Pulse transformer circuit for isolating electrical signals

• US 5,499,176 A
• Filed: 08/12/1993
• Issued: 03/12/1996
• Est. Priority Date: 08/12/1993
• Status: Expired due to Term

• Current Assignee: Asahi Kasei Toko Power Device Corp. (Asahi Kasei Corporation)
• Original Assignee: TOKO America Incorporated (Murata Manufacturing Co Limited)
• Inventors: Erisman, Brian P.
• Primary Examiner(s): Wong, Peter S.
• Application Number:
  US08/105,390
• Time in Patent Office: 943 Days
• Field of Search: 363/21, 363/64, 363/97, 363/131, 323/902
• US Class Current: 363/21.01
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H03F 3/38 DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers switched capacitor amplifiers H03F3/005
• CPC Class Codes: Y10S 323/902 Optical coupling to semiconductor

Abstract

A signal isolator circuit employing a pulse transformer overcomes the disadvantages of both prior art opto-coupler and pulse transformer signal isolator circuits by employing an active signal retrieval circuit which, in a higher accuracy configuration, repetitively performs the following steps on the electrical side of the pulse transformer where the signal information is required: 1) drives a current pulse into the pulse transformer; 2) samples or detects the voltage across the pulse transformer after it has been stabilized; 3) holds or stores the sampled voltage for a full cycle of operation; and, if necessary, 4) filters the sampled signal. On the other electrical side of the pulse transformer, the retrieval circuitry is configured such that when the pulse transformer is being driven by the current pulse, the voltage will be clamped by the source signal reset. In a lower accuracy configuration, the signal retrieval circuit of the present invention performs the same steps set forth above with the exception that, rather than sampling the voltage across the pulse transformer, the reflected impedance is detected as being either high or low, by some quantitative measure, and the detector output will be set to either a high or low voltage corresponding to the detected impedance.

Claims

1. A process for retrieving, as a target signal, a source signal that has been conveyed across an isolation boundary, the process comprising:

providing a puse transformer having a primary side to which the source signal is applied and having a secondary side from which the target signal is retrieved;

repetitively performing, in synchronization with a clocking signal, the following steps on the secondary side of the pulse transformer;

(1) driving a current pulse into the pulse transformer;

(2) sampling the voltage across the pulse transformer after it has stabilized but while the current pulse is still active; and

(3) storing the sampled voltage for a full clock cycle; and

performing the step on the primary side of the pulse transformer of clamping the voltage across the pulse transformer by the source signal during a portion of a clock cycle when the pulse transformer is being driven by the current pulse.

2. A process as in claim 1 wherein the steps repetitively performed on the secondary side of the pulse transformer further comprise the step of:

(4) filtering the sampled voltage.

3. A process for retrieving, as a target signal, a source signal that has been conveyed across an isolation boundary, the process comprising:

providing a pulse transformer having a primary side to which the source signal is applied and having a secondary side from which the target signal is retrieved;

repetitively performing, in synchronization with a clocking signal, the following steps on the secondary side of the pulse transformer;

(1) driving a current pulse into the pulse transformer;

(2) sampling the voltage across the pulse transformer after it has stabilized but while the current pulse is still active; and

(3) detecting a reflected impedance as being high or low by quantitatively measuring the sampled voltage; and

(4) setting a detector to a high or low voltage in correspondence with the detected impedance;

performing the step on the primary side of the pulse transformer of clamping the voltage across the pulse transformer by the source signal during a portion of a clock cycle when the pulse transformer is being driven by the current pulse.

4. A circuit for conveying a source signal across an isolation boundary and for retrieving the source signal as a target signal, the circuit comprising:

a pulse transformer having a primary winding and a secondary winding;

a PNP transistor having base, emitter, and collector terminals, the emitter and collector terminals being connected across the primary winding of said pulse transformer and the base and collector terminals being connected to receive said source signal;

a clamping diode connected across the secondary winding of said pulse transformer for clamping a voltage across the secondary winding and for providing a current path to allow said pulse transformer to reset;

clock means for providing a clocking signal;

a current source connected in series with said clamping diode and further connected to receive said clocking signal; and

a sample and hold circuit having a pair of input terminals connected across said clamping diode, having a trigger input for receiving said clocking signal, and having a pair of output terminals across which said target signal is provided.