CA2213193C - Electronic circuit for protecting power supply to a load - Google Patents
Electronic circuit for protecting power supply to a load Download PDFInfo
- Publication number
- CA2213193C CA2213193C CA 2213193 CA2213193A CA2213193C CA 2213193 C CA2213193 C CA 2213193C CA 2213193 CA2213193 CA 2213193 CA 2213193 A CA2213193 A CA 2213193A CA 2213193 C CA2213193 C CA 2213193C
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- CA
- Canada
- Prior art keywords
- transistor
- current
- resistor
- control
- load
- 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 - Fee Related
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/025—Disconnection after limiting, e.g. when limiting is not sufficient or for facilitating disconnection
-
- 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
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
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- Emergency Protection Circuit Devices (AREA)
- Dc-Dc Converters (AREA)
- Protection Of Static Devices (AREA)
Abstract
A circuit provides instantaneous restriction of current supplied to a load from a power supply to a predetermined maximum current by controlling fluid current through a first transistor using a second transistor responsive to voltage across a resister in series of the first transistor to control flow of a current from the base of the first transistor. The actuation of the first transistor to restrict maximum current causes charging of a capacitor at a predetermined rate to a predetermined threshold voltage at which time a threshold device actuates the second transistor to cause switching off of the first transistor to halt any current flow to the load.
Description
ELECTRONIC CIRCUIT FOR PROTECTING POWER SUPPLY TO A LOAD
This invention relates to an electronic circuit for providing power supply protection to a load and particularly for providing limitation of current supplied to the load to maximum current and for halting supply of current to the load when the maximum current has been supplied for a predetermined time.
Various techniques are widely used for protecting power supply to a load to prevent damage to the load in the event of a fault.
SUMMARY OF THE INVENTION
It one aspect of the present invention to provide an improved circuit for this purpose which is relatively simple, inexpensive and can be located in a limited space.
According to the first aspect of the invention there is provided an electronic circuit comprising:
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a control transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the control transistor and the first resistor, the control transistor having a first connection for controlling the flow of current through the control transistor;
a first circuit element connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the control transistor to limit current to the load to said pre-determined maximum current;
This invention relates to an electronic circuit for providing power supply protection to a load and particularly for providing limitation of current supplied to the load to maximum current and for halting supply of current to the load when the maximum current has been supplied for a predetermined time.
Various techniques are widely used for protecting power supply to a load to prevent damage to the load in the event of a fault.
SUMMARY OF THE INVENTION
It one aspect of the present invention to provide an improved circuit for this purpose which is relatively simple, inexpensive and can be located in a limited space.
According to the first aspect of the invention there is provided an electronic circuit comprising:
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a control transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the control transistor and the first resistor, the control transistor having a first connection for controlling the flow of current through the control transistor;
a first circuit element connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the control transistor to limit current to the load to said pre-determined maximum current;
a capacitor/resistor circuit element arranged so as to be responsive to said actuation of the control transistor to control current to cause charging of a capacitor at a predetermined rate;
and a threshold device responsive to charging of the capacitor to a predetermined voltage to cause the first circuit element to actuate the control transistor to halt current through the control transistor to the load.
Preferably the threshold device is arranged such that discharge of the capacitor caused by disconnection of the power supply or the load causes the threshold device to fall below a threshold and thus allow current through the control transistor.
Preferably the capacitor is connected in series with a second resistor and wherein the capacitor and a second resistor are connected in parallel to the first resistor and the control transistor.
Preferably the threshold device is connected between the capacitor and the second resistor.
Preferably the first circuit element comprises a transistor.
Preferably the first circuit element comprises an operational amplifier arranged to compare the voltage across the resistor with a reference voltage.
Preferably the threshold device comprises a light emitting diode so as to indicate actuation of the threshold device.
Preferably the control transistor is of the bipolar type and wherein the first connection comprises a base of the control transistor.
Preferably the control transistor is of the field effect type and wherein the first connection comprises a gate of the control transistor.
and a threshold device responsive to charging of the capacitor to a predetermined voltage to cause the first circuit element to actuate the control transistor to halt current through the control transistor to the load.
Preferably the threshold device is arranged such that discharge of the capacitor caused by disconnection of the power supply or the load causes the threshold device to fall below a threshold and thus allow current through the control transistor.
Preferably the capacitor is connected in series with a second resistor and wherein the capacitor and a second resistor are connected in parallel to the first resistor and the control transistor.
Preferably the threshold device is connected between the capacitor and the second resistor.
Preferably the first circuit element comprises a transistor.
Preferably the first circuit element comprises an operational amplifier arranged to compare the voltage across the resistor with a reference voltage.
Preferably the threshold device comprises a light emitting diode so as to indicate actuation of the threshold device.
Preferably the control transistor is of the bipolar type and wherein the first connection comprises a base of the control transistor.
Preferably the control transistor is of the field effect type and wherein the first connection comprises a gate of the control transistor.
According to the second aspect of the invention there is provided an electronic circuit comprising:
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a first transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the first transistor and the first resistor, the first transistor having a first connection for controlling the flow of current through the first transistor;
a second transistor connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the second transistor to control current in the first connection of the first transistor so as to actuate the first transistor to limit current through said first transistor said pre-determined maximum current;
a capacitor and a second resistor in series connected in parallel to the first resistor and the first transistor arranged such that actuation of the first transistor to control current to cause charging of the capacitor at a predetermined rate;
a diode connected between the capacitor and the control connection of the second transistor such that charging of the capacitor to a voltage greater than a threshold voltage of the diode causes conduction through the second transistor to control current in the first connection of the first transistor so as to actuate the first transistor to halt current through the first transistor to the load.
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a first transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the first transistor and the first resistor, the first transistor having a first connection for controlling the flow of current through the first transistor;
a second transistor connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the second transistor to control current in the first connection of the first transistor so as to actuate the first transistor to limit current through said first transistor said pre-determined maximum current;
a capacitor and a second resistor in series connected in parallel to the first resistor and the first transistor arranged such that actuation of the first transistor to control current to cause charging of the capacitor at a predetermined rate;
a diode connected between the capacitor and the control connection of the second transistor such that charging of the capacitor to a voltage greater than a threshold voltage of the diode causes conduction through the second transistor to control current in the first connection of the first transistor so as to actuate the first transistor to halt current through the first transistor to the load.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described in conjunction with the accompanying drawings in which:
Figure 1 is a first circuit schematic showing an example of a circuit according to the present invention.
Figure 2 is a second circuit schematic showing an example of a circuit according to the present invention.
Figure 3 is a third circuit schematic showing an example of a circuit according to the present invention.
In the drawings like characters of reference indicate corresponding parts in the different figures.
DETAILED DESCRIPTION
In Figure 1 is shown a power supply P and a load L together with a protection circuit generally indicated at 10. The protection circuit comprises a first transistor 12 and a second transistor 14.
The circuit further includes a first resistor 16, a capacitor 18, a second resistor 20, a third resistor 22, and a threshold device or diode 24.
The first resistor 16 and the first transistor 12 are connected in series so that current from the power supply P passes through the first transistor and the first resistor.
The capacitor 18 and the second resistor 20 are arranged in series with those elements in parallel to the first resistor and the first transistor.
The second transistor has the gate thereof connected between the first resistor 16 and the first transistor 12 through the third resistor 32.
The second transistor is connected in a circuit connecting to ground and controlling the current from the base of the first transistor. Between the base of the first transistor and ground is connected a fourth resistor 28. The second transistor is connected so that voltage across the emitter and base of the second transistor is responsive to the voltage across the first resistor 16.
Embodiments of the invention will now be described in conjunction with the accompanying drawings in which:
Figure 1 is a first circuit schematic showing an example of a circuit according to the present invention.
Figure 2 is a second circuit schematic showing an example of a circuit according to the present invention.
Figure 3 is a third circuit schematic showing an example of a circuit according to the present invention.
In the drawings like characters of reference indicate corresponding parts in the different figures.
DETAILED DESCRIPTION
In Figure 1 is shown a power supply P and a load L together with a protection circuit generally indicated at 10. The protection circuit comprises a first transistor 12 and a second transistor 14.
The circuit further includes a first resistor 16, a capacitor 18, a second resistor 20, a third resistor 22, and a threshold device or diode 24.
The first resistor 16 and the first transistor 12 are connected in series so that current from the power supply P passes through the first transistor and the first resistor.
The capacitor 18 and the second resistor 20 are arranged in series with those elements in parallel to the first resistor and the first transistor.
The second transistor has the gate thereof connected between the first resistor 16 and the first transistor 12 through the third resistor 32.
The second transistor is connected in a circuit connecting to ground and controlling the current from the base of the first transistor. Between the base of the first transistor and ground is connected a fourth resistor 28. The second transistor is connected so that voltage across the emitter and base of the second transistor is responsive to the voltage across the first resistor 16.
5 In operation, normally, current to the load flows through the first resistor and the first transistor. Provided this current is below the predetermined maximum current, the voltage across the first resistor is maintained below a predetermined maximum voltage and the first transistor is maintained in saturated condition. The first resistor is selected so that when the voltage across the first resistor is less than the predetermined maximum voltage, the voltage across the emitter and base of the second transistor are less than the trigger voltage of one-half volt so the second transistor is not conducting.
In the event that the current to the load approaches the predetermined maximum current, the voltage across the first resistor also approaches the predetermined maximum voltage which is sufficient to cause conduction through the second transistor. This conduction causes current to flow to ground thus causing current to flow from the base of the first transistor and causing the first transistor to restrict the current to the load. The first and second transistors and the voltage across the first resistor 16 are therefore maintained in balance so the current through the first transistor is maintained at the predetermined maximum current.
The reduction in current by the first transistor 12 causes an increase in voltage across the capacitor 18. This voltage is dependent upon the amount of the overload condition which can vary from a small over voltage to a dead short condition. The capacitor 18 is thus charged at a predetermined rate dependent upon the overload condition and the selected values of the capacitance and the resistor 20 until the voltage between the capacitor 18 and resistor 20 reaches a predetermined threshold voltage measured by the threshold diode 24. In the event that the voltage exceeds the threshold voltage, the diode 24 comes into conduction which causes the second transistor to come into conduction thus causing the first transistor to switch off terminating the flow of current from the power supply to the load.
The simple circuit arrangement therefore instantaneously provides a restriction on the current supplied to the load to a maximum predetermined current in the event of a fault causing an over current condition at the load.
Within a predetermined time period dependent upon the overload condition and prior to the generation of sufficient heat to cause damage, the capacitor and threshold system cause the shut down of current flow.
Automatic resetting of the circuit occurs on discharge of the capacitor 18 and this can be achieved by disconnecting the power supply or by disconnecting the load in the event of a reconnection and a fresh overload conditions, the circuit is again triggered to instantaneously limit the maximum current and then to halt that current after a predetermined period.
The device is particularly effective in that within a small area, an instantaneous restriction of the current can be obtained to avoid a temporary over current condition causing damage to a sensitive load.
In Figure 2 is shown an arrangement which is substantially identical to that of Figure 1 except that the control transistor 12 is replaced by a field effect type transistor 12A. In addition there is provided a further diode 30 which acts to limit the forward gate voltage on the transistor 12A. A second diode which is LED 32 acts as an indicator in the event that the transistor 14 is triggered by an overcurrent condition.
In Figure 3 is shown a further modified arrangement including the field effect transistor 12A. In this arrangement the transistor 14 is replaced by another circuit element which is responsive to an increase in voltage across the resistor 16 to trigger the control effect of the transistor 12A. In this arrangement the circuit element, provided by the transistor 14 in the previous embodiments, is replaced by an operational amplifier 14A having an input voltage Vref for comparison with the voltage across the resistor 16. Vref is generated by a voltage divider 50 connected between the power supply and ground and therefore is dependent upon any fluctuations in the power supply. This arrangement has the advantage that the voltage drop across the resistor 16 much smaller so that the value of resistor 16 can be reduced thus reducing power loss at the resistor during normal operation.
In addition the input terminal 14B connected to Vref receives an input from the voltage across the capacitor 18 so as to be actuated by the charging of the capacitor 18 so as to turn off the transistor 12A as previously described.
Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.
In the event that the current to the load approaches the predetermined maximum current, the voltage across the first resistor also approaches the predetermined maximum voltage which is sufficient to cause conduction through the second transistor. This conduction causes current to flow to ground thus causing current to flow from the base of the first transistor and causing the first transistor to restrict the current to the load. The first and second transistors and the voltage across the first resistor 16 are therefore maintained in balance so the current through the first transistor is maintained at the predetermined maximum current.
The reduction in current by the first transistor 12 causes an increase in voltage across the capacitor 18. This voltage is dependent upon the amount of the overload condition which can vary from a small over voltage to a dead short condition. The capacitor 18 is thus charged at a predetermined rate dependent upon the overload condition and the selected values of the capacitance and the resistor 20 until the voltage between the capacitor 18 and resistor 20 reaches a predetermined threshold voltage measured by the threshold diode 24. In the event that the voltage exceeds the threshold voltage, the diode 24 comes into conduction which causes the second transistor to come into conduction thus causing the first transistor to switch off terminating the flow of current from the power supply to the load.
The simple circuit arrangement therefore instantaneously provides a restriction on the current supplied to the load to a maximum predetermined current in the event of a fault causing an over current condition at the load.
Within a predetermined time period dependent upon the overload condition and prior to the generation of sufficient heat to cause damage, the capacitor and threshold system cause the shut down of current flow.
Automatic resetting of the circuit occurs on discharge of the capacitor 18 and this can be achieved by disconnecting the power supply or by disconnecting the load in the event of a reconnection and a fresh overload conditions, the circuit is again triggered to instantaneously limit the maximum current and then to halt that current after a predetermined period.
The device is particularly effective in that within a small area, an instantaneous restriction of the current can be obtained to avoid a temporary over current condition causing damage to a sensitive load.
In Figure 2 is shown an arrangement which is substantially identical to that of Figure 1 except that the control transistor 12 is replaced by a field effect type transistor 12A. In addition there is provided a further diode 30 which acts to limit the forward gate voltage on the transistor 12A. A second diode which is LED 32 acts as an indicator in the event that the transistor 14 is triggered by an overcurrent condition.
In Figure 3 is shown a further modified arrangement including the field effect transistor 12A. In this arrangement the transistor 14 is replaced by another circuit element which is responsive to an increase in voltage across the resistor 16 to trigger the control effect of the transistor 12A. In this arrangement the circuit element, provided by the transistor 14 in the previous embodiments, is replaced by an operational amplifier 14A having an input voltage Vref for comparison with the voltage across the resistor 16. Vref is generated by a voltage divider 50 connected between the power supply and ground and therefore is dependent upon any fluctuations in the power supply. This arrangement has the advantage that the voltage drop across the resistor 16 much smaller so that the value of resistor 16 can be reduced thus reducing power loss at the resistor during normal operation.
In addition the input terminal 14B connected to Vref receives an input from the voltage across the capacitor 18 so as to be actuated by the charging of the capacitor 18 so as to turn off the transistor 12A as previously described.
Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.
Claims (10)
1. An electronic circuit comprising:
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a control transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the control transistor and the first resistor, the control transistor having a first connection for controlling the flow of current through the control transistor;
a first circuit element connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a first predetermined voltage by a current through the first resistor and the first control transistor to the load approaching a pre-determined maximum current causes actuation of the control transistor to limit current to the load to said pre-determined maximum current;
a capacitor/resistor circuit element arranged so as to be responsive to said actuation of the control transistor to control current to cause charging of a capacitor at a predetermined rate;
and a threshold device responsive to charging of the capacitor to a second predetermined voltage to cause the first circuit element to actuate the control transistor to halt current through the control transistor to the load.
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a control transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the load passes through the control transistor and the first resistor, the control transistor having a first connection for controlling the flow of current through the control transistor;
a first circuit element connected to said first connection and arranged such that generation of a voltage across the first resistor approaching a first predetermined voltage by a current through the first resistor and the first control transistor to the load approaching a pre-determined maximum current causes actuation of the control transistor to limit current to the load to said pre-determined maximum current;
a capacitor/resistor circuit element arranged so as to be responsive to said actuation of the control transistor to control current to cause charging of a capacitor at a predetermined rate;
and a threshold device responsive to charging of the capacitor to a second predetermined voltage to cause the first circuit element to actuate the control transistor to halt current through the control transistor to the load.
2. The circuit according to Claim 1 wherein the threshold device is arranged such that discharge of the capacitor caused by disconnection of the power supply or the load causes the threshold device to fail below a threshold and thus allow current through the control transistor.
3. The circuit according to Claim 1 or 2 wherein the capacitor is connected in series with a second resistor and wherein the capacitor and the second resistor are connected in parallel to the first resistor and the control transistor.
4. The circuit according to Claim 3 wherein the threshold device is connected between the capacitor and the second resistor.
5. The circuit according to any one of Claims 1 to 4 wherein the first circuit element comprises a transistor.
6. The circuit according to any one of Claims 1 to 4 wherein the first circuit element comprises an operational amplifier arranged to compare the voltage across the resistor with a reference voltage.
7. The circuit according to any one of Claims 1 to 6 wherein the threshold device comprises a light emitting diode so as to indicate actuation of the threshold device.
8. The circuit according to any one of Claims 1 to 7 wherein the control transistor is of the bipolar type and wherein the first connection comprises a base of the control transistor.
9. The circuit according to any one of Claims 1 to 7 wherein the control transistor is of the field effect type and wherein the first connection comprises a gate of the control transistor.
10. An electronic circuit comprising:
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a first transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the Toad passes through the first transistor and the first resistor, the first transistor having a first control connection for controlling the flow of current through the first transistor;
a second transistor connected to said first control connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the second transistor to control current in the first control connection of the first transistor so as to cause actuation of the first transistor to limit current through said first transistor said pre-determined maximum current;
the second transistor having a second control connection for controlling the flow of current through the second transistor;
a capacitor and a second resistor in series connected in parallel to the first resistor and the first transistor and arranged such that said actuation of the first transistor to control current acts to cause charging of the capacitor at a predetermined rate;
a diode connected between the capacitor and the second control connection of the second transistor such that charging of the capacitor to a voltage greater than a threshold voltage of the diode causes conduction through the second transistor to control current in the first control connection of the first transistor so as to actuate the first transistor to halt current through the first transistor to the load.
a first terminal for connection to a power supply;
a second terminal for connection to a load;
a first transistor and a first resistor connected in series between the first terminal and the second terminal so that current to the Toad passes through the first transistor and the first resistor, the first transistor having a first control connection for controlling the flow of current through the first transistor;
a second transistor connected to said first control connection and arranged such that generation of a voltage across the first resistor approaching a predetermined voltage by a current through the first resistor and the first transistor to the load approaching a pre-determined maximum current causes the second transistor to control current in the first control connection of the first transistor so as to cause actuation of the first transistor to limit current through said first transistor said pre-determined maximum current;
the second transistor having a second control connection for controlling the flow of current through the second transistor;
a capacitor and a second resistor in series connected in parallel to the first resistor and the first transistor and arranged such that said actuation of the first transistor to control current acts to cause charging of the capacitor at a predetermined rate;
a diode connected between the capacitor and the second control connection of the second transistor such that charging of the capacitor to a voltage greater than a threshold voltage of the diode causes conduction through the second transistor to control current in the first control connection of the first transistor so as to actuate the first transistor to halt current through the first transistor to the load.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2213193 CA2213193C (en) | 1997-08-15 | 1997-08-15 | Electronic circuit for protecting power supply to a load |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2213193 CA2213193C (en) | 1997-08-15 | 1997-08-15 | Electronic circuit for protecting power supply to a load |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2213193A1 CA2213193A1 (en) | 1999-02-15 |
| CA2213193C true CA2213193C (en) | 2006-10-10 |
Family
ID=29274978
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2213193 Expired - Fee Related CA2213193C (en) | 1997-08-15 | 1997-08-15 | Electronic circuit for protecting power supply to a load |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2213193C (en) |
-
1997
- 1997-08-15 CA CA 2213193 patent/CA2213193C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2213193A1 (en) | 1999-02-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20140815 |