Multiple-output Converter Research Articles

Secondary side post regulator for improving cross regulation and reducing standby power consumption

The quest for improved energy savings is driving research into power converter high-efficiency operation under extremely light-load conditions. The use of multiple output converters to satisfy circuit needs and cost requirements adds additional complication to the standby mode power-consumption problem. This is due to the difficulty of satisfying both good cross-regulation under various load conditions as well as high efficiency in the standby mode simultaneously; because topologies that exhibit a good cross-regulation performance, such as resonant converters, generally have a poor efficiency problem under extremely light-loads. A secondary side post regulator (SSPR) is proposed to reduce the standby power consumption and to improve the cross-regulation performance of single- controller multiple-output channel power converters. It is capable of reducing the power consumption of the power converter as well as the SSPR. The SSPR is analysed using its operational principles and small signal models. A 110 W experimental prototype was built to verify the standby power consumption and cross-regulation performance using the proposed SSPR.

Adaptive pseudo-continuous conduction mode operation schemes and circuit designs for single-inductor multiple-output switching converters

As single-inductor multiple-output (SIMO) switching converters proliferate in integrated power management designs, pseudo-continuous conduction mode (PCCM) operation with freewheel switching has been well adopted owing to its effectiveness on cross-regulation, voltage ripple and switching noise issues, especially in heavy load scenarios. However, the technique faces a direct challenge in unbalanced loading conditions. Potential lengthy freewheel switching periods and high I dc current levels could lead to conduction and switching power losses, degrading the efficiency of the converters. To alleviate this problem, this paper presents adaptive PCCM operation schemes with the respective distributed and unified freewheel switching schemes. The optimal freewheel switching durations are achieved in various load conditions by adaptively adjusting the phase durations and freewheel switching I dc current level, thereby reducing the conduction and switching losses effectively. The switching power loss is further reduced by turning on/off the freewheel switch less frequently, without compromising the performance of operation. The proposed schemes have been implemented and verified in digital and analog-based SIMO power converters designed with 130 nm CMOS process.

Predictive Digital Current Control of Single-Inductor Multiple-Output Converters in CCM With Low Cross Regulation

This paper presents a new digital current-mode control technique for single-inductor multiple-output converters in continuous-conduction mode. This predictive control method can calculate all the required duty cycles corresponding to the outputs for the next switching cycle. Since the calculation is based on every current reference representing the load current, all current control loops corresponding to different outputs are theoretically independent, which can greatly reduce the cross regulation. To avoid subharmonic oscillation, proper predictive digital current control is adopted. Inductor current estimation is used to remove the current sensing circuit, and corresponding calibration techniques are presented. Simulation and experimental results are given to verify the effectiveness of this control technique.

Topologies and control of a class of single inductor multiple-output converters operating in continuous conduction mode

In this paper, continuous conduction mode (CCM) operation of a class of single inductor multiple output dc-dc converters is proposed. The power stage combines boost and buck-boost structures loading non-inverted and inverted outputs. The control strategy is based on current mode control under an interleaving scheme, in which each output is controlled by a specific channel. These channels use different dynamic references, which are obtained from a set of proportional-integral (PI) controllers associated to the voltage outputs. The dynamical behaviour of this system is described by means of a large signal averaged model and direct simulations of the switched circuit-based model. Small signal stability analysis of the slow scale dynamics is also carried out by using the averaged model. Finally, some experimental results are provided to validate the theoretical predictions and the numerical simulations.

On-Chip Single-Inductor Multiple-Output Power Converter Design with Adaptive Cross Regulation and Supply Variation Control for Power-Efficient VLSI Systems

Dynamic voltage and frequency scaling (DVFS) algorithms are widely used power management techniques which enable the optimization of system-level power dissipation, energy consumption and operation performance. One cost-effective hardware-enabling platform to implement the DVFS is through single-inductor multiple-output (SIMO) DC-DC converters. However, the major drawback with such converters is cross regulation, which leads to undesired supply voltage variations. These variations have significant impact on modern VLSI applications, from the circuit to the system level. Based on these challenges, this paper presents a cross-layered design of two SIMO DC-DC converters with an adaptive freewheel switching technique. The proposed converters are able to minimize cross regulation by adaptively adjusting the freewheel switching durations and currents. This also increases the efficiency of the SIMO converters, by reducing the conduction losses due to the lossy freewheel switch. To verify the cross regulation performance of the SIMO converters, its influence on clock frequencies generated by a ring oscillator is investigated. By simulating various load transient conditions, it is shown that the SIMO converters are able to significantly minimize frequency variations. The operation of the converters is verified through transistor-based HSPICE simulation results, with a 130-nm CMOS process. The SIMO converter with the digital-based adaptive freewheel switching controller achieves a maximum efficiency of 93.2%, while the analog counterpart achieves a maximum efficiency of 93.4%. For a load change from 200 mA to 40 mA, the proposed technique reduces the conduction losses during the freewheel switching duration by 99.96%, compared with traditional methods.

A modified non-dissipative LC snubber circuit for MOSFET based fly-back converters

High frequency converters with different switching topologies are now being widely used over a wide range of applications, which mainly includes different types of power supplies. Snubber circuit design for high frequency-switched converters using MOSFET as a power device assumes different dimension as regards the minimisation of the power dissipation in the snubber resistance. This paper shows a different mode of operation to reduce the clamp voltage across the device used in fly-back type converter. The LC snubber circuit is almost lossless and of energy regenerative type. A reduced clamp voltage is required not only for device protection, but also to reduce the cross regulation effect in multiple output converters. Simulations and experimental results validate the concept.

Enabling Power-Efficient DVFS Operations on Silicon

With the perpetual power increase in modern VLSI systems, efficient and effective power management has been critical to next-generation IC designs. To overcome this grand challenge, techniques, such as dynamic voltage/frequency scaling (DVFS), have been proposed to jointly optimize power, energy and operating performance, leading to significantly improved system reliability, efficiency and battery lifetime. From both system-level and circuit-level perspectives, this paper investigates key design issues, control schemes, circuit architectures and future research directions, involved in the development of application-aware, multiple- and variable-output DC-DC power converters. The article first discusses key multiple-output converters such as the single-inductor multiple-output (SIMO) DC-DC converters and their system-level integration for DVFS power management, followed by our investigation on various adaptive-output power converter topologies and corresponding design challenges. The paper also addresses the importance of hardware-software co-design for future power management systems. With the integration of the enabling hardware platform, power processing, in addition to the traditional signal processing, rises to become another key factor to next-generation VLSI designs. This naturally enables effective on-chip power tracking, power processing and thermal monitoring. More importantly, it would significantly change traditional design concepts and largely benefit signal processing in return, eventually leading to revolutionary changes on system reliability, performance, efficiency and operating lifetime.

A Power Management Unit With Integrated Stand-bySupply for Computer Motherboards:Control and VLSI Design

This paper focuses on the control strategy of a multiple-output active-clamp forward converter devoted to PC power supplies. The primary- and secondary-side switches of the forward converter are driven by dedicated ASIC units. In detail, regulation of the main-switch duty-cycle is achieved by a primary IC implementing feed-forward control, while the outputs of the converter are locally regulated by two ASICs independently from the primary-switch duty-cycle. Since no communication is required during normal mode, the duty -cycle is definied by the the primary IC which controls the main switch in such a way that the primary duty-cycle is larger than the secondary one. A peak overall efficiency higher than 90% at 50% load has been obtained in normal operative conditions. During stand-by mode, communication between the primary controller and the secondary ones is however required to increase the low-power-mode efficiency. The working principle of the proposed converter is described in detail both in normal and stand-by mode. Several experimental results are carried out to validate the approach discussed throughout this paper.

Single-switch dual output flyback DC/DC converter with time multiplexing control

Controlling two outputs with a single controlling switch in the power converter presents difficulties when two contrasting actions are required to raise one output and decrease the other. This paper studies the application of time multiplexing control (TMC) technique on power converters, with particular interest on single-switch multiple-output converters. Each output has its own feedback control circuit but these discrete feedback control loops are intermittently switched to regulate the duration of the 'on period' and 'off period' of the power switches. The inclusion of multiplexing logic to incorporate multiple controllers will improve the regulation of the auxiliary outputs and the main output within the tolerances required for electronic equipment. The output errors can be distributed between the outputs according to the time sharing factor of the time multiplexing logic controller. Simulation and experimental results on a single-switch dual-output flyback converter with and without TMC are reported to verify the error sharing capability of the proposed method. This control approach suggests a possible solution in improving the overall performance of the power supply in terms of output voltage regulation.

42-V/3-V Watkins-Johnson converter for automotive use

In this paper, the Watkins-Johnson (WJ) converter was found to best step down the future automotive 42-V power network to 3 V or lower for the supply of microcontrollers and semiconductors. The particularity of the WJ converter is that it only employs a tapped-inductor and three other components. The use of a tapped-inductor is well-known and gives an extra-degree of freedom by the insertion of the winding ratio of the tapped-inductor into the transfer function of the WJ converter. It also permits the duty cycle to be adjusted to a value at which the efficiency of the converter is improved. The converter can be slightly modified and used as a multiple output converter while employing few components, diminishing the weight, size, cost, and complexity of a system. Practical test results for the single-output WJ converter are presented.

Small-Signal Modeling of a Controlled Transformer Parallel Regulator as a Multiple Output Converter High Efficient Post-Regulator

This paper presents a post-regulator based on the use of a controlled transformer, which adds or subtracts an additional voltage to the output filter of a converter in order to regulate its output voltage. So, their actuation is complementary to that of more known post-regulators, such as the magnetic amplifier (magamp) and synchronous switch post-regulator (SSPR), because the regulation is achieved by controlling the voltage across the filter inductor instead of its charge time. Besides, the post-regulator processes the power in parallel to the one flowing from input to output and only handles a percentage of it. The post-regulation by controlled transformer is suitable of being employed in any isolated PWM power converter and combines a good efficiency and the easiness of design of classical switched power supplies. The work describes the post-regulation strategy for obtaining two outputs independently regulated, and presents a model to obtain the control transfer function and the cross-impedance expressions.

A pseudo-CCM/DCM SIMO switching converter with freewheel switching

This paper presents a single-inductor multiple-output (SIMO) converter operating in pseudo-continuous conduction mode (PCCM) and/or discontinuous conduction mode (DCM). With the proposed freewheel switching control, this converter can handle large load currents with a much smaller current ripple, while retaining low cross regulation. It can also work in DCM for high efficiency at light loads. A prototype of a single-inductor dual-output (SIDO) boost converter was fabricated with a standard 0.5-/spl mu/m CMOS n-well process. The two outputs are regulated at 2.5 and 3.0 V, respectively. At an oscillator frequency of 1 MHz, the efficiency reaches 89.4% at a total output power of 320 mW. Compared with prior designs, both current and voltage ripples are reduced. This design can be extended to have multiple outputs and for different types of dc-dc conversions, or be applied to single-output converters for fast transient response.

Modeling of cross-regulation in converters containing coupled inductors

A general model of the multiple-winding coupled inductor is described, in which all parameters can be directly measured. The magnetics and the resulting cross-regulation models are employed in a tutorial explanation of the mechanisms by which leakage inductances and effective turns ratios affect cross regulation and discontinuous conduction mode boundaries in a multiple-output converter with arbitrary number of outputs. Analytical results are found for the discontinuous mode boundaries and for the steady-state characteristics when one of the outputs operates in discontinuous conduction mode. Three basic approaches to coupled-inductor design are compared: near-ideal coupling, practical moderate coupling, and the zero-ripple approach. It is shown that the best cross regulation can be obtained via the zero-ripple approach with relatively loose coupling in applications where there is at least one output whose load current variations are relatively small so that all windings can always operate in continuous conduction mode. The conclusions are supported by experimental results.

Small-signal analysis of a synchronous-switch post regulator with coupled inductors

A small-signal model of the synchronous-switch post regulator with coupled inductors is developed. Performance variations of the synchronous switch post regulator due to different coupling coefficients are investigated. Comparison of the multiple-output converter using the technique of post regulation with the multiple-output converter using the scheme of weighted-mode control is also discussed. Experiments are given to verify the validity of the proposed small-signal model.

Current-mode control for multiple-output converters

A small-signal model for multiple-output forward converter with current-mode control is derived. The model can accurately predict the small-signal characteristics for current-mode control. It is observed that the power stage pole-zero relative positions, which are critical to the compensator design, are not affected by introducing current-mode control.

A new multiple-output hybrid power supply

A novel hybrid power supply to perform the precise regulation of multiple-output voltages is presented. It is composed of an improved forward-type multiple-output converter as a preregulator and continuous series regulators using MOSFETs as voltage droppers. The steady-state and the dynamic cross-regulation characteristics are analyzed and compared both theoretically and experimentally for the conventional and improved forward-type multiple-output converters. As a result, it is clearly demonstrated that the improved forward-type multiple-output is superior to its conventional counterpart in terms of steady-state and dynamic cross-regulation characteristics, and that the proposed multiple-output power supply has sufficiently precise multiple-output voltage regulation and a satisfactorily high power efficiency. >

Improvement of the dynamic characteristics in multiple-output dc-dc converter by using the magnetic coupling of the energy-storage reactor

The dynamic cross regulation characteristics of the improved forward-type multiple-output converter is examined and compared with that of the conventional one. In the conventional forward-type multiple-output converter, the regulation performance of the cross regulated output voltages is deteriorated by the dynamic change of the load even when the proportional gain of the feedback controller is sufficiently large. On the other hand, in the improved converter, the dynamic cross regulation performance is ameliorated along with the increase in the proportional gain. Further, it can be improved more satisfactorily by using the appropriate P-D control. In this case, the magnetic coupling of the energy-storage reactor plays a key role in the dynamic cross regulation. That mechanism is clarified theoretically through the equivalent circuit models.

Comparison of Multiple-Output DC-DC Converters Using Cross Regulation

A new multiple-output dc-dc converter is analyzed, in which the cross regulation is performed by the energy-storage reactor as well as the transformer. The steady-state and the dynamic characteristics of this converter are compared both theoretically and experimentally with those of the conventional one composed of the step-up-down type circuit. As the results of comparative analysis, it is revealed that this new converter is superior to the conventional one in the steady-state and the dynamic performances. Further, it is demonstrated experimentally that the cross regulation performance of this new multiple-output converter is less affected by the leakage flux in the energy-storage reactor, and also that this converter is very useful as a preregulator for the continuous series regulator in cases requiring a high degree of regulation of the multiple-output voltages.

Dynamic characteristics of the improved forward‐type multiple‐output dc‐dc power converter using cross regulation

AbstractThe conventional forward‐type multiple‐output dc‐dc converter has a deficiency in that when the output load current drops below a certain value, and the reactor current becomes discontinuous, or when the load changes dynamically, the cross‐regulation function is lost.The authors previously proposed a means to improve the steady‐state characteristics via a forward‐type multiple output converter in which magnetic couplings of windings in the transformer and reactor are utilized.In this paper, the improved forward‐type multiple‐output converter was studied including analysis of its dynamic characteristics. First, the steady‐state characteristic was analyzed. Second, the dynamic characteristic was disclosed in which it was shown that, due to the magnetic coupling between reactor windings and P‐D feedback control, a dynamic cross‐regulation function was obtained and even when the smoothing capacitors are relatively small, the variations of output voltages on load change are well suppressed. Further, comparisons were made with the conventional forward‐type multiple‐output converter and the superiority of the improved circuit was clearly shown.