Saturable Cores for Mag-Amps
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The Mag-amp method is one of the few different output voltage regulation methods used in switching power supplies. A saturable core is used in the secondary side of the main transformer to regulate voltage by magnetic pulse width modulation (PWM). The Mag-amp method is especially effective and economically attractive in low voltage/high current circuits and is frequently used in power supplies for information processing equipment, such as desktop PCs and computer servers; in power supplies for office equipment, such as photocopy machines and printers, and in power supplies for communication equipment, such as mobile phone stations. Miniaturization, high efficiency, low noise, high reliability, and high precision can be easily realized by adopting Utilizing the unique magnetic characteristics of cobalt-based amorphous alloys, we have realized low loss at high frequencies, which cannot be realized using other materials. Our lineup consists of MS series cores, which are well suited for general purpose applications, and MT cores, which have lower loss than the MS Basic Circuit Diagram of Mag-Amp method Basic Characteristics (Typical Value) Comparison of Core Temperature Rise in a Power Supply Core Loss

Standard Specifications MT Standard Wired Series Effective Core Cross Section Mean Flux Path Length Total Flux*; "1 The amount of magnetic flux is equal to (N) x(0c ). "2 Measuring condition : 100kHz. 80A/m (sine wave). R.T. *3 Recommend for designing (note : A design of a transformer in the case may be unable to use this data. Please set up the operating magnetic flux 70% or less of the magnetic flux.) "4 Dimensions of the Finished Insulating Covers : Tolerance : ± 0.2mm *5 Reference value *6 Insulating cover is made with UL94V-0 approved material A : Black PET. B : Black PBT. C : Red LCP....

As seen above, when the Mag-amp method is used in regulating output voltage of switching power supplies, excellent characteristics can be achieved in size, efficiency, noise, reliability, and precision. Advantages in cost performance are especially realized in low voltage / high current circuits (example: 3.3V-5A). Full Mag-Amp Method The simple Mag-amp method is used mainly for voltage control of the post circuit in power supplies, called the cross-regulation (master-slave) method. This cross-regulation method stabilizes the output voltage by feedback of the main circuit to the primary...

Flyback converter (ON-OFF Type) Ringing choke converter (RCC) Push-pull converter (Center tap type) Full bridge converter Forward Converter (ON-ON Type) Characteristics (Typical Value) Magnetic flux density A B Examples of a use other than Mag-Amp : Resonancer for Switching Power Supply ( Partial Resonace Element). CT Magnetic Sensor. _Transformer Core for Self-lnvertor Oscillator. High Frequency Saturable Core for Current Delay or Timing Control

Mag-Amp Operating Prim The Mag-Amp method is a switching regulation method for D.C power supply in which the magnetic switch is created through using saturated area and unsaturated area of the saturable core. Voltage regulation at the secondary side of the switching supply is ralized by P.W.M. (Pulse Width Modulation). When the "ON" pulse is from the main transformer, the flux changes as " I" on the actual magnetization curve. At this time, the saturable core has very high inductance because the core's magnetization is in an unsaturated area. When voltage is added, it is handled at both...

The standard methodology for designing and selecting the proper size mag-amp is to first determine the product of the secondary voltage of the transformer and the "on duty" time, measured in seconds. The proper size mag-amp can then be selected by determining which mag-amp core can adequately handle the highest product of this secondary voltage and "on duty" time, otherwise known as core flux. All calculations must be made on the condition that this on-pulse product of voltage and time is at its •fc On-pulse maximum product of time The on-pulse maximum product of time A0V2 is calculated...

Here, we show a design example when regulating a 5V-10A circuit using a forward converter with an ■ftOn-pulse maximum voltage-time product The Ea on the secondary side of the main transformer and the maximum on duty cycle are assumed to When using a Mag-amp to also protect against over currents, A 0mag= A 0V2. Here, we assume that the mag-amp only regulates voltage and set the incremental increase at the time of no current load as ■ftChoice of core size The wire winding coefficient, Kf. is the coefficient that it is possible to wind on the inside of a toroidal core. Usually, Kf=0.4 is used....

Generally, the range of the flux becomes large at no, or small current load. There is a possibility that the mag-amp may not be able to control the output voltage because there is a shortage of core flux. This problem occurs because the large range of the flux density causes saturating on the other side and there is not enough ability to control the voltage-time product. In order to set the allowances for design, the wire winding for the Mag-amp is reduced and the operating range is confirmed. However, the core flux necessary at the time of no current load is largely influenced by such...