Magamp Post Regulators Research Articles

High Cross-Regulation Multioutput $LLC$ Series Resonant Converter With Magamp Postregulator

A magnetic amplifier (Magamp) postregulator using a time-sharing control strategy is proposed when using a multioutput LLC series resonant converter. The operating principles of the proposed converter and the Magamp postregulator are analyzed in detail. Furthermore, the design criterion for the Magamp core is presented, and the dead-time problem of the Magamp postregulator is analyzed. Compared with a flyback converter, the dead-time impact in the LLC structure is much better for two main reasons. The first one is that there is no reverse-recovery resetting effect for the Magamp postregulator in an LLC topology, and the second is that, when the same dead time is applied in both converters, the effect is better by using an LLC topology than a flyback topology. Finally, an experimental prototype of 310-V input and 24-V/3-A and 18-V/2-A outputs was built and tested to verify the zero-voltage-switching (zero-current-switching) operation and the high cross-regulating ratio. The experimental results prove that the dead-time impact over a Magamp in an LLC converter is much better than that when using a flyback converter, since a high cross-regulating ratio was easily achieved without using complicate resetting methods or large dead load.

Paralleling magamp-postregulator modules with sliding-mode-control method

This paper presents the parallel application of the magnetic amplifier (magamp) postregulators with a sliding-mode control. The system can be robust and with fast dynamic response based on the sliding-mode control. The controller can be designed in the time domain directly, which makes the design strategy easier and realizable. When the load increases, the parallel operation is adequate to be adopted. With the sliding-mode control and proper current distribution, the output currents of the parallel modules can be same when the capacity of the individual module is equal. Even if the capacities of the modules are different, the module with more capacity can also provide more output current and work well. Therefore, the purposes of controlling the output current distribution and achieving the stability of output voltage based on this kind of control strategy are achieved. Simulations and experimental results show that the parallel modules of magamp postregulators with the sliding-mode control can obtain the well dynamic behavior and proper current distribution.

Analysis and design of sliding mode control applied to magamp post regulators

This paper presents the application of sliding mode control to a magnetic amplifier (magamp) post regulator. The system can be robust and with fast dynamic response based on the sliding mode control. The related design criteria and considerations are explained in this paper. Simulation and experimental results show that the magamp post regulator with sliding mode control can obtain a good dynamic behavior. Copyright © 2005 John Wiley & Sons, Ltd.

Small-signal modeling of magnetic amplifier post regulators with current-mode control

The continuous-mode and the discontinuous-mode small-signal dynamic models of the magamp post regulator using the external-reset and the self-reset methods with current-mode control are presented in this paper. Based on the developed models, the dynamic performance of the magamp post regulator can be expressed in terms of circuit parameters. A procedure for designing the feedback compensation is given and experiments were conducted to verify the models.

Analysis and implementation of a series-parallel resonant converter with magamp postregulators

A half-bridge series-parallel resonant converter (SPRC) with and without post-regulators is investigated in discontinuous conduction mode operation, A comprehensive analysis of the SPRC is presented. The SPRC is superior to the pure series and parallel converters, having the desirable characteristics of each, without the disadvantages. The SPRC with a magnetic amplifier (magamp)which blocks the rising edge of the secondary voltage, is analysed. Modified topological modes and steady-state analysis are proposed. Experimental results show that the SPRC with postregulators has good cross-regulation. A 100 kHz SPRC with and without magamp postregulators is designed and tested.

Techniques for reduction of required headroom in high-frequency magamp postregulators

High headroom in a magamp postregulator increases circuit losses, including power transistor losses, saturable reactor core loss, and freewheeling diode snubber loss. Higher headroom also requires the use of higher voltage diodes. The authors describe common causes for large headroom requirement and discuss various techniques to reduce it.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magamp postregulators for symmetrical topologies with emphasis on half-bridge configuration

The authors point out the major differences between symmetrical topology magamps and the forward converter magamp. In a forward converter, a small portion of the magnetizing current of the power transformer is diverted to the secondary for reset of the magamp's saturable reactor. In symmetrical topologies, the transformer's magnetizing current is not used for reset of the saturable reactor(s). The magnetizing current shifts to the secondary where it causes a series of problems. The authors examine these problems, identify solutions, and explain why a half-bridge magamp supply is inherently less versatile than is the forward converter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of control loop behavior of magamp post regulators

Small signal-control models are presented for a magnetic amplifier switching-mode post regulator for SMPS applications. Two commonly used current reset schemes are considered; an external reset scheme and a self-reset scheme. It is mathematically shown that the open-loop gain is a two-pole, single-zero transfer function for continuous-mode operation and is a single pole transfer function for discontinuous mode operation. The equations for predicting the open-loop gains for both types of reset circuits are derived and verified experimentally. It is shown that the open-loop gain characteristics of a magnetic-amplifier regulator depends on power circuit parameters, the reset-circuit parameters, and the saturable reactor parameters. Models for both continuous mode and discontinuous modes of operation that provide designers with useful tools for designing a compensation network for the feedback error amplifier are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A simple model predicts small-signal control loop behavior of magamp post-regulator

A block diagram approach is used to provide an insight into magamp feedback control operation. The analysis reveals a pole-shifting phenomenon inherent in the type-A loop transfer function. A procedure for calculating the gain and open-loop poles in the control loop of each reset circuit is given. The procedure also shows how to compensate the error amplifier for stable operation. The detailed example of a 50 kHz magamp is given; however, the validity of the model has been demonstrated experimentally at 100 kHz. With a factor of two included in the Faraday's law block, the model describes loop behavior for a magamp with two saturable reactors for symmetrical topology. >