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AC-DC Forward Power Supplies

AC-DC forward power supplies with a relatively simple circuit configuration are widely used for power supply applications with a wattage of a few hundred watts. AC-DC forward power supplies exhibit a higher transformer efficiency than flyback power supplies. Therefore, AC-DC forward power supplies are used for applications with a wattage of up to 500 W. Toshiba offers a wide range of MOSFETs with a VDSS of 600 V to 800 V ideal for AC-DC forward power supply applications.

Block Diagram

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フォワード型AC-DC電源の回路例

Blocking Diode PFC MOSFET PFC Controller ICs Main Switch MOSFET Photocoupler Gate Driver Rectification MOSFET

Documents

Whitepaper

Whitepaper
Name Outline Date of issue
Describes the features of the DTMOSV series and the improvements from the previous series 9/2017

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  • DTMOS Applications (Noise Reduction)
Describes the mechanism of noise generation and noise reduction techniques 9/2017 coming soon

Application Note

Application note
Name outline Date of issue
Describes planar, trench and super-junction power MOSFETs 11/2016
Describes the absolute maximum ratings, thermal impedance and safe operating area of power MOSFETs 11/2016
Describes electrical characteristics shown in datasheets 11/2016
Describes how to select power MOSFETs, temperature characteristics, the impacts of wires and parasitic oscillation, avalanche ruggedness, snubber circuits and so on 11/2016
Describes thermal equivalent circuits, examples of channel temperature calculation and considerations for heatsink attachment 2/2017
Describes the guidelines for the design of a gate driver circuit for MOSFET switching applications and presents examples of gate driver circuits 8/2017

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Describes the oscillation mechanism of MOSFETs for switching applications 8/2017

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Video

Video List
When you click on a thumbnail below, you can view the video.

"Introducing the U-MOSⅨ-H Series: Existing video"

Evaluates the performance of the U-MOSIX-H trench MOS series in an isolated DC-DC/DC converter and compares it with products from other companies

Date: 1-Sep-2017

Time: 02:16

    DTMOS
    DTMOS

"DTMOS"

Describes the features of DTMOS

  • Circuit Overview

    When the switch is closed, the energy stored in the primary winding of a transformer is transferred to the secondary winding.

    In contrast to flyback converters, the polarity of the secondary winding of a transformer in forward converters is opposite to that of the primary winding. Additionally, to build an AC-DC power supply, forward converters require an inductor (L) and a freewheel diode.


    The output voltage of a forward converter is a function of the transformer turns ratio and the transistor on/off ratio.

    Vo=(Ns/Np)[Ton/(Ton+Toff)]Vin
    where, Ns is the number of turns of the secondary winding of a transformer, Np is the number of turns of the primary winding, Ton and Toff are the "on" and "off" periods of the transistor.

    Forward-coupled converters (forward converters) are used for hundreds of watts power supply applications.


 *Click the headline to open it

  • Operation

    When Q1 is turned on, the energy stored in the primary winding of a transformer is transferred to the secondary winding.

    1. Q1 ON

    An electric current flows to Np.

    The stored energy is transferred to the secondary winding at the same time, causing a current to flow through D2 and L1 and charging C1.

    When power transistor Q1 is on, it supplies power to the output load. Therefore, the cathode voltage of the diode in a forward converter, Vor, is calculated as follows:

    Vor=[(Vdc-VDS1(ON))(Nm/Np)]-Vd2

    VDS1 is the Drain to Source voltage of Q1

    Np : the number of Primary winding

    VD2 is the Anode to Cathode voltage of D2

    Nm : the number of Secondary winding

    2. Q1 OFF

    When Q1 is turned off, the current flowing through D2 decreases, causing both the primary and secondary windings of the transformer to develop a negative voltage relative to the winding's dot end. The energy stored in the transformer is delivered through D1 as an excitation current and resets the transformer. At this time, the voltage across Nr becomes Vdc+0.7 V.
    The voltage across Np reverses, developing a voltage equal to the voltage across Nr. Consequently, the drain-source voltage of Q1 becomes 2Vdc (2Vdc+0.7V ≈2Vdc). When A1=A2, the drain voltage of Q1 (2Vdc) is maintained.

    Output Voltage

    The output voltage, Vo, is compared to the reference voltage, and its differential output signal is fed to a PWM controller via an error amplifier. The PWM pulse output, in turn, switches on and off the MOSFET (Q1). Vor is maintained at a constant voltage by this negative feedback loop. Vo is calculated as follows:

    Vo=[(Vdc-VDS1(ON))(Nm/Np)-Vd2](Ton/T)
    T : Cycle period  Ton : On-time of Q1 in one cycle



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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.