control the inductor current iL so that the average inductor current iL is linearly and directly related to the line input voltage VX. A CCM PFC controller, model number UCC28019A, available from Texas Instruments, Inc., Texas, USA is an example of switch state controller 114. The switch state controller 114 controls the pulse width (PW) and period (TT) of control signal CS0. To regulate the amount of energy transferred and maintain a power factor close to one, switch state controller 114 varies the period of control signal CS0 so that the input current iL tracks the changes in input voltage VX and holds the output voltage VLINK constant. Thus, as the input voltage VX increases, switch state controller 114 increases the period TT of control signal CS0, and as the input voltage VX decreases, switch state controller 114 decreases the period of control signal CS0. At the same time, the pulse width PW of control signal CS0 is adjusted to maintain a constant duty cycle (D) of control signal CS0, and, thus, hold the output voltage VLINK constant.
In at least one embodiment, the switch state controller 114 updates the control signal CS0 at a frequency much greater than the frequency of input voltage VX. The frequency of input voltage VX is generally 50-60 Hz. The frequency 1/TT of control signal CS0 is, for example, between 20 kHz and 130 kHz. Frequencies at or above 20 kHz avoid audio frequencies and frequencies at or below 130 kHz avoid significant switching inefficiencies while still maintaining good power factor, e.g. between 0.9 and 1, and an approximately constant output voltage VLINK.
As previously described, FET 108 is fabricated using a higher breakdown voltage process relative to a process used to fabricate PFC and output voltage controller 114. Accordingly, FET 108 is located external to PFC and output voltage controller 114 because the processes used to fabricate devices in PFC and output voltage controller 114 are incompatible with the process used to fabricate FET 108. Higher voltage switches have higher breakdown voltages. However, high voltage FET 108 has disadvantages relative to a low breakdown voltage switch. For example, relative to lower breakdown voltage switches, FET 108 requires more charge to change conduction state and has higher parasitic diode and capacitance related characteristics. Additionally, turning FET 108 “on” and “off” requires charging and discharging a gate of FET 108, and the charge on gate of FET 108 is discharged through a ground reference node and is therefore lost.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, an apparatus includes an integrated circuit controller to at least control a switching power converter. The controller is configured to control the switching power converter by generating a switch control signal to control a first switch, wherein the first switch is internal to the controller. The integrated circuit includes a node to couple the first switch to a second switch in a cascode configuration. A breakdown voltage of the first voltage switch is approximately less than or equal to one-half of a breakdown voltage of the second switch.
In another embodiment of the present invention, a method includes generating a switch control signal and controlling conductivity of a first switch using the control signal. The method also includes controlling conductivity of a second switch of a switching power converter with the first switch. A breakdown voltage of the first switch is approximately less than or equal to one-half of a breakdown voltage of the second switch.
In a further embodiment of the present invention, an apparatus includes a switching power converter. The switching power converter includes a first switch to control an output voltage of the switching power converter. The apparatus also includes an integrated circuit controller, coupled to the first switch, to generate a switch control signal to control a second switch. The second switch is internal to the controller. The integrated circuit includes a node to couple the second switch to the first switch of the switching power converter in a cascode configuration. A breakdown voltage of the second switch is approximately less than or equal to one-half of a breakdown voltage of the first switch of the switching power converter.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
FIG. 1 (labeled prior art) depicts an electronic system having a switching power converter and a high voltage switch controlled by a pulse-width modulated control signal.
FIG. 2 depicts an electronic system having an integrated circuit that includes an internal switch to control an external switch in cascode configuration with the internal switch.
FIG. 3 depicts an embodiment of the electronic system of FIG. 2 with field effect transistors.
FIG. 4 depicts signal graphs for shaping a current in the electronic systems of FIGS. 2, 5, and 6.
FIG. 5 depicts an embodiment of the electronic system of FIG. 2 with bipolar junction transistors.
FIG. 6 depicts an embodiment of the electronic system of FIG. 2 with a switching power converter load.



DETAILED DESCRIPTION
An electronic system includes a low breakdown voltage (LBV) switch internal to an integrated circuit controller to control conductivity of an external, high breakdown voltage (HBV) switch. In at least one embodiment, the internal LBV switch and a cascode configuration of the LBV and HBV switches allow the controller to control the LBV switch and the HBV switch using an internal (“on-chip”) control signal. In at least one embodiment, the cascode configuration of the LBV switch and the HBV switch also allows the controller to control the LBV and HBV switches with more accuracy, less electromagnetic interference, and less parasitic losses relative to directly controlling the HBV switch. Additionally, in at least one embodiment, the electronic system is configured to allow charge on a node of the HBV switch to be at least partially recovered rather than discarded. Thus, in contrast to conventional technology, in at least one embodiment, the controller provides a switch control signal to the LBV switch, and the LBV switch controls conductivity of the HBV switch, rather than the controller providing the switch control signal directly to the HBV switch.
In at least one embodiment, the low breakdown voltage switch is fabricated as part of an integrated circuit controller, and the high breakdown voltage switch is fabricated separately and located external to the integrated circuit controller. The descriptive terms “internal” and “external” with reference to a switch refer to a location of the switch as being part of an integrated circuit, i.e. “on-chip”, or separate from an integrated circuit, i.e. “off-chip”. “High breakdown voltage” and “low breakdown voltage” are relative terms indicating, in at least one embodiment, a difference in breakdown voltages of the internal and external switches.
In at least one embodiment, the controller is configured to allow the internal, lower breakdown voltage switch to connect in series with the external, higher breakdown voltage switch in a cascode configuration. The controller controls conductivity of the internal switch, and conductivity of the internal switch controls conductivity of the external switch. Because the internal switch has a lower breakdown voltage than the high voltage switch, in at least one embodiment, the lower breakdown voltage switch costs less to manufacture, can be more precisely controlled, and has lower parasitic characteristics. The combination of the internal and external switches can be used in higher voltage operations, such as switching power conversion operations involving 110V and greater. The cascode configuration reduces conventional disadvantages of the high breakdown voltage switch by, for example, substantially reducing or eliminating some parasitic characteristics (such as Miller capacitance and parasitic diodes) and operational difficulties associated with the high breakdown voltage switch.
The cascoded internal, low breakdown voltage and external, high breakdown voltage switches can be used to control current in any load. For example, in at least one embodiment, the internal LBV switch is part of an integrated circuit controller configured to control a switching power converter, and the external HBV switch part of the switching power converter. In at least one embodiment, the internal and external cascoded switches can control current in a light emitting diode (LED) based light source or any other load.
In at least one embodiment, when the LBV and HBV switches are turned “on”, current flows through the LBV and HBV switches. In at least one embodiment, the controller shapes the current to reduce certain detrimental effects, such as power losses and electromagnetic interference that can occur when, for example, the HBV switch is rapidly turned “on” without controlled shaping of the current. In at least one embodiment, the controller shapes the current by controlling a current magnitude versus time profile of the current.
In at least one embodiment, during operation of the LBV and HBV switches, a maximum operational voltage across any nodes of the LBV switch is less than a maximum operational voltage across any nodes of the HBV switch. In at least one embodiment, the maximum operational voltage across any nodes of the LBV switch is less than or equal to 30V, and the maximum operational voltage across any nodes of the HBV switch is greater than or equal to 60V.
FIG. 2 depicts electronic system 200 that includes a controller 202 to control controlled current iCCT. Controller 202 includes a control signal generator 204 to generate a control signal CS1, and provide the control signal CS1 to a control node of low breakdown voltage (LBV) switch 206 to control LBV switch 206. The control node of LBV switch 206 is a gate or a base for respective field effect transistor or bipolar transistor based implementations of LBV switch 206. Electronic system 200 also includes a high breakdown voltage (HBV) switch 210. In at least one embodiment, a control node of the HBV switch 210 does not receive a control signal from controller 202. The terms “low” and “high” used in relation to switches 206 and 210 are terms relative to switches 206 and 210 to indicate that switch 206 has a lower breakdown voltage BVLOW than switch 210, and therefore, switch 210 has a higher breakdown voltage BVHIGH than switch 206. In at least one embodiment, switch 206 has a breakdown voltage less than equal to one-half the breakdown voltage of switch 210, i.e. BVLOW≦BVHIGH/2. In at least one embodiment, switch 206 has a breakdown voltage BVLOW equal to 30V or less, and switch 210 has a breakdown voltage BVHIGH of at least 60V, i.e. BVLOW≦30V, and BVHIGH≧60V. The particular type(s) of switches 206 and 210, such as bipolar or FET types, is (are) a matter of design choice. In at least one embodiment, switches 206 and 210 are semiconductor switches, each includes one or more field effect transistors (FETs) or one or more bipolar junction transistors (BJTs). HBV switch 210 can also include one or more insulated gate bipolar transistors (IBGTs). Switches 206 and 210 can be the same or different types.
In at least one embodiment, controller 202 is an integrated circuit. The internal LBV switch 206 allows control signal generator 204 to control LBV switch 206 using an internal (“on-chip”) switch control signal CS1. In at least one embodiment, directly controlling the internal LBV switch 206 with switch control signal allows controller 202 to indirectly control HBV switch 210 with more accuracy and less parasitic losses relative to directly controlling HBV switch 210 with control signal CS1.
Controller 202 includes an exemplary node 212 to allow LBV switch 206 to connect in series with HBV switch 210 so that LBV switch 206 and HBV switch 210 are arranged in a cascode configuration. In at least one embodiment, node 212 is a conductive pad of controller 202. In a cascode configuration, HBV switch 210 represents a load to LBV switch 206, and LBV switch 206 controls conductivity of HBV switch 210. The cascoded configuration of LBV switch 206 and HBV switch 210 substantially reduces or eliminates some parasitic characteristics and operational difficulties associated with the higher breakdown voltage switch. Such parasitic characteristics can include Miller capacitance and parasitic diodes. Operational difficulties can include high turn-on current and high charge storage relative to lower breakdown voltage switches.
In at least one embodiment, controller 202 is implemented as an integrated circuit. In at least one embodiment, LBV switch 206 is fabricated as part of controller 202 and is, thus, internal to controller 202. In at least one embodiment, controller 202 is fabricated using a lower breakdown voltage process than a higher breakdown process used to fabricate HBV switch 210.
In at least one embodiment, control signal CS1 is a duty cycle modulated signal having exemplary pulses 214. In at least one embodiment, HBV switch 210 is biased with a bias signal BIAS so that during a pulse of control signal CS1, LBV switch 206 conducts and causes HBV switch 210 to conduct. Bias signal BIAS can be any signal that allows HBV switch 210 to conduct as controlled by LBV switch 206. For example, in some embodiments, HBV switch 210 is a FET, BJT, or IGBT, and the bias signal BIAS is respectively a gate voltage for a FET embodiment or a base voltage for a BJT or IGBT embodiment. In the cascode configuration, if HBV switch 210 is a FET, the gate is referred to herein as a bias node, and if HBV switch 210 is a BJT or IGBT, the base is referred to herein as a bias node. When switches 206 and 210 conduct (are “on”), controlled current iCCT flows through switches 206 and 210. The duty cycle of control signal CS1 corresponds to an average resistance of switches 206 and 210 and, thus, corresponds to an average value of controlled current iCCT. Accordingly, control signal CS1 controls the average value of controlled current iCCT. Controlled current iCCT flows through load 216. Load 216 can be any load utilizing controlled current iCCT. For example, in at least one embodiment, load 216 is a switching power converter and a load connected to the switching power converter. In at least one embodiment, load 216 is a light source, such as an LED.
Control signal generator 204 generates control signal CS1. The particular configuration of control signal generator 204 is a matter of design choice. In at least one embodiment, load 216 represents a switching power converter, and control signal generator generates control signal CS1 to control power factor correction and output voltage regulation of load 216 as illustratively described in U.S. patent application Ser. No. 11/967,269, entitled Power Control System Using A Nonlinear Delta-Sigma Modulator With Nonlinear Power Conversion Process Modeling, filed on Dec. 31, 2007, inventor John L. Melanson, and assignee Cirrus Logic, Inc. U.S. patent application Ser. No. 11/967,269 is referred to herein as “Melanson I” and is hereby incorporated herein in its entirety.
FIG. 3 depicts electronic system 300, which represents an exemplary embodiment of electronic system 200. Electronic system includes controller 302, and controller 302 includes n-channel LBV FET 304. In at least one embodiment, controller 302 is an integrated circuit. In at least one embodiment, LBV FET 304 is fabricated as part of controller 302 using a lower voltage process than a process used to fabricate HBV FET 306. Node 212 of controller 302 couples a drain of LBV FET 304 to a source of n-channel HBV FET 306. The source of LBV FET 304 is coupled to a reference voltage VREF, such as a ground voltage, via node 309. In at least one embodiment, node 309 is a conductive pad of controller 302. Capacitor 310 is connected between node 312 and node 309. Capacitor 310 stores charge and can serve as an auxiliary power supply for devices connected to node 312.
Controller 302 receives a supply voltage VDD via node 312. In at least one embodiment, node 312 is a conductive pad of controller 302. Diode 314 connects node 212 to node 312. Diode 314 provides overvoltage protection at node 212 by ensuring that node 212 does not increase above VDD plus a forward voltage drop VF of diode 314 for any significant length time. Additionally, as subsequently explained in more detail, in at least one embodiment, the signal path through diode 314 between nodes 212 and 312 allow a voltage supply (not shown) supplying voltage VDD to recover some power when LBV FET 304 is turned “off”. The gate of HBV FET 306 is coupled to node 312 and is biased by the gate voltage VG. The gate of HBV FET 306 is either connected directly to node 312 and supply voltage VDD or is coupled to node 312 and supply voltage VDD via optional resistor 316. The supply voltage VDD provides a sufficient gate voltage for HBV FET 306 to allow HBV FET 306 to conduct when LBV FET 304 conducts. The particular value of supply voltage VDD is a matter of design choice and depends on, for example, the voltage specifications for controller 302 and loads driven by controller 302. In at least one embodiment, supply voltage VDD is +12V. In at least one embodiment, resistor 316 is connected between node 312 and the gate of HBV switch 306. Resistor 316 is shown in dashed lines as an optional component. When included in electronic system 300, resistor 316 assists in regulating a charging time of the gate of HBV FET 306 when HBV FET 306 turns “on”. Regulating the charging time of the gate of HBV FET 306 can, for example, prevent conduction oscillations of HBV FET 306, control electromagnetic interference, and reduce switching power losses.
During operation of controller 302, control signal generator 308 generates a duty cycle modulated switch control signal CS1. In at least one embodiment, control signal generator 308 is identical to control generator 204. During a pulse 214 of control signal CS1, LBV FET 304 conducts. When LBV FET 304 conducts, the source of HBV FET 306 is coupled to the reference voltage VREF, and current flows to the gate of HBV FET 306. The gate voltage VG minus the sum of the reference voltage VREF and a drain-to-source voltage VDS—304 is greater than a threshold voltage VTH of HBV FET 306, i.e. VG−(VDS—304+VREF)>VTH. Thus, when control signal CS1 causes LBV FET 304 to conduct, the conduction of LBV FET 304 causes HBV FET 306 to also conduct. When switches 304 and 306 conduct, controlled current iCCT flows through switches 304 and 306.
When the pulse 214 of control signal CS1 ends, LBV FET 304 turns “off”. HBV FET 306 remains “on” until node 212 charges to at least VDD−VTH. In at least one embodiment, controlled current iCCT actually charges node 212 to a voltage VS, which is above a sum of voltage VDD and the forward voltage drop VF of diode 314, i.e. VS>VDD+VF. When VS>VDD+VF. Thus, diode 314 is forward biased, and the controlled current iCCT actually provides charge to a voltage supply providing voltage VDD or to capacitor 310. Thus, in this embodiment, charge is recovered by the voltage supply (not shown) or stored by capacitor 310 rather than being discarded as with conventional systems, such as electronic system 100 (FIG. 1).
In at least one embodiment, LBV FET 304 and HBV FET 306 function as a symbiotic pair. In at least one embodiment, LBV FET 304 facilitates more accurate control of controlled current iCCT and reduces detrimental effects as previously discussed, and HBV FET 306 facilitates control of a high voltage circuit. When switches 304 and 306 are nonconductive, voltage VD−VS is across HBV FET 306. In some embodiments, voltage VD−VS is hundreds of volts, such as 400 V, which, in at least one embodiment, would exceed the breakdown voltage of LBV FET 304. The higher breakdown voltage BVHIGH of HBV FET 306 prevents breakdown of HBV FET 306. Diode 314 provides a discharge path from the drain of LBV FET 304 at node 212 to node 312, which prevents the voltage across LBV FET 304 from exceeding VS−VREF.
FIG. 4 depicts signal graphs 400 of the drain voltage VD of HBV FET 306, the controlled current iCCT, and switch control signal CS1 in an embodiment that generates switch control signal CS1 to shape controlled current iCCT. Referring to FIGS. 3 and 4, in at least one embodiment, control signal generator 308 controls the rise of a pulse of switch control signal CS1 to control the drain-to-source resistance of LBV FET 304 and, thus, shape the controlled current iCCT as indicated in the current magnitude versus time profile 402 of controlled current iCCT. Shaping the controlled current iCCT controls the turn ‘on’ rate of HBV FET 306 by controlling a decrease in voltage at node 212 and, thus, controlling charging of the gate of HBV FET 306. In at least one embodiment, turning ‘on’ HBV FET 306 too slow wastes power, and turning ‘on’ HBV FET 306 too fast can increase electromagnetic interference and waste power in parasitic of HBV FET 306.
Referring to the signal graphs 400 and electronic system 300, when switch control signal CS1 is 0V, the drain voltage VD of HBV FET 306 is ‘high’. The ‘high’ value of the drain voltage depends on the operating environment of electronic system 300. At time t0, control signal generator 308 begins a pulse of switch control signal CS1. Between times t0 and t1, control signal generator 308 allows switch control signal CS1 to rise to V1. Between times t0 and t1, LBV FET 304 and HBV FET 306 have a “soft” turn ‘on’ so that the rate of increase of controlled current iCCT and the rate of decrease of drain voltage VD is less than the rates if switch control signal CS1 pulses as depicted by pulses 214. At time t1, control signal generator 308 causes switch control signal CS1 to increase to a maximum voltage value VMAX. Consequently, drain voltage VD decreases to approximately the reference voltage VREF, and controlled current iCCT increases to a steady state value ISS.
At time t2, switch control signal CS1 drops to 0, thus, turning LBV FET 304 ‘off”. The controlled current iCCT decreases until node 212 sufficiently charges to turn HBV FET 306 ‘off’ at time t3. As controlled current iCCT decreases, the drain voltage VD increases until a steady state, maximum voltage is reached is reached at time t3. The particular values of the drain voltage VD and the controlled current iCCT are functions of the particular circuit components used in electronic system 300. The particular timing of switch control signal CS1 is a matter of design choice. In at least one embodiment, t1−t0 and t3−t2 are each 50 nanoseconds. The total duration, t3−t0, of a pulse of control signal CS1 is determined by control signal generator 308 and, for example, depends on a desired average current value of controlled current iCCT. In at least one embodiment, t3−t0 is approximately 5 microseconds. In signal graphs 400, the rise of control signal CS1 is a step function between times t1 and t0. However, the rise function of control signal CS1 is a matter of design choice. For example, the rise function can have one intermediate step V1 between an initial value 0 and a final value VMAX of control signal CS1 as shown in FIG. 4, can have multiple steps in a ramp function, can be a linear or non-linear continuous function rise, etc. The particular voltage levels of switch control signal CS1 is also a design choice. In at least one embodiment, voltage V1=1 to 1.25 V, and voltage VMAX=12 V.
FIG. 5 depicts electronic system 500, which represents an exemplary embodiment of electronic system 200. Electronic system 500 includes controller 302, and controller 302 includes LBV FET 304. Node 212 of controller 302 couples a drain of LBV FET 304 to an emitter of n-channel HBV BJT 502. In at least one embodiment, the source of LBV FET 304 is coupled to a reference voltage VREF, such as a ground voltage.
During operation of controller 302, control signal generator 308 generates a duty cycle modulated switch control signal CS1. In at least one embodiment, control signal generator 308 is identical to control signal generator 204. During a pulse 214 of control signal CS1, LBV FET 304 conducts. The base of HBV BJT 502 is coupled to node 312 and held at base voltage VB. When LBV FET 304 conducts, the emitter of HBV BJT 502 is coupled to the reference voltage VREF, and the base voltage VB minus the sum of the reference voltage VREF and voltage VDS—304 is greater than the base-to-emitter voltage VBE to turn-on HBV BJT 502, i.e. VB−(VDS—304+VREF)>VBE—ON, wherein VBE—ON is the value of the base-to-emitter voltage VBE that allows controlled current iCCT to flow from the collector to the emitter of HBV BJT 502. Thus, when control signal CS1 causes LBV FET 304 to conduct, the conduction of LBV FET 304 causes HBV BJT 502 to also conduct. The current into base of HBV BJT 502 is regulated by a current regulation circuit, such as resistor 504. For example, in the embodiment of electronic system 500 depicted in FIG. 5, resistor 504 assists in regulating a current flowing into the base of HBV FET HBV BJT 502 when HBV BJT 502 turns “on”.
When switches 304 and 502 conduct, controlled current iCCT flows through switches 304 and 502. When switch control signal CS1 turns LBV FET 304 ‘off’, the controlled current iCCT charges node 212 until HBV BJT 502 turns ‘off’. Diode 314 provides a discharge path to node 212 if the voltage of node 212 increases above the sum of the forward voltage VF of diode 314 and voltage VDD. When switches 304 and 502 are nonconductive, voltage VCE=VC−VE is across HBV FET 306. “Voltage VC” is the collector voltage of HBV BJT 502, and “voltage VE” is the emitter voltage of HBV BJT 502. In some embodiments, collector voltage VC is hundreds of volts, such as 400 V. The higher breakdown voltage BVHIGH of HBV BJT 502 prevents breakdown of HBV BJT 502. By providing a discharge path to node 312, diode 314 prevents the voltage across LBV FET 304 from exceeding supply voltage VDD+ the forward voltage VF of diode 314—the reference voltage VREF, i.e. VDS—304≦(VDD+VF)−VREF. The breakdown voltage of LBV FET 304 is greater than (VDD+VF)−VREF. Electronic system 500 can also generate switch control signal CS1 to shape controlled current iCCT as previously described with reference to FIGS. 3 and 4.
FIG. 6 depicts electronic system 600, which represents one embodiment of electronic system 200. Electronic system 600 includes an integrated circuit controller 602, and controller 602 includes a LBV FET 304. Electronic system 600 also includes HBV FET 606 arranged in a cascode configuration with LBV FET 304. The internal LBV FET 304 allows control signal generator 204 to control LBV FET 304 using an internal switching power converter switch control signal CS1. The LBV FET 304 and the cascode configuration of LBV FET 304 and HBV FET 606 allow controller 602 to control LBV FET 304 and HBV FET 606 with more accuracy and less parasitic losses relative to directly controlling HBV FET 606 with control signal CS1. In at least one embodiment, the cascode arrangement of LBV FET 304 and HBV FET 606 allows controller 602 to more accurately control current iCCT because the internal LBV FET 304 is more responsive to control signal CS1. The cascode arrangement of LBV FET 304 and HBV FET 606 has less parasitic losses, such as Miller capacitance losses. In at least one embodiment, a controlled turn “on” of HBV FET 606 can be especially valuable when switching power converter 608 operates in continuous conduction mode (CCM) because, in at least one embodiment, a reverse recovery of diode 618 can cause noise and power loss if switched too rapidly. Controlled switching of LBV FET 304 and HBV FET 606 can also minimize electromagnetic interference and switching power loss as previously described.
In at least some embodiments, LBV FET 304 is a FET or a BJT, such as respective LBV FET 304 (FIG. 3) or LBV BJT 404 (FIG. 4). In at least some embodiments, HBV FET 606 is a FET or a BJT, such as respective LBV FET 306 (FIG. 3) or HBV BJT 406 (FIG. 4). In at least one embodiment, implementing switch 606 as an NPN bipolar transistor in cascode configuration with LBV FET 304, allows switch 606 to have a higher breakdown voltage and less degradation due to leakage effects versus a FET implementation.
Electronic system 600 also includes switching power converter 608. Voltage supply 610 provides an AC supply voltage VIN. In at least one embodiment, voltage supply 610 is identical to voltage supply 101. Full-bridge diode rectifier 612 rectifies the supply voltage VIN to generate input voltage VX. Capacitor 614 provides high frequency filtering. During a pulse 214 of control signal CS1, LBV FET 304 conducts and discharges node 616 towards reference voltage VREF. Voltage VG biases a gate of HBV FET 606 so that when node 616 discharges towards reference voltage VREF, HBV FET 606 conducts. Thus, the internal LBV FET 304 controls conduction of HBV FET 606. As previously discussed, diode 314 provides, for example, a discharge path for node 212 to recover charge from controlled current iCCT when LBV FET 304 is turned ‘off’ and to provide voltage protection for LBV FET 304.
When switches 304 and 606 conduct, controlled current iCCT equals the inductor current iL, diode 618 is reverse biased, and the inductor current iL increases a voltage across inductor 616. When the pulse 214 of control signal CS1 ends, FET 304 and, thus, FET 606 turn “off”, diode 618 is forward biased, and inductor current iL charges capacitor 620. Control signal generator 204 generates control signal CS1 with a sufficiently high frequency to provide power factor correction for switching power converter 608 and regulate link voltage VLINK to an approximately constant value. Switching power converter 608 provides the link voltage to load 622. Load 622 can be any load. Electronic system 600 can also generate switch control signal CS1 to shape controlled current iCCT as previously described with reference to FIGS. 3 and 4. Resistor 624 is shown in dashed lines as an optional component. When included in electronic system 600, resistor 624 assists in regulating a charging time of the base of HBV FET 606 to voltage VDD when HBV FET 606 turns “on”. Regulating the charging time of the base of HBV FET 606 can, for example, prevent conduction oscillations of HBV FET 606.
Thus, an electronic system includes an internal (“on-chip”) LBV switch of an integrated circuit controller in cascode configuration with an external (“off-chip”) HBV switch. The internal LBV switch allows a control signal generator of the controller to control the LBV switch using an internal control signal to, for example, provide more responsiveness of a controlled current to the internal control signal relative to using the control signal to drive the external HBV switch. In at least one embodiment, as previously, illustratively described, the LBV switch and the cascode configuration of the LBV switch and HBV switch allow the controller to control the LBV switch and the HBV switch with more accuracy and less parasitic losses relative to directly controlling the HBV switch with the controller.
Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.

## Claims

1. An apparatus comprising:
an integrated circuit controller to at least control a switching power converter, wherein the controller is configured to control the switching power converter by generating a switch control signal to control a first switch, wherein the first switch is internal to the controller, the integrated circuit includes a node to couple the first switch to a second switch in a cascode configuration, a breakdown voltage of the first voltage switch is approximately less than or equal to one-half of a breakdown voltage of the second switch; a first node to couple to a voltage supply; and a second node to couple to the first switch and the second switch; and
a charge recovery circuit coupled between the first node and the second node to provide charge recovery to the voltage supply during at least a portion of a time when the control signal turns the first switch off.

2. The apparatus of claim 1 wherein:
the first switch comprises a switch selected from a group consisting of a field effect transistor, a bipolar junction transistor, and an insulated gate bipolar transistor; and
the second switch comprises a switch selected from a group consisting of a field effect transistor, a bipolar junction transistor, and an insulated gate bipolar transistor.

3. The apparatus of claim 1 wherein the first switch and the second switch are identical types.

4. The apparatus of claim 1 wherein the first switch and the second switch are different types.

5. The apparatus of claim 1 wherein the controller is configured to control power factor correction of the switching power converter.

6. The apparatus of claim 1 wherein the controller is configured to generate the control signal to shape current in the switches.

7. The apparatus of claim 6 wherein the controller is configured to generate one or more intermediate steps of the switch control signal between an initial and final value of a pulse of the control signal to control the increase of the current in the switches.

8. The apparatus of claim 1 wherein the charge recovery circuit is a diode, and the diode is included in the integrated circuit.

9. The apparatus of claim 8 wherein the first node is also for coupling to a bias node of the second switch.

10. The apparatus of claim 1 wherein the breakdown voltage of the first switch is approximately less than or equal to 30 V and the breakdown voltage of the second switch is approximately greater than or equal to 60 V.

11. A method comprising:
generating a switch control signal;
controlling conductivity of a first switch using the control signal;
controlling conductivity of a second switch of a switching power converter with the first switch; and
providing charge recovery from a node coupled between the first and second switches to a voltage supply during at least a portion of a time when the control signal turns the first switch off;
wherein a breakdown voltage of the first switch is approximately less than or equal to one-half of a breakdown voltage of the second switch.

12. The method of claim 11 wherein generating the switch control signal comprises generating the switch control signal with an integrated circuit controller, and the integrated circuit controller includes the first switch.

13. The method of claim 11 further comprising:
controlling power factor correction and output voltage regulation of a switching power converter using the switch control signal.

14. The method of claim 11 wherein:
the first switch comprises a switch selected from a group consisting of a field effect transistor, a bipolar junction transistor, and an insulated gate bipolar transistor; and
the second switch comprises a switch selected from a group consisting of a field effect transistor, a bipolar junction transistor, and an insulated gate bipolar transistor.

15. The method of claim 11 wherein the first switch and the second switch are identical types.

16. The method of claim 11 wherein the first switch and the second switch are different types.

17. The method of claim 11 wherein the first switch comprises a bipolar junction transistor and the second switch comprises a bipolar junction transistor.

18. The method of claim 11 wherein generating the switch control signal further comprises:
generating the control signal to shape current in the switches.

19. The method of claim 18 wherein generating the switch control signal further comprises:
generating one or more intermediate steps of the switch control signal between an initial and final value of a pulse of the control signal to control the increase of the current in the switches.

20. The method of claim 11 further comprising:
discharging a node coupled between the first switch and the second switch to a power supply after the low and second switches are turned “off” by the switch control signal.

21. The method of claim 11 wherein the breakdown voltage of the first switch is approximately less than or equal to 30 V and the breakdown voltage of the second switch is approximately greater than or equal to 60 V.

22. An apparatus comprising:
a switching power converter having a first switch to control an output voltage of the switching power converter; and
an integrated circuit controller, coupled to the first switch, to generate a switch control signal to control a second switch, wherein the second switch is internal to the controller, the integrated circuit includes a node to couple the second switch to the first switch of the switching power converter in a cascode configuration, a breakdown voltage of the second switch is approximately less than or equal to one-half of a breakdown voltage of the first switch of the switching power converter; a first node to couple to a voltage supply; and a second node to couple to the first switch and the second switch; and
a charge recovery circuit coupled between the first node and the second node to provide charge recovery to the voltage supply during at least a portion of a time when the control signal turns the first switch off.

23. The apparatus of claim 22 wherein the controller is configured to generate one or more intermediate steps of the switch control signal between an initial and final value of a pulse of the control signal to control the rise of the current in the switches.

24. The method of claim 11 wherein providing charge recovery to the voltage supply during at least a portion of the time when the control signal turns the first switch off comprises:
discharging a diode coupled between the first and second switches to provide charge recovery to the voltage supply during at least a portion of the time when the control signal turns the first switch off.

25. The apparatus of claim 1 wherein the controller is further configured to generate the switch control signal with at least two discrete states to cause the first switch to conduct less current during a first of the at least two discrete states than during a subsequent second state of the with at least two current resistance states.

26. The method of claim 11 wherein controlling conductivity of a first switch using the control signal comprises controlling conductivity of the first switch with at least two conductive discrete states to cause the first switch to conduct less current during a first of the at least two discrete states than during a subsequent second state of the with at least two current resistance states.

27. The apparatus of claim 22 wherein the controller is further configured to generate the switch control signal with at least two discrete states to cause the first switch to conduct less current during a first of the at least two discrete states than during a subsequent second state of the with at least two current resistance states.