Patent ID: 12212243

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG.3shows a second stage of a converter. The second stage includes a transformer TX1that divides the second stage into a primary side (on the left side ofFIG.3) and a secondary side (on the right side ofFIG.3). The transformer TX1includes a primary winding P1and two secondary windings TX1, TX2. As shown inFIG.3, the primary winding P1can include 6 turns, and the secondary windings S1, S2can include 14 turns. The primary winding P1and the secondary windings S1, S2can have any number of turns.

The primary side of the second stage includes an IC U1that includes a power switch or power switches. The IC U1includes an input voltage terminal VIN; an enable terminal EN that turns on the IC U1when a voltage is applied and that turns off the IC U1when no voltage is applied; a switch-output terminal SW connected to an output of the power switch or the power switches; a feedback terminal FB that monitors the output of the IC U1; and a ground terminal GND. The IC U1can include a not-connected terminal NC that is not connected to any other element of the converter. The not-connected terminal NC can be allowed to float.

The primary side of the second stage can include input terminals +input, −input that are connected to input capacitor C3. The input terminal +input and a first terminal of the input capacitor C3can be connected to the input voltage terminal VIN and the enable terminal EN. The input terminal −input and a second terminal of the input capacitor C3can be connected to the ground terminal GND. The switch-output terminal SW can be connected to the primary winding P1. The primary winding P1can be connected in series with a capacitor C5. The feedback terminal FB can be connected to the switch-output terminal SW. The feedback terminal FB can be connected to the switch-output terminal SW before any inductor or LC filter connected to the switch-output terminal. As shown inFIG.3, the feedback terminal FB can be connected to the switch-output terminal SW through a voltage divider defined by resistors R6, R7that are connected in series across the switch-output terminal SW and the input terminal −input.

The IC U1can be a non-resonant, step-down POL IC, which can include an internal high-side power switch and an internal low-side power switch connected in series with other and connected to the input voltage and which can include a forced continuous-conduction mode (CCM) function that allows negative current to flow into the internal low-side switch. Some POL ICs include discontinuous mode (DCM) at light-load conditions to improve efficiency by preventing negative current. Usually, the POL IC detects negative current in the inductor by detecting a voltage drop in the low-side switch. Once the POL IC detects the negative voltage drop, the switch is turned off to prevent negative current into the switch. On the other hand, if POL IC is used in an isolated half-bridge converter, the flow of the inductor current is negative in each cycle. If POL IC includes DCM function, the negative current is prevented by DCM control, preventing the converter from working properly. Based on a feedback signal of the output voltage, the non-resonant, step-down POL IC can regulate the output voltage by changing the duty cycle of the internal high-side and low-side power switches. An example of a non-resonant, step-down POL IC that can be used is Texas Instruments' TLV62568A as described in the datasheet: Texas Instruments, “TLV6256xA 1-A, 2-A Step Down Converter with Forced PWM in SOT563 Package,” revised March 2020, 23 pages, which is incorporated herein by reference in its entirety. The IC U1does not have to include pulse frequency modulation (PFM) control at light loads (or the ability to disable PFM control), a pulse-skipping mode, or any light-load efficiency-improvement feature.

Conventionally, the feedback terminal FB is connected to the capacitor C5after an inductor and through a resistor, as shown inFIG.1. But the feedback terminal FB in the second stage of the converter shown inFIG.3is connected to the switch-output terminal SW through a voltage-sense circuit that can include a voltage divider defined by the resistors R6, R7, where the resistor R6can be directly connected to the switch-output terminal SW and before any inductor or transformer winding that receives the output of the switch-output terminal SW. An average of the voltage at the switch-output terminal SW voltage is maintained by the voltage divider defined by resistors R6, R7, keeping constant the voltage on the feedback terminal FB. The IC U1can include an internal operational amplifier (OP amp) (not shown) that includes a plus terminal connected to a reference voltage and a negative terminal connected to the node between the resistors R6, R7through the feedback terminal FB. When the reference voltage applied to the plus terminal and the voltage on the feedback terminal applied to the negative terminal are the same, the plus and negative terminals of the internal OP amp can be considered to be imaginarily shorted. Connecting the feedback terminal FB to the switch-output terminal SW can achieve 50% duty cycle operation which is required in resonance operation. Exact 50% duty cycle is not required. Approximately 50% duty cycle, e.g., 47.5%-52.5% duty cycle, can still be used to achieve resonance operation. Resonance operation avoids instability issues that are normally caused by the LC filter defined by the primary winding P1and the capacitor C5because of less gain and phase margin in the control loop. The LC filter defined by the primary winding P1and the capacitor C5includes an 180°-phase shift and an increased gain at the resonant frequency. If the gain with a 180°-phase shift of the LC filter defined by the primary winding P1and the capacitor C5is too large, then the convertor can oscillate. Using a non-resonant step-down POL IC as shown inFIG.3can eliminate or significantly reduce the effect that the LC filter defined by the primary winding P1and the capacitor C5on the control of the converter. The switching frequency of the IC U1can be matched to the resonance frequency of a resonant circuit defined by the leakage inductance of the primary winding P1and the capacitance of the capacitor C5by adjusting the values of the leakage inductance of the primary winding P1and the capacitance of the capacitor C5.FIG.4shows resonant waveforms in the second stage ofFIG.3when the feedback terminal FB is connected to the switch-output terminal, where the voltage across the capacitor C5is about 5 V, within manufacturing and/or measurement tolerances, and where the output current Iout is about 0.2 A, within manufacturing and/or measurement tolerances. Load regulation of the second stage can be improved, as shown inFIG.5, by about 12%, within manufacturing and/or measurement tolerances.

FIG.6is a first stage of a converter that can be used with the second stage ofFIG.3as a pre-regulator. The first stage can be used to reduce fluctuations in the input voltage provided to the second stage. The first stage includes an IC U2that includes a power switch or power switches. The IC U2includes an input voltage terminal VIN; an enable terminal EN that turns on the IC U2when a voltage is applied and that turns off the IC U2when no voltage is applied; a switch-output terminal SW connected to an output of the power switch or the power switches; a feedback terminal FB; a bootstrap terminal BST that can be connected to the switch-output terminal SW through capacitor C9; and a ground terminal GND.

The first stage can include input terminals +input, −input and output terminals +input and −input that are connected to the second stage. The input terminals +input, −input are connected to input capacitor C4. The input terminal +input and a first terminal of the input capacitor C4can be connected to the input voltage terminal VIN and can be connected to the enable terminal EN through resistor R5. The output terminal −input and a second terminal of the input capacitor C4can be connected to the ground terminal GND and to the output terminal −input. The switch-output terminal SW can be connected to an output capacitor C2and the output terminal +input through inductor L1. The feedback terminal FB can be connected to a node between the inductor L1and the output terminal +input by a voltage divider defined by resistors R23, R18that are connected in series across the node between the inductor L1and the output terminal +input and the output terminal −input.

The IC U2can be a step-down IC. The IC U2can accept a wide input voltage, e.g. about 4.5 V to about 24 V, within manufacturing and/or measurement tolerances, and can provide a fixed output voltage of the first stage that is provided to the second stage (i.e., the fixed input voltage received by the second stage) so that the second stage maintains a 50% duty cycle, which allows resonance operation in the second stage. Allowing the second stage to maintain a 50% duty cycle can eliminate the need for line regulation in the second stage as shown inFIG.7and can achieve constant output voltage with wide input voltage. In addition, the output voltage accuracy can be set both by adjusting the transformer ratio and by adjusting the output voltage of the second stage. The output voltage of the first stage (i.e., the input voltage of the second stage) can be set accurately by the voltage divider defined by resistors R23, R18. The resistors R6, R7in the second stage can be adjusted in accordance the input voltage of the second stage to keep 50% duty cycle and thus resonance operation.

FIG.7Ashows the load regulation of a two-stage resonant converter with the first stage ofFIG.6and the second stage ofFIG.3and of the known converter ofFIG.1at various input voltages.FIG.7Bshows the line regulation of the two-stage resonant converter with the first stage ofFIG.6and the second stage ofFIG.3and of the known converter ofFIG.1.

FIG.8shows first and second stages of a converter with a load-compensation circuit. The first stage at the top ofFIG.8is similar to the first stage ofFIG.6, and the second stage at the bottom ofFIG.8is similar to the second stage ofFIG.3. Similar elements and components in the first stages shown inFIGS.6and8and in the second stages shown inFIGS.3and8are labeled with the same reference numbers, and a description of the similar elements and components is omitted here.

The first stage ofFIG.8additionally includes a compensation circuit including a resistor R8and a capacitor C7connected in parallel with each other and between the input terminal Vin− and the output terminal −input. A first end of the resistor R8and a first end of the capacitor C7can be connected to the input terminal Vin−, and a second end of the resistor R8and the second end of the capacitor C7can be connected to the output terminal −input. The voltage divider defined by resistors R23, R18is connected to a node between the input terminal Vin− and the load compensation circuit. The current through resistor R8can have a pulsed waveform without the capacitor C7. The capacitor C7filters the pulsed waveform into DC voltage to affect the voltage from the voltage divider defined by resistors R23, R18.

The second stage ofFIG.8additionally includes an operational amplifier (OP amp) X1and peripheral circuitry. The noninverting input of the OP amp X1is connected to the switch-output terminal SW through resistor R4, and the inverting input of the OP amp X1is connected to the input terminal +input through a voltage divider defined by resistors R1, R2that are connected in parallel with each other between the input terminals +input, −input. The positive power-supply voltage of the OP amp X1is connected to the input terminal +input, and the negative power-supply voltage of the OP amp X1is connected to the input terminal −input. Resistor R3is connected to the output of the OP amp X1and to the feedback terminal FB. InFIG.8, the OP amp X1is connected across the switch-output terminal SW and the input terminal −input to amplify the difference between the signal of the switch-output terminal SW and the divided voltage signal between the input terminals +input, −input at the node between the resistors R1, R2to maintain a fixed duty cycle for any condition on the input terminal +input. The capacitor C6is included in the feedback circuit to help stabilize the control of the IC U1. The resistors R3, R4are the output gain control resistors of the OP amp X1to adjust the gain of the OP amp X1. Resistor R4prevents large currents being applied to non-inverting input of the OP amp X1, i.e., resistor R4is an output gain control resistor.

The input voltage of the second stage can be adjusted by the input current detected by the resistor R8in the first stage. When the output current increases, the voltage drop across the resistor R8also increases when the input current increases. The resistor R8is connected to the resistor R18included in the voltage divider defined by resistors R23, R18. The input voltage of the second stage increases in accordance with an increase in the voltage drop across resistor R8. To keep 50% duty cycle in the second stage, the OP amp X1and peripheral circuitry discussed above can be used. The OP amp X1monitors the input terminal +input using the voltage divider defined by resistors R1, R2and provides a signal to the feedback terminal of the IC U1. By using the load-compensation circuit in the first stage and the OP amp X1in the second stage, even though the input of the second stage input is increased by the input current, the second stage maintains a 50% duty cycle, compensating for any output-voltage drop. Compensation gain is controlled by the value of the resistor R8.

FIG.9shows first and second stages of a converter with an OP-amp load-compensation circuit in the first stage. The converter inFIG.9is similar to the converter inFIG.8except that the load-compensation circuits in the first stages of the converters are different. Similar elements and components in the converter shown inFIGS.8and9are labeled with the same reference numbers, and a description of the similar elements and components is omitted here.

The first stage inFIG.9includes an additional OP amp X2in the load-compensation circuit connected across the resistor R8. Because the OP amp X2amplifies the signal across the resistor R8, the resistance of the resistor R8can be smaller, reducing losses. The compensation gain is controlled by the gain of the OP amp X2. The OP amp X2includes two inputs connected across the resistor R8. The noninverting input of the OP amp X2is connected to the first end of the resistor R8and the input terminal Vin− through resistor R10, and the inverting input of the OP amp X2is connected to the second end of the resistor R8through resistor R9, is connected to input terminal Vin+ through resistor R12, and is connected to the output of the OP amp X2through the resistor R11and the capacitor C8. The positive power-supply voltage of the OP amp X2is connected to the input terminal Vin+, and the negative power-supply voltage of the OP amp X2is connected to the input terminal Vin−. Resistor R13is connected to the output of the OP amp X2and to the feedback terminal FB. InFIG.9, the OP amp X2is connected across the resistor R8to amplify the signal across the resistor R8, reducing the loss from resistor R8. The capacitors C8and C7are included in the feedback circuit to help stabilize the control of the IC U2.

FIG.10shows first and second stages of a converter that uses a feedback optocoupler to regulate the output voltage. The first stage ofFIG.10is similar to the first stage ofFIG.6, except that the capacitor C7is used in the first stage ofFIG.10instead of the output capacitor C2in the first stage ofFIG.6. The second stage ofFIG.10is similar to the second stage ofFIG.8, except that the capacitor C7is used in the second stage ofFIG.10instead of the input capacitor C3in the second stage ofFIG.8. That is, inFIG.10, the capacitor C7replaces both of the output capacitor C2inFIG.6and the input capacitor C3inFIG.3. Similarly, the capacitors C2and C3inFIGS.3and6, inFIG.8, and inFIG.9can be combined into a single capacitor. In addition, in the second stage, the OP amp X2monitors the voltage on capacitor C7(i.e., the output voltage of the first stage/the input voltage of the second stage), and a feedback circuit including a feedback optocoupler is used in the converter ofFIG.10. Similar elements and components in the first stages shown inFIGS.6and10and in the second stages shown inFIGS.8and10are labeled with the same reference numbers, and a description of the similar elements and components is omitted here.

The feedback circuit inFIG.10monitors the output voltage across the output terminals Vout+, Vout− and sends a signal corresponding to the monitored output voltage across the isolation barrier defined by the transformer TX1using an optocoupler. The optocoupler is defined by a photo transistor Q2and a light-emitting diode (LED) D3. The OP amp X2monitors the voltage the capacitor C7.

The noninverting input of the OP amp X2is connected to a node between the primary winding P1and the capacitor C5. When the voltage on the capacitor C5is maintained at half the voltage on capacitor C7, the IC U1is operating at 50% duty cycle. The OP amp X2can be connected to either the switch-output terminal SW or the node between the primary winding P1and the capacitor C5because the average voltages are the same. The inverting input of the OP amp X2is connected a node between resistors R4, R5, where the resistor R5is connected to the capacitor C7. The positive power-supply voltage of the OP amp X2is connected to the capacitor C7, and the negative power-supply voltage of the OP amp X2is connected to the input terminal Vin−. Resistor R3is connected to the output of the OP amp X2and to the feedback terminal FB. InFIG.10, the OP amp X2is connected across the node between the primary winding P1and the capacitor C5and the input terminal Vin− to amplify the difference between the signal at the node between the primary winding P1and the capacitor C5and the divided voltage signal of the capacitor C7at the node between the resistors R5, R4to maintain a fixed duty cycle. The capacitor C8is included in the feedback circuit to help stabilize the control of the IC U1.

The feedback circuit includes an optocoupler for sending signals from the secondary side to the primary side to the feedback terminal FB of the IC U1. The optocoupler includes a photo transistor Q2and an LED D3. The collector and emitter of the photo transistor Q2are connected across the resistor R23of the voltage divider defined by the resistors R23, R18. The anode of the LED D3is connected to the output terminal Vout+ through resistor R10, and the cathode of the LED D3is connected to the shunt regulator U3. A reference voltage is provided to the shunt regulator U3by the voltage divider defined by resistors R11, R9and the capacitor C10. The voltage divider defined by resistors R11, R9is connected between the output terminals Vout+, Vout−. The capacitor C10is connected to a node between the series-connected resistors R11, R9and is connected to the output terminal Vout−. The on-resistance of the photo transistor Q2's is controlled by the amount of forward current in the LED D3, which cases the photo transistor Q2to operate as a variable resistor.

FIG.11shows first and second stages of a converter with a regulated output voltage that uses capacitive isolation. The first stage inFIG.11is similar to the first stage inFIG.10, and the second stage inFIG.11is similar to the second stage inFIG.10. The converter inFIG.10includes a feedback circuit that includes the IC U4and the OP amp X3. The feedback circuit can preserve isolation between the primary and secondary sides by including capacitors C2, C3. The capacitor C2can be connected between the OP amp X3and the IC U4, and the capacitor C3can be connected between the input terminal Vin- and the output terminal Vout-. The capacitors C2and C3can be isolation capacitors that can withstand high voltage, such as, for example, about 3 kV or about 5 kV.

The IC U4can be the same IC as the IC U1and can be used to monitor the output voltage at the output terminal Vout+. The IC U4can include an input voltage terminal VIN connected to the output terminal Vout+; an enable terminal EN that is connected to the output terminal Vout+, that turns on the IC U4when a voltage is applied, and that turns off the IC U4when no voltage is applied; a switch-output terminal SW connected to the inverting terminal of the OP amp X3through capacitor C2; a feedback terminal FB that monitors the switch-output terminal SW through a voltage divider defined by resistors R2, R1; and a ground terminal GND. The IC U4can include a not-connected terminal NC that is not connected to any other element of the converter. The not-connected terminal NC can be allowed to float.

The feedback circuit includes an OP amp X3. The noninverting input of the OP amp X3is connected to the input terminal Vin− and the capacitor C3, and the inverting input of the OP amp X3is connected to the switch-output terminal SW of the IC U4through the capacitor C3. A capacitor C6is connected across the inverting input of the OP amp X3and the output of the OP amp X3. The positive power-supply voltage of the OP amp X3can be connected to a node between the inductor L1and the input voltage terminal VIN of the IC U1, and the negative power-supply voltage of the OP amp X3can be connected to ground. Resistor R9is connected to the output of the OP amp X3and to the feedback terminal FB. The capacitor C6is included to help stabilize the control of the IC U2.

The output voltage of the converter is regulated by the IC U4. The IC U4provides duty-controlled square waveform signals to the OP amp X3through the capacitors C2and C3. The OP amp X3and the capacitor C6define an integrator because the gain of the OP amp X3is determined by the value of capacitor C6. The output of the integrator defined by OP amp X1and the capacitor C6is injected into the feedback terminal FB through the resistor R9which adjust the gain of the IC U2. A 50% duty cycle is defined by the resistors R1, R2at the target output voltage Vout+ to provide stable operation. The duty cycle is maintained even if the output voltage Vout+ is varied, for example, if the load increases. When the duty cycle of IC U4is higher than 50% because the output voltage of the second stage is lower that the target output voltage Vout+, then the output voltage of the first stage increases to compensate the lower output voltage of the second stage. And when the duty cycle of IC U4is lower than 50% because the output voltage of the second stage is higher that the target output voltage Vout+, then the output voltage of the first stage decreases to compensate the higher output voltage of the second stage. Thus, the output voltage of the second stage is constant under any conditions.

FIG.12shows a converter with first and second stages similar to the first and the second stages of the converter ofFIG.10. The converter inFIG.12does not include the OP amp X2and peripheral circuitry but does include an inductor L2in the secondary circuit of the second stage. The converter ofFIG.12cannot be used in a resonance operation because of the inductor L2.

The principal operation of the second stage of the converter ofFIG.12is similar to the operation of converter inFIG.1, but the switching stability can be improved by connecting the feedback terminal FB to the switch-output terminal SW as described above. That is, the effect of the LC filter on the control of the converter can be reduced or eliminated. Even though there might poor load regulation using normal switching operation (i.e., not using resonance operation) discussed with respect toFIG.2, the poor load regulation can be compensated by the first stage. Furthermore, to keep the duty cycle fixed, the OP amp X2and peripheral circuitry ofFIG.10can be used in the second stage circuit to boost efficiency.

FIG.13shows a converter with first and second stages similar to the first and the second stages of the converter ofFIG.11. The converter inFIG.13does not include the OP amp X2and peripheral circuitry but does include an inductor L2in the secondary circuit of the second stage. As with the converter inFIG.12, the converter ofFIG.13cannot be used in a resonance operation.

FIG.14shows a converter with first and second stages. The first stage ofFIG.14is similar to the first stage ofFIG.6. The second stage includes IC U1and IC U3arranged in phase-shift, full-bridge topology. The switching of IC U1and IC U3can be synchronized using the sync function of IC U3. The IC U1can be the master, and the IC U3can be the slave. The phase between the IC U1and the IC U2can be shifted by a signal delay using an internal circuit of the IC U1along with the resistor R3and the capacitor C6. Load regulation of the converter can be improved by adding the OP-amp load-compensation circuit, the optocoupler feedback, or the POL IC feedback shown inFIGS.8,9,10and11. In the converter ofFIG.14, the duty of each of IC U1and IC U3can be controlled by OP amps to keep 50% duty under any conditions.

The converters discussed above, except for the phase-shift, full-bridge converter ofFIG.14can use different primary and secondary circuits.FIGS.15-21show different examples of secondary and primary circuits that can be used. Any combination of these primary and secondary circuit can be used in the converters discussed above, except for the phase-shift, full-bridge converter ofFIG.14. In addition, the diodes inFIGS.15-19can be replaced by field-effect transistors (FETs) to increase efficiency.

FIG.15shows a secondary circuit with a full-bridge rectifier connected to the secondary winding S1and the output capacitor C1. The full-bridge rectifier is defined by diodes D1, D2, D3, and D4. The resistor R1represents the load.FIG.16shows a secondary circuit similar to the secondary circuit ofFIG.15, but the full-bridge rectifier is connected to the inductor L1. The cathodes of diodes D1and D2are connected to the inductor L1.

FIG.17shows a secondary circuit including capacitors C10-C13and diodes D5-D8arranged as a voltage quadrupler circuit. The voltage quadrupler circuit is connected to the output capacitor C2. The resistor R2represents the load.FIG.18shows a secondary circuit including capacitors C10, C11and diodes D5, D6arranged as a voltage-doubler circuit. The voltage-doubler circuit is connected to output capacitor C2.FIG.19shows a secondary circuit including capacitors C6, C7and diodes D1, D3arranged in another voltage-doubler circuit.FIG.19includes one less component thanFIG.18as only one capacitor is need, but when the diode D3is conducting, current only flow into capacitor C6. In contrast,FIG.18includes the additional capacitor, but when the diode D5is conducting, current flows not only into C11but also from capacitor C10. Thus, the voltage double ofFIG.18is more expensive but more efficient than the voltage double ofFIG.19.

FIG.20shows a primary circuit of a second stage of a converter with a capacitive divider. The capacitor divider includes capacitors C5, C6connected in series with each other and across the input terminals +input, −input. A node between the capacitors C5, C6is connected to the primary winding P1. When the low-side switch in IC U1is on, current is from both capacitors C5and C6, instead of only capacitor C5. Sharing current between capacitors C5and C6improves efficiency.FIG.21shows a primary circuit of a second stage of a converter similar to the primary circuit ofFIG.20. The primary circuit inFIG.21additionally includes a resonant capacitor C3connected to the node between the capacitors C5, C6and the primary winding P1.

The converter discussed above can be used with any boost converter technology such as LED boost converter technology and wireless charging technology.

It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.