transformer | PartQuest™ Explore

This is a circuit design for a typical wall-plug power adapter. The sinusoidal source represents a typical US 60 Hz, 120V AC wall supply. A transformer steps the voltage down to a manageable range to be rectified for a 5V DC supply, but the waveform is still sinusoidal. The 4 diode bridge rectifier takes this lower amplitude sinusoidal signal and produces a DC biased result, but still with noise resulting from the rectification process.The capacitor before the voltage regulator chip helps smooth some of this noise. Then the regulator chip provides a self-contained, feedback controlled mechanism to keep the output voltage at the specified value. The output capacitor further smooths any output ripple and provides a reservoir of charge to supply any surge in current load that may be encountered.This example includes a load resistor that allows the exploration of the effects of load. The load is varied during the simulation and it can be seen that above a load of 100 mA, the regulation of the output voltage begins to deteriorate.The addition of a few components can make it possible for such a circuit to provide significantly higher power loads. See http://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator for an example.

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Demo for Karthik

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AC-DC Transformer and Rectifier

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AC-DC Transformer and Rectifier

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Transformer Magnetizing In-rush Current

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Description

This transformer design example demonstrates a current in-rush or "peaking" effect that depends on the phase or timing of the AC supply switch closure. A rather counter-intuitive result is shown;Case 1: Set the initial_delay of the digital pulse to 4.17m seconds, which causes the switch to closed when the sinusoidal AC line input voltage is at its peak, one quarter-cycle at its 60 Hz frequency. The current into the primary winding will immediately follow its nominal steady-state no-load profile, with a peak of just under 100mA. Case 2: Set the digital pulse initial_delay to 0 seconds, so that the line voltage is applied to the transformer immediately at its rising zero-crossing. This results in a large non-sinusoidal peaking current which exceeds 500mA on its initial cycle!This is a direct result of saturation in the magnetic core. To produce the necessary "volt-seconds" in Case 2, the magnetic flux in the core must be twice that of Case 1. But if the transformer is sized such that its peak flux density is somewhat close to the the saturation level for nominal steady-state operation, then a start-up transient with the unfortunate timing of Case 2 will result in a large in-rush current.Note that the flux density "b" is displayed for the magnetic core. The core saturation flux density is specified as 1.5 Tesla, a typical value for Electrical Steel. You can also select "B vs. H from Table" to see the performance for a specific type of NGO Electrical Steel -35PN250 from the manufacturer Posco.

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ePower_030

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ePower_020

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AC-DC Power Adapter

clara.yeung
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Description

This is a circuit design for a typical wall-plug power adapter. The sinusoidal source represents a typical US 60 Hz, 120V AC wall supply. A transformer steps the voltage down to a manageable range to be rectified for a 5V DC supply, but the waveform is still sinusoidal. The 4 diode bridge rectifier takes this lower amplitude sinusoidal signal and produces a DC biased result, but still with noise resulting from the rectification process.The capacitor before the voltage regulator chip helps smooth some of this noise. Then the regulator chip provides a self-contained, feedback controlled mechanism to keep the output voltage at the specified value. The output capacitor further smooths any output ripple and provides a reservoir of charge to supply any surge in current load that may be encountered.This example includes a load resistor that allows the exploration of the effects of load. The load is varied during the simulation and it can be seen that above a load of 100 mA, the regulation of the output voltage begins to deteriorate.The addition of a few components can make it possible for such a circuit to provide significantly higher power loads. See http://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator for an example.

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AC-DC Transformer and Rectifier

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