Switching circuit with low conducted electromagnetic interference characteristics

• US 4,701,645 A
• Filed: 01/24/1985
• Issued: 10/20/1987
• Est. Priority Date: 01/24/1985
• Status: Expired due to Fees

• Current Assignee: Cox USA
• Original Assignee: Cox USA
• Inventors: Ferguson, Thomas F. W.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Phan, Trong Quang
• Application Number:
  US06/694,626
• Time in Patent Office: 999 Days
• Field of Search: 307/252 B, 307/252 M, 307/570, 307/571, 307/575, 307/252 A, 307/252 R, 307/577, 307/252 UA, 307/252 N, 307/253, 307/254, 307/252 Q, 307/252 T , 307/584, 307/304
• US Class Current: 327/451
• CPC Class Codes: H03K 17/133 in field-effect transistor switches
• CPC Class Codes: H03K 17/16 Modifications for eliminating interference voltages or currents
• CPC Class Codes: H03K 5/1536 Zero-crossing detectors in measuring circuits G01R19/175

Abstract

A pass network includes a switching element having a non-smooth conduction characteristic in the transition region about zero-crossover of an AC signal to be switched. A bypass network is connected in parallel with the pass network and has a smooth conduction characteristic in that transition region.

Claims

1. An AC switching circuit with low conducted electromagnetic interference characteristics, comprising:

a pass network including a switching element having a non-smooth conduction characteristic in a transition region about zero-crossover; and

a bypass network connected in parallel with the pass network and having in said transition region a smooth conduction characteristic, the bypass network comprising a FET.

2. The circuit of claim 1, wherein the FET is of a type which includes a body diode between its source and drain.

3. The circuit of claim 1, wherein the pass network comprises an SCR.

4. The circuit of claim 3, wherein the SCR is connected in inverse parallel with a diode.

5. The circuit of claim 1, wherein the pass network comprises a TRIAC and the bypass network comprises two FET'"'"'s connected back-to-back in series.

6. A half-wave switching circuit with low conducted electromagnetic interference characteristics, comprising:

an SCR;

a power diode connected in inverse parallel with the SCR; and

an FET connected in parallel with the SCR and power diode in a manner that a body diode in the FET is connected in inverse parallel with the SCR.

7. A full-wave switching circuit with low conducted electromagnetic interference characteristics, comprising:

a TRIAC; and

two FET'"'"'s connected back-to-back in parallel with the TRIAC.