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WO1995001668A1 - Method and apparatus for protecting an electric circuit - Google Patents

Method and apparatus for protecting an electric circuit Download PDF

Info

Publication number
WO1995001668A1
WO1995001668A1 PCT/FI1994/000299 FI9400299W WO9501668A1 WO 1995001668 A1 WO1995001668 A1 WO 1995001668A1 FI 9400299 W FI9400299 W FI 9400299W WO 9501668 A1 WO9501668 A1 WO 9501668A1
Authority
WO
WIPO (PCT)
Prior art keywords
voltage
interference
cutter
transistor
cutting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/FI1994/000299
Other languages
French (fr)
Inventor
Jarmo Loukusa
Kauko Varanka
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nokia Oyj
Original Assignee
Nokia Telecommunications Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Telecommunications Oy filed Critical Nokia Telecommunications Oy
Priority to AU71255/94A priority Critical patent/AU7125594A/en
Publication of WO1995001668A1 publication Critical patent/WO1995001668A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
    • H02H9/043—Protection of over-voltage protection device by short-circuiting
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
    • H02H9/045—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage adapted to a particular application and not provided for elsewhere
    • H02H9/046—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage adapted to a particular application and not provided for elsewhere responsive to excess voltage appearing at terminals of integrated circuits

Definitions

  • the present invention relates to a method for protecting an electric circuit against interference voltage with a voltage cutter, and corresponding appar ⁇ atus comprising a fuse component and a voltage cutter.
  • Electric circuits such as integrated circuits, are often sensitive to variations of the operating volt ⁇ age and other interference voltages. A sudden overvolt- age can easily cause disturbances in the operation of the circuit, damage the circuit or even completely des ⁇ troy the circuit. Therefore electric circuits are often provided with overvoltage protection to prevent AC in ⁇ terference voltages and surge voltages and to secure the operation of the circuit.
  • the object of the present invention is to pro ⁇ vide a method and apparatus, which can protect an elec- trie circuit against interference voltages simply and reliably and which can also protect itself from being destroyed.
  • the method according to the invention which is characterized in that the dura- tion and level of the interference voltage is monitored, and if the interference voltage persists longer than a predetermined period, the cutting voltage is lowered, and the remaining power in the voltage cutter is de ⁇ creased in proportion to the level of the interference voltage by cutting the input of the interference voltage to the voltage cutter and the protected circuit.
  • the apparatus according to the invention is characterized in that the voltage cutter comprises means for monitor ⁇ ing the duration and level of the interference voltage and decreasing the level of the cutting voltage and re ⁇ ducing the remaining power in the voltage cutter in pro ⁇ portion to the level of the interference voltage so as to activate the fuse component when the interference voltage persists longer than a predetermined period.
  • Figure 1 shows the above described example of a prior art interference voltage protecting device
  • Figure 2 shows the circuit diagram of an inter ⁇ ference voltage protecting device according to the in ⁇ vention.
  • the interference voltage protecting device can monitor the voltage over the protecting device, and if the interference voltage persists too long, the protecting device can cut the voltage to prevent the protecting device from being destroyed.
  • a fuse component PTC2 is series connected in the voltage line at the input of the protected circuit 21.
  • a voltage cutter 20 is connected in parallel with the input.
  • the voltage cutter comprises a forward-dir- ected diode D12 connected in series between the input of the protected circuit and the ground potential, a low ohmic resistor R13 and an NPN transistor Q6 in the col ⁇ lector-emitter direction.
  • the base of the transistor Q6 is connected to the collector of a PNP transistor Q10 by way of the series connection of resistors R4 and R3, which collector is connected to the emitter of the tran ⁇ sistor Q6 and to the ground potential by way of the par ⁇ allel connection of a resistor R5 and a capacitor Cl.
  • the base of the transistor Q10 is connected directly to the collector of the transistor Q6.
  • the cathode of a reverse-directed Zener diode Zl is connected to the junction of diode D12 with resistor R13, and the anode to the junction of resistors R3 and R4.
  • the cathode of the Zener diode Zl is also connected to the emitter of the transistor Q10 through a resistor R2.
  • the capacitor Cl is charged through the transistor Q10.
  • the tran- sistor Q10 becomes conductive and starts to feed base current to the transistor Q6.
  • the transistor Q6 goes to a saturation state and the cutting voltage of the voltage cutter 20 and the remaining power in the cutter are reduced.
  • the remaining power in the fuse component PTC2 increases and the fuse component cuts the incoming interference voltage.

Landscapes

  • Emergency Protection Circuit Devices (AREA)

Abstract

The present invention relates to a method for protecting an electric circuit against interference voltages with a voltage cutter (20), and corresponding apparatus. For protecting the voltage cutter from being destroyed, the apparatus comprises means (C1, Q10) for monitoring the duration of the interference voltage and decreasing the level of the cutting voltage so as to activate a fuse component (PTC2) when the interference voltage persists longer than a predetermined period.

Description

Method and apparatus for protecting an electric circuit
The present invention relates to a method for protecting an electric circuit against interference voltage with a voltage cutter, and corresponding appar¬ atus comprising a fuse component and a voltage cutter. Electric circuits, such as integrated circuits, are often sensitive to variations of the operating volt¬ age and other interference voltages. A sudden overvolt- age can easily cause disturbances in the operation of the circuit, damage the circuit or even completely des¬ troy the circuit. Therefore electric circuits are often provided with overvoltage protection to prevent AC in¬ terference voltages and surge voltages and to secure the operation of the circuit.
In the prior art solution, overvoltage protec¬ tion is achieved by using a fuse component, such as a PTC resistor, and a voltage cutter. The voltage cutter must withstand high, long-lasting interference voltages. A voltage cutter has earlier been constructed for ex¬ ample by means of series connection of heavy-duty Zener diodes. The prior art solution is illustrated by an ex¬ emplary circuit diagram, which is shown in Figure 1. The figure shows a protected circuit 11, a fuse component PTC1 and a voltage cutter 10, which has a forward-dir¬ ected diode D01 connected in series, and four Zener diodes Z02, Z03, Z04, Z05 in reverse direction. With a solution like this there is the problem that when the interference voltage has persisted longer than a prede- termined period, the Zener diodes are destroyed. The number of Zener diodes used in the connection to prevent this has grown unreasonably high.
The object of the present invention is to pro¬ vide a method and apparatus, which can protect an elec- trie circuit against interference voltages simply and reliably and which can also protect itself from being destroyed.
This is achieved with the method according to the invention, which is characterized in that the dura- tion and level of the interference voltage is monitored, and if the interference voltage persists longer than a predetermined period, the cutting voltage is lowered, and the remaining power in the voltage cutter is de¬ creased in proportion to the level of the interference voltage by cutting the input of the interference voltage to the voltage cutter and the protected circuit. The apparatus according to the invention is characterized in that the voltage cutter comprises means for monitor¬ ing the duration and level of the interference voltage and decreasing the level of the cutting voltage and re¬ ducing the remaining power in the voltage cutter in pro¬ portion to the level of the interference voltage so as to activate the fuse component when the interference voltage persists longer than a predetermined period. In the following the invention will be de¬ scribed in more detail with reference to examples ac¬ cording to the accompanying drawings, in which
Figure 1 shows the above described example of a prior art interference voltage protecting device, and Figure 2 shows the circuit diagram of an inter¬ ference voltage protecting device according to the in¬ vention.
According to the invention, the interference voltage protecting device can monitor the voltage over the protecting device, and if the interference voltage persists too long, the protecting device can cut the voltage to prevent the protecting device from being destroyed. In the following the operation according to the invention will be illustrated by means of an appar- atus according to the invention shown in Figure 2. A fuse component PTC2 is series connected in the voltage line at the input of the protected circuit 21. A voltage cutter 20 is connected in parallel with the input. The voltage cutter comprises a forward-dir- ected diode D12 connected in series between the input of the protected circuit and the ground potential, a low ohmic resistor R13 and an NPN transistor Q6 in the col¬ lector-emitter direction. The base of the transistor Q6 is connected to the collector of a PNP transistor Q10 by way of the series connection of resistors R4 and R3, which collector is connected to the emitter of the tran¬ sistor Q6 and to the ground potential by way of the par¬ allel connection of a resistor R5 and a capacitor Cl. The base of the transistor Q10 is connected directly to the collector of the transistor Q6. The cathode of a reverse-directed Zener diode Zl is connected to the junction of diode D12 with resistor R13, and the anode to the junction of resistors R3 and R4. The cathode of the Zener diode Zl is also connected to the emitter of the transistor Q10 through a resistor R2.
When an interference voltage occurs in the input of the protected circuit 21, the voltage cutter
20 limits the voltage applied to the electric circuit
21 to a value determined by the Zener voltage of the Zener diode Zl and the base-emitter voltage of the tran¬ sistor Q6. If the interference voltage continues, the capacitor Cl is charged through the transistor Q10. When the voltage of the capacitor Cl exceeds the value of the base-emitter voltage of the transistor Q6, the tran- sistor Q10 becomes conductive and starts to feed base current to the transistor Q6. As a result of this, the transistor Q6 goes to a saturation state and the cutting voltage of the voltage cutter 20 and the remaining power in the cutter are reduced. Thus the remaining power in the fuse component PTC2 increases and the fuse component cuts the incoming interference voltage. In this way the voltage cutter 20 and the Zener diode Zl therein are not destroyed even if the overload persists for an extended period. In a conventional voltage protecting device this would not be possible. The solution according to the in¬ vention can be used in all electronic devices in which protection against interference voltages is needed.
In the above the invention has been described by means of an example according to the accompanying drawing, but it is to be understood that the invention is not limited to that embodiment only, but it can be varied in many ways without departing from the scope defined by the attached claims.

Claims

Claims
1. A method for protecting an electric circuit against interference voltages with a voltage cutter, c h a r a c t e r i z e d in that the duration and level of the interference voltage is monitored, and if the interference voltage persists longer than a prede¬ termined period, the cutting voltage is lowered, and the remaining power in the voltage cutter is decreased in proportion to the level of the interference voltage by cutting the input of the interference voltage to the voltage cutter and the protected circuit.
2. Apparatus for protecting an electric circuit against interference voltage, which apparatus comprises a fuse component (PTC2) and a voltage cutter (20), c h a r a c t e r i z e d in that the voltage cutter (20) comprises means (Cl, Q10) for monitoring the dura¬ tion and level of the interference voltage and decreas¬ ing the level of the cutting voltage and reducing the remaining power in the voltage cutter (20) in proportion to the level of the interference voltage so as to activ¬ ate the fuse component (PTC2) when the interference voltage persists longer than a predetermined period.
3. Apparatus according to Claim 2, c h a r - a c t e r i z e d in that the cutting circuit of the voltage cutter comprises the series connection of a forward-directed diode (D12), a low ohmic resistor (R13), a transistor (Q6) in the collector-emitter direc¬ tion, and a Zener diode (Zl) connected in reverse direc- tion between the base of the transistor (Q6) and the diode (D12).
4. Apparatus according to Claim 3, c h a r ¬ a c t e r i z e d in that the cutting voltage at the start of the interference voltage burst is the sum of the Zener voltage of the Zener diode (Zl) and the base- emitter voltage of the transistor (Q6).
5. Apparatus according to Claim 2, c h a r ¬ a c t e r i z e d in that the means for monitoring the duration of the interference voltage and for decreasing the level of the cutting voltage comprise a transistor (Q10) in the collector-emitter direction connected be¬ tween a diode (D12) and the base of a transistor (Q6) and a capacitor (Cl ) connected between the base of the transistor (Q6) and the ground plane.
6. Apparatus according to Claim 5, c h a r ¬ a c t e r i z e d in that the cutting voltage remains constant for the time it takes for the capacitor (Cl) to be charged to the same voltage as the base-emitter voltage of the transistor (Q6) .
7. Apparatus according to Claim 2, c h a r ¬ a c t e r i z e d in that the fuse component is con¬ nected in series with the input of the protected cir¬ cuit.
8. Apparatus according to any one of the pre¬ ceding claims, c h a r a c t e r i z e d in that the fuse component is a PTC resistor.
PCT/FI1994/000299 1993-07-02 1994-06-29 Method and apparatus for protecting an electric circuit Ceased WO1995001668A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU71255/94A AU7125594A (en) 1993-07-02 1994-06-29 Method and apparatus for protecting an electric circuit

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI933069A FI933069A7 (en) 1993-07-02 1993-07-02 Method and apparatus for protecting an electrical circuit
FI933069 1993-07-02

Publications (1)

Publication Number Publication Date
WO1995001668A1 true WO1995001668A1 (en) 1995-01-12

Family

ID=8538268

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI1994/000299 Ceased WO1995001668A1 (en) 1993-07-02 1994-06-29 Method and apparatus for protecting an electric circuit

Country Status (3)

Country Link
AU (1) AU7125594A (en)
FI (1) FI933069A7 (en)
WO (1) WO1995001668A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004063708A1 (en) * 2004-12-28 2006-07-13 Endress + Hauser Flowtec Ag Voltage limiting circuit for feeding a safety circuit has voltage monitor and transistor short circuit arrangement
US7231037B2 (en) 2002-03-20 2007-06-12 Sennheiser Communications A/S Active audio compressing in telecommunication

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3539865A (en) * 1968-11-12 1970-11-10 Roband Electronics Ltd Crowbar protection device
US3594612A (en) * 1970-02-24 1971-07-20 Forbro Design Corp Overvoltage protector for the load of fast-slewing regulated power supplies
US3686511A (en) * 1971-04-16 1972-08-22 Stanton Magnetics Speaker protective circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3539865A (en) * 1968-11-12 1970-11-10 Roband Electronics Ltd Crowbar protection device
US3594612A (en) * 1970-02-24 1971-07-20 Forbro Design Corp Overvoltage protector for the load of fast-slewing regulated power supplies
US3686511A (en) * 1971-04-16 1972-08-22 Stanton Magnetics Speaker protective circuit

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7231037B2 (en) 2002-03-20 2007-06-12 Sennheiser Communications A/S Active audio compressing in telecommunication
EP1931171A3 (en) * 2002-03-20 2008-10-22 Sennheiser Communications A/S Active audio compressing in telecommunication
USRE42093E1 (en) * 2002-03-20 2011-02-01 Sennheiser Communications A/S Active audio compressing in telecommunication
DE102004063708A1 (en) * 2004-12-28 2006-07-13 Endress + Hauser Flowtec Ag Voltage limiting circuit for feeding a safety circuit has voltage monitor and transistor short circuit arrangement
DE102004063708B4 (en) * 2004-12-28 2010-12-16 Endress + Hauser Flowtec Ag Circuit for voltage limiting

Also Published As

Publication number Publication date
AU7125594A (en) 1995-01-24
FI933069L (en) 1995-01-03
FI933069A7 (en) 1995-01-03
FI933069A0 (en) 1993-07-02

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