Power factor correction

Abstract

A bridgeless power factor correction (PFC) control circuit includes a non-linear current sensor (218). The non-linear current sensor (218) includes a non-linear shunt (222, 224), a comparator (228), and a reference voltage circuit (230). The non-linear shunt includes a capacitor connection terminal and a ground terminal. The comparator (228) includes a first input, a reference voltage input, and a zero-crossing detector output. The first input is coupled to the capacitor connection terminal. The reference voltage circuit (230) is coupled to the reference voltage input.

Description

[Technical field]

[0001] Electrical power supplies commonly use diode rectifiers to convert alternating current (AC) to direct current (DC). Diode rectifiers conduct current only when the rectifier's input voltage exceeds the rectifier's output voltage, resulting in harmonically rich, non-sinusoidal input currents and a power factor significantly less than unity.

[0002] Because current harmonics and low power factor are detrimental to commercial power distribution systems, many power supplies include power factor correction to reduce the harmonics in the input current. Power factor correction (PFC) refers to the process of attenuating the harmonic content of the current.

[0003] The bridgeless PFC circuit eliminates the input rectifier bridge, and therefore provides a cost-effective and highly efficient power supply solution for a wide variety of products, such as server and communications power equipment, set-top boxes, televisions, displays, etc. Summary of the Invention

[0004] In one example, a bridgeless power factor correction (PFC) control circuit includes a nonlinear current sensor. The nonlinear current sensor includes a nonlinear shunt, a comparator, and a reference voltage circuit. The nonlinear shunt includes a capacitor connection terminal and a ground terminal. The comparator includes a first input, a reference voltage input, and a zero-crossing detector output. The first input is coupled to the capacitor connection terminal. The reference voltage circuit is coupled to the reference voltage input.

[0005] In another example, a bridgeless PFC control circuit includes a nonlinear current sensor and a comparator. The nonlinear current sensor includes a ground terminal and a capacitor connection terminal. The nonlinear current sensor is configured to detect a current at the capacitor connection terminal. The comparator is coupled to the nonlinear current sensor. The comparator is configured to compare an output signal of the nonlinear current sensor with a zero-crossing threshold.

[0006] In a further example, a bridgeless PFC correction circuit includes a boost inductor, a first switch, a second switch, an output capacitor, a nonlinear current sensor, a comparator, and a PFC controller. The first switch is coupled to the boost inductor. The second switch is coupled to the boost inductor. The output capacitor is coupled to the second switch. The nonlinear current sensor is coupled between the output capacitor and a ground node. The comparator includes an input and an output. The input is coupled to the nonlinear current sensor. The PFC controller includes an input and an output. The input of the PFC controller is coupled to the output of the comparator. The output of the PFC controller is coupled to the first switch and the second switch. [Brief description of the drawings]

[0007] For a detailed description of various examples, reference will now be made to the accompanying drawings.

[0008] [Figure 1] FIG. 1 is a block diagram of an example power supply circuit including bridgeless power factor correction (PFC) circuitry having a bridgeless PFC control circuit as described herein.

[0009] [Diagram 2] FIG. 2 is a block diagram of an example of the bridgeless PFC circuitry of FIG.

[0010] [Diagram 3] 3 is a timing diagram illustrating example signals generated by operation of a nonlinear current sensor to enable valley switching in the bridgeless PFC circuitry of FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In power factor correction (PFC) circuits, to support critical conduction mode (CRM) (also called "transition mode") or discontinuous conduction mode (DCM) with valley switching, the instantaneous current in the inductor or switch needs to be sensed and the time of valley ringing on the switching node needs to be determined. In bridgeless PFC circuits, none of these parameters (inductor current, valley ring time) are directly accessible because the inductor is not referenced to the ground of the PFC circuit. Hall effect sensors and other complex circuits that have been applied to measure the inductor current in bridgeless PFC add cost and complexity.

[0012] The bridgeless PFC control circuit described herein reduces PFC circuit cost and complexity by enabling a PFC controller designed for use with a diode bridge to control a bridgeless PFC circuit. To facilitate application of the PFC controller in a bridgeless PFC circuit, the bridgeless PFC control circuit provides switching node valley detection, cycle-by-cycle current estimation, and switch short-circuit detection for use by the PFC controller. A nonlinear current sensor coupled to an output capacitor of the PFC circuit implements switching node valley detection. A shunt resistor coupled to the nonlinear current sensor provides switch short-circuit detection. An integrator circuit coupled to an AC voltage source that charges an inductor provides cycle-by-cycle current estimation.

[0013] A bridgeless PFC circuit using the bridgeless PFC control circuit described herein may include superjunction (SJ) transistors (rather than more expensive silicon carbide transistors) in a totem pole configuration to further reduce cost. When using an SJ transistor totem pole, turning on one transistor when the voltage of the other transistor is very low can result in very high switching losses caused by forced charging of the output capacitance (Coss) of the complementary transistor. This is the main reason why SJ transistors do not perform well in half-bridge non-ZVS applications (beyond the reverse recovery of the body diode). When the current in the transistor acting as the boost rectifier drops to zero, the output voltage can build up a negative current in the boost inductor because its large Coss charges very slowly. This negative current causes the switching node voltage to drop to a valley value that is much lower than what is achievable with a very fast rectifier. The bridgeless PFC control circuit described herein detects this deep valley and controls the switch timing to reduce the turn-on losses in the boost transistor (thereby enabling the use of SJ transistors). Accurate detection of the valley is necessary for low switching loss operation, and a fixed time delay cannot be used for valley detection because the interval from the first zero crossing of the inductor current to the valley changes significantly with input and output voltage variations. A nonlinear current sensor detects the valley based on the change in direction of the inductor current.

[0014] 1 is a block diagram of a power supply circuit 100. The power supply circuit 100 includes a bridgeless PFC circuit 102 and a DC-DC converter circuit 104. The bridgeless PFC circuit 102 receives and rectifies an AC voltage to generate a DC voltage for use by the DC-DC converter circuit 104. The bridgeless PFC circuit 102 may be a boost PFC circuit. The DC-DC converter circuit 104 converts the DC voltage generated by the bridgeless PFC circuit 102 to a DC voltage suitable for powering a load circuit 110. For example, the bridgeless PFC circuit 102 may convert 120 volts AC to 400 volts DC, and the DC-DC converter circuit 104 may convert the 400 volts DC to 5 volts DC for use by the load circuit 110. The load circuit 110 may be any circuit element powered by the DC-DC converter circuit 104.

[0015] The bridgeless PFC circuit 102 includes a PFC controller 106 and a bridgeless PFC control circuit 108. The PFC controller 106 may be designed for use with a bridge circuit (e.g., a diode bridge) that rectifies an AC voltage. For example, in one implementation of the bridgeless PFC circuit 102, the PFC controller 106 may be a UCC 28056 integrated circuit manufactured by Texas Instruments. Some implementations of the bridgeless PFC circuit 102 may use different PFC controllers.

[0016] The bridgeless PFC control circuit 108 is coupled to the PFC controller 106 and other components of the bridgeless PFC circuit 102 (such as switching transistors, output capacitors, etc.) for generating signals provided to the PFC controller 106 to control the bridgeless PFC circuit 102. The bridgeless PFC control circuit 108 provides switching node valley detection, cycle-by-cycle current estimation, and switch short detection for use by the PFC controller 106.

[0017] 2 is a block diagram of the bridgeless PFC circuit 102. The bridgeless PFC circuit 102 includes an inductor 206 (boost inductor), a diode 208, and a diode 210 coupled to AC power. A capacitor 212 is in parallel with the diode 208, and a capacitor 214 is in parallel with the diode 210. In some implementations of the bridgeless PFC circuit 102, the diode 208 and the diode 210 may be implemented using transistors. The transistor 204 and the transistor 202 are coupled to the inductor 206 for charging and discharging. The transistor 202 and the transistor 204 may be SJ NFETs. In some implementations of the bridgeless PFC circuit 102, the transistor 202 may be configured as a diode or replaced with a diode. An output capacitor 216 is coupled to the transistor 202.

[0018] The bridgeless PFC control circuit 108 is coupled to the PFC controller 106. In some implementations, the PFC controller 106 is coupled to and controls the transistor 204 and the transistor 202 based on a signal received from the bridgeless PFC control circuit 108. The bridgeless PFC control circuit 108 includes a nonlinear current sensor 218, an integrator circuit 248, and a switch short detection circuit 250. The nonlinear current sensor 218 is coupled to a terminal of the output capacitor 216 (to a bottom plate of the output capacitor 216) to detect a reversal of the current flowing through the inductor 206. The nonlinear current sensor 218 includes a diode 222 and a diode 224, a comparator 228, and a reference voltage circuit 230. The diode 222 and the diode 224 may be Schottky diodes. The diode 222 and the diode 224 are connected in anti-parallel to form a nonlinear shunt. That is, the anode of diode 222 is coupled to the cathode of diode 224 (to form a capacitor connection terminal) and to output capacitor 216. The cathode of diode 222 is coupled to the anode of diode 224 (to form a ground terminal) and to the ground node.

[0019] The voltage across the diodes 222 and 224 provides an indication when the current in the inductor 206 changes direction. A first input (e.g., an inverting input) of the comparator 228 is coupled to the anode of the diode 222 and the cathode of the diode 224. A second (reference voltage) input (e.g., a non-inverting input) of the comparator 228 is coupled to a reference voltage circuit 230. The output voltage of the reference voltage circuit 230 sets a threshold for zero current detection. For example, when the voltage across the diodes 222 and 224 falls below the threshold, a change in current flow from positive to negative is detected, and when the voltage across the diodes 222 and 224 rises above the threshold, a change in current flow from negative to positive (or zero) is detected. An output (zero crossing detector output) of the comparator 228 is coupled to an input (zero crossing detection input) of the PFC controller 106 to provide zero crossing detection information to the PFC controller 106. The PFC controller 106 may begin charging the inductor 206 (through control of the transistor 204 ) based on the zero-crossing information provided by the non-linear current sensor 218 .

[0020] FIG. 3 is a timing diagram illustrating the operation of the bridgeless PFC control circuit 108 with valley detection. FIG. 3 shows the inductor current 302, the voltage 304 across the diodes 222 and 224, the boost-on signal 252 provided by the PFC controller 106 to control the transistor 204, and the voltage 306 at the switching node 254. In FIG. 3, before time 310, the transistor 204 is off and the inductor 206 discharges through the transistor 202 (e.g., through the body diode or channel of the transistor 202). When the inductor current 302 reverses direction (crosses zero) at time 308, the voltage 304 across the diodes 202 and 204 goes from positive to negative. At time 310, the voltage at the switching node 254 is at a valley, the inductor current 302 returns to zero, and the voltage 304 across the diodes 222 and 224 rises to zero. The negative-to-zero transition of the voltage 304 across the diodes 222 and 224 is detected by the comparator 228, whose output is provided to the PFC controller 106. In response to the signal received from the comparator 228, the PFC controller 106 initiates a boost cycle at its transistor drive output (activates the boost on signal 252) and pulls the switching node 254 to ground to charge the inductor 206. In this manner, the detection of the negative-to-zero transition of the voltage 304 across the diodes 222 and 224 by the bridgeless PFC control circuit 108 enables valley switching in the bridgeless PFC circuit 102 for all operating conditions.

[0021] Returning to FIG. 2, the switch short detection circuit 250 detects a potential fault in a switch (transistor 202 or 204, or diode 208 or 210) of the bridgeless PFC circuit 102. The switch short detection circuit 250 includes a resistor 226, a reference voltage circuit 234, and a comparator 232. The resistor 226 connects the diodes 222 and 224 to a ground node. A first terminal of the resistor 226 is coupled to the cathode of the diode 222 and the anode of the diode 224. A second terminal of the resistor 226 is coupled to ground. The resistance of the resistor 226 is relatively low. For example, in some implementations, the resistor 226 may have a resistance in the range of 10 milliohms (mQ) to 100 mQ. A first terminal of the resistor 226 is coupled to the reference voltage circuit 234. A first input (inverting input) of the comparator 232 is coupled to a reference voltage circuit 234, and a second input (non-inverting input) of the comparator 232 is coupled to ground. An output of the comparator 232 is coupled to an input (e.g., an over-voltage sense input) of the PFC controller 106.

[0022] When the bridgeless PFC circuit 102 is operating normally, the voltage across the resistor 226 is very small. However, if one of the switches (transistor 202 or 204, or diode 208 or 210) fails as a short circuit, the output capacitor 216 is discharged through the short circuit and a large current flows through the resistor 226, increasing the voltage dropped across the resistor 226. The comparator 232 detects the increase in the voltage drop across the resistor 226 and provides a fault signal to the PFC controller 106. In response to the fault signal, the PFC controller 106 may disable the switching of the transistor 204 and the transistor 202.

[0023] The integrator circuit 248 estimates the current through the inductor 206 based on the AC line voltage and may also be referred to as an inductor current estimation circuit. The integrator circuit 248 includes a transistor 236, a capacitor 238, a resistor 240, an inverter 242, and a rectifier circuit 244. A first terminal of the resistor 240 is coupled to the rectifier circuit 244, and a second terminal of the resistor 240 is coupled to a first terminal of the capacitor 238 and to a drain of the transistor 236. A second terminal of the capacitor 238 is coupled to ground. A source terminal of the transistor 236 is coupled to ground. A control terminal (gate terminal) of the transistor 236 is connected to an output of the PFC controller 106 via the inverter 242. A drain terminal of the transistor 236 (and a top plate of the capacitor 238) is coupled to a control input of the PFC controller 106. The transistor 236 may be an NFET.

[0024] Rectifier circuit 244 rectifies the AC line voltage to produce its absolute value 2025511169000002.tif38. The input terminal of the rectifier circuit 244 is coupled to the AC power terminal. While the inductor 206 is charging, the capacitor 238 is charged through the resistor 240. The voltage across the capacitor 238 (the voltage stored in the capacitor 238) is the time integral of the voltage charging the inductor 206 and thus represents the current flowing through the inductor 206. When the inductor 206 is discharging, the capacitor 238 is discharged by the transistor 236. The voltage across the capacitor 238 is provided to the PFC controller 106. The PFC controller 106 may compare the voltage across the capacitor 238 with a threshold. If the voltage exceeds the threshold (indicating that the current flowing through the inductor 206 is too large), the PFC controller 106 may disable the switching of the transistors 204 and 202.

[0025] In some implementations of the bridgeless PFC circuit 102, portions of the bridgeless PFC control circuit 108 may be provided as components of an integrated circuit.

[0026] An implementation of the bridgeless PFC circuit 102 that actively controls the transistor 202 may include a drive steering circuit 246. The drive steering circuit 246 includes an input coupled to the PFC controller 106, a first output coupled to a gate of the transistor 204, and a second output coupled to a gate of the transistor 202. The drive steering circuit 246 may alternately route the output (the gate control signal (boost on signal 252)) received from the PFC controller 106 to either the transistor 202 or the transistor 204. For example, the drive steering circuit 246 may route the drive pulses received from the PFC controller 106 to the transistor 204 during the positive portion of the AC cycle and may route the drive pulses received from the PFC controller 106 to the transistor 202 during the negative portion of the AC cycle.

[0027] In an implementation of the bridgeless PFC circuit 102 that does not actively control transistor 202, the output of 106 may be coupled to the gate of 204 while 202 is connected as a diode or replaced with a diode.

[0028] In this description, the term "couple" may encompass a connection, communication, or signal path that enables a functional relationship consistent with this description. For example, if device A generates a signal that controls device B to perform an action, (a) in a first example, device A is coupled to device B by a direct connection, or (b) in a second example, device A is coupled to device B via an intervening component C such that device B is controlled by device A via a control signal generated by device A, where intervening component C does not change the functional relationship between device A and device B.

[0029] A device that is "configured to" perform a certain task or function may be configured (e.g., programmed and / or hardwired) at the time of manufacture by a manufacturer to perform that function and / or may be configurable (or reconfigurable) by a user after manufacture to perform that function and / or other additional or alternative functions. Such configuration may be through the firmware and / or software programming of the device, through the configuration and / or layout of hardware components, through the device's interconnections, or through a combination thereof.

[0030] Although the use of particular transistors is described herein, other transistors (or equivalent devices) may be substituted. For example, a p-channel field effect transistor ("PFET") may be substituted for an n-channel field effect transistor ("NFET") with little or no modification to the circuit. Also, other types of transistors may be used, such as bipolar junction transistors (BJTs).

[0031] As used herein, the terms "terminal," "node," "interconnect," "pin," and "lead" are used interchangeably. Unless otherwise noted, these terms are used generally to mean an interconnection between, or the termination of, a device element, a circuit element, an integrated circuit, a device, or other electronic or semiconductor component.

[0032] A circuit or device described herein as including certain components may instead be adapted to be coupled to those components to form the described circuit or device. For example, a structure described as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and / or inductors), and / or one or more sources (such as voltage and / or current sources) may instead include only the semiconductor elements in a single physical device (e.g., a semiconductor die and / or integrated circuit (TC) package) and may be adapted to be coupled to at least some of the passive elements and / or sources during or after manufacture, e.g., by an end user and / or a third party, to form the described structure.

[0033] The circuits described herein are reconfigurable to include additional or different components to provide functionality at least partially similar to that available prior to the component replacement. Components depicted as transistors generally represent any one or more transistors coupled in parallel to provide a desired channel width or emitter size, unless otherwise indicated.

[0034] Modifications may be made to the exemplary embodiments described, and other embodiments are possible, within the scope of the invention.

Claims

1. A power factor correction (PFC) circuit, A nonlinear current sensor, A nonlinear shunt having a capacitor connection terminal and a ground terminal, A first diode having a cathode connected to the capacitor connection terminal and an anode connected to the ground terminal, A second diode having a cathode connected to the ground terminal and an anode connected to the capacitor connection terminal, The nonlinear shunt includes, A first comparator having a first input connected to the capacitor connection terminal, a reference voltage input, and a zero-crossing detector output configured to be connected to the control circuit, A first reference voltage circuit coupled to the reference voltage input, The nonlinear current sensor includes, An inductor current estimation circuit, A rectifier circuit having AC power input and output, A first resistor having a first terminal coupled to the output of the rectifier circuit and a second terminal configured to be coupled to the control circuit, A capacitor having a first terminal connected to the second terminal of the first resistor and a second terminal connected to a ground node, An inductor current estimation circuit, A PFC circuit, including [a specific component].

2. A PFC circuit according to claim 1, A PFC circuit further comprising a second resistor coupled between the ground terminal of the nonlinear shunt and the ground node.

3. The PFC circuit according to claim 2, A second reference voltage circuit coupled to the second resistor, A second comparator having a first input connected to the ground node, a second input connected to the second reference voltage circuit, and a switch-disable output, A PFC circuit further includes the following.

4. A PFC circuit according to claim 1, A switch having a first terminal connected to the first terminal of the capacitor, a second terminal connected to the second terminal of the capacitor, and a control terminal, An inverter having an input configured to be coupled to the output of the control circuit and a second output coupled to the control terminal of the switch, A PFC circuit further includes the following.

5. The PFC circuit according to claim 4, A PFC circuit further includes a drive steering circuit having an input coupled to the control terminal of the switch, a first transistor-controlled output, and a second transistor-controlled output.

6. A power factor correction (PFC) circuit, A shunt having a ground terminal and a capacitor connection terminal, wherein the shunt includes a first diode and a second diode coupled in antiparallel to the first diode, configured to detect current at the capacitor connection terminal, A first comparator having a first input coupled to the capacitor terminal of the shunt and a second input coupled to a voltage reference, the first comparator being configured to compare the output signal of the shunt with a zero crossing threshold associated with the voltage reference, An inductor current estimation circuit, A rectifier circuit connected to the AC power terminal, An integrator circuit coupled to the rectifier circuit, configured to generate a voltage indicating the current flowing through a boost inductor, The inductor current estimation circuit includes, A PFC circuit, including [a specific component].

7. The PFC circuit according to claim 6, The first diode has a cathode coupled to a first terminal of the nonlinear current sensor and an anode coupled to a second terminal of the nonlinear current sensor. A PFC circuit in which the second diode has an anode coupled to the first terminal of the nonlinear current sensor and a cathode coupled to the second terminal of the nonlinear current sensor.

8. The PFC circuit according to claim 6, It further includes a resistor, A PFC circuit in which the resistor and the first comparator constitute a nonlinear current sensor, and the resistor is coupled between the nonlinear current sensor and a ground node.

9. The PFC circuit according to claim 8, A PFC circuit further comprising a second comparator coupled to the resistor, the second comparator configured to detect a short circuit in the switch.

10. The PFC circuit according to claim 6, The inductor current estimation circuit, A capacitor configured to store a voltage representing the current flowing through a boost inductor, A switch coupled to the capacitor, configured to discharge the capacitor when the boost inductor is discharged, A PFC circuit further includes the following.

11. A PFC circuit according to claim 10, A PFC circuit further includes a drive steering circuit configured to switch a gate control signal to a first transistor or a second transistor coupled to the boost inductor.

12. A power factor correction (PFC) circuit, Boost inductor and A first switch coupled to the boost inductor, A second switch coupled to the boost inductor, The output capacitor coupled to the second switch described above, A nonlinear current sensor having a first terminal coupled to the output capacitor and a second terminal coupled to a ground node, the nonlinear current sensor including a first comparator having a first input coupled to the first terminal of the nonlinear current sensor and a second input and output coupled to a voltage reference, A second comparator having an input and an output coupled to the nonlinear current sensor, A controller having a first input coupled to the output of the first comparator, a second input coupled to the output of the second comparator, and outputs coupled to the first switch and the second switch, A PFC circuit, including [a specific component].

13. The PFC circuit according to claim 12, The aforementioned nonlinear current sensor, A first diode having a cathode coupled to a first terminal of the nonlinear current sensor and an anode coupled to a second terminal of the nonlinear current sensor, A second diode having an anode coupled to the first terminal of the nonlinear current sensor and a cathode coupled to the second terminal of the nonlinear current sensor, A PFC circuit further includes the following.

14. The PFC circuit according to claim 13, A PFC circuit further comprising a resistor coupled between the nonlinear current sensor and the ground node.

15. The PFC circuit according to claim 12, An inductor current estimation circuit, A rectifier circuit having an input and an output coupled to the boost inductor, A resistor having a first terminal coupled to the output of the rectifier circuit and a second terminal coupled to the second input of the controller, A capacitor having a first terminal connected to the second terminal of the resistor and a second terminal connected to the ground node, A PFC circuit further comprising the inductor current estimation circuit, including the inductor current estimation circuit.

16. The PFC circuit according to claim 15, A PFC circuit further includes a third switch having a first terminal connected to the first terminal of the capacitor, a second terminal connected to the second terminal of the capacitor, and a control terminal connected to the output of the controller.

17. The PFC circuit according to claim 15, A PFC circuit further includes a drive steering circuit having an input coupled to the output of the controller, a first output coupled to the first switch, and a second output coupled to the second switch.

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