GB1589343A - Circuits for switching of inductive loads - Google Patents

Circuits for switching of inductive loads Download PDF

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Publication number
GB1589343A
GB1589343A GB3385677A GB3385677A GB1589343A GB 1589343 A GB1589343 A GB 1589343A GB 3385677 A GB3385677 A GB 3385677A GB 3385677 A GB3385677 A GB 3385677A GB 1589343 A GB1589343 A GB 1589343A
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United Kingdom
Prior art keywords
transistor
switching
inductive load
switching transistor
free
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.)
Expired
Application number
GB3385677A
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Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
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 Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of GB1589343A publication Critical patent/GB1589343A/en
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
    • H03K17/082—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit
    • H03K17/0826—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit in bipolar transistor switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/60—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors
    • H03K17/64—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors having inductive loads

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  • Electronic Switches (AREA)
  • Relay Circuits (AREA)
  • Power Conversion In General (AREA)

Description

(54) IMPROVEMENTS IN CIRCUITS FOR SWITCHING OFF INDUCTIVE LOADS (71) We, ROBERT BOSCH GMBH. a German Company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to circuit arrangements for switching off inductive loads.
In previously proposed circuit arrangements for this purpose, a free-wheeling diode is connected in parallel with the inductive load. When the current supply to the load is interrupted by blocking a switching transistor in series with the load, the decay or free-wheeling current which continues to flow through the load discharges via the free-wheeling diode. However, this has the disadvantage that the voltage at that terminal of the inductive load, which is not connected to the supply voltage but to the switching transistor, is clamped to the potential of that pole of the supply voltage to which the other terminal of the inductive load is connected. The free-wheeling or decay current as a result flows to this pole.This is particularly disadvantageous if the supply voltage pole, to which the inductive load is connected, is not available directly but only via a relatively high ohmic connection, since the voltage of the other terminal of the inductive load should be clamped as near as possible to the working voltage, for example, in order to protect the switching transistor. Such disadvantages are present, especially with integrated circuits.
The present invention resides in a circuit arrangement for an inductive load wherein the inductive load is connected in series with the switching path of a supply current switching transistor and such series arrangement is connected between the two poles of a D.C. current source to enable the inductive load to receive current, and wherein the switching path of a free-wheeling control transistor is connected between two electrodes of the switching transistor, with the emitter of the free-wheeling control transistor connected to the junction between the switching transistor and the inductive load, and the control electrode of the free-wheeling control transistor is connected via a currentlimiting resistor to that pole of the current source to which the inductive load is connected.
By this means the terminal of the inductive load which is not connected to the supply voltage, is clamped approximately to the potential of the said working voltage pole, whilst the free-wheeling or decay current discharges to the other pole of the supply voltage. The said pole of the supply voltage to which the inductive load is connected can be coupled with an electronic circuit via a relatively high ohmic resistor.
It is of particular advantage to connect to the collector of the free-wheeling control transistor a register whose value preferably corresponds to the D.C. resistance of the inductive load. An advantage here is that the collectoremitter voltage of the free-wheeling control transistor is the same as, or is only slightly in excess of, the saturation voltage of the switching transistor up to the instant of transfer of the current from the switching transistor to the free-wheeling control transistor and that the collector-emitter voltage only increases in value as the free-wheeling current decays.
This greatly reduces the power-loss in the free-wheeling control transistor at switch-off, and in addition eases the load on its collector blocking layer. The danger of a disruptive discharge and the consequent creation of a conductive path in the blocking layer, is minimised by this means.
The invention is further described, by way of example, with reference to the accompanying drawings, in which: Fig. lisa first embodiment of circuit arrangement in which an inductive load is connected to the positive pole of a supply voltage source; and Fig. 2 is a second embodiment of circuit arrangement in which an inductive load is connected to the negative pole of a supply voltage source.
Referring to Fig. 1 of the drawings, a circuit arrangement for switching on and off an inductive load 12 comprises an integrated circuit (IC) having a preliminary stage 10 and a final stage 11. The preliminary stage 10 can be of any conventional design and will not be further des cribed. The final stage 11 comprises an npn-type switching transistor whose base is connected to the preliminary stage 10. The emitter of the final stage switching transistor 11 is earthed and its collector is connected via the inductive load 12, to the positive pole 13 of a supply voltage source. The positive pole 13 is coupled to the integrated circuit 10 11 via a current limiting resistor 14. The limiting resistor 14 is not normally included in integrated form in an IC.As all elements in an integrated circuit form a diode on the substrate, two diodes, 110 and 111, which respectively bridge the preliminary stage 10 and the finial stage 11, are shown in the drawing as part of the circuit. The inductive load 12 and current limiting resistor 14 are bridged by the emitter-base path of a likewise integratable free-wheeling control transistor 15, whose collector is earthed via a resistor 16.
When the switching transistor 11 is in its conductive state, the free-wheeling control transistor 15, in the form of a pnp-transistor, is blocked, as its emitter potential is more negative than its base potential. When the current through the load 12 is to be interrupted, the switching transistor 11 is blocked by a control signal from the preliminary stage 10, whereby the potential at the emitter of the free-wheeling control transistor 15 increases. On its exceeding the potential at the terminal 13, the freewheeling control transistor 15 becomes conductive and the decay current of the inductive load 12 flows via the switching path of the freewheeling control transistor 15 and the resistor 16 to earth.
The resistor 16 is of the same value as, or somewhat smaller than the D.C. resistance of the inductive load 12, in order to minimise the power loss in the free-wheeling control transistor 15 on switch-off and to reduce the load on its collector blocking layer.
The second embodiment illustrated in Fig. 2 is in principle of the same construction as the first embodiment, apart from the fact that the inductive load 12 and the switching transistor 11 are interchanged with respect to the polarity of the supply voltage. The switching transistor 11 now becomes a pnp-transistor with its emitter connected to the terminal 13. The current limiting resistor 14 is positioned between earth and the IC 10/11. The free-wheeling control transistor 15 now becomes an npn-transistor, its three electrodes however remaining unchanged as regards their connections to the components 12,14 and 16. The resistor 16 is now connected to the base of the switching transistor 11.Furthermore, the base of the transistor 15 is now connected to the terminal 13 via a voltage limiting device 17, which is represented by a Zener diode, although any other kind of voltage limiting device may be used. A reverse polarity protection diode 18, to protect the IC from incorrect polarity at the supply voltage source, bridges the switching junction of the switching transistor 11. The diode 18 may be dispensed with since it is effectively identical to the implicit diode 111 of Fig. 1.
The mode of operation of the second embodiment corresponds to a large extent to that of the first, in that the free-wheeling control transistor 15 becomes conductive after the switching transistor 11 has been blocked. The decay current does not however flow via the transistor 15; instead the transistor 15 renders switching transistor 11 conductive again so that the decay current discharges directly via the switching transistor 11.
An additional component in the circuit, a voltage-limiting device 17 serves as a protection against excess voltage. Should excess voltage occur, which is greater than the threshold voltage limiting device, e.g. greater than the breakdown voltage of the Zener diode 17, then the latter will become conductive, the base potential of the transistor 15 will increase, converting the latter into a conductive state. As a result the switching transistor 11 will itself in turn become conductive and the voltage between the positive terminal 13 of the supply voltage and the point of connection of the transistors 17 and 15 to the inductive load, will likewise be limited.
The components 17 and 18 can of course be inserted in similar fashion in the first embodiment.
WHAT WE CLAIM IS: 1. A circuit arrangement for an inductive load wherein the inductive load is connected in series with the switching path of a supply current switching transistor and such series arrangement is connected between the two poles of a D.C. current source to enable the inductive load to receive current, and wherein the switching path of a free-wheeling control transistor is connected between two electrodes of the switching transistor, with the emitter of the free-wheeling control transistor connected to the junction between the switching transistor connected to the junction between the switching transistor and the inductive load, and the control electrode via a current-limiting resistor to that pole of the current source to which the inductive load is connected.
2. A circuit arrangement as claimed in claim 1, in which the switching path of the freewheeling control transistor is connected in parallel with the switching path switching transistor so that the decay current flows through the free-wheeling control transistor.
3. A circuit arrangement as claimed in claim 1, in which the switching path of the freewheeling control transistor is connected between the control electrode of the switching transistor and said junction between the latter and the inductive load.
4. A circuit arrangement as claimed in any preceding claim in which a resistor is serially connected to the collector of the free-wheeling control transistor.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. cribed. The final stage 11 comprises an npn-type switching transistor whose base is connected to the preliminary stage 10. The emitter of the final stage switching transistor 11 is earthed and its collector is connected via the inductive load 12, to the positive pole 13 of a supply voltage source. The positive pole 13 is coupled to the integrated circuit 10 11 via a current limiting resistor 14. The limiting resistor 14 is not normally included in integrated form in an IC. As all elements in an integrated circuit form a diode on the substrate, two diodes, 110 and 111, which respectively bridge the preliminary stage 10 and the finial stage 11, are shown in the drawing as part of the circuit.The inductive load 12 and current limiting resistor 14 are bridged by the emitter-base path of a likewise integratable free-wheeling control transistor 15, whose collector is earthed via a resistor 16. When the switching transistor 11 is in its conductive state, the free-wheeling control transistor 15, in the form of a pnp-transistor, is blocked, as its emitter potential is more negative than its base potential. When the current through the load 12 is to be interrupted, the switching transistor 11 is blocked by a control signal from the preliminary stage 10, whereby the potential at the emitter of the free-wheeling control transistor 15 increases. On its exceeding the potential at the terminal 13, the freewheeling control transistor 15 becomes conductive and the decay current of the inductive load 12 flows via the switching path of the freewheeling control transistor 15 and the resistor 16 to earth. The resistor 16 is of the same value as, or somewhat smaller than the D.C. resistance of the inductive load 12, in order to minimise the power loss in the free-wheeling control transistor 15 on switch-off and to reduce the load on its collector blocking layer. The second embodiment illustrated in Fig. 2 is in principle of the same construction as the first embodiment, apart from the fact that the inductive load 12 and the switching transistor 11 are interchanged with respect to the polarity of the supply voltage. The switching transistor 11 now becomes a pnp-transistor with its emitter connected to the terminal 13. The current limiting resistor 14 is positioned between earth and the IC 10/11. The free-wheeling control transistor 15 now becomes an npn-transistor, its three electrodes however remaining unchanged as regards their connections to the components 12,14 and 16. The resistor 16 is now connected to the base of the switching transistor 11.Furthermore, the base of the transistor 15 is now connected to the terminal 13 via a voltage limiting device 17, which is represented by a Zener diode, although any other kind of voltage limiting device may be used. A reverse polarity protection diode 18, to protect the IC from incorrect polarity at the supply voltage source, bridges the switching junction of the switching transistor 11. The diode 18 may be dispensed with since it is effectively identical to the implicit diode 111 of Fig. 1. The mode of operation of the second embodiment corresponds to a large extent to that of the first, in that the free-wheeling control transistor 15 becomes conductive after the switching transistor 11 has been blocked. The decay current does not however flow via the transistor 15; instead the transistor 15 renders switching transistor 11 conductive again so that the decay current discharges directly via the switching transistor 11. An additional component in the circuit, a voltage-limiting device 17 serves as a protection against excess voltage. Should excess voltage occur, which is greater than the threshold voltage limiting device, e.g. greater than the breakdown voltage of the Zener diode 17, then the latter will become conductive, the base potential of the transistor 15 will increase, converting the latter into a conductive state. As a result the switching transistor 11 will itself in turn become conductive and the voltage between the positive terminal 13 of the supply voltage and the point of connection of the transistors 17 and 15 to the inductive load, will likewise be limited. The components 17 and 18 can of course be inserted in similar fashion in the first embodiment. WHAT WE CLAIM IS:
1. A circuit arrangement for an inductive load wherein the inductive load is connected in series with the switching path of a supply current switching transistor and such series arrangement is connected between the two poles of a D.C. current source to enable the inductive load to receive current, and wherein the switching path of a free-wheeling control transistor is connected between two electrodes of the switching transistor, with the emitter of the free-wheeling control transistor connected to the junction between the switching transistor connected to the junction between the switching transistor and the inductive load, and the control electrode via a current-limiting resistor to that pole of the current source to which the inductive load is connected.
2. A circuit arrangement as claimed in claim 1, in which the switching path of the freewheeling control transistor is connected in parallel with the switching path switching transistor so that the decay current flows through the free-wheeling control transistor.
3. A circuit arrangement as claimed in claim 1, in which the switching path of the freewheeling control transistor is connected between the control electrode of the switching transistor and said junction between the latter and the inductive load.
4. A circuit arrangement as claimed in any preceding claim in which a resistor is serially connected to the collector of the free-wheeling control transistor.
5. A circuit arrangement as claimed in claim
4, in which the resistance of said resistor is substantially equal to or less than the D.C. resistance of the inductive load.
6. A circuit arrangement as claimed in any preceding claim in which a voltage-limiting device is connected between the control electrode of the free-wheeling control transistor and that pole of the voltage source to which the semi-conductor switch is connected.
7. A circuit arrangement as claimed in claim 6 in which the voltage-limiting device comprises a Zener diode.
8. A circuit arrangement as claimed in any preceding claim in which a reverse polarity protection diode is connected in parallel with the switching path of the switching transistor.
9. A circuit arrangement as claimed in any preceding claim in which the switching transistor and the free-wheeling control transistor are comprised by an integrated circuit.
10. A circuit arrangement for an inductive load substantially as herein described with reference to and as illustrated in Fig. 1 of the accompanying drawings.
11. A circuit arrangement for an inductive load substantially as herein described with reference to and as illustrated in Fig. 2 of the accompanying drawings.
GB3385677A 1976-08-14 1977-08-12 Circuits for switching of inductive loads Expired GB1589343A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2636676 1976-08-14

Publications (1)

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GB1589343A true GB1589343A (en) 1981-05-13

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GB3385677A Expired GB1589343A (en) 1976-08-14 1977-08-12 Circuits for switching of inductive loads

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JP (1) JPS5323554A (en)
FR (1) FR2361777A1 (en)
GB (1) GB1589343A (en)
IT (1) IT1084407B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0805554B1 (en) * 1996-04-30 2003-07-30 STMicroelectronics S.r.l. Circuit for the controlled recycle without oscillation of a discharge current from an inductive load

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57178424A (en) * 1981-04-27 1982-11-02 Toshiba Corp Semiconductor integrated circuit device
EP0287525B1 (en) * 1987-04-14 1992-06-10 STMicroelectronics S.r.l. Transitory current recirculation through a power switching transistor driving an inductive load

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2223376C3 (en) * 1972-05-12 1975-01-23 Siemens Ag, 1000 Berlin Und 8000 Muenchen Protective circuit arrangement for a shadow transistor in the inductive load circuit
DE2423258C3 (en) * 1974-05-14 1978-09-07 Siemens Ag, 1000 Berlin Und 8000 Muenchen Circuit arrangement for supplying power to an inductive consumer
DE2638179A1 (en) * 1976-08-25 1978-03-09 Bosch Gmbh Robert Switching circuit for inductive load driven by integrated circuit - has energy release transistor switch shunting main series switch

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0805554B1 (en) * 1996-04-30 2003-07-30 STMicroelectronics S.r.l. Circuit for the controlled recycle without oscillation of a discharge current from an inductive load

Also Published As

Publication number Publication date
FR2361777A1 (en) 1978-03-10
IT1084407B (en) 1985-05-25
JPS5323554A (en) 1978-03-04

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