US 5,963,438 A · Bi-directional magnetic isolator

Abstract

A bi-directional, magnetic isolator which can pass an isolated housekeeping supply voltage from an input side to an output side and can also transfer an isolated error signal from the output side to the input side of the isolator. The dual functions of the magnetic isolator allow a power supply to operate properly during either a no-load or output short circuit condition. The magnetic isolator comprises a pair of pulse transformers each having a primary and a secondary winding. The housekeeping supply voltage is transferred through one of the pulse transformers by pulsing the supply voltage from the primary winding to a secondary winding, rectifying the pulsating voltage and storing the rectified voltage on an output capacitor. The error signal is transferred in an opposite direction through the second pulse transformer using the same technique, i.e., the error signal is chopped to create a pulsating signal that can be transferred from a primary winding to a secondary winding of the second pulse transformer where it is rectified and stored on an output capacitor as a voltage representative of the error signal. A fixed on-time clock is used to pulse both the supply voltage and the error signal.

Claims15

Dependent claims

A bi-directional, magnetic, electrical isolator for use in a feedback control circuit for an electrical power supply;

a first transformer having a primary winding and a secondary winding, said secondary winding being connected to a rectifier and capacitor circuit for developing a DC voltage on the capacitor, said primary winding being coupled via a controllable switching means to a DC voltage source whereby voltage can be developed on the capacitor by periodically gating the switching means into conduction;
a second transformer having a primary winding and a secondary winding, said primary winding of said second transformer having one terminal coupled to receive a feedback signal referenced to a circuit ground plane for transfer to said secondary winding of said second transformer and having a second terminal coupled through a second controllable electronic switching means to said circuit ground plane whereby said feedback signal is transferred to said secondary winding of said second transformer upon energization of said second controllable switching means;
and
means coupling voltage on said secondary winding of said first transformer to said second controllable switching means for effecting conduction of said second switching means generally concurrently with conduction of said first switching means.

1 more element

A method for magnetically isolating an input circuit from an output circuit in a switching mode power supply, the power supply including a magnetically isolated power stage and a magnetically isolated feedback stage, an error circuit for supplying an error signal representative of a difference between an actual output of the power stage and a desired output, switch means for selectively coupling the error signal to the feedback stage and a controller responsive to the error signal for controlling operation of the power stage, the feedback stage including transformer means for coupling a voltage from the input circuit to the output circuit and for coupling the error signal from the output circuit to the input circuit, the method comprising the steps of:

applying a voltage pulse of predetermined time duration to the transformer means at the input circuit for developing a bias voltage at the output circuit;
and
coupling the bias voltage to the switch means for enabling transfer of the error signal through the transformer means during at least the time duration of the voltage pulse.

Dependencies are inferred from the claim text.

Bi-directional magnetic isolator

Life of this patent

Bi-directional magnetic isolator

Life of this patent

Abstract

Claims15