Protective impedance for a mains voltage supplied electronic circuit

• US 6,084,757 A
• Filed: 10/23/1998
• Issued: 07/04/2000
• Est. Priority Date: 10/25/1997
• Status: Expired due to Fees

• Current Assignee: Danfoss A/S
• Original Assignee: Danfoss A/S
• Inventors: Fogh, Hans Erik, Sch.o slashed.nwandt, Axel
• Primary Examiner(s): Jackson, Stephen W.
• Application Number:
  US09/178,014
• Time in Patent Office: 620 Days
• Field of Search: 361/58, 361/18, 361/115, 361/118, 361/113
• US Class Current: 361/58
• CPC Class Codes: H01C 7/003 Thick film resistors
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16
• CPC Class Codes: H02H 9/008 Intrinsically safe circuits

Abstract

A protective impedance for a mains voltage supplied electronic circuit has ohmic resistors which are applied to a substrate as film. At least two resistors form a series connection. At least two series connections are connected in parallel. This permits relatively large operating currents with relatively short series connections.

Claims

1. Protective impedance for a mains voltage supplied electronic circuit with ohmic resistors applied as film on a substrate, comprising at least two resistors forming a series connection, and including at least two of said series connections, each having at least two resistors, and said series connections being connected in parallel.

2. Protective impedance according to claim 1, in which all individual resistors have approximately the same value, and their number is the same in all parallel connections.

3. Protective impedance according to claim 1, including two series connections for every three resistors.

4. Protective impedance according to claim 1, in which a said series connection comprises a straight film strip applied on a substrate, the film strip having in the middle of its length at least one electrically well conducting covering.

5. Protective impedance according to claim 4, in which, for the formation of the parallel connection, at least two film strips with coverings are located on a substrate next to each other and have common connection electrodes at opposite ends.

6. Protective impedance according to claim 5, in which a distance between neighbouring film strips is from 0.2 to 0.5 mm.

7. Protective impedance according to claim 1, in which the resistors are formed so that the voltage drop during normal operation is <

50 V (rms).

8. Protective impedance according to claim 1, in which the series connections connected in parallel are covered by an isolating layer.