HK1194870A - Off-line power converter and integrated circuit suitable for use in same - Google Patents

Description

Off-line power converter and integrated circuit suitable for use therein

Technical Field

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

Background

The offline power converter may be implemented using an integrated circuit power factor controller to provide power factor correction for the offline appliance. Power factor correction helps to improve the efficiency of power transfer to the load and reduce electromagnetic interference (EMI). The integrated circuit drives the power factor correction stage and may be operated in a critical conduction mode to provide light load operation control as well as other useful control and safety features. However, it would be desirable to reduce the cost of an offline power converter while maintaining the power factor correction and safety features of existing designs.

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, wherein:

FIG. 1 illustrates, in partial block diagram and partial schematic form, an offline power converter including an integrated circuit power factor controller as known in the prior art;

FIG. 2 illustrates, in partial block diagram and partial schematic form, an offline power converter including an integrated circuit power factor controller in accordance with one embodiment of the present invention;

FIG. 3 illustrates, in partial block diagram and partial schematic form, the integrated circuit power factor controller of FIG. 2;

FIG. 4 shows in diagrammatic form voltage sensing in accordance with an alternative embodiment of the voltage sensing circuit of FIG. 2;

FIG. 5 shows in diagrammatic form a buffer circuit in accordance with an alternative embodiment of the buffer of FIG. 3; and

fig. 6 shows two timing diagrams suitable 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

Fig. 1 illustrates, in partial block diagram and partial schematic form, an offline power converter 100 including an 8-pin integrated circuit power factor controller 160 as known in the prior art. Offline power converter 100 generally includes rectifier 110, transformer 120, drive transistor 130 labeled "Q1", sensing circuit 140, output circuit 150, integrated circuit power factor controller 160, line sensing circuit 170, labeled "R_fb1"resistor 180, labeled" R_fb2"resistor 182, labeled" R_Z"resistor 184, labeled" C_Z"capacitor 186, labeled" C_p"capacitor 188 and labeled" R_FF"of resistors 190.

Rectifier 110 includes an electromagnetic interference ("EMI") filter 112, a diode 114, a diode 115, a diode 116, a diode 117, and a reference "C_{Input device}"of the capacitor 118. The rectifier 110 has an input terminal connected to a first "AC line" power supply terminal, an input terminal connected to a second AC line power supply terminal, an output terminal to provide a first power supply terminal, and an output terminal connected to ground, which serves as a reference voltage terminal for the offline power converter 100. Diode 114 has an anode connected to the first power supply terminal provided by EMI filter 112 and is configured to provide a voltage labeled "V_{Input device}"cathode of voltage. Diode 115 has an anode connected to ground and a cathode connected to the anode of diode 114. The diode 116 has an anode connected to the second power supply terminal provided by the EMI filter 112 and a cathode connected to the cathode of the 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. The primary winding 122 has a primary winding for receiving V_{Input device}And a second terminal. The secondary winding 124 has a first terminal connected to ground and a second terminal.

The drive 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.

The sensing circuit 140 includes a reference labeled "D_zcd"diode 142, labeled" R_zcd"resistor 144, labeled" R_ocp"resistor 146 and labeled" R_Sensing"resistor 148. 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. The resistor 146 has a first terminal connected to the second terminal of the resistor 144 and a second terminal connected to the source electrode of the driving transistor 130. Resistor 148 has a second end connected to resistor 146A first terminal of the sub and a second terminal connected to ground.

The output circuit 150 includes a diode 152 labeled "D1", labeled "C_{High capacity}"a bulk capacitor 154, and a load 156. Diode 152 has an anode connected to the drain electrode of drive transistor 130 and is provided with a mark "V_{High capacity}"cathode of voltage. 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 a first terminal of bulk capacitor 154 and a second terminal connected to ground.

The 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 the resistor 146, a fifth terminal connected to ground, a sixth terminal connected to the gate electrode of the drive transistor 130, a fourth terminal to receive a signal labeled "V" and a fourth terminal to receive a signal_CC"and an eighth terminal to receive a signal labeled" feedback ".

Line sensing circuit 170 includes a reference labeled "R_X1"resistor 172, labeled" R_X2"resistor 174, labeled" R_bo1"resistor 176 and labeled" R_bo2"of resistors 178. Resistor 172 has a first terminal connected to the first AC line power supply terminal, and a second terminal. Resistor 174 has a first terminal connected to the second AC line power supply 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 the 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.

The resistor 180 has a resistor receiving V_{High capacity}And a second terminal to provide a feedback signal. Resistor 182 has an eighth terminal connected to the integrated circuit power factor controller 160A first terminal and a second terminal connected to ground. The resistor 184 has a first terminal connected to the first terminal of the 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, the rectifier 110 provides a full wave rectified voltage vin with filtering between the mains (AC line) and the downstream circuitry of the offline power converter 100. Specifically, the rectifier 110 manages the propagation of unwanted energy from the AC line to downstream circuits by passing the signal through the EMI filter 112. The EMI filter 112 filters EMI interference so that downstream circuitry is not disturbed during operation. EMI filter 112 receives the AC line signal and provides a filtered AC signal to its output terminals. Diodes 114, 115, 116 and 117 will store and filter the rectified input voltage V via capacitor 118_{Input device}To the downstream circuitry of the offline power converter 100.

For transformer 120, the varying alternating current passing through primary winding 122 produces a varying magnetic flux in transformer core 126 of transformer 120, thereby producing a varying alternating voltage across primary winding 122. The changing magnetic flux produces a changing magnetic field in the coil of the secondary winding 124 through inductive coupling. As is known, the voltage induced in the secondary winding 124 is a mathematical function of the voltage across the primary winding 122 and is defined by the ratio of the number of turns in the secondary winding 124 to the number of turns in the primary winding 122.

At the on time (' T)_{Is connected to}") to provide a positive drive voltage on the gate electrode of drive transistor 130, which is an N-channel metal oxide semiconductor field effect transistor (" MOSFET "). Driving deviceThe phototransistor 130 transitions to an "on state" and provides a low impedance current path to ground at the second terminal of the primary winding 122. Rectifier 110 provides I_LAnd I is_LThrough primary winding 122, drive transistor 130, and resistor 148. The drive transistor 130 operates to lower the drain electrode voltage towards ground, and the transformer 120 establishes its magnetic field and is dependent on I_LEnergy is stored.

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. The resistor 148 supplies a positive voltage to the terminal 4 in accordance with a current flowing from the drain electrode to the source electrode of the driving transistor 130. If the voltage on terminal 4 exceeds the threshold, the integrated circuit power factor controller 160 determines that the drive transistor 130 is operating in an overcurrent condition and deactivates the drive transistor 130.

At disconnection (' T)_Disconnect") time, the integrated circuit power factor controller 160 pulls down the terminal 6 to render the drive transistor 130 non-conductive. The drive transistor 130 transitions to an "off state" and provides a high impedance current path at the second terminal of the primary winding 122. In response, the primary winding 122 resists changing I_LAnd operates to raise the voltage at the second terminal of the primary winding 122. Diode 152 turns on to connect I depending on the voltage provided by primary winding 122_LIs provided to the output circuit 150 and increases V_{High capacity}. Bulk capacitor 154 is based on I_LStoring V across a load 156_{High capacity}And filters the high frequency voltage transitions across the load 156.

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

Line sensing circuit 170 senses the instantaneous voltage of the AC line by dividing the AC line voltage by the values of resistors 172, 174, 176, and 178. A second terminal of resistor 176 forms a voltage at terminal 2 of integrated circuit power factor controller 160. If the voltage on terminal 2 is less than the threshold, the integrated circuit power factor controller 160 detects an under-voltage condition and stops operation to prevent excessive stress.

Offline power converter 100 will be V_{High capacity}Is provided to a first terminal of resistor 180 to provide a feedback signal depending on the values of resistors 180 and 182. A second terminal of resistor 180 forms a voltage at terminal 8 of integrated circuit power factor controller 160. Depending on the voltage on terminal 8, the integrated circuit power factor controller 160 regulates the duty cycle of the drive transistor 130 and immediately deactivates it if the output voltage is too high.

The integrated circuit power factor controller 160 provides a signal from the output of the internal error amplifier, implemented as an operational transconductance amplifier used in a voltage regulation loop, to terminal 1. The 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 in dependence upon the current provided by the AC line. Depending on the voltage on 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 the 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.

Fig. 2 illustrates, in partial block diagram and partial schematic form, an offline power converter 200 with an integrated circuit power factor controller 260 in accordance with one embodiment of the present invention. Offline power converter 200 generally includes rectifier 110 and output circuit 150 as shown above, inductor 220 labeled "L1", drive transistor 230 labeled "Q1", and reference numeral "R_Sensing"sense resistor 232, voltage sense circuit 240, integrated circuit power factor controller 260, feedback circuit 280, and compensation network 290.

Inductor 220 has a capacitor for receiving V_{Input device}And a second terminal connected to the anode of diode 152.

Drive transistor 230 has a gate electrode to receive 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. The sense resistor 232 has a first terminal connected to the source electrode of the drive transistor 230 and a second terminal connected to ground.

The voltage sensing circuit 240 includes a reference labeled "R_cs1"resistor 242 and labeled" R_cs2"resistor 244. Resistor 242 has a first terminal connected to the drain electrode of drive transistor 230 and a second terminal to provide a signal labeled "CS/ZCD". The resistor 244 has a first terminal connected to the second terminal of the resistor 242 and a second terminal connected to the source of the driving transistor 230.

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

Feedback circuit 280 includes a reference labeled "R_fb1"resistor 282 and labeled" R_fb2"resistor 284. Resistor 282 has a resistor connected to V_{High capacity}And a second terminal connected to a feedback terminal 261 of the 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 reference labeled "R_z"resistor 292, labeled" C_z"capacitor 294 and labeled" C_p"of the capacitor 296. 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, a varying alternating current produces a varying magnetic flux to the inductor 220, thereby producing a varying alternating voltage across the inductor 220. At T_{Is connected to}Meanwhile, the integrated circuit power factor controller 260 provides a positive driving voltage on the gate electrode of the driving transistor 230. The drive transistor 230 transitions to an on state and provides a low impedance current path at the second terminal of the inductor 220. Rectifier 110 provides I_LWhich flows through inductor 220, drive transistor 230, and sense resistor 232. Drive transistor 230 operates to lower the drain electrode voltage towards ground, and inductor 220 establishes its magnetic field and is in accordance with I_LEnergy is stored.

At T_{Is connected to}Meanwhile, the sense resistor 232 provides a voltage on its first terminal proportional to the current flowing through the driving transistor 230. Integrated circuit power factor controller 260When the signal DRV is activated, the drain-to-source voltage of the drive transistor 230 is small and the voltage drop across the voltage sense circuit 240 is also small. Therefore, the voltage at the multi-function input terminal 263 is substantially equal to the voltage at the first terminal of the sense resistor 232, and the multi-function input terminal 263 can be used to sense the current flowing through the driving transistor 230. The internal processing circuit compares the voltage of the multifunction input terminal 263 to an overcurrent protection threshold. If the voltage of the multifunction input terminal 263 exceeds this threshold, the integrated circuit power factor controller 260 deactivates the signal DRV.

At T_DisconnectMeanwhile, the integrated circuit power factor controller 260 renders the driving transistor 230 substantially non-conductive. The drive transistor 230 transitions to an off state and provides a high impedance current path at the second terminal of the inductor 220. In response, inductor 220 resists the changing I_LAnd operates to raise the voltage at the second terminal of inductor 220. Diode 152 turns on to connect I as a function of the voltage provided by the second terminal of inductor 220_LTo the output circuit 150. Bulk capacitor 154 stores charge to make V across load 156_{High capacity}Smoothing and filtering the high frequency voltage transitions across the load 156.

Multifunction input terminal 263 operates as a multifunction input terminal to sense various voltages and currents, including I_L、V_{Drain electrode}Average V_{Input device}And V_{High capacity}. The integrated circuit power factor controller 260 uses these voltages and currents to detect several conditions, including over-current, demagnetization phases, under-voltage, and over-voltage, and adjust its operation accordingly. By using the multifunction input terminal 263 as the multifunction terminal, the 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. Thus, the offline power converter 200 has a significantly reduced cost compared to the offline power converter 100.

Feedback circuit 280 receives V_{High capacity}And will be composed of a resistor282 and 284 of the value determination of a fraction V_{High capacity}To feedback terminal 261. The integrated circuit power factor controller 260 uses the voltage on the feedback terminal 261 to regulate the duty cycle of the DRV. In addition, it compares the voltage at feedback terminal 261 to a threshold. If the voltage at the feedback terminal 261 is above this threshold, the integrated circuit power factor controller 260 detects the overvoltage condition and immediately deactivates the DRV signal. In this way, the integrated circuit power factor controller 260 uses two different terminals to provide redundant OVPs. It improves safety since it can detect overvoltage even in the event of failure of one circuit element.

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

The offline power converter 200 uses a 6-pin integrated circuit to provide efficient power factor control. At the same time, it improves safety by adding redundant overvoltage sensing while maintaining the protection features of the offline power converter 100. In addition, the offline power converter 200 uses a single multi-function pin to provide several current and voltage sensing features; replacing the transformer 120 with a less expensive but more reliable inductor 220; and provides for sensing and processing V_{High capacity}Average V_{Input device}、I_LAnd a safer redundant method of detecting undervoltage, overcurrent, and overvoltage conditions and demagnetization phases.

Fig. 3 illustrates, in partial block diagram and partial diagrammatic form, the integrated circuit power factor controller 260 of fig. 2. The integrated circuit power factor controller 260 generally includes a conditioning circuit 310, an evaluation circuit 350, an overvoltage protection circuit 370, and a controller 380. The conditioning circuit 310 and the evaluation circuit 350 operate together to form the processing circuit of the integrated circuit power factor controller 260.

Offline power converter 200 also includes a reference labeled "C_CS' ofCapacitor 302, as shown in fig. 3. The capacitor 302 has a first terminal connected to the multifunction input terminal 263 of the integrated circuit power factor controller 260 and a second terminal connected to ground.

The conditioning circuit 310 includes a buffer 312, a switching circuit 320, a resistor-capacitor ("RC") circuit 330, and a switching circuit 340. Buffer 312 includes an OPAMP314 having a positive input connected to the first terminal of capacitor 302, a negative input, and a positive input connected to the negative input to provide a signal labeled "K_CS.V_{Drain electrode}"is output. Switching circuit 320 includes a switch 322, an inverter 324, and a switch 326. Switch 322 has an enable input to receive the DRV, a first terminal connected to the output of OPAMP314, and a second terminal to provide a signal labeled "R_Sensing·I_L"to the signal. 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 a reference labeled "R_f"resistor 332 and labeled" C_f"of the capacitor 334. Resistor 332 has a first terminal connected to the output of OPAMP314 and is operative to provide a signal labeled "K_CS·<V_{Input device}>"to the signal. Capacitor 334 has a first terminal connected to the second terminal of resistor 332 and a second terminal connected to ground. The switching circuit 340 includes a switch 342, an inverter 344, and a switch 346. Switch 342 has an enable input, a first terminal connected to the output of OPAMP314, and a first terminal to provide a signal labeled "K_CS·(V_{Output of}+V_f) "to the signal. Inverter 344 has an input to receive the DRV and an output connected to the enable input of switch 342. Switch 346 has an enable input to receive the DRV signal, a first terminal connected to the second terminal of switch 342, and a second terminal connected to ground.

The evaluation circuit 350 includes a comparator 352, a reference voltage generator 354, a comparator 356, a comparator 358, a reference voltageA voltage generator 360, a comparator 362, and a reference voltage generator 364. Comparator 352 has a positive input connected to the first terminal of switch 326, a negative input, and an output to provide a signal labeled "OCP". Reference voltage generator 354 has a negative input connected to 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 OPAMP314, a negative input connected to the first terminal of capacitor 334, and an output to provide a signal labeled "ZCD". Comparator 358 has a positive input, a negative input connected to the second terminal of resistor 332, and an output to provide a signal labeled "BO". Reference voltage generator 360 has a positive input connected to 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 to provide a signal labeled "OVP 2". Reference voltage generator 364 has a negative input connected to comparator 362 to provide a reference voltage labeled "V_OVP2"and a negative terminal connected to ground.

The 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 to provide a signal labeled "OVP 1". Reference voltage generator 374 has a negative input connected to 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, at T_DisconnectMeanwhile, the voltage sensing circuit 240 applies the drain voltage "V" of the driving transistor 230_{Drain electrode}"is marked as" K_CS"is provided to the multi-function input terminal 263. At T_{Is connected to}Meanwhile, the voltage sensing circuit 240 provides the voltage at the first terminal of the sense resistor 232 to the multi-function input terminal 263 so as to represent the current conducted via the drive transistor 230.

The voltage sensing circuit 240 supports the use of the multifunction input terminal 263 because it develops a voltage that is representative of the current conducted in the offline power converter 200 when the DRV is active and the voltage provided to the load 156 when the DRV is inactive. The buffer 312 drives the internal circuit while providing a high impedance to the multifunction input terminal 263, and the adjusting circuit 310 extracts several pieces of information from the signal provided by the buffer 312. In addition, conditioning circuit 310 provides a number of signals of interest to evaluation circuit 350, including AND I via switching circuit 320_LProportional voltage, V via RC circuit 330_{Input device}And a voltage proportional to the output voltage via the switching circuit 340. When DRV is active, the switch circuit 320 connects the signal from the multifunction input terminal 263 to the input terminal of the comparator 352. The evaluation circuit 350 operates using a set of comparators and a reference voltage generator to provide a plurality of functional inputs to the 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, the conditioning circuit 310 provides the AND/when DRV is active_LProportional signal using relation V₂₆₃=R_Sensing·I_LIn which V is₂₆₃Equal to the voltage on the multifunction input terminal 263. The comparator 352 compares the voltage with V_OCPMaking a comparison, and if it is greater than V_OCPThe signal OCP is provided to the controller 380.

Buffer 312 will equal K_CS·V_{Drain electrode}Is provided to the positive of comparator 356Input of, wherein K_CSIs equal to R_CS2/(R_CS1+R_CS2). RC circuit 330 will equal K_CS·<V_{Input device}>Is supplied to the negative input of comparator 356, wherein "<V_{Input device}>"is the average V_{Input device}. 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, the RC circuit 330 will represent the voltage function "K_CS·<V_{Input device}>"directly provided to the controller 380, said function representing" VIN ", where VIN is a time-averaged function" V₂₆₃(t)=V₂₆₃₍₂₎(t)=K₂₆₃·V_{Drain electrode}(t) ". Comparator 358 compares V_BOAnd K_CS·<V_{Input device}>Make a comparison, and if V_BOGreater than K_CS·<V_{Input device}>Then comparator 352 provides BO to controller 380.

Comparators 362 and 372 provide redundant OVPs based on independent OVP1 and OVP2 signals. Regulating circuit 310 is based on relation V_{Drain electrode}=V_{High capacity}+V_FTo determine V_{High capacity}In which V is_FThe forward bias of diode 152 is switched in voltage. The switch 340 provides this voltage to the comparator 362. The comparator 362 compares the voltage with V_OVP2Making a comparison, and if it is greater than V_OVP2The OVP2 is provided to the controller 380. Comparators 362 and 372 provide individual OVP signals OVP1 and OVP2 based on signals received from the individual pins. Feedback circuit 280 provides the Fb signal to comparator 372 if Fb is greater than V_OVP1Then the comparator provides the signal OVP1 to the controller 380.

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

Fig. 4 shows, in diagrammatic form, a voltage sensing circuit 400 in accordance with an alternative embodiment of the voltage sensing circuit 240 of fig. 2. The voltage sensing circuit 400 generally includes a reference labeled "R_CS1"resistor 402, labeled" C_CS1"capacitor 406, labeled" R_CS2"resistor 404 and labeled" C_CS2"of the capacitor 408. Resistor 402 has a resistor to receive a signal labeled "V_{Drain electrode}"and a second terminal to provide signal CS/ZCD. Resistor 404 has a first terminal connected to the second terminal of resistor 402 and is operative to receive a signal labeled "V_{Source electrode}"to the second terminal of the voltage. 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 are matched to the voltage division ratio of resistors 402 and 404, respectively. Capacitors 406 and 408 provide higher bandwidth and less sensitivity to parasitic capacitance between multifunction input terminal 263 and ground.

Fig. 5 shows, in diagrammatic form, a buffer 500 in accordance with an alternative embodiment of the buffer 312 of fig. 3. Buffer 500 generally includes a reference labeled "R_{Input device}"resistor 502, labeled" C_{Input device}"capacitor 504, OPAMP506, labeled" R₂"resistor 508, labeled" C₂"and capacitor 510 labeled" C₁"capacitor 512. Resistor 502 has a first terminal connected to the multifunction input terminal 263 of the 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. OPAMP506 has a positive input connected to the first terminal of capacitor 504, a negative input, and a positive input to provide a voltage labeled "VCS_int"is output. Resistor 508 has a connection to OA first terminal of an output of PAMP506 and a second terminal connected to a 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, when considering mathematical complex plane analysis, voltage sensing circuit 240 provides a delayed voltage to OPAMP506 from capacitor 302, where the "pole" frequency is defined as:

the buffer 500 feeds its output node back to its negative input via an RC network. The voltage sensing circuit 240 may provide the function V_{Drain electrode}Or may provide a function V_{Source electrode}To the positive terminal of the buffer circuit 500. Buffer 500 operates to execute frequency f_p0The removal of the lower pole by setting "zero" at a frequency defined as:

buffer 500 by providing f_p1Function and/or f_p2The function provides further compensation so that buffer 500 amplifies only the desired frequency of the signal received from multi-function input terminal 263.

Fig. 6 shows two timing diagrams 600 suitable for understanding the operation of the offline power converter 200 of fig. 2. For the upper timing diagram, the horizontal axis represents time in microseconds (μ sec) and the vertical axis represents amplitude in volts (V). The upper timing diagram shows two waveforms of interest, labeled "K_CS·<V_{Input device}>"waveform 602 and a waveform labeled" K_CS·V_{Drain electrode}"waveform 604. For the lower timing diagram, the horizontal axis represents time in units of μ sec and the vertical axis represents amplitude in volts. The lower timing diagram shows the label "V_ZCD"606. For the upper and lower timing diagrams, the horizontal axis shows two particular periods of interest, including a first period from about 0 μ sec to about 4 μ sec when the drive transistor 230 is in the on state and a second period from about 4 μ sec to about 20 μ sec when the drive transistor 230 is in the off state.

In operation, for the first timing diagram and the second timing diagram 600, at about 4 μ sec, the integrated circuit power factor controller 260 pulls down the drive terminal 265 to render the drive transistor 230 non-conductive. The drive transistor 230 transitions to an off state and provides a high impedance current path at the second terminal of the inductor 220. In response, inductor 220 resists the changing I_LAnd operates to raise the voltage at the second terminal of inductor 220. When the instantaneous voltage K_CS·V_{Drain electrode}Greater than the average voltage K_CS·<V_{Input device}>At this time, comparator 352 provides ZCD at high to controller 380 and the demagnetization phase begins (I)_LBegins to decrease).

At about 17 μ sec, the end of the demagnetization phase occurs (I)_L=0), inductor 220 pair I_LReacts and enters the demagnetizing phase. Inductor 220 provides a "ringing" voltage level on its second terminal. In general, 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 value less than V_{Input device}Until a stable "valley" voltage.

Thus, the disclosed integrated circuit power factor controller allows for the construction of an offline power converter with reduced cost. It reduces pin count to 6 pins while maintaining power factor correction and safety features by using a multi-function pin for an integrated circuit power factor controller for detecting over-current, over-voltage and demagnetization conditions. The offline power converter replaces the transformer with an inexpensive inductor and uses a simple resistive divider connected across the drain and source of the drive transistor to generate the voltage that is delivered to the multi-function pin. When the drive transistor is conducting, the voltage on the multi-function input terminal reflects the amount of current flowing through the drive transistor and is used by the integrated circuit power factor controller to detect an overcurrent condition. When the drive transistor is non-conductive, the voltage on the multi-function input terminal reflects the voltage on the drain of the drive transistor, which is related to the output voltage and used by the integrated circuit power factor controller to generate the redundant overvoltage protection signal. The integrated circuit power factor controller detects the demagnetization state by determining when the instantaneous voltage on the multi-function terminal exceeds the average voltage.

The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the claims. For example, in the illustrated implementation, the integrated circuit power factor controller 260 is a 6-pin product, but in other implementations, the integrated circuit power factor controller 260 may have a larger or smaller 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 an input signal to evaluation circuit 350.

Further, the estimation circuit 350 includes comparators 352, 356, 358, and 362, but in other embodiments, the estimation 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 comprises a first switching circuit for connecting the multi-function input terminal to the first input terminal of the second comparator when the drive 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 for connecting the multi-function input terminal to the first input terminal of the first comparator when the drive signal is inactive. The controller further has an input terminal for receiving a first overvoltage protection signal and further selectively provides a 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 a 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 the reference voltage terminal.

For this aspect, the at least one current signal comprises a zero current detection signal, and the processing circuit further comprises 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.

Furthermore, the at least one voltage signal may comprise a brown-out detection signal, and the processing circuit may further comprise a second comparator having a first input terminal connected to the second terminal of the resistor, a second input terminal for receiving a 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 connection to a power supply rail 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 drive 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 sense resistor. The voltage sensing circuit has a first input terminal connected to the first current electrode of the drive transistor, a second input terminal connected to the second current electrode of the drive transistor, and an output terminal connected to the multi-function input terminal.

For 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.

For 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, the first circuit comprises: a resistor having a first terminal connected to the 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 the reference voltage terminal.

According to yet another aspect, the first circuit is connected to the 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 the 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 a brown-out signal, and the controller may further hold the drive signal inactive in response to the brown-out 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, comprising:

a multifunctional input terminal;

a driving terminal for supplying a driving signal to a gate of the driving transistor;

processing circuitry connected to the multi-function input terminal and providing at least one current signal representative of current conducted in the offline power converter and at least one voltage signal representative of voltage provided to a load based on a voltage on the multi-function 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.

2. The offline power converter of claim 1, wherein the at least one current signal comprises a zero-current-detect signal, and the processing circuitry comprises:

a resistor having a first terminal connected to the multi-function input terminal 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

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.

3. The offline power converter of claim 2, wherein the at least one current signal is an overcurrent protection signal, and the processing circuit further comprises:

a second comparator having a first input terminal connected to the multi-function terminal, 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 comprises an under-voltage detection signal, and the processing circuit further comprises:

a second comparator having a first input terminal connected to the second terminal of the resistor, a second input terminal for receiving an under-voltage threshold voltage, and an output terminal for providing the under-voltage detection signal.

5. The offline power converter of claim 4, wherein:

the integrated circuit power factor controller is characterized as a 6-pin chip that further includes a feedback terminal, a control voltage terminal connected to an output of an error amplifier of the integrated circuit power factor controller, a supply voltage terminal, and a reference voltage terminal.

6. The offline power converter of claim 1, wherein the processing circuit comprises:

a first comparator having 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 second switching circuit for connecting the multi-function input terminal to the first input terminal of the first comparator when the drive signal is inactive,

wherein 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 circuit comprises:

a second comparator having 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,

wherein 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, comprising:

an input terminal;

a driving terminal for supplying a driving signal to a gate of the driving transistor;

a first circuit connected to the input terminal for providing an average voltage signal representative of an average of the voltage at the input terminal;

a second circuit for comparing the voltage at the input terminal with the average voltage signal so as 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.

9. An integrated circuit, comprising:

a feedback terminal;

an input terminal;

a driving terminal for supplying a driving signal to a gate of the driving 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 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 to regulate the voltage on the feedback terminal and for maintaining the drive signal inactive in response to the first or second overvoltage protection signal.

10. The integrated circuit of claim 9, further comprising:

a first circuit connected to the input terminal for providing an average voltage signal proportional to an average value of the input terminal; and

a second circuit for comparing the input terminal with the average voltage signal so as to provide a zero current detection signal,

the controller further selectively provides the drive signal in response to the average voltage signal and the zero current detection signal.