WO2016172684A1

WO2016172684A1 - Method and apparatus for controlled voltage levels for one or more outputs

Info

Publication number: WO2016172684A1
Application number: PCT/US2016/029168
Authority: WO
Inventors: Ionel Jitaru; Marco Antonio Davila; Andrei Savu; Adrian Loan LITA
Original assignee: Rompower Energy Systems Inc.
Priority date: 2015-04-24
Filing date: 2016-04-25
Publication date: 2016-10-27

Abstract

Methodologies to reduce the cost, complexity and improve efficiency of a power delivery USB output for two or more outputs.

Description

Title: Method and Apparatus for Controlled Voltage Levels for One or more Outputs

Inventor: Ionel Jitaru et al.

Related Application/Claim of Priority

This application is related to and claims the priority of Provisional Application No.

62/152722, filed April 24, 2015, and entitled Method and Apparatus for Controlled Voltage Levels for One or more Outputs; and which provisional application is incorporated by reference herein.

1. Introduction

[0001] The present invention relates to new and useful methodologies aimed at increasing the performance of an offline converter that has two or more outputs fed from an isolated converter. It addresses standby power, feedback for the main isolation converter, individual feedback, and control of the switching elements to comply with the Power Delivery Specification version 2.0 for at least two USB 3.1 ports. This new USB specification is aimed at reducing the types of power supplies used for computing devices. It allows multiple output voltages and currents based on a negotiating procedure. This allows power supplies that comply with the new specification to be used universally, which promotes reuse and reduces waste. The old USB standard has been used in this way and has been mandated in several countries, the new specification expands on this universal use by allowing multiple voltages on the USB bus. This is needed since most laptop computers consume more than 10W which is what the old USB standard allowed. By allowing higher voltage more power can be delivered on the new 3 A rated cable and connector.

[0002] The efficiency of the unit is always a major consideration and now with more restrictive specifications at light load the efficiency at all load conditions is important. The difficulty in providing low power at light loads is complicated further by having two or more independent outputs. The new specification allows detection of the connecting cable which can help to comply with this specification. This requires that the controller detecting the cable insertion to have a very low power consumption.

[0003] This disclosure provides a set of methodologies that are aimed on complying with all these new requirements.

Summary of The Present Invention

[0004] In one basic embodiment of the invention, a converter circuit comprising an offline isolated converter has two or more outputs fed from the isolated converter which has a regulated output voltage that can be changed and wherein determination of the regulated output voltage of the isolated converter is based on the output voltage(s) of the outputs.

[0005] In one version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, placed after the isolated converter, each of which comprises a forward switch(s) and a freewheeling switch(s), wherein the regulation of the output voltage of the isolated converter is based on the highest of the output voltage(s) of the outputs, and which output(s) are regulated by turning on the forward switch continuously. In this version, the forward switch is preferably kept on by means of a charge pump.

[0006] In another version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit.

[0007] In still another version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit and allow the necessary headroom for said buck converter or said buck boost converter in order to eliminate the output ripple at the output of said bulk converter or said buck boost converter.

[0008] In a second basic embodiment of the present invention, a circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter has a regulated output voltage and the isolated converter is configured to go into standby for low power requirement and wherein determination of the output voltage of the isolated converter is based on the output voltage (s) of the outputs and the need to eliminate ripple which is present at the output of the isolated converter.

[0009] In another basic embodiment of the present invention an offline isolated converter that has two or more outputs fed from said an isolated converter wherein the regulation of the outputs is provided by a buck converter or a buck boost converter, each of which can be controlled also to discharge an output capacitor and to send the excess energy back to the output of said isolated converter.

[0010] In yet another basic embodiment of the present invention, circuit comprising an offline isolated converter has two or more outputs fed from said an isolated converter, wherein regulation of the outputs is provided (a) by a buck converter or a buck boost converter, wherein an additional switch is placed in series with the output capacitor of each of said outputs and by (b) controlling said additional switch to prevent inrush current on the output.

[0011] In still another basic embodiment of the present invention, a circuit comprising an offline isolated converter has two or more outputs fed from said an isolated converter, wherein regulation of the outputs is provided by a buck converter or a buck boost converter, wherein the current measurement through an output inductor of at least one of the said outputs is done by monitoring the voltage at a switch node of said buck or buck boost converter versus time.

[0012] These and other features of the present invention will become apparent from the following Detailed Description and the accompanying drawings

Brief Description of the figures

[0013] Figure 1 illustrates an example of a post regulator stage circuit, using a buck topology;

[0014] Figure 2 illustrates a circuit that produces the regulation voltage for an isolated converter, in accordance with the principles of the present invention;

[0015] Figure 3 A shows waveforms for the circuit of Figure 1, in accordance with the

principles of the present invention;

[0016] Figure 3B shows two implementations of detecting drain waveform for the

freewheeling switch of the circuit of Figure 1, in accordance with the present invention;

[0017] Figure 4 shows a circuit in accordance with the present invention, with a buck converter and a high side/ low side driver;

[0018] Figure 5A is an illustration of a circuit in accordance with the present invention, that uses a flyback as an isolated converter;

[0019] Figure 5B shows secondary power stages from the power delivery in a circuit, in

accordance with the principles of the present invention; and

[0020] Figure 6 illustrates how head room is optimized and maintained by controlling the

output voltage of the isolated converter, in accordance with the present invention.

Detailed Description

2.1 Power Architecture

[0021] Shown in Multiple Power Delivery Block Diagram, Figure 5A is the proposed implementation. A flyback converter or any other topology converter can be used to regulate and isolate from the main AC line. Two or more Buck, Boost, or Buck Boost stages, referred in this patent as post regulator converters, are used in the case in which any of the outputs requested is different than the isolated converter output.

[0022] It is important for this implementation that the isolating converter has a regulated output voltage that can be changed by the secondary controller. Also it is needed that the converter to be able to go into standby for low power requirement. After negotiation on each connected USB port the output and current requested of each post regulator converter is known. It is assumed that each post regulator stage is able to monitor its output voltage and current.

[0023] The post regulator stages can be buck, boost or buck-boost type. They can be combined to have multiple outputs, ex: 2 buck stages, 1 boost stage etc.

2.2 Regulation

[0024] Once the output voltages are known then the maximum voltage can be determined.

[0025] In Figure 1 is presented an example of a post regulator stage using a buck topology. In the Buck topology there are two switching elements. The first switching element referred as the Forward switch is connected to the input voltage , in this case, Vfly, which is the output voltage of the isolated converter and the common connection of the output inductor, 103 and the second switching element, 102, referred in this application as the Freewheeling switch. If the output of the isolating converter is set to this maximum voltage at least one of the post regulator converters will be at maximum duty cycle including 100%. If the duty cycle is 100% this post regulator converter does not have to switch and the Forward switch is kept on and the Freewheeling switch is kept off. In the case of buck topology for the post regulator the upper switch, Forward switch, can be kept on by a charge pump or other means. This greatly improves the efficiency of that converter because we eliminated in this way the switching and driving losses. and-Because the converter that is producing the highest voltage has the most impact of the overall efficiency of the system increasing the efficiency of the highest output voltage converter will have a significant impact in increasing the efficiency of the power system. Furthermore, if both buck converters are at the same voltage both converters will not have to switch, also improving the efficiency further. This requires that the isolating converter (a flyback converter in the example block diagram shown in Figure 5A) to be able to change its output regulation voltage (the voltage at the input of the post regulator stage converters). In one of the key embodiment the regulation voltage of the isolated converter is going to be equal or slight higher than the highest voltage output of the post regulator converters, tailored for maximum efficiency and elimination of the ripple present at the output of the isolated converter. Let's consider an example wherein we have two output voltages and both outputs request 20V. In that case both post regulators will operate at 100% duty cycle wherein the Forward switch in on and the isolated converter delivers a voltage slight higher than 20V to compensate for the voltage drop across the forward switch. In the case that there is a ripple at the output of the isolated converter outside of the specification limits, then the output voltage of the isolated converter will be higher to offer the necessary headroom for the post regulator.

In the situation wherein one output requires 20V and the second output requires 12V the post regulator which delivers the highest voltage, 20V, will operate at 100% duty cycle and the post regulator delivering 12V will operate at a narrower duty cycle to regulate the 12V output. In the case wherein both output voltages require 12V, the isolated converter regulates a voltage slight higher than 12V to compensate for the voltage drop on the Forward switch. In the event both of the output requires 5V output then the isolated output will provide a voltage higher than 5V chosen for maximum efficiency of the systems containing the isolated converter and post regulaor in series. In some application that may be slight higher than 5V and 5V post regulator will operate at 100% duty cycle keeping the Forward switch on and in other application the most efficient way is for the isolated converter to regulate a higher voltage than 5 V and the post regulator to operate at a lower duty cycle than 100% to regulated the output voltage.

If there is a centralized controller for the USB communication and for all secondary stage converters referred in this application as post regulator converters then this controller can set the regulation point of the isolating converter and be able to determine if each of the secondary stage converters needs to switch or statically produce voltage. The centralized controller described above can be either a single chip or multiple controllers acting as one, otherwise, the controllers can communicate the regulation voltages using digital or analog lines to select each regulation setting. A circuit that takes the results of these lines can process these signals, producing the regulation voltage for the isolating converter. This is represented symbolically in figure 2. This can also represent the internal logic or algorithm in the case of a unified (centralized) controller.

It could also be the case that the flyback or isolating converter in combination with the final stage converter to be more efficient with the flyback converter regulating at some other voltage rather than the maximum requested voltage. As mentioned previously, if the request is for two 5V outputs and if the combination of the flyback converter at 12V with the buck converters at 5V is more efficient than with the flyback at 5V then the controller can choose to produce this combination instead. In other words the controller can set the most efficient combination for the requested output voltage combination.

[0029] In some application the output of the isolated converter may have a large ripple. The post regulator converter will need a certain head room to produce a regulated output and eliminate the output ripple. In the case wherein the isolated converter is a converter which does also the power factor correction shaping the input current in sinusoidal shape as the input line or in any other shape as described in the application serial number 14/680,778, filed April 7, 2015, "Input current distortion for minimization of the bulk capacitor" (a copy of which is Exhibit A hereto) , there will be a low frequency ripple at the output of the isolated converter. The post regulators have to eliminate this ripple by maintaining the proper head room in between the voltage at the output of the isolated converter and the output of the post regulator. This head room is optimized and maintained by controlling the output voltage of the isolated converter. This is depicted in Figure 6.

[0030] 2.3 Output Discharge and Disconnect

[0031] In figure 1, a typical synchronized rectified buck converter consists of two switches (101), (100) with an output choke (100) and output capacitor (104). The new USB requirements state that the output must be discharged to achieve zero volts and also to disconnect the output bulk capacitor so that ' ho ' insertions does not disturb the USB power bus. A "hot" insertion occurs when the bulk capacitor at the output of the post regulator is charged. This is typically done with another two switches on the output of the secondary stage converter. But shown in this disclosure it is possible to accomplish this with the components shown in Figure 1 only.

[0032] To accomplish discharge, the bottom switch, referred also as a Freewheeling switch (102) can switched on and off with a pulse width modulated pattern that would reverse current flow in the inductor (103). When turning off the current in the inductor returns back to Vfly (back to the output of the flyback converter) so the energy that was in the output capacitor is conserved and placed back into the input voltage source. This removes the need to have an extra switch to discharge the output.

[0033] To disconnect the bulk capacitor, instead of two switches on the output, only one switch is needed. This is shown as switch (105). Any voltage on the bus will not inrush back into the output bulk capacitor. Switch (101) acts also as the turn off switch for the channel. Another advantage of switch (105) instead of two output switches is power dissipation. Switch (105) only has the bulk capacitor ripple current not the output current. This is a much smaller value and in addition to being the only switch, it reduces the losses compared to the typical circuit. The control of these functions just requires a slightly smarter controller (106).

2.4 Current Sensing Using Synchronized Switch Drain Waveform

[0034] Current sensing is needed in any converter. A new method was discovered to sense the current in the buck converter by monitoring the synchronous rectifier (102) drain voltage. If a circuit is designed that measures the time/voltage after the moment the synchronized switch (102) is turned off and the top switch, referred also as the Forward switch , is turned on, it can be determined if the converter is in continuous, critical, or beyond critical mode. Since the time that the switch (102) is off, the output voltage, and the output inductor (103) values are known, the amount of ripple current in the inductor can be calculated. If the output average current is equal to half this amount, the current at the end of the on period for switch (102) is zero. It would create a slow moving drain waveform shown in figure 3A for the critical condition. If the output current is below this halfway point, it would produce a faster moving waveform shown in figure 3A as the pushback > 0 waveform. Push back is amount of negative current (reverse current) in the output choke (103). If the output current is greater than half the ripple current, then the drain waveform will not rise at all until the top switch (101) turns on to force it high. If the controller is designed to keep the unit in critical conduction, the controller can use the measurement of the drain to determine whether is above or below this critical mode point. If the controller works in this critical mode and by knowing the ripple current, then the output current would be one half of the ripple current.

Two implementations of detecting drain waveform of switch (102) are shown in figure 3B. In the option A implementation, the cathode of diode (303) is connected to the drain of switch (102). The diode blocks high voltages during the time the drain voltage on switch (102) is high. At the moment of time the gate on switch (102), Figure 1, is turned off and the drain of switch (102) is still low, and capacitor (308) is discharged. Therefore, the output of NOR gate (309) will produce a high and start to charge capacitor (311). When the drain voltage of switch (102) reaches the gate threshold of Schmitt trigger gate (305) minus the diode (303) drop the output of gate (305) will go high and charge capacitor (308) and then will turn off the NOR gate (309) output. The pulse size produced by the NOR gate is averaged by the resistor (310) and the capacitor (311). This level is then read by any controller downstream. Capacitor (308) is needed to blank out the drain signal when the top switch (101) turns off the bottom switch (102) is about to turn on. Since capacitor (308) is still charged from the time that drain of switch (102) is high it has a delay so that the down going transition of the drain does not produce a pulse on the NOR gate output. The circuit is designed to measure the time from low to high of switch (102) not high to low. Option B is another way to solve this high to low and low to high problem. Again diode (314) performs the same role as diode (303) in the previous circuit. In this case the gate waveform of switch (102) is fed into an inverter (312) and when a high to low signal is detected on the gate of switch (102) it produces a low to high transition on the clock input of D flip-flop (315). This latches in a high output, which starts to charge capacitor (317) through resistor (316) which then perform the same role of averaging as the capacitor (311) and resistor (310) of the option A circuit. When the drain waveform rises and crosses the threshold of the clear input of the D flip-flop (315) the output of the flip- flop at the Q pin goes low. In this way only when the switch (102) is turned off is the drain waveform measured to determine the rise time.

[0036] There are some advantages in running the buck converter in critical mode. Running in critical mode has the advantage of very low switching losses in both switches and also has the advantage of producing very low high frequency noise due to reverse recovery effects. The disadvantage is that the converter has higher RMS currents compared to a continuous mode buck converter and requires that the output choke be designed with magnetic material that has relatively lower core losses.

[0037] If the buck converter is not switching then current sensing can be done by other typical methods.

2.5 Sustained On

[0038] If a buck converter is not switching but is commanded to be at 100% duty cycle, there is a problem in keeping the upper switch, referred also as the Forward switch, (101) on. A high side/ low side driver is shown in figure 4. The converter switching diode (406) refills the upper bias when switch (403) is on. This is commonly used. But if switch (403) is not turned on because of the 100% duty, capacitor (407) will slowly lose bias. In order to continue to support this floating bias an extra circuit consisting of a charge pump is added. The square wave coming into the charge circuit can be generated by gates or by a microcontroller. Each buck converter can use this waveform to run a charge pump consisting of capacitor (411), diodes (412) and (413). The output of this charge pump is connected to capacitor (407) to sustain bias. This ability is required if the buck converter is not switching and is shown in figure 4 as one way to accomplish this top side biasing method.

2.6 Output sharing, output multiplexing and interleaving

[0039] The secondary power stages from the power delivery block diagram, Figure 5B, can share an output and work in parallel if only one output is needed from the adapter. This way, the secondary stage efficiency can be improved. This can be achieved by a decision in the secondary controller. When one of the outputs has a new cable connected, the controller disconnects the parallel operation of the secondary power stages.

[0040] If one of the secondary stages develops an internal fault its output can be automatically multiplexed to a working secondary stage. The faulty USB output will be internally routed to a working secondary stage. This is achieved in a multiplexing stage controlled by the secondary controller.

[0041] The secondary power stages can operate in interleaved mode and/or in parallel and interleaved. The interleaving is achieved by phase shifting the control signals generated in the secondary controller. The phase shift between the signals can be constant or can vary with a variable or constant speed.

[0042] From the foregoing detailed description, it will be clear to those in the art that the present invention is characterized as follows;

[0043] In one basic embodiment of the invention, a converter circuit comprising an offline isolated converter has two or more outputs fed from the isolated converter which has a regulated output voltage that can be changed and wherein determination of the regulated output voltage of the isolated converter is based on the output voltage(s) of the outputs.

[0044] In one version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, placed after the isolated converter, each of which comprises a forward switch(s) and a freewheeling switch(s), wherein the regulation of the output voltage of the isolated converter is based on the highest of the output voltage(s) of the outputs, and which output(s) are regulated by turning on the forward switch continuously. In this version, the forward switch is preferably kept on by means of a charge pump.

[0045] In another version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit.

[0046] In still another version of the basic embodiment, the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit and allow the necessary headroom for said buck converter or said buck boost converter in order to eliminate the output ripple at the output of said bulk converter or said buck boost converter.

[0047] In a second basic embodiment of the present invention, a circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter has a regulated output voltage and the isolated converter is configured to go into standby for low power requirement and wherein determination of the output voltage of the isolated converter is based on the output voltage (s) of the outputs and the need to eliminate ripple which is present at the output of the isolated converter.

[0048] In another basic embodiment of the present invention an offline isolated converter that has two or more outputs fed from said an isolated converter wherein the regulation of the outputs is provided by a buck converter or a buck boost converter, each of which can be controlled also to discharge an output capacitor and to send the excess energy back to the output of said isolated converter.

[0049] In yet another basic embodiment of the present invention, circuit comprising an offline isolated converter has two or more outputs fed from said an isolated converter, wherein regulation of the outputs is provided (a) by a buck converter or a buck boost converter, wherein an additional switch is placed in series with the output capacitor of each of said outputs and by (b) controlling said additional switch to prevent inrush current on the output.

[0050] In still another basic embodiment of the present invention, a circuit comprising an offline isolated converter has two or more outputs fed from said an isolated converter, wherein regulation of the outputs is provided by a buck converter or a buck boost converter, wherein the current measurement through an output inductor of at least one of the said outputs is done by monitoring the voltage at a switch node of said buck or buck boost converter versus time.

[0051] With the foregoing disclosure in mind, the manner in which performance of an offline converter that has two or more outputs fed from an isolated converter can be increased will be apparent to those in the art.

Claims

1. A converter circuit that has two or more outputs fed from an offline isolated converter

which has a regulated output voltage that can be changed and wherein determination of the regulated output voltage of the isolated converter is based on the output voltage(s) of the outputs.

2. The circuit of claim 1, wherein the regulation of the outputs is done by a buck converter or a buck boost converter, placed after said isolated converter, each of which comprises a forward switch(s) and a freewheeling switch(s), wherein the regulation of the output voltage of the isolated converter is based on the highest of the output voltage(s) of the outputs, and which output(s) are regulated by turning on the forward switch continuously.

3. The circuit of claim 2 wherein the forward switch is kept on by means of a charge pump.

4. The circuit of claim 1 , wherein the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit.

5. The circuit of claim 1, wherein the regulation of the outputs is done by a buck converter or a buck boost converter, each of which comprises a forward switch and a freewheeling switch, wherein the regulation of the output voltage of the isolated converter is configured to obtain maximum efficiency of the entire circuit and allow the necessary headroom for said buck converter or said buck boost converter in order to eliminate the output ripple at the output of said bulk converter or said buck boost converter.

6. A circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter which has a regulated output voltage and the isolated converter is configured to go into standby for low power requirement and wherein determination of the output voltage of the isolated converter is based on the output voltage (s) of the outputs and the need to eliminate ripple which is present at the output of the isolated converter. A circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter wherein the regulation of the outputs is provided by a buck converter or a buck boost converter, each of which can be controlled also to discharge an output capacitor and to send the excess energy back to the output of said isolated converter.

A circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter wherein regulation of the outputs is provided (a) by a buck converter or a buck boost converter, wherein an additional switch is placed in series with the output capacitor of each of said outputs and by (b) controlling said additional switch to prevent inrush current on the output.

A circuit comprising an offline isolated converter that has two or more outputs fed from said an isolated converter wherein regulation of the outputs is provided by a buck converter or a buck boost converter, wherein the current measurement through an output inductor of at least one of the said outputs is done by monitoring the voltage at a switch node of said buck or buck boost converter versus time.