Information
-
Patent Grant
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6275017
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Patent Number
6,275,017
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Date Filed
Thursday, May 25, 200024 years ago
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Date Issued
Tuesday, August 14, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
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US Classifications
Field of Search
US
- 323 266
- 323 270
- 323 271
- 323 273
- 323 282
- 323 901
- 307 31
- 307 32
- 307 36
- 307 42
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International Classifications
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Abstract
It is an object of the present invention to provide an assist circuit for a vehicle controller power supply which requires multiple voltage outputs. The assist circuit allows for the supply of a higher voltage which aids the supply of a lower voltage during transient power up. Once both voltages have achieved a specified level, during transient power up, and other power supply components, such as a linear voltage regulator, have stabilized, the assist circuit effectively switches off, allowing the higher voltage to be supplied by a switching power supply and the lower voltage to be supplied by the linear regulator. The assist circuit is most useful in vehicle controllers which have a current foldback feature, by assisting to supply peak current demands before a current foldback can occur during a transient power up stage.
Description
FIELD OF THE INVENTION
The present invention relates generally to vehicle controllers and more particularly to vehicle controllers which have a power supply with current foldback features.
BACKGROUND AND SUMMARY OF THE INVENTION
Vehicle controllers are typically powered by a power supply which offers a dual voltage output. The higher of the two voltage commonly powers the input/output (I/O) ring of the controller which comprises logic gates requiring a standard voltage level. The lower voltage level powers the internal bus logic of the digital core. The lower voltage output is becoming a necessity because of the increasing speed and lower power target of modern microprocessors. The source of the lower voltage output typically contains a current limiting and current foldback feature which controls and reduces the amount of power dissipation during a short circuit.
At a power on event, the higher and lower voltage gradually ramp up to their designed voltage level. The higher voltage is generated directly from a switching power supply, whereas the lower voltage results from feeding the higher back through a linear voltage regulator. Therefore, during the voltage ramp up, the controller monitors the ramping of the higher voltage and begins to ramp up the lower voltage at a designated point. This designated point is a function of the differential which must be maintained between the higher and lower voltage.
The vehicle controller power supply protects itself in the event of a short circuit by having a current foldback feature. Both the higher and lower voltage sources are designed to handle a specified operating current. If the transient current load during power up is higher than the maximum normal operating current of the lower voltage source, the foldback feature will never allow it to reach its designated voltage value. As a result, the specified differential between the higher and lower voltage is violated. Typically the short circuit current value is 15-20% of the maximum steady -state current. By the foldback feature limiting the current to this value, the lower voltage will not achieve its steady -state.
It is an object of the present invention to provide a circuit which prevents the lower voltage source from being held by the foldback feature in response to large transient demands during power up.
This invention is directed to a power up assist circuit for use with a multiple voltage output power supply. The power up assist circuit includes a first circuit loop. The first circuit loop has a first voltage output. A second circuit loop has a second voltage output. During an initial power up stage, the first circuit loop supplies the second voltage output so that the second voltage output is assisted by the first voltage output through the first circuit loop. The second circuit loop deactivates the first circuit loop after the second voltage output achieves a predetermined value so that the first circuit loop no longer supplies said second voltage output.
Implementation of the assist circuit of the present invention does not allow the higher and lower voltages to violate the specified difference between the two. Therefore, the controller remains operable, not going into a foldback state upon a large transient demand.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1
is a schematic view of a power source according to the principles of the present invention;
FIG. 2
is a schematic view of a vehicle controller according to the principles of the present invention;
FIG. 4
is a graph of the current characteristics of a voltage regulator with the foldback feature;
FIG. 3
is a schematic layout of a portion of the vehicle controller power supply of
FIG. 2
; and
FIG. 5
is a schematic view of a power-up assist circuit of FIG.
3
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The embodiment of the present invention is merely exemplary in nature and is not intended to limit the invention or its applicability. With reference to
FIG. 1
, a schematic view of a typical dual output power supply is shown. The power supply
12
sources loads V
1
and V
2
.
FIG. 2
is a detailed schematic view of an exemplary vehicle controller
10
. The vehicle controller
10
comprises a plurality of sub-controllers
14
,
16
, a power supply
12
and multiple intermediate circuits (not shown). It should be noted that a preferred embodiment of the present invention uses two sub-controllers
14
,
16
but does not limit the use of more or fewer sub-controllers. In the preferred embodiment, sub-controller
14
is an engine controller comprising a micro-controller
14
a
and a digital application specific integrated circuit (ASIC)
14
b
. Sub-controller
16
is a transmission controller comprising a micro-controller
16
a
and a digital ASIC
16
b.
Power supply
12
supplies the controllers with multiple voltage outputs V
1
and V
2
. It should be noted that V
1
(the higher voltage) has a greater value than V
2
(the lower voltage). Again, the preferred embodiment of the present invention does not limit the use of more or fewer voltage outputs. As shown in
FIG. 1
, voltage V
1
supplies micro-controller
14
a
, digital ASIC
14
b
, micro-controller
16
a
, and digital ASIC
16
b
. Both engine controller
14
and the transmission controller
16
share a common reference ground
18
. The micro-controller
14
a
of the engine controller
14
also requires the lower voltage V
2
supplied by the power supply
12
.
The power supply
12
is further detailed in FIG.
3
. The main power source within the power supply
12
is a switching power supply
20
. The switching power supply
20
generates the higher voltage V
1
which is then fed back into a linear voltage regulator
22
to generate the lower voltage V
2
. The power supply
20
is capable of sourcing transient demands even during the initial transient power up stage of the circuit.
During power up, the linear voltage regulator
22
does not sufficiently handle transient demands. Additionally, the linear voltage regulator
22
is configured to have a current foldback means to avoid possible damage to the power supply
12
. As a result, if any peak load demands are placed upon the linear voltage regulator
22
by the engine micro-controller
14
a
, the power supply
12
goes into a current foldback state. This foldback reaction is best shown in FIG.
4
. Upon a transient demand, the linear voltage regulator folds the current back to 15-20% of its steady-state value, as described earlier. To avoid this, an assist circuit
24
allows the circuit to complete power up. As shown in
FIG. 3
, the assist circuit
24
schematically bridges the higher voltage V
1
and lower voltage V
2
outputs, but is physically integrated into the controller
10
board circuitry.
FIG. 5
is a circuit schematic detailing the assist circuit
24
of the power supply
12
. The circuit comprises two integral yet distinct loops A, B. First loop A comprises a capacitor
26
, a first transistor
28
, a higher voltage node
40
, and lower voltage node
42
. Second loop B comprises a plurality of resistors
30
,
32
,
36
, a second transistor
34
, and the lower voltage node
42
. Upon an initial power up event, such as ignition, the switching power supply begins ramping up the higher voltage V
1
. As the higher voltage V
1
begins ramping, the capacitor
26
begins charging. The positive rate of change of voltage across capacitor
26
provides a base current drive to transistor
28
. Transistor
28
becomes saturated, turning on, thus placing a short circuit between nodes
40
and
42
. The short circuit allows voltage node
40
to assist by supplying current to lower voltage node
42
. If a transient current demand is subsequently placed on the lower voltage node
42
, the assistance allows for this demand to be met. It should be noted that the charging of capacitor
26
controls the bridging of higher and lower voltage nodes
40
,
42
. The bridging will only occur when there exists a positive rate of change of voltage across capacitor
26
. Once capacitor
26
is fully charged, the bridging ceases.
Resistors
30
and
32
create a voltage divider, and are sized such that the second transistor
34
becomes saturated and turns on at essentially the same time the lower voltage node
42
achieves a predetermined value. This value is designated as the V
2
voltage minus allowable tolerances. Once the second transistor
34
becomes saturated and turns on, the base current of the first transistor
28
is reduced. The first transistor
28
becomes desaturated, turning off, and the short-circuit between nodes
40
and
42
is eliminated. With the second transistor
34
on, the base emitter of the first transistor
28
is reversed biased, preventing it form turning on. At this point, the lower voltage node
42
is now fed by the linear voltage regulator
22
which is fully able to handle any transient current demands. The third resistor
36
, disposed between loops A and B, keeps the base emitter of transistor
28
reverse biased when capacitor
26
is discharging. Resistor
36
also aids in providing the base of transistor
28
a DC discharge path to ground.
During the power down sequence, both the higher voltage V
1
and lower voltage V
2
ramp down towards ground. As a result, second transistor
34
becomes cut-off. The rate of change of voltage across capacitor
26
becomes negative. Thus, base current is not provided to transistor
28
, thereby keeping transistor
28
cut-off. Therefore, a short-circuit between higher voltage node
40
and lower voltage node
42
cannot exist during power down.
Overall, the assist circuit
24
of the present invention only provides a short-circuit between higher
40
and lower
42
voltage nodes during the power-up sequence and only until the lower voltage node
42
reaches a predetermined value.
Various other advantages of the present invention will become apparent to those skilled in the art after having the benefit of studying the foregoing text and drawing taken in conjunction with the following claims.
Claims
- 1. A power up assist circuit for use with a power supply, comprising:a first circuit loop, said first circuit loop having a first voltage output; and a second circuit loop, said second circuit loop having a second voltage output such that during an initial power up stage said first circuit loop supplies said second voltage output, said second voltage output being assisted by said first voltage output through said first circuit loop and said second circuit loop causing deactivation of said first circuit loop after said second voltage output achieves a predetermined value such that said first circuit loop no longer supplies said second voltage output.
- 2. The power up assist circuit of claim 1, further comprising a first switch, wherein in a first mode said first switch enables said second voltage output to be supplied with current from a first power supply source.
- 3. The power up assist circuit of claim 2, further comprising a capacitor wherein said capacitor activates said first switch during a power up event and prevents said power up assist circuit from activating during a power down event.
- 4. The power up assist circuit of claim 3, further comprising a resistor disposed between said first and second loops, wherein said resistor reverse biases said capacitor and provides a discharge path to a ground.
- 5. The power up assist circuit of claim 2, wherein said first switch is a transistor.
- 6. The power up assist circuit of claim 1, further comprising a second switch, wherein in a first mode said second switch enables said second voltage output to be supplied with current from a second power supply source.
- 7. The power up assist circuit of claim 6, wherein said second switch is a transistor.
- 8. A vehicle controller comprising:at least one sub-controller; a power supply, said power supply powering said at least one subcontroller, said power supply including: a first voltage source, said first voltage source providing a first supply voltage; a first linear voltage regulator, said first linear voltage regulator receiving said first supply voltage and generating a second supply voltage, said second supply voltage being less than said first supply voltage; a power up assist circuit including: a first circuit loop, said first circuit loop having a first voltage output; and a second circuit loop, said second circuit loop having a second voltage output such that during an initial power up stage said first circuit loop supplies said second voltage output, said second voltage output being assisted by said first voltage output through said first circuit loop and said second circuit loop causing deactivation of said first circuit loop after said second voltage output achieves a predetermined value such that said first circuit loop no longer supplies said second voltage output.
- 9. The power up assist circuit of claim 8, further comprising a first switch, wherein in a first mode said first switch enables said second voltage output to be supplied with current from a first power supply source.
- 10. The power up assist circuit of claim 9, further comprising a capacitor wherein said capacitor activates said first switch during a power up event and prevents said power up assist circuit from activating during a power down event.
- 11. The power up assist circuit of claim 10, further comprising a resistor disposed between said first and second circuit loops, wherein said resistor reverse biases said capacitor and provides a discharge path to a ground.
- 12. The power up assist circuit of claim 8, further comprising a second switch, wherein in a first mode said second switch enables said second voltage output to be supplied with current from a second power supply source.
- 13. A multi-voltage power supply, comprising:a first voltage source, said first voltage source providing a first supply voltage; a first linear voltage regulator receiving said first voltage as input, said first linear voltage regulator providing a second voltage, said second voltage being less than said first voltage; and a power up assist circuit positioned between outputs of said first power supply and said first linear voltage regulator, said power up assist circuit supplementing said second voltage during a power up mode.
- 14. The multi-voltage power supply of claim 13, wherein said power up assist circuit includes:a first circuit loop, said first circuit loop having a first voltage output; and a second circuit loop, said second circuit loop having a second voltage output such that during an initial power up stage said first circuit loop supplies said second voltage output, said second voltage output being assisted by said first voltage output through said first circuit loop and said second circuit loop causing deactivation of said first circuit loop after said second voltage output achieves a predetermined value such that said first circuit loop no longer supplies said second voltage output.
US Referenced Citations (17)