1. A control circuit for an inductive load driver comprising:
a control block activated by a trigger signal for providing a first current;
a power element having a control terminal coupled to the control block; and
an auxiliary current generator including a pinched resistor JFET for providing a second current that is added to the first current to supply a driving current to the control terminal of the power element.
2. The circuit of claim 1, wherein a voltage proportional to a collector voltage of the power element is provided to the auxiliary current generator.
3. The circuit of claim 1, wherein the first and second currents are added by a logic gate.
4. The circuit of claims 3, wherein the logic gate comprises an OR gate.
5. The circuit of claim 1, wherein the power element comprises an IGBT transistor.
6. The circuit of claim 1, wherein the second current is provided from an epitaxial layer of the power element coupled to a pad on the edge structure of the power element.
7. The circuit of claim 1, wherein the components of the control circuit are realised with high voltage technology in excess of 100 volts.
8. The circuit of claim 7, wherein the auxiliary current generator block comprises the JFET integrated inside the control circuit.
9. The circuit of claim 8, wherein the JFET transistor pinches at high voltage of about 100 volts.
10. The circuit of claim 1, wherein the auxiliary current generator block comprises the JFET integrated inside the power element.
11. The circuit of claim 10 further comprising a voltage reference block.
12. The circuit of claim 10 further comprising an operational amplifier operating as current limiter.
13. The circuit of claim 12, wherein the control block delivers the driving current when the trigger signal is higher than the control voltage on the power element.
14. The circuit of claim 12, wherein the control block does not absorb current.
15. An inductive load driver comprising:
a power element, having a control terminal, for providing a current to an inductive load;
a control block for receiving a trigger signal and for providing a first current;
an auxiliary current generator including a pinched resistor JFET coupled to the power element for providing a second current; and
a summing circuit for adding the first and second currents coupled to the control terminal of the power element.
16. The inductive load driver of claim 15 wherein the power element comprises an IGBT transistor.
17. The inductive load driver of claim 15 wherein the control block is not coupled to a battery.
18. The inductive load driver of claim 15 wherein the summing circuit comprises an OR gate.
19. The inductive load driver of claim 15 further comprising a sense transistor coupled to the power element.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. Subsurface object location apparatus for determining the position of an object located below a surface, comprising:
a subsurface unit having transmitter and being arranged to be mounted on an object the location of which is to be monitored;
a plurality of surface units disposed at spaced locations at the surface and each having a receiver; and
a processing unit arranged for determining at least one of, the times of reception and relative times of reception at the plurality of receivers, of a signal transmitted from the transmitter and determining the location of the object on the basis of at least one of, the times and the relative times of reception, characterised in that the transmitter and receiver are arranged respectively to transmit and receive inductive signals.
2. Apparatus according to claim 1 in which the processing unit is arranged for taking a plurality of measurements of the signal received at each surface unit in order to determine the time of reception or relative time of reception of the signal at each surface unit.
3. Apparatus according to claim 1 in which the processing unit is arranged for performing a cyclic correlation to determine one of the times of reception and relative times of reception of the signal at each surface unit.
4. Apparatus according to claim 3 in which the cyclic correlation is performed between the received signal and a synthesised signal.
5. Apparatus according to claim 1 in which the processing unit is arranged to compare the time of reception of the signal and to determine the location of the object on the basis of said comparison.
6. Apparatus according to claim 1 further comprising a central unit which is connected by a communication link to each of the surface units.
7. Apparatus according to claim 6 in which each communication link is a high quality link having known characteristics and the central unit is arranged to compare the time of reception by each surface unit, of a signal transmitted from the subsurface unit on the basis of the time of reception, at the central unit, of a relay signal passed from each surface unit and the known characteristics of the high quality links.
8. Apparatus according to claim 6 in which each surface unit is arranged to determine the time of reception of a signal from the subsurface unit by reference to a master clock and to relay a signal indicating the determined time of reception, via the respective link, to the central unit.
9. A method for determining the position of an object located below a surface, comprising the steps of:
mounting a subsurface unit having a transmitter on the object;
disposing at spaced locations at the surface a plurality of surface units each having a receiver;
using the transmitter to transmit an inductive signal from the object;
determining at least one of the times and relative times at which the inductive signal is received at each of the receivers; and
determining the location of the object on the basis of, at least one of the times and relative times of reception.
10. A method according to claim 9 comprising the step of taking multiple measurements of the signal received at each surface unit in order to determine, at least one of the time of reception and relative time of reception of the signal at each surface unit.
11. A method according to claim 9 comprising the step of performing a cyclic correlation to determine, at least one of the times of reception and relative times of reception of the signal at each surface unit.
12. A method according to claim 11 in which the cyclic correlation is performed between the received signal and a synthesised signal.
13. A method according to claim 9 which includes the steps of comparing the times of reception of the signal and determining the location of the object on the basis of said comparison.
14. A method according to claim 9 comprising the step of connecting each of the surface units via a communication link to a central unit .
15. A method according to claim 14 in which each communication link is a high quality link having known characteristics and the method comprises the steps of, at the central unit, comparing the time of reception by each surface unit, of the signal transmitted from the subsurface unit on the basis of the time of reception, at the central unit, of a relay signal passed from each surface unit and the known characteristics of the high quality links.
16. A method according to claim 14 comprising the steps of, at each surface unit, determining the time of reception of the signal from the subsurface unit at the respective surface unit by reference to a master clock and relaying a signal indicating the time of reception via the respective link to the central unit.
17. A method according to claim 9 in which four surface units are provided.
18. Apparatus according to claim 1 in which four surface units are provided.
19. A method according to claim 9 in which the signals used in determining the position of the object are also used to carry data.
20. Apparatus according to claim 1 in which the signals used in determining the position of the object are also used to carry data.