# US 4,395,647 A · Half-wave signal isolator with means for controlling flux in the coupling transformer

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- Number: US 4,395,647 A
- Document ID: US4395647A
- Status: Granted
- Kind: A
- Application number: 06/203,451
- Filed: 1980-11-03
- Granted: 1983-07-26
- Earliest claimed: 1980-11-03
- Assignees: Analog Devices, Inc.
- Inventors: William H. Morong, III
- Web page: https://patentgrep.com/patent/US4395647A

## CPC

- H01F 27/42: Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils (circuits for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output H02P13/00; impedance networks H03H)
- A61B 5/0002: {Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network (endoradiosondes A61B5/07)}
- H02M 3/33584: {Bidirectional converters}
- H03F 3/387: with semiconductor devices only
- H03K 17/601: {using transformer coupling (H03K17/61 takes precedence)}
- H03K 17/64: having inductive loads
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- H03F: AMPLIFIERS
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)

## Abstract

A signal isolator including a coupling transformer with modulate/demodulate switches in series with the primary and secondary windings. The switches are driven in synchronism by an oscillator. Resonating capacitors are connected in parallel with the transformer windings to form an LC tank circuit tuned approximately to the operating frequency of the switch-drive oscillator. When the switches are closed, the current in the transformer windings ramps in a linear fashion in response to application of the input voltage, and when the switches are opened, the current varies in a cosine curve to provide smooth transitions at both ends to the ramp current, thus controlling the flux in the transformer core so as to minimize instability effects.

## Claims

### Claim 1

In a signal isolator of the half-wave type comprising a coupling transformer having primary and secondary windings; first and second switches connected to said transformer windings, respectively, one of said switches serving to modulate a signal applied to the transformer primary and the other serving to demodulate the signal developed at the secondary of said transformer; and means for driving said switches in synchronism between closed and open states at a relatively high frequency;
that improvement in such signal isolator comprising:
resonating capacitor means coupled to said transformer during the open switch state to form therewith a resonant circuit tuned at least approximately to said frequency and providing controlled transformer current variations during the open switch state with relatively smooth transitions between the open and closed switch states.

### Claim 2 (depends on 1)

A signal isolator as in claim 1, wherein said resonating capacitor means comprises first and second capacitors connected in parallel with said primary and secondary windings respectively to form an LC tank circuit resonant at least approximately at said frequency.

### Claim 3 (depends on 1)

A signal isolator as in claim 1, including first and second reservoir capacitors coupled to said primary and seondary windings respectively to provide large-capacity signal sources for the signal to be translated.

### Claim 4 (depends on 1)

A signal isolator as in claim 1, including an input amplifier providing an intensified signal for said transformer primary winding.

### Claim 5 (depends on 1)

A signal isolator as in claim 1, including an output amplifier coupled to said secondary winding to provide a buffered output signal from said isolator.

### Claim 6 (depends on 1)

A signal isolator as in claim 1, wherein said resonant circuit is tuned to provide a switch-open state which is slightly longer than one-half cycle of said switch operating frequency.