HK1194870B - Off-line power converter and integrated circuit suitable for use in same - Google Patents

Description

Off-line power converter and integrated circuit suitable therefor

Technical Field

The present disclosure relates generally to power converters, and more particularly to control circuits for power converters.

Background Art

Offline power converters can be implemented using integrated circuit power factor controllers to provide power factor correction for offline appliances. Power factor correction helps improve the efficiency of power delivery to the load and reduces electromagnetic interference (EMI). The integrated circuit drives the power factor correction stage and can operate in critical conduction mode to provide light load operation control and other useful control and safety features. However, it would be desirable to reduce the cost of offline power converters while maintaining the power factor correction and safety features of existing designs.

Summary of the Invention

According to one aspect of the present invention, an offline power converter is provided, comprising: an integrated circuit power factor controller, comprising: a multifunctional input terminal, wherein the multifunctional input terminal is adapted to receive a voltage representing a voltage based on a voltage generated by a voltage sensing circuit and proportional to a current flowing through a drive transistor; a drive terminal for providing a drive signal to a gate of the drive transistor; a processing circuit connected to the multifunctional input terminal and providing at least one current signal representing a current conducted in the offline power converter and at least one voltage signal representing a voltage provided to a load based on the voltage on the multifunctional input terminal; and a controller for selectively providing the drive signal in response to the at least one current signal and the at least one voltage signal.

According to another aspect of the present invention, an offline power converter is provided, comprising: an integrated circuit power factor controller, comprising: an input terminal; a drive terminal for providing a drive signal to a gate of a drive transistor; a first circuit connected to the input terminal via a buffer for providing an average voltage signal representing an average value of a voltage at the input terminal; a second circuit for comparing the voltage at the input terminal with the average voltage signal to form a zero current detection signal; and a controller for selectively providing the drive signal in response to the average voltage signal and the zero current detection signal.

According to another aspect of the present invention, an integrated circuit is provided, comprising: a feedback terminal; an input terminal; a drive terminal for providing a drive signal to the gate of a drive transistor; a first comparator having a first terminal connected to the feedback terminal, a second terminal for receiving a first reference voltage, and an output terminal for providing a first overvoltage protection signal; a second comparator having a first terminal connected to the input terminal through a switch when the drive signal is inactive, a second terminal for receiving a second reference voltage, and an output terminal for providing a second overvoltage protection signal; and a controller connected to the drive terminal for selectively activating the drive signal so as to regulate the voltage on the feedback terminal, and for keeping the drive signal inactive in response to the first overvoltage protection signal or the second overvoltage protection signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art, by referencing the accompanying drawings, in which:

FIG1 illustrates, in partial block diagram and partial diagrammatic form, an off-line power converter including an integrated circuit power factor controller as known in the prior art;

FIG2 illustrates, in partial block diagram and partial diagrammatic form, an offline power converter including an integrated circuit power factor controller according to one embodiment of the present invention;

FIG3 illustrates, in partial block diagram and partial diagrammatic form, the integrated circuit power factor controller of FIG2 ;

FIG4 diagrammatically illustrates voltage sensing according to an alternative embodiment of the voltage sensing circuit of FIG2 ;

FIG5 diagrammatically illustrates a buffer circuit according to an alternative embodiment of the buffer of FIG3 ; and

FIG. 6 shows two timing diagrams useful for understanding the operation of the offline power converter of FIG. 2 .

The use of the same reference symbols in different drawings indicates similar or identical items.

DETAILED DESCRIPTION

1 illustrates, in partial block diagram and partial diagrammatic form, an off-line power converter 100 known in the art that includes an 8-pin integrated circuit power factor controller 160. Off-line power converter 100 generally includes a rectifier 110, a transformer 120, a drive transistor 130 labeled “Q1,” a sensing circuit 140, an output circuit 150, an integrated circuit power factor controller 160, a line sensing circuit 170, a resistor 180 labeled “ _Rfb1 ,” a resistor 182 labeled “ _Rfb2 ,” a resistor 184 labeled “ _Rz ,” a capacitor 186 labeled “ _Cz ,” a capacitor 188 labeled “ _Cp ,” and a resistor 190 labeled “ _Rff .”

Rectifier 110 includes an electromagnetic interference ("EMI") filter 112, a diode 114, a diode 115, a diode 116, a diode 117, and a capacitor 118 labeled " _CIN ." Rectifier 110 has an input terminal connected to a first "AC LINE" power terminal, an input terminal connected to a second AC LINE power terminal, an output terminal for providing a first power terminal, and an output terminal connected to ground, which serves as a reference voltage terminal for offline power converter 100. Diode 114 has an anode connected to the first power terminal provided by EMI filter 112 and a cathode for providing a voltage labeled " _VIN ." Diode 115 has an anode connected to ground and a cathode connected to the anode of diode 114. Diode 116 has an anode connected to the second power terminal provided by EMI filter 112 and a cathode connected to the cathode of diode 114. Diode 117 has an anode connected to ground and a cathode connected to the anode of diode 116. Capacitor 118 has a first terminal connected to the cathode of diode 116 and a second terminal connected to ground.

Transformer 120 includes a primary winding 122 labeled "L1," a secondary winding 124, and a transformer core 126. Primary winding 122 has a first terminal for receiving _Vin and a second terminal. Secondary winding 124 has a first terminal connected to ground and a second terminal.

The driving transistor 130 has a gate electrode, a drain electrode connected to the second terminal of the primary winding 122 , a source electrode, and a substrate electrode connected to the source electrode.

Sense circuit 140 includes a diode 142 labeled " _Dzcd ," a resistor 144 labeled " _Rzcd ," a resistor 146 labeled " _Rocp, " and a resistor 148 labeled " _Rsense ." Diode 142 has an anode connected to the second terminal of secondary winding 124, and a cathode. Resistor 144 has a first terminal connected to the cathode of diode 142, and a second terminal. Resistor 146 has a first terminal connected to the second terminal of resistor 144 and a second terminal connected to the source electrode of drive transistor 130. Resistor 148 has a first terminal connected to the second terminal of resistor 146 and a second terminal connected to ground.

Output circuit 150 includes a diode 152 labeled "D1," a bulk capacitor 154 labeled " _Cbulk ," and a load 156. Diode 152 has an anode connected to the drain electrode of drive transistor 130 and a cathode for providing a voltage labeled " _Vbulk ." Bulk capacitor 154 has a first terminal connected to the cathode of diode 152 and a second terminal connected to ground. Load 156 has a first terminal connected to the first terminal of bulk capacitor 154 and a second terminal connected to ground.

Integrated circuit power factor controller 160 has a first terminal, a second terminal, a third terminal, a fourth terminal connected to the first terminal of resistor 146, a fifth terminal connected to ground, a sixth terminal connected to the gate electrode of drive transistor 130, a seventh terminal for receiving a supply voltage labeled “V _CC ”, and an eighth terminal for receiving a signal labeled “FEEDBACK”.

Line sense circuit 170 includes a resistor 172 labeled "R _X1 ," a resistor 174 labeled "R _X2 ," a resistor 176 labeled "R _{bo1 ,} " and a resistor 178 labeled "R _bo2 ." Resistor 172 has a first terminal connected to a first AC line power terminal and a second terminal. Resistor 174 has a first terminal connected to a second AC line power terminal and a second terminal connected to the second terminal of resistor 172. Resistor 176 has a first terminal connected to the second terminal of resistor 174 and a second terminal connected to a second terminal of integrated circuit power factor controller 160. Resistor 178 has a first terminal connected to the second terminal of resistor 176 and a second terminal connected to ground.

Resistor 180 has a first terminal for receiving _Vbulk and a second terminal for providing a feedback signal. Resistor 182 has a first terminal connected to the eighth terminal of integrated circuit power factor controller 160 and a second terminal connected to ground. Resistor 184 has a first terminal connected to the first terminal of integrated circuit power factor controller 160 and a second terminal. Capacitor 186 has a first terminal connected to the second terminal of resistor 184 and a second terminal connected to ground. Capacitor 188 has a first terminal connected to the first terminal of resistor 184 and a second terminal connected to ground. Resistor 190 has a first terminal connected to the third terminal of integrated circuit power factor controller 160 and a second terminal connected to ground.

In operation, rectifier 110 provides full-wave rectified voltage V input, wherein between power mains (AC line) and the downstream circuit of off-line power converter 100, there is filtering.Specifically, rectifier 110 manages unwanted energy from AC line propagation to downstream circuit by making signal pass through EMI filter 112.EMI filter 112 filters EMI interference so that downstream circuit is not disturbed during operation.EMI filter 112 receives AC line signal and filtered AC signal is provided to its output terminal.Diode 114,115,116 and 117 will store and filter via capacitor 118 rectified input voltage V _{input and} provide to the downstream circuit of off-line power converter 100.

For transformer 120, the varying AC current passing through primary winding 122 generates a varying magnetic flux in transformer core 126 of transformer 120, thereby generating a varying AC voltage across primary winding 122. Through inductive coupling, the varying magnetic flux generates a varying magnetic field in the coils of secondary winding 124. As is known, the voltage induced in secondary winding 124 is a mathematical function of the voltage across primary winding 122 and is defined by the ratio of the number of turns in secondary winding 124 to the number of turns in primary winding 122.

During the on-time (" _Ton "), the integrated circuit power factor controller 160 pulls up terminal 6 to provide a positive drive voltage on the gate electrode of the driver transistor 130, which is an N-channel metal oxide semiconductor field effect transistor ("MOSFET"). The driver transistor 130 transitions to the "on state" and provides a low impedance current path to ground at the second terminal of the primary winding 122. The rectifier 110 provides I _L , and I _L flows through the primary winding 122, the driver transistor 130, and the resistor 148. The driver transistor 130 operates to reduce the drain voltage toward ground, and the transformer 120 builds its magnetic field and stores energy according to I _L.

Resistor 148 senses the current flowing through drive transistor 130 and provides a voltage level to terminal 4 of integrated circuit power factor controller 160. Resistor 148 provides a positive voltage to terminal 4 depending on the current flowing from the drain electrode to the source electrode of drive transistor 130. If the voltage on terminal 4 exceeds a threshold, integrated circuit power factor controller 160 determines that drive transistor 130 is operating under an overcurrent condition and deactivates drive transistor 130.

During the off time (" _Toff "), integrated circuit power factor controller 160 pulls terminal 6 down to render driver transistor 130 non-conductive. Driver transistor 130 transitions to the "off state" and provides a high-impedance current path at the second terminal of primary winding 122. In response, primary winding 122 resists the changing _IL and operates to increase the voltage at the second terminal of primary winding 122. Diode 152 switches on in response to the voltage provided by primary winding 122 to provide _IL to output circuit 150 and increase _Vbulk . Bulk capacitor 154 stores _Vbulk across load 156 in response to _IL and filters high-frequency voltage transitions across load 156.

In addition, secondary winding 124 operates to increase the voltage on the anode of diode 142 of sensing circuit 140. In response to the voltage induced in secondary winding 124, diode 142 turns on and allows current to flow through resistors 144, 146, and 148. Sensing circuit 140 provides a voltage to terminal 4 of integrated circuit power factor controller 160 to indicate when the magnetic field of secondary winding 124 is in a "demagnetizing" phase by detecting when secondary winding 124 is providing zero current, a detection process known as zero current detection ("ZCD"). Based on the voltage on terminal 4, if integrated circuit power factor controller 160 detects ZCD, then integrated circuit power factor controller 160 adjusts the operation of certain internal circuits. Secondary winding 124 and diode 142 operate to prevent interference between OCP detection when drive transistor 130 is in the on state and ZCD detection when drive transistor 130 is in the off state.

Line sensing circuit 170 senses the instantaneous voltage of the AC line by dividing the AC line voltage according to the values of resistors 172, 174, 176, and 178. The second terminal of resistor 176 develops a voltage at terminal 2 of integrated circuit power factor controller 160. If the voltage at terminal 2 is less than a threshold, integrated circuit power factor controller 160 detects an undervoltage condition and ceases operation to prevent overvoltage.

Offline power converter 100 provides _Vbulk to a first terminal of resistor 180 to provide a feedback signal based on the values of resistors 180 and 182. The second terminal of resistor 180 develops a voltage at terminal 8 of integrated circuit power factor controller 160. Based on the voltage at terminal 8, integrated circuit power factor controller 160 adjusts the duty cycle of drive transistor 130 and immediately disables it if the output voltage is too high.

Integrated circuit power factor controller 160 provides a signal from the output of an internal error amplifier, implemented as an operational transconductance amplifier for use in a voltage regulation loop, to terminal 1. A circuit network formed by resistor 184, capacitor 186, and capacitor 188 and connected to terminal 1 adjusts the regulation loop bandwidth and phase margin.

The integrated circuit power factor controller 160 provides the output voltage at terminal 3 to a resistor 190 to form a voltage according to the current provided by the AC line. According to the voltage at terminal 3, the integrated circuit power factor controller 160 adjusts the dead time and initiates cycle skipping.

During circuit operation, the offline power converter 100 provides power factor control using an 8-pin integrated circuit power factor controller 160 and various safety and protection features. However, it would be desirable to reduce the cost of the offline power factor converter 100 while maintaining all of its safety and protection features.

FIG2 shows in partial block diagram and partial diagrammatic form an offline power converter 200 having an integrated circuit power factor controller 260 according to one embodiment of the present invention. The offline power converter 200 generally includes the rectifier 110 and output circuit 150 as shown above, an inductor 220 labeled “L1,” a drive transistor 230 labeled “Q1,” a sense resistor 232 labeled “ _Rsense ,” a voltage sensing circuit 240, an integrated circuit power factor controller 260, a feedback circuit 280, and a compensation network 290.

Inductor 220 has a first terminal for _receiving Vin and a second terminal connected to the anode of diode 152 .

Drive transistor 230 has a gate electrode for receiving a signal labeled "DRV," a drain electrode connected to the second terminal of inductor 220, a source electrode, and a substrate electrode connected to the source electrode. Sense resistor 232 has a first terminal connected to the source electrode of drive transistor 230 and a second terminal connected to ground.

Voltage sensing circuit 240 includes a resistor 242 labeled “R _cs1 ” and a resistor 244 labeled “R _cs2 .” Resistor 242 has a first terminal connected to the drain electrode of drive transistor 230 and a second terminal for providing a signal labeled “CS/ZCD.” Resistor 244 has a first terminal connected to the second terminal of resistor 242 and a second terminal connected to the source of drive transistor 230.

The integrated circuit power factor controller 260 has a first terminal 261 for receiving a signal marked as "Fb", a second terminal 262 for providing a signal marked as "Vctrl", a third terminal 263 for receiving CS/ZCD, a fourth terminal 264 connected to ground, a fifth terminal 265 connected to the gate electrode of the driving transistor 230, and a sixth terminal 266 for receiving a power supply voltage marked as "Vcc".

Feedback circuit 280 includes a resistor 282 labeled “R _fb1 ” and a resistor 284 labeled “R _fb2 .” Resistor 282 has a first terminal connected to V _BULK and a second terminal connected to feedback terminal 261 of integrated circuit power factor controller 260. Resistor 284 has a first terminal connected to the second terminal of resistor 282 and a second terminal connected to ground.

Compensation network 290 includes a resistor 292 labeled " _Rz ," a capacitor 294 labeled " _Cz, " and a capacitor 296 labeled " _Cp ." Resistor 292 has a first terminal connected to terminal 262 of integrated circuit power factor controller 260, and a second terminal. Capacitor 294 has a first terminal connected to the second terminal of resistor 292 and a second terminal connected to ground. Capacitor 296 has a first terminal connected to the first terminal of resistor 292 and a second terminal connected to ground.

In operation, the varying AC current in inductor 220 generates a varying magnetic flux, thereby generating a varying AC voltage across inductor 220. During the T _on period, integrated circuit power factor controller 260 provides a positive drive voltage on the gate electrode of driver transistor 230. Driver transistor 230 transitions to the on state and provides a low-impedance current path at the second terminal of inductor 220. Rectifier 110 provides I _L , which flows through inductor 220, driver transistor 230, and sense resistor 232. Driver transistor 230 operates to lower the drain voltage toward ground, and inductor 220 builds its magnetic field and stores energy according to I _L .

During the T _on period, sense resistor 232 provides a voltage at its first terminal that is proportional to the current flowing through drive transistor 230. When integrated circuit power factor controller 260 activates signal DRV, the drain-to-source voltage of drive transistor 230 is low, and the voltage drop across voltage sensing circuit 240 is also low. Consequently, the voltage at multi-function input terminal 263 is substantially equal to the voltage at the first terminal of sense resistor 232, and multi-function input terminal 263 can be used to sense the current flowing through drive transistor 230. Internal processing circuitry compares the voltage at multi-function input terminal 263 to an overcurrent protection threshold. If the voltage at multi-function input terminal 263 exceeds this threshold, integrated circuit power factor controller 260 deactivates signal DRV.

During the _Toff period, integrated circuit power factor controller 260 renders driver transistor 230 substantially non-conductive. Driver transistor 230 transitions to an off state and provides a high-impedance current path at the second terminal of inductor 220. In response, inductor 220 resists the changing _IL and operates to increase the voltage at the second terminal of inductor 220. Diode 152 turns on in response to the voltage provided by the second terminal of inductor 220 to provide _IL to output circuit 150. Bulk capacitor 154 stores charge to smooth _Vbulk across load 156 and filter high-frequency voltage transitions across load 156.

Multifunctional input terminal 263 operates as a multifunctional input terminal for sensing various voltages and currents, including _IL , _Vdrain , average _Vinput , and _Vbulk . Integrated circuit power factor controller 260 uses these voltages and currents to detect several conditions, including overcurrent, demagnetization phase, undervoltage, and overvoltage, and adjusts its operation accordingly. By using multifunctional input terminal 263 as a multifunctional terminal, integrated circuit power factor controller 260 can be implemented with a reduced pin count and can use a simple inductor rather than a more expensive transformer. Therefore, compared to offline power converter 100, offline power converter 200 has a significantly reduced cost.

Feedback circuit 280 receives _Vbulk and provides a portion _{of Vbulk} , determined by the values of resistors 282 and 284, to feedback terminal 261. IC power factor controller 260 uses the voltage on feedback terminal 261 to regulate the duty cycle of the DRV. Additionally, it compares the voltage at feedback terminal 261 to a threshold. If the voltage at feedback terminal 261 exceeds this threshold, IC power factor controller 260 detects an overvoltage condition and immediately deactivates the DRV signal. In this way, IC power factor controller 260 provides redundant OVP using two different terminals. This improves safety by enabling overvoltage detection even if a circuit component fails.

Integrated circuit power factor controller 260 uses the Fb signal and an internal error amplifier to regulate the duty cycle of the DRV signal. It provides the error amplifier output at terminal 262, and the circuit arrangement of resistor 292, capacitor 294, and capacitor 296 adjusts the regulation loop bandwidth.

Offline power converter 200 uses a 6-pin integrated circuit to provide active power factor control. At the same time, it improves safety by adding redundant overvoltage detection while maintaining the protection features of offline power converter 100. In addition, offline power converter 200 uses a single multi-function pin to provide several current and voltage sensing features; replaces transformer 120 with a less expensive but more reliable inductor 220; and provides a safer, redundant method for sensing and processing _Vbulk , average _Vinput , _Il , and detecting undervoltage, overcurrent, overvoltage conditions and demagnetized phases.

FIG3 illustrates, in partial block diagram and partial diagrammatic form, the integrated circuit power factor controller 260 of FIG2 . The integrated circuit power factor controller 260 generally includes a regulation circuit 310, an evaluation circuit 350, an overvoltage protection circuit 370, and a controller 380. The regulation circuit 310 and the evaluation circuit 350 operate together to form the processing circuitry of the integrated circuit power factor controller 260.

Offline power converter 200 also includes a capacitor 302 labeled " _CCS ," as shown in Figure 3. Capacitor 302 has a first terminal connected to multi-function input terminal 263 of integrated circuit power factor controller 260 and a second terminal connected to ground.

Regulation circuit 310 includes buffer 312, switch circuit 320, resistor-capacitor ("RC") circuit 330, and switch circuit 340. Buffer 312 includes OPAMP 314, which has a positive input connected to the first terminal of capacitor 302, a negative input, and an output connected to the negative input to provide a signal labeled " _KCS · _VDRAIN ." Switch circuit 320 includes switch 322, inverter 324, and switch 326. Switch 322 has an enable input for receiving DRV, a first terminal connected to the output of OPAMP 314, and a second terminal for providing a signal labeled " _RSENSE · _IL ." Inverter 324 has an input connected to the enable input of switch 322, and an output. Switch 326 has an enable input connected to the output of inverter 324, a first terminal connected to the second terminal of switch 322, and a second terminal connected to ground. RC circuit 330 includes resistor 332 labeled " _Rf " and capacitor 334 labeled " _Cf. " Resistor 332 has a first terminal connected to the output of OPAMP 314 and a second terminal for providing a signal labeled "K _CS · <V _IN >." Capacitor 334 has a first terminal connected to the second terminal of resistor 332 and a second terminal connected to ground. Switch circuit 340 includes switch 342, inverter 344, and switch 346. Switch 342 has an enable input, a first terminal connected to the output of OPAMP 314, and a second terminal for providing a signal labeled "K _CS · (V _OUT + V _f )." Inverter 344 has an input for receiving DRV and an output connected to the enable input of switch 342. Switch 346 has an enable input for receiving the DRV signal, a first terminal connected to the second terminal of switch 342, and a second terminal connected to ground.

Evaluation circuit 350 includes comparator 352, reference voltage generator 354, comparator 356, comparator 358, reference voltage generator 360, comparator 362, and reference voltage generator 364. Comparator 352 has a positive input connected to the first terminal of switch 326, a negative input, and an output for providing a signal labeled "OCP." Reference voltage generator 354 has a positive terminal connected to the negative input of comparator 352 to provide a reference voltage labeled "V _OCP ," and a negative terminal connected to ground. Comparator 356 has a positive input connected to the output of OPAMP 314, a negative input connected to the first terminal of capacitor 334, and an output for providing a signal labeled "ZCD." Comparator 358 has a positive input, a negative input connected to the second terminal of resistor 332, and an output for providing a signal labeled "BO." Reference voltage generator 360 has a positive terminal connected to the positive input of comparator 358 to provide a reference voltage labeled "V _BO ," and a negative terminal connected to ground. Comparator 362 has a positive input connected to the first terminal of switch 346, a negative input, and an output for providing a signal labeled “OVP2.” Reference voltage generator 364 has a positive terminal connected to the negative input of comparator 362 to provide a reference voltage labeled “V _OVP2 ,” and a negative terminal connected to ground.

Overvoltage protection circuit 370 includes a comparator 372 and a reference voltage generator 374. Comparator 372 has a positive input connected to feedback terminal 261 of integrated circuit power factor controller 260, a negative input, and an output for providing a signal labeled "OVP1." Reference voltage generator 374 has a positive terminal connected to the negative input of comparator 372 to provide a reference voltage labeled "V _OVP1 " and a negative terminal connected to ground.

Controller 380 has an input connected to the output of comparator 352, an input connected to the output of comparator 356, an input connected to the negative input of comparator 356, an input connected to the output of comparator 358, an input connected to the first terminal of switch 346, an input connected to the output of comparator 362, an input connected to the output of comparator 372, and an output connected to drive terminal 265.

In operation, during the T _-off period, the voltage sensing circuit 240 provides a portion of the drain electrode voltage “ _Vdrain ” of the drive transistor 230, labeled “K _CS ,” to the multi-function input terminal 263. During the T _-on period, the voltage sensing circuit 240 provides the voltage at the first terminal of the sense resistor 232 to the multi-function input terminal 263 to represent the current conducted through the drive transistor 230.

Voltage sensing circuit 240 supports the use of multi-function input terminal 263 because the voltage it forms represents the current conducted in offline power converter 200 when DRV is active and the voltage provided to load 156 when DRV is inactive. Buffer 312 drives internal circuitry while providing a high impedance to multi-function input terminal 263, and conditioning circuit 310 extracts several pieces of information from the signal provided by buffer 312. In addition, conditioning circuit 310 provides several signals of interest to evaluation circuit 350, including a voltage proportional to _IL via switch circuit 320, a voltage proportional to the average value of _Vin via RC circuit 330, and a voltage proportional to the output voltage via switch circuit 340. When DRV is active, switch circuit 320 connects the signal from multi-function input terminal 263 to the input terminal of comparator 352. Evaluation circuit 350 operates using a set of comparators and a reference voltage generator to provide multiple functional inputs to controller 380. The controller 380 further processes the functional inputs to determine, for example, the switching period, slew rate, on-time, and off-time of the DRV.

Specifically, regulation circuit 310 provides a signal proportional to _IL when DRV is active using the relationship _V263 = _Rsense · _IL , where _V263 equals the voltage on multi-function input terminal 263. Comparator 352 compares this voltage to _VOCP and provides signal OCP to controller 380 if it is greater than _VOCP .

Buffer 312 provides a voltage equal to K _CS ·V _DRAIN to the positive input of comparator 356, where K _CS is equal to R _CS2 /(R _CS1 +R _CS2 ). RC circuit 330 provides a voltage equal to K _CS ·<V _IN > to the negative input of comparator 356, where “<V _IN >” is the average V _IN . Comparator 356 compares the voltages to each other, and when the instantaneous drain voltage of drive transistor 230 exceeds the average voltage, comparator 352 senses the demagnetization phase and provides signal ZCD to controller 380. In addition, for the demagnetization process, RC circuit 330 provides a representative voltage function “K _CS ·<V _IN >” directly to controller 380, which represents “V IN ”, where V IN is the time-averaged function “V ₂₆₃ (t)=V _{263 (2)} (t)=K ₂₆₃ ·V _DRAIN (t)”. Comparator 358 compares V _BO with K _CS ·<V _IN >, and if V _BO is greater than K _CS ·<V _IN >, comparator 352 provides BO to controller 380 .

Comparators 362 and 372 provide redundant OVP based on independent OVP1 and OVP2 signals. Regulation circuit 310 determines _Vbulk based on the relationship _Vdrain = _Vbulk + _Vf , where _Vf is the forward-bias cut-in voltage of diode 152. Switch 340 provides this voltage to comparator 362. Comparator 362 compares this voltage with V _OVP2 and, if it is greater than V _OVP2 , provides OVP2 to controller 380. Comparators 362 and 372 provide independent OVP signals OVP1 and OVP2 based on signals received from separate pins. Feedback circuit 280 provides the Fb signal to comparator 372, which provides the OVP1 signal to controller 380 if Fb is greater than V _OVP1 .

The integrated circuit power factor controller 260 provides processing circuitry to generate several current and voltage sense signals using the voltage on a single multi-function pin. It uses these signals to provide a drive signal to the gate of the driver transistor to control the power factor of the offline power converter while maintaining the safety and protection features of existing designs.

FIG4 illustrates, in diagrammatic form, a voltage sensing circuit 400 according to an alternative embodiment of voltage sensing circuit 240 of FIG2 . Voltage sensing circuit 400 generally includes a resistor 402 labeled “R _CS1 ,” a capacitor 406 labeled “C _CS1 ,” a resistor 404 labeled “R _CS2 ,” and a capacitor 408 labeled “C _CS2 .” Resistor 402 has a first terminal for receiving a voltage labeled “V _DRAIN ” and a second terminal for providing a signal CS/ZCD. Resistor 404 has a first terminal connected to the second terminal of resistor 402 and a second terminal for receiving a voltage labeled “V _SOURCE .” Capacitor 406 has a first terminal connected to the first terminal of resistor 402 and a second terminal connected to the first terminal of resistor 404. Capacitor 408 has a first terminal connected to the second terminal of capacitor 406 and a second terminal connected to the second terminal of resistor 404.

In operation, the voltage division ratio of capacitors 406 and 408 matches the voltage division ratio of resistors 402 and 404, respectively. Capacitors 406 and 408 provide higher bandwidth and less sensitivity to parasitic capacitance between multi-function input terminal 263 and ground.

FIG5 diagrammatically illustrates a buffer 500 according to an alternative embodiment of buffer 312 of FIG3 . Buffer 500 generally includes a resistor 502 labeled " _Rin ," a capacitor 504 labeled " _Cin ," an OPAMP 506, a resistor 508 labeled " _R2 ," a capacitor 510 labeled "C2," and a capacitor 512 labeled " _C1 ." Resistor 502 has a first terminal connected to multi-function input terminal 263 of _integrated circuit power factor controller 260, and a second terminal. Capacitor 504 has a first terminal connected to the second terminal of resistor 502 and a second terminal connected to ground. OPAMP 506 has a positive input connected to the first terminal of capacitor 504, a negative input, and an output for providing a signal labeled "VCS _int ." Resistor 508 has a first terminal connected to the output of OPAMP 506 and a second terminal connected to the negative input of OPAMP 506. Capacitor 510 has a first terminal connected to the first terminal of resistor 508 and a second terminal connected to the second terminal of resistor 508. Capacitor 512 has a first terminal connected to the second terminal of capacitor 510 and a second terminal connected to ground.

In operation, the voltage sensing circuit 240 provides a delayed voltage to the OPAMP 506 according to the capacitor 302 when considering mathematical complex plane analysis, where the “pole” frequency is defined as:

Buffer 500 feeds its output node back to its negative input via an RC network. Voltage sensing circuit 240 may provide a function _Vdrain or may provide a function Vsource _{to the} positive terminal of buffer circuit 500. Buffer 500 operates to perform pole removal at frequency _fp0 by setting a "zero" at a frequency defined as follows:

The buffer 500 provides further compensation by providing an f _p1 function and/or an f _p2 function so that the buffer 500 amplifies only desired frequencies of the signal received from the multi-function input terminal 263 .

Fig. 6 illustrates two timing diagrams 600 that are applicable to the operation of the offline power converter 200 of Fig. 2 that understand.For the upper timing diagram, the horizontal axis represents the time in microseconds (μsec), and the vertical axis represents the amplitude in volts (V).The upper timing diagram illustrates two waveforms of interest, i.e., the waveform 602 labeled " _KCS · _＜Vinput＞ " and the waveform 604 labeled " _KCS · _Vdrain ".For the lower timing diagram, the horizontal axis represents the time in μsec, and the vertical axis represents the amplitude in volts.The lower timing diagram illustrates the waveform 606 labeled " _VZCD ".For the upper and lower timing diagrams, the horizontal axis illustrates two specific time periods of interest, including a first time period from about 0μsec to about 4μsec when the driver transistor 230 is in the on-state and a second time period from about 4μsec to about 20μsec when the driver transistor 230 is in the off-state.

In operation, for both the first and second timing diagrams 600, at approximately 4 μsec, integrated circuit power factor controller 260 pulls down drive terminal 265 to render drive transistor 230 non-conductive. Drive transistor 230 transitions to an off state and provides a high-impedance current path at the second terminal of inductor 220. In response, inductor 220 resists the changing _IL and operates to increase the voltage at the second terminal of inductor 220. When the instantaneous voltage _KCS · _VDRAIN is greater than the average _{voltage KCS} ·<VIN>, comparator 352 provides a high ZCD signal to controller 380, and the demagnetization phase begins ( _IL begins to decrease).

At approximately 17 μsec, the end of the demagnetization phase occurs ( _IL = 0), and the inductor 220 reacts to the changing value of _IL and enters the demagnetization phase. The inductor 220 provides a "ringing" voltage level at its second terminal. Generally, to compensate for this ringing effect, the integrated circuit power factor controller 260 will delay turning on the drive transistor 230 until the voltage from the drain electrode to the source electrode reaches a stable "valley" voltage value less than _VIN .

Thus, the disclosed integrated circuit power factor controller allows for the construction of a cost-effective offline power converter. It reduces the pin count to six while maintaining power factor correction and safety features by using the integrated circuit power factor controller's multifunction pin for detecting overcurrent, overvoltage, and demagnetization conditions. The offline power converter replaces the transformer with an inexpensive inductor and uses a simple resistor divider connected across the drain and source of the driver transistor to generate the voltage transmitted to the multifunction pin. When the driver transistor is conducting, the voltage on the multifunction input terminal reflects the amount of current flowing through the driver transistor and is used by the integrated circuit power factor controller to detect an overcurrent condition. When the driver transistor is non-conducting, the voltage on the multifunction input terminal reflects the voltage on the drain of the driver transistor, which is related to the output voltage and is used by the integrated circuit power factor controller to generate a redundant overvoltage protection signal. The integrated circuit power factor controller detects a demagnetization condition by determining when the instantaneous voltage on the multifunction terminal exceeds the average voltage.

The subject matter disclosed above is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true scope of the claims. For example, in the illustrated embodiment, the integrated circuit power factor controller 260 is a 6-pin product, but in other embodiments, the integrated circuit power factor controller 260 may have a greater or lesser number of pins.

In the illustrated embodiment, conditioning circuit 310 includes switching circuits 320 and 340 and RC circuit 330 , but in other embodiments, conditioning circuit 310 may include other types of circuits to provide input signals to evaluation circuit 350 .

Furthermore, the evaluation circuit 350 includes comparators 352 , 356 , 358 , and 362 , but in other embodiments, the evaluation circuit 350 may include more or fewer comparators to provide more or fewer comparison results to the controller 380 .

According to one aspect, the processing circuit includes a first switching circuit for connecting the multi-function input terminal to the first input terminal of the second comparator when the driving signal is active.

According to another aspect, the processing circuit includes a first comparator and a second switching circuit. The first comparator has a first input terminal, a second input terminal for receiving a first overvoltage threshold signal, and an output terminal for providing a first overvoltage protection signal. The second switching circuit is configured to connect the multi-function input terminal to the first input terminal of the first comparator when the drive signal is inactive. The controller further includes an input terminal for receiving the first overvoltage protection signal and further selectively provides the drive signal in response to the first overvoltage protection signal.

For this aspect, the offline power converter may further include a feedback terminal, and the processing circuit further includes a second comparator. The second comparator has a first input terminal connected to the feedback terminal, a second input terminal for receiving a second overvoltage threshold signal, and an output terminal for providing a second overvoltage protection signal. The controller further has an input terminal for receiving the second overvoltage protection signal, and further selectively provides a drive signal in response to the second overvoltage protection signal.

According to another aspect, the processing circuit includes a resistor and a capacitor. The resistor has a first terminal connected to the multi-function input terminal and a second terminal for providing an average voltage signal. The capacitor has a first terminal connected to the second terminal of the resistor and a second terminal connected to a reference voltage terminal.

For this aspect, the at least one current signal includes a zero current detection signal, and the processing circuit further includes a first comparator having a first input terminal connected to the multi-function terminal, a second input terminal connected to the second terminal of the resistor, and an output terminal for providing the zero current detection signal.

Additionally, the at least one voltage signal may include a brown-out detection signal, and the processing circuit may further include a second comparator having a first input terminal connected to the second terminal of the resistor, a second input terminal for receiving the brown-out threshold voltage, and an output terminal for providing the brown-out detection signal.

According to yet another aspect, the offline power converter further includes a rectifier, an inductor, and a voltage sensing circuit. The rectifier has an input for connecting to a power mains and an output for providing a rectified input voltage. The inductor has a first terminal connected to the output of the rectifier, and a second terminal. The driver transistor further has a first current electrode connected to the second terminal of the inductor and a second current electrode connected to a reference voltage terminal via a sensing resistor. The voltage sensing circuit has a first input terminal connected to the first current electrode of the driver transistor, a second input terminal connected to the second current electrode of the driver transistor, and an output terminal connected to a multi-function input terminal.

In this aspect, the voltage sensing circuit may include a first resistor and a second resistor. The first resistor has a first terminal connected to the first current electrode of the drive transistor and a second terminal connected to the multi-function input terminal. The second resistor has a first terminal connected to the multi-function input terminal and a second terminal connected to the second current electrode of the drive transistor.

In this aspect, the voltage sensing circuit may further include a first resistor, a second resistor, a first capacitor, and a second capacitor. The first resistor has a first terminal connected to the first current electrode of the drive transistor and a second terminal connected to the multi-function input terminal. The second resistor has a first terminal connected to the multi-function input terminal and a second terminal connected to the second current electrode of the drive transistor. The first capacitor has a first terminal connected to the first current electrode of the drive transistor and a second terminal connected to the multi-function input terminal. The second capacitor has a first terminal connected to the multi-function input terminal and a second terminal connected to the second current electrode of the drive transistor.

According to yet another aspect, a first circuit includes a resistor having a first terminal connected to an input terminal and a second terminal for providing an average voltage signal; and a capacitor having a first terminal connected to the second terminal of the resistor and a second terminal connected to a reference voltage terminal.

According to yet another aspect, a first circuit is connected to an input terminal via a buffer having an input terminal connected to the input terminal and an output terminal connected to the first circuit.

For this aspect, the buffer may include: a first resistor having a first terminal connected to the input terminal, and a second terminal; a first capacitor having a first terminal connected to the second terminal of the first resistor and a second terminal connected to a reference voltage terminal; an operational amplifier having a non-inverting input connected to the second terminal of the first resistor, an inverting input, and an output forming an output terminal of the buffer; a second resistor having a first terminal connected to the output terminal of the operational amplifier and a second terminal connected to the inverting input of the operational amplifier; a second capacitor having a first terminal connected to the output terminal of the operational amplifier and a second terminal connected to the inverting input of the operational amplifier; and a third capacitor having a first terminal connected to the inverting input of the operational amplifier and a second terminal connected to the reference voltage terminal.

According to yet another aspect, the integrated circuit may include a third comparator having a first terminal for receiving the average voltage signal, a second terminal for receiving a third reference voltage, and an output terminal for providing an undervoltage signal, and the controller may further maintain the drive signal inactive in response to the undervoltage signal.

Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims (10)

1. An offline power converter, comprising: An integrated circuit power factor controller includes: A multi-function input terminal, wherein the multi-function input terminal is adapted to receive a voltage that represents a voltage based on a voltage sensed by a voltage sensing circuit and is proportional to the current flowing through a drive transistor; A drive terminal, which is used to provide drive signals to the gate of the drive transistor; A processing circuit connected to the multifunction input terminal and providing, based on the voltage at the multifunction input terminal, at least one current signal representing the current conducted in the offline power converter and at least one voltage signal representing the voltage supplied to the load; and A controller for selectively providing the drive signal in response to the at least one current signal and the at least one voltage signal. 2. The offline power converter of claim 1, wherein the at least one current signal includes a zero current detection signal, and the processing circuit includes: A resistor having a first terminal connected to the multi-function input terminal via a buffer and a second terminal for providing an average voltage signal; A capacitor having a first terminal connected to the second terminal of the resistor and a second terminal connected to a reference voltage terminal; and The first comparator has a first input terminal connected to the multifunction input terminal, a second input terminal connected to the second terminal of the resistor, and an output terminal for providing the zero current detection signal. 3. The offline power converter as claimed in claim 2, wherein the at least one current signal is an overcurrent protection signal, and the processing circuit further comprises: The second comparator has a first input terminal connected to the multi-function input terminal via a switch, a second input terminal for receiving an overcurrent threshold signal, and an output terminal for providing the overcurrent protection signal. 4. The offline power converter of claim 2, wherein the at least one voltage signal includes an undervoltage detection signal, and the processing circuit further includes: The third comparator has a first input terminal connected to the second terminal of the resistor, a second input terminal for receiving an undervoltage threshold voltage, and an output terminal for providing the undervoltage detection signal. 5. The offline power converter as described in claim 4, wherein: The integrated circuit power factor controller is characterized as a 6-pin chip, which further includes a feedback terminal, a control voltage terminal connected to the output of the error amplifier of the integrated circuit power factor controller, a power supply voltage terminal, and a reference voltage terminal. 6. The offline power converter of claim 1, wherein the processing circuit comprises: A fourth comparator has a first input terminal, a second input terminal for receiving a first overvoltage threshold signal, and an output terminal for providing a first overvoltage protection signal; and A switching circuit is provided to connect the multi-function input terminal to the first input terminal of the fourth comparator when the drive signal is inactive. The controller further has an input terminal for receiving the first overvoltage protection signal, and further selectively provides the drive signal in response to the first overvoltage protection signal. 7. The offline power converter of claim 6, further comprising a feedback terminal, wherein the processing circuitry includes: The fifth comparator has a first input terminal connected to the feedback terminal, a second input terminal for receiving a second overvoltage threshold signal, and an output terminal for providing a second overvoltage protection signal. The controller further has an input terminal for receiving the second overvoltage protection signal, and further selectively provides the drive signal in response to the second overvoltage protection signal. 8. An offline power converter, comprising: An integrated circuit power factor controller includes: Input terminals; A drive terminal, which is used to provide drive signals to the gate of the drive transistor; A first circuit, connected to the input terminal via a buffer, is used to provide an average voltage signal representing the average value of the voltage at the input terminal; A second circuit is used to compare the voltage at the input terminal with the average voltage signal to form a zero-current detection signal; and A controller that selectively provides the drive signal in response to the average voltage signal and the zero current detection signal. 9. An integrated circuit, comprising: Feedback terminal; Input terminals; A drive terminal, which is used to provide drive signals to the gate of the drive transistor; The first comparator has a first terminal connected to the feedback terminal, a second terminal for receiving a first reference voltage, and an output terminal for providing a first overvoltage protection signal. A second comparator having a first terminal connected to the input terminal via a switch when the drive signal is inactive, a second terminal for receiving a second reference voltage, and an output terminal for providing a second overvoltage protection signal; and A controller, connected to the drive terminal, is configured to selectively activate the drive signal to regulate the voltage on the feedback terminal, and to keep the drive signal inactive in response to either the first overvoltage protection signal or the second overvoltage protection signal. 10. The integrated circuit of claim 9, further comprising: A first circuit, connected to the input terminal via a buffer, is used to provide an average voltage signal proportional to the average value of the input terminal; and The second circuit compares the input terminal with the average voltage signal to provide a zero-current detection signal. The controller further selectively responds to the average voltage signal and the zero current detection signal to provide the drive signal.