CONTROLLER FOR MULTI-OUTPUT SINGLE MAGNETIC COMPONENT CONVERTER WITH INDEPENDENT REGULATION OF CONSTANT CURRENT AND CONSTANT VOLTAGE OUTPUTS
1. A method of converting power comprising:
- transferring power pulses from a primary side of a power converter to a secondary side that comprises multiple output windings, wherein transferring power pulses comprises;
switching a primary side power switch in response to a power pulse request; and
providing an independently controlled and regulated output from each of the multiple output windings, wherein providing the independently controlled and regulated output comprises;
generating the power pulse request in response to a power demand of the independently controlled and regulated output;
acknowledging the power pulse request; and
synchronizing switching action between the primary side power switch and a synchronous rectifier.
A power converter includes a primary winding and multiple output windings to provide multiple independently controlled and regulated outputs with a common return line. The outputs are coupled to independently regulate constant current, constant voltage, or both constant current and constant voltage outputs. A secondary control block is coupled to control a synchronous rectifier switch coupled to the common return line to synchronize switching with a primary side power switch to provide complementary conduction of the primary winding and the multiple output windings. A plurality of controlled power pulse switches is coupled to the multiple output windings. A request of a power pulse from each of the outputs is transferred through the secondary control block to a primary switch control block to turn on the primary side power switch to transfer a power pulse to the multiple output windings and through controlled power pulse switches to the outputs.
- 1. A method of converting power comprising:
transferring power pulses from a primary side of a power converter to a secondary side that comprises multiple output windings, wherein transferring power pulses comprises; switching a primary side power switch in response to a power pulse request; and providing an independently controlled and regulated output from each of the multiple output windings, wherein providing the independently controlled and regulated output comprises; generating the power pulse request in response to a power demand of the independently controlled and regulated output; acknowledging the power pulse request; and synchronizing switching action between the primary side power switch and a synchronous rectifier.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
- 21. A method of controlling multiple outputs in a power converter comprising:
setting a hold-off signal high and resetting a timer in response to a primary side power switch turning on; setting the hold-off signal low and setting a target hold-off time value equal to a first value that is a function of a timer when a change in load is detected before the timer reaches the target hold-off time value; setting the hold-off signal low and setting the target hold-off time value equal to a second value that is the function of the timer when; no change in load is detected, the timer has reached the target hold-off time value, and there is a power pulse request pending; and setting the hold-off signal low and setting the target hold-off time value equal to a third value that is the function of the timer when; no change in load is detected, the timer has reached the target hold-off time value, there is no power pulse request pending, a new power pulse request has been issued.
This application is a continuation of U.S. patent application Ser. No. 15/607,075, filed on May 26, 2017, which claims the benefit of U.S. Provisional Application No. 62/428,962, filed on Dec. 1, 2016, and the contents of which are incorporated herein by reference.
This application relates generally to switch mode power supplies and more specifically the invention relates to multi output converters with regulated constant current and constant voltage outputs powering electronic circuits.
Power converters with multiple output and constant current (CC) and/or Constant Voltage (CV) control are of interest and widely used due to their benefits in cost, volume and efficiency in applications that require various levels of the regulated output voltages in CV mode as well as the controlled regulated current in CC mode. The multiple outputs are applied over multiple loads and are independently controlled based on each output load demand controlled and regulated.
In most of the multiple output converters developed so far only one output may tightly be regulated. They may require multiple secondary windings and magnetic components to be regulated independently that would increase cost and size of the power converter.
Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.
In the following description, specific details are set forth, such as device types, voltages, component values, circuits, etc., in order to provide a thorough understanding of the embodiments described. However, persons having ordinary skill in the relevant arts will appreciate that these specific details may not be needed to practice the embodiments described. It is further appreciated that well-known circuit structures and elements have not been described in detail, or have been shown in block diagram form, in order to avoid obscuring the embodiments described.
Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments or examples. Particular features, structures or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art.
In the context of the present application, when a transistor is in an “off-state” or “off” the transistor does not substantially conduct current. Conversely, when a transistor is in an “on-state” or “on” the transistor is able to substantially conduct current. By way of example, in one embodiment, a high-voltage transistor comprises an N-channel metal-oxide-semiconductor field-effect transistor (NMOS) with the high-voltage being supported between the first terminal, a drain, and the second terminal, a source. The high voltage MOSFET comprises a power switch that is driven by an integrated controller circuit to regulate energy provided to a load. For purposes of this disclosure, “ground” or “ground potential” refers to a reference voltage or potential against which all other voltages or potentials of an electronic circuit or Integrated circuit (IC) are defined or measured.
A multi output with secondary-side Constant Current (CC) and Constant Voltage (CV) controller for electronic appliance applications is disclosed. It integrates independent CC/CV regulations wherein CV outputs include precision reference voltages and CC outputs may include adjustable load current. In one example application, the CC output may be used for dimmable LED strings (e.g., arrays) of a monitor screen (e.g., a TV monitor device with LED strings and an adjustable dimming current). Control Loops in the controller provide precise and independent regulation of CC and CV outputs.
The multi-output CC/CV independent control may use a Time Slot Power Distribution Control (TSPDC) process to regulate all the outputs in high precision in an optimized timing.
The proposed converter topology in one example is a single stage multi-output flyback converter targeting applications with multiple independently regulated constant voltage and/or constant current outputs. Example targets for such products may include monitor and TV applications, which include a CC controlled output for the parallel strings (e.g., arrays) of backlight LEDs requiring regulated adjustable (e.g., dimming) constant current output with for example a 40-50 V voltage drop plus one or more CV controlled outputs for powering logic, USB, and audio that should satisfy a strict regulation accuracy requirement for each output.
It is appreciated that in the following description and example drawings, the concept of independently controlled CC/CV multi-outputs is illustrated mostly with series couplings of the secondary windings on the energy transfer element (e.g., transformer). However, it should not be considered as a limitation and it is appreciated that based on the application and the load power requirement on each of multiple outputs, the independently regulated CV/CC outputs may be arranged in any coupling combination of series windings, parallel windings, or both series windings and parallel windings with a common return line for all of the independently controlled and regulated outputs in accordance with the teachings of the present invention.
The synchronous rectifier switch (SR) 145 on the return line 135/155 is controlled through a secondary SR control block 162 that synchronizes switching actions of primary switching device 130 with the synchronous rectifier switch SR 145 on secondary side. In the depicted example, one SR switch 145 is illustrated as being coupled to the common return line return line 135/155. In other examples, it is appreciated that multiple synchronous rectifier switches may be coupled to some or all of the return lines of the output windings. The secondary SR control block 162 SR feedback control signals 166 from the secondary side of power converter and generates control signals 167 to synchronize switching of synchronous rectifier SR switch 145 with the primary switching device 130. In one example (e.g., flyback topology of power converter) when primary switching device 130 is turned on, the synchronous rectifier switch SR 145 remains at off state to prevent transfer of energy to the secondary side and let energy be stored in the magnetic component. When primary switching device 130 turns off, synchronous rectifier switch SR 145 switches to on-state so that the stored energy in the magnetic component generates a power pulse that based on the selected states of the controlled switching devices may be transferred to the output loads demanding for more power. Load block 150, which may include multiple regulated and independently controlled constant voltage CV loads, constant current CC loads, or both constant voltage CV loads and constant current CC loads (e.g., Load1, Load2 and up to Load(n)), receives rectified dc output voltages VO1 152, VO2 153 and up to VO(n) 154 in reference to a single common return line RTN 155 for all of the independently controlled and regulated outputs.
The rectification of output voltages and selective transfer of power pulses from input to each individual output of the power converter is performed by controlled switches in the block of secondary switching devices 140. The multi-output control block 163 by receiving multi-output feedback signals 168 from each output generates multi-output control signals 169 and controls independent regulation of each load in the multi-load block 150. In an isolated converter topology, such as isolated flyback that primary and secondary control signals are referenced to different ground levels the primary switching control block 161 should have galvanic isolation from the secondary SR control block 162. In one example the required communication between primary switching control block 161 and secondary SR control block 162 may be provided through an isolated communication link 165. The multi-output control block 163 and the secondary SR control block 162 may directly exchange control signals 170 to check status of switching devices and to request power pulses from primary switching device. In one example the three control blocks of primary switching control 161, secondary SR control 162 and multi-output control 163 could be included in one single package IC controller 160.
In option “No” 209, if a limited number of outputs are demanding power, then in conditional (i.e., decisional) block 210, it is decided if more than one output is requesting (or demanding) power. In option “No” 213, when only one output is demanding power, then in block 214 it is decided to dedicate all power delivery pulses to the demanding output until its feedback increases above the reference threshold. On the other hand, if still more than one output is demanding power, or option “Yes” 211, then in block 212 power pulses are sequentially delivered to all outputs which have simultaneous demand of power. This process of checking on all output feedback signals for their demand of power would go back to start link 218 to be repeated regularly via the “monitor power demand” links 215 and 216 to provide a fast and fair regulation of all outputs.
Whenever the feedback signal from a CV output drops below the threshold reference signal 226 the output signal (either CV1 246, CV2 256 or CV3 266) of the associated CV comparator would go high to enable the energy transfer request pulse for that specific power demanding output.
In example of
At first row 281, sequence 1, the constant voltage output CV1 receives a power pulse delivery. At second row 282, sequence 2, the constant voltage output CV2 receives a power pulse delivery. At third row 283, sequence 3, either the constant voltage output CV3 or in the case of a constant current load the constant current output CC would receive the power pulse delivery. At next row 284, sequence 4, for an easier transition the power pulse goes back to the constant voltage output CV2 and in sequence 5, row 5 285, power pulse is delivered to output CV1 before returning in the sequence 6 back to deliver a power pulse to the optional CV3 or CC output in row 286. The same pattern of power pulse delivery will continue in the next sequences (row 7 287, row 8, 288 and row 9 289).
The first CV output VO1 371 is coupled through a first power pulse transfer switch 319 to the secondary winding 314. The second CV output VO2 361 is coupled through a second power pulse transfer switch 317 and a diode 316 to the secondary winding 313. The third output of power converter 300 in example of
In a multi-output power converter, contrary to a single output flyback converter, when the primary switch is conducting and all switches on the secondary side are off, there is no conduction path defining the voltage on the secondary side of the transformer. Based on the primary to secondary turns ratio of the transformer and the primary side input voltage, voltages on the secondary connections of the transformer may go high. Without zener diode 318 (and body diode of MOSFET 319), the voltage would depend on parasitic capacitances and could vary from design to design. The clamping zener diode 318 together with the body diode of MOSFET 319, determines the voltage on drain of MOSFET 319 when the primary switch is turned on. The zener diode 318 prevents excessive voltage stress on the secondary components. The total control of the multi-output power converter 300 consists of a primary control block 334 to control switching of primary power switch 332 through switching signal 338 in response to switch current Isw 308 entering drain 331 of power switch 332. Switch current Isw 308 may be sensed (Isns 337) across source 333 of power switch 332. Capacitor 339 is coupled across a primary supply terminal BPP of primary control 334 in reference to primary ground 301.
The secondary control block 336 may control and synchronize the switching of the synchronous rectifier SR 320 and regulate the output for a single output design (i.e., a non-multi-output design). Due to isolation between primary and secondary windings and the isolated primary and secondary reference grounds 301 and 302, the primary control 334 and secondary control 336 have galvanic isolation and may only communicate optically or magnetically (e.g., through isolation link 335) to synchronize the switching of the primary SW 332 and secondary SR 320 switches. In one example, the drain of SR switch 320 is coupled to the low potential side of the output winding 314, the return line for all the multiple outputs and through a resistor 322 coupled to a forward (FWD) pin on the secondary control block 336 to detect the turn-off instant of the primary power switch 332. The gating/control signal for the SR switch 320 is referenced to source terminal of SR switch 320 which is coupled to the secondary ground terminal Gnd 324. Supply voltage to secondary control block 336 is across terminal BPS 325 and across capacitor 326 referenced to return ground 380. The secondary supply as well as the supply BP 387 across capacitor 386 to the multi-output control block 340 are provided from one of the multi-outputs. During start up when VO1 is not rising fast enough, the control supply may be taken from other outputs with higher voltage levels.
The multi-output control 340 may include block 342 “Multi-output signal process and interface blocks” and block 345 “LED Current Sharing and dimming control” which are linked through signals 343. Terminals on multi-output control 340 are listed in Table 399 “Table of External Terminal Labels for Multi-Output Control Block”. In one example (number and nature of terminals not limited to this example) these terminals on multi-output control 340 may include:
It is appreciated that in an example in which only one LED string is used at the CC output, all the input terminals for string currents on multi-output control block (Icc1, Icc2, . . . Icc(m)) could be shorted together.
In one example, the feedback signal FB1 for the first CV output VO1 371 is provided through a resistive divider 372 and 373 across output capacitor CO1374. The feedback signal FB2 for the second CV output VO2 361 is provided through a resistive divider 362 and 363 across output capacitor CO2364, and similarly the feedback signal FB3 for the third CC output VO3 351 is provided through a resistive divider 352 and 353 across output capacitor CO3 354.
An external capacitor 378 is applied from terminal CDr1 377 to the control terminal of the first power pulse switch 319 on the first CV output VO1 371. Similarly, another external capacitor 368 is applied from terminal CDr2367 to control terminal of the second power pulse switch 317 on the second CV output VO2 361.
The power limit for first CV output VO1 371 is defined by an external resistance 384 from terminal PLim1 394 to the return ground Rtn 380. Similarly, the power limit for second CV output VO2 361 is defined by another external resistance 383 from terminal PLim2 383 to the return ground Rtn 380. The constant current terminal CC-Cntrl 392 is also defined through an external capacitor 382 coupled to return ground Rtn 380.
In one example, primary control 334 and secondary control 336 blocks are integrated and packaged in a single IC controlling an external power switch 332. In another example to simplify design, the power switch 332 is also packaged in the same IC as the primary control 334 and secondary control 336. In yet another example, power switch 332, primary control 334, secondary control 336 as well as the multi-output control are all included in a single IC.
In summary, a control scheme for a single magnetic multiple output CC/CV converter in accordance with the teachings of the present invention is implemented through three well synchronized control sections with correlated functions:
- The primary controller for the primary power switch on-off control which has a Ramp Time Modulation (RTM) built-in engine with peak-current control. On reception of a pulse from the secondary control block through an isolation link (e.g., a magnetic link), the primary will immediately issue a pulse. The peak current is determined by the RTM engine.
- The secondary side controller drives the SR MOSFET and produces demand pulses to the primary switch control.
- The multi-output control block for current/voltage regulation that regulates the output quantity on each multi-output by dedicating power pulses based on each output loading and power demand. It also includes a current sharing block that controls current in multiple LED strings and the total current by regulating the voltage drop over a sense current resistor. This block may also assure that the currents in all strings are equal.
Detailed examples of internal blocks and terminals of the multi-output control block for multi-output CV and CC independent regulation in a multi-output power converter with single magnetic component are described in
The BP regulator 410 regulates voltage on the BP terminal 412. In normal operation, BP regulator 410 uses one of the multi-outputs (e.g., VCV(2) 432(2)) as a primary source. However, when this output is low (e.g., during start up) it may use other outputs (e.g., VVCV(3) or VLED 411). The BP regulator should provide sufficient power for both the multi-output control block plus the secondary control block.
The high voltage HV shunt 414 and low voltage LV shunt 415 may be required to limit voltage on some CV output terminals that could be subject to peak-charging. In example of
The level of signal on terminal PWM/ADim 480 could determine or distinguish between an analog or digital dimming option of the LED strings. If signal level PWM/ADim 480 is above VREF 441, the output signal of comparator 442, which is PWM signal 443, goes high and through multi-output signal process block 420 selects digital dimming. Otherwise, the ADim signal 458 through the control block 450, which is LED current sharing and dimming control, selects the analog dimming for LED strings. Comparator 462 detects a low level of PWM/ADim signal in comparison to VLow threshold 461 to generate signal LOW 463 to the multi-output signal process block 420. The multi-output signal process block 420 also requires transferring signals enable 453 and Vsat 454 to and from LED current sharing and dimming control block 450. As well, signals 465 and 466 are transferred to and from the block 460, which is the interface to secondary control (block 336,
- 1) A forward control (FWC) signal 446 from secondary control (346 in
FIG. 3, which is the FWD terminal information on secondary MOSFET SR drain providing the turn on and off instant of the primary power switch).
- 2) Req signal 447 to secondary control (347 in
FIG. 3, which is the power pulse request from a CV or CC output).
- 3) Acknowledge signal Ack 448 from secondary control (348 in
FIG. 3to acknowledge the request of a power pulse).
- 4) The drive signal of synchronous rectifier MOSFET primary 320, synchronous rectifier (SR) signal 449 (349 in
FIG. 3from secondary control terminal SR 321) is also received by multi-output control through interface block 460.
- 1) A forward control (FWC) signal 446 from secondary control (346 in
The LED current sharing and dimming control block 450 is responsible to receive current from all individual LED strings to process as illustrated in example of
In one embodiment of the multi-output power converter, the CC output may be used for current regulated strings of LED load that in one example is utilized in TV or PC monitors. The current sharing and dimming function for multiple paralleled strings of LEDs is provided by control block LED current sharing and dimming control 450 in
The example regulation loop in
In one example, phase-shifted PWM pulses for multiple paralleled LED strings at the CC output may be used to obtain a more uniform output light of LED strings with reduced shimmer/flicker. In the example, it is achieved by more time-distributed power demand of the LED strings. This reduces audible noise and improve efficiency.
In other words, the first LED string would be on during high signal 632. The second LED string would be ON during high signal 642 with ¼ TPWM delay (or shift) from the first string (PWM1 control signal 630). The third LED string goes ON during high signal 652 with ¼ TPWM delay (or shift) from the second string (PWM2 control signal 640), and the fourth string turns on with ¼ TPWM delay (or shift) from the third LED string (PWM3 control signal 650). Even though the PWM frequency is rather low (e.g., 100 Hz to few ten kHz) and the on duration (high signal) is rather short, the four-channel symmetric distribution of PWM control pulses during each PWM period (TPWM) results in a uniform distribution of light (e.g., in the backlight application of a monitor or TV).
The second graph PWM 730 shows in-phase PWM pulses for all strings with logic high 732 and logic low 734 may control a simultaneous dimming on all the LED strings.
The third graph 740 shows secondary request pulses (Req 347 in
It is appreciated that a fixed on-time control may be used where the on-time for all switching drive pulses remains constant in all the states/modes of operation, but the off-time in each state increases by load reduction to increase the switching period and reduce switching frequency when the load varies towards low loads:
- Ton=Ton=Ton= . . . =Ton[i]= . . . =Ton[k−1]=Ton[k]=Ton
- Toff<Toff<Toff< . . . <Toff[i]< . . . <Toff[k−1]<Toff[k].
Therefore, the on-time, Ton, is fixed for each state from state 851 through state [k] 855. However, the off time, Toff, varies, or increases from state 851 to state[k] 855.
As shown in the example depicted in
In a single output converter, an output regulation module (e.g., secondary controller) may regulate the CV or CC output based on the incoming request for (or demand of) power through the FB signal. In a multi-output converter on the other hand, as explained above, there is an extra/third control module of multi-output regulation (e.g., 340 in
The summarized flow chart in
On the other hand, from conditional block 910, if the request is triggered after the primary off-time ends (link “Yes” 912), then in next conditional block 920 in which it is determined if state index i>0, it is verified if the state index is greater than 0 or not. If the answer is “No” 924 and state is still on 0, then processing stays at state (block 960). If the answer is “Yes” 922 and state index is greater than 0, then in the next step block 940, the state is pulled down from [i] to [i−1], which decreases the hold-off time of the primary switch due to an increasing load until a maximum load is reached when the index i=0. Either after keeping state at 0 (minimum state) or reducing/pulling the state down to a lower state, the loop through link 945 loops back to the starting check point 904 on link 905 and repeats.
In other words, it could be concluded that if the primary switch enable signal triggers before the off-time ends, the operational state should be pulled down towards the minimum state ; OR if the primary switch enable signal triggers after the off-time ends, the operational state should be pushed up towards the maximum state [k].
At start 1001, and through link 1002, conditional block 1005 determines if the any secondary winding has begun discharging (transferring the energy that was stored in flyback transformer during on-time of primary power switch to the output). For instance, in one example, the start of any secondary winding discharge may be determined by the detection of a discharging condition signal on the FWD terminal (e.g.; 323 in
In conditional block 1015, if no change in load is detected (e.g., no transient load condition is detected), then processing continues through No 1018 to conditional block 1020, in which it is checked if the timer has reached the target time value yet. If the timer has not yet reached the target hold-off time value (No 1024), then processing loops back to node 1012, to check again if a change in load is detected in conditional block 1015, and if the timer has reached to the target hold-off time value in conditional block 1020. On the other hand, when the timer value reaches the target hold-off time value (Yes 1022) before a change in load is detected in conditional block 1015, the hold-off time signal is set to zero in the next step, block 1030. Block 1030 is followed by another conditional block 1040 to verify if the previous request is still pending or expired. If the previous request is still pending (Yes 1044) the target hold-off time value is set to a second value that is a function of the timer (i.e., Target=f(Timer)), and processing loops back through link 1003 back to start point 1002.
However, if the previous switching request has been expired and not pending (No 1042), then in conditional block 1050 it is checked if the new request has been received. If new request has not yet been received (No 1054), processing loops back to conditional block 1050 to wait for a new request to be received (Yes 1052) to proceed to the final block 1060 the target hold-off time value is set to a third value that is a function of the timer (i.e., Target=f(Timer)), and processing loops back through link 1003 back to start point 1002.
The above description of illustrated example embodiments, including what is described in the Abstract, are not intended to be exhaustive or to be limitation to the precise forms or structures disclosed. While specific embodiments and examples of the subject matter described herein are for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it is appreciated that the specific example currents, voltages, resistances, device sizes, etc., are provided for explanation purposes and that other values may also be employed in other embodiments and examples in accordance with the teachings of the present invention.