JPH0382336A - Power distributing circuit provided with overcurrent detection - Google Patents

Abstract

PURPOSE: To obtain a power distribution circuit having an accurate and reliable overcurrent protective function by providing an overcurrent detection circuit responsive to the state of a high potential current path and detecting a moment when the current in the high potential current path exceeds a predetermined level. CONSTITUTION: In order to feed a DC current to a load 14 appropriate signals are applied individually to the gates G1 , G4 of switches S1 , S4 which are thereby turned on. In order to prevent an overcurrent state breaking down the switches S1 , S3 arranged in the high potential side leg of an H bridge 10 or the load 14, overcurrent detectors of a control circuit respond to the individual electric state of the high potential legs L1 , L3 .

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a power distribution circuit for supplying load current to a load, and more particularly to a circuit including means for detecting an overcurrent condition.

[Conventional technology]

Power distribution circuits that supply load current to a load and include overcurrent detection means are known. For example, U.S. Patent 4°705,99
See No. 7 and No. 4.654.586. Such circuits include a current switch placed between the load and ground, typically on the low potential side of the load. The overcurrent detection means is responsive to the current level at the low potential side switch. Typically such circuits require a bipolar power supply to provide a negative bias to the overcurrent detection device, which is typically comprised of an operational amplifier circuit.

[Problem to be solved by the invention]

In a typically unipolar powered environment such as a car, the prior art circuits described above which require a bipolar power supply cannot be used. It is also known to use a MOSFET for current detection in a power switch on the high potential side. However, these devices use more complex control circuitry, which is accomplished by integrating the sensing circuitry into an IC. It is therefore an object of the present invention to provide a power distribution circuit having a switch located on the high potential side of the load and having simple and reliable discrete circuit means for detecting overcurrent conditions in the load. There is a particular thing. The power distribution circuit preferably includes means for interrupting current through the switch upon detection of an overcurrent condition to prevent destruction of the switch or load. The following types of circuits are particularly suitable for use with single 1i sources, such as those typically supplied in vehicles. Another object of the invention is to provide a power distribution circuit with overcurrent protection that functions accurately and reliably despite the large temperature changes typically encountered in vehicles. Another object of the invention is to provide a current distribution circuit with overcurrent protection that is inexpensive to manufacture using readily available discrete components.

[Means to solve the problem]

According to a preferred aspect of the invention, a power distribution circuit is provided for supplying load current to a load. The circuit includes a power node for connecting to a power source, a load node for connecting to a load, and a high potential current path for supplying current from the power node to the load mate. The high potential current path includes a current switch whose state is controlled by a control signal coupled to a control terminal. The power distribution circuit further includes a positive overcurrent detection circuit responsive to high potential current path conditions. The overcurrent detection circuit detects when the current in the high potential current path exceeds a predetermined level. The power distribution circuit preferably further includes current interrupt means for turning off current to the load when an overcurrent condition is detected. In a particularly preferred embodiment of the invention for accurate and reliable overcurrent detection, the current switch in the high potential current path comprises a multi-cell device with a large number of terminals connected to the power means as a large number of terminals. a first main current terminal connecting a large number of device cells to an electrical load; a second main current terminal connecting a large number of device cells to an electrical load; one termination connecting a small number of device cells to provide a current generally proportional to the main device current; A first auxiliary terminal is connected to the terminal, and a second auxiliary terminal is connected to a plurality of device cells. The overcurrent detection circuit in this embodiment preferably has a first
The branch has one branch connected between the auxiliary terminal of the transistor and ground, which branch is connected to a bias-controlled impedance conversion device such as a transistor, and between the impedance conversion device and ground, and has one end connected to the main device current. a series circuit of resistors providing a voltage approximately proportional to , and also including another branch connected between the second auxiliary terminal and the grounding means and providing a bias current for the impedance transformation device of the first branch. . The impedance transformation device in the above-mentioned overcurrent detection circuit advantageously couples the current from the first auxiliary node on the high potential side to the resistor at the lower potential, which is preferably described below. It can be set to a low value such as

[Example] In the figures, the same reference numbers indicate the same parts unless otherwise specified. FIG. 1 shows a general schematic diagram of the power distribution circuit of the present invention used in conjunction with a typical "H" bridge circuit 10. The power distribution circuit of FIG. 1 optionally includes a control circuit 12 coupled to an H-bridge circuit 10. The power distribution circuit of FIG. Considering the H-bridge circuit 10, the load leg L0 extends horizontally and includes a load 14, such as an electric motor. The vertical leg extends between the leftmost node 16 of load leg L0 and the top node 18, which is typically 12 volts for automotive applications. The load factor extends between node 16 and node 20, which is typically at ground potential. The load foot is connected between the rightmost node 22 and the upper node 18' of the load foot L0. Load addition 4 is
It is connected between the node 22 and the ground node 20'. The various leg orientations of the H-bridge circuit 10 with respect to "vertical" and "horizontal" are, of course, for descriptive purposes only and do not accurately depict the layout of the actual H-bridge circuit. Sometimes it's true, sometimes it's not. High potential nodes 18 and 18 as shown in phantom lines
' are generally interconnected and earth nodes 20 and 20
° are also interconnected for the same reason. In addition to the load, or in L4, there is an individual current switch S,
to S4 are included. These switches are controlled by individual signals applied to their gates G to G4. As used herein, the term "gate" encompasses all forms of control means for changing the switching state of a current switch. That’s why “
The word "gate" is synonymous with the "base" of a bipolar transistor, for example. In order to cause a direct current to flow through the load 14 in the direction shown by the arrow 25, an appropriate signal is applied to the gate G of the switches S1 and S. , and G
4 are applied individually to turn on these switches,
On the other hand, during this time, appropriate signals are applied to the gates of switches S and S to turn them off. Conversely, in order to flow a DC current to the load 14 in the direction of the arrow 27,
Switches S, and S are made conductive by appropriate controls on their gates, while switches S1 and 84 are kept off during this time. Switches Sl and Sa (“high potential switches”) located on the high potential side leg of the load 14 or the H-bridge circuit IO
), overcurrent detectors 24 and 30, shown as part of the control circuit 12, respond to the presence of a high potential and a respective electrical condition at L3. . In a preferred configuration, overcurrent detector 24 is responsive to an electrical condition at switch S, described below in connection with FIGS. 2A and 3. Continuing in FIG. 1, when an overcurrent condition is detected by detector 24, gate disable circuit 26 disables normal gate control function 28 and switches S1 and S described above.
Make sure to turn 4 off. Similarly, upon detection of an overcurrent condition at switch S by detector 30, gate disable circuit 32 prevents normal gate control function 34 from turning on switches S and S. Switch S1 and overcurrent detector 24 are shown in more detail in FIG. 2A. Switch S and overcurrent detector 30 have configurations corresponding to switch SI and detector 24. Looking at Figure 2A, switch S is the trademark “
Like those sold at 'HEX Sense',
The MO8FET device is shown as a symbol. H.E.
The main load terminal of the device Sl of X S sense is
Shown at terminals 16 and 18. Terminal 16 is the main source terminal of switch S, and terminal 18 is the only drain terminal of the switch. Gate G corresponds to gate G of current switch Sl in FIG. The HEX sense device S further includes two auxiliary terminals 40 and 42. Auxiliary terminals 40 and 4
2 to the main terminal 16 is Sui Nochi S1 in FIG.
This will be explained in relation to the circuit diagram. Cell C8 in Figure 3
to Cn designate the individual cells of the HEX 5ense device S1. Common gate G1 is connected to cell C8
A common gate signal is applied to each gate of Cn to Cn. The drain electrode 18 functions as a common drain electrode for all cells C3 to Cn. Source terminal 16 serves as a common source for the majority of cells of switch S1, ie, cells C1 to Cn, while terminal 42 is connected to source electrode 16 with the exception of a small metallized resistor (not shown). It functions as a commonly connected auxiliary source electrode. Auxiliary terminal 40 serves as a source electrode for only a small number of cells of switch S1, namely cells C3 and C7. In an actual denomination device with thousands or more cells, the auxiliary terminal 40 would likely serve as a source for several hundred cells. The HEX sense device Sl is formed of an integrated circuit, each of its cells having the same characteristics as the other cells. For this reason, the current flowing from the drain to the auxiliary source 40 is approximately proportional to the current flowing from the drain 18 to the main source 16, where the proportionality is greater than the small number of cells connected to the terminal 40 versus the terminal 16 determined by the ratio of the majority of cells connected to the Further details of the HE X S sense device S1 can be found at
No. AN-959 published in 1986 by the assignee.
It is shown in "Application Notes for Power MO3FET" and is described here for reference. From the description of the multi-cell structure of switch S1 mentioned above, H
It will be obvious to those skilled in the art that other types of multi-cell switching devices may be used here instead of EXS sense devices. For example, a multi-cell thyristor device would be a suitable replacement. Returning to FIG. 2A, auxiliary terminals 40 and 42 are connected to a current sensing circuit 43 consisting of PNP bipolar transistors 44 and 46 and resistors 48 and 50. Current from switch SI flowing through auxiliary terminal 40 is directed to transistor 44 controlled by a bias signal, resulting in a voltage drop across resistor 48 . transistor 44
Neglecting the base current of , the voltage drop across resistor 48 is proportional to the current flowing through terminal 40 and therefore
proportional to the load current flowing through the The voltage at node 52 is then proportional to the load current. Transistor 44 functions as an impedance conversion device that couples from auxiliary node 4'0 on the high potential side to resistor 48 on the low potential side. This allows resistor 48 to have a preferred low value, such as: Transistor 46 of circuit 43, which shorts the base and collector and functions as a PN diode, provides a bias current to the mirror circuit. Transistors 44 and 46 are preferably formed of matched silicon to have equal turn-on thresholds from emitter to base. Resistors 48 and 50 of current sensing circuit 43 are preferably, but not necessarily, selected such that a current equal to their resistance flows when an overcurrent condition occurs in the load (at the overcurrent trip point). Ru. The circuit designer determines that the voltage at node 52 is based on the ratio of the number of cells in the HEX sense switch S, connected to the auxiliary terminal 4.0 to the number of cells in such a switch connected to the load 14. Resistor 4 so that it changes linearly with the load current.
8 and 50 can be selected. The circuit designer
However, resistors 48 and 50 may be selected based on ratios different from those described above so that the voltage at node 52 varies linearly with load current. This allows the circuit designer to use resistor 4 to convert the relative voltage change at node 52 into a change in current level at load 14.
8 and 50 can be selected. With the line voltage at the node (FIG. 2A) nominally 12V, PNP transistors 44 and 46 are typically 20V.
have a β value of 0 and a breakdown voltage of 60V, and resistors 48 and 50 are typically 487Ω and 9.5Ω, respectively. lKΩ
has the value of In order to eliminate any sharp current potential at turn-on, an additional 0.001 or 0. O
A 1 μF capacitor 49 (shown as a phantom line) connects the resistor 48
connected to. The voltage at node 52 of current detection circuit 43 is applied to the input of comparator 62, the other input node of which is connected to a reference voltage level 64 selected for determining the overcurrent level. The output of the comparator 62 is connected to a 12V to 5V level shifter 66 for convenient processing with standard 5V logic circuits. When the voltage at node 60 exceeds the voltage at reference level voltage 64, comparator 62
It is output, processed by a voltage reference shifter 66, and applied to the gate override circuit 26 described in connection with FIGS. 1 and 4. Current sensing circuit 43 may be replaced by any other circuit that provides a voltage at node 60 of comparator 62 that is exactly proportional to the load current. Another preferred current sensing circuit is shown as circuit 70 in FIG. 2B. Similar to the circuit 43 of FIG. 2A, the circuit 43 of FIG.
The illustrated circuit 70 preferably includes two bipolar transistors 44' and 46' and resistors 48° and 50'. Transistor 44° and resistor 48 of circuit 70
' functions in the same manner as the similarly labeled elements of circuit 43 of FIG. 2A. However, separately the PNP bipolar transistor 72
is coupled to transistor 46°. The addition of transistor 72 provides constant operation of circuit 70 despite large changes in ambient temperature and provides some improvement in stability of operation as the supply voltage changes. With the exception of matched silicon transistors 44 and 46, both current sensing circuits 43 and 70 (FIGS. 2A and 2B) are advantageously formed from inexpensive discrete individual components. In the current detection circuit 70, the PNP) transistor 44'
, 46' and 72 preferably have a β value of generally 200 and a breakdown voltage of 60V, and resistors 48'' and 50' preferably have a β value of 240Ω and 60V, respectively.
．． It has Ω at 5. A shunt capacitor 49' (shown in phantom) is additionally connected to resistor 48' to remove the sharp current potential during turn-on. Typically its value is 0.001 or 0.01 μF. In FIG. 4, the gate override circuit 26 described with respect to FIG. 1 is shown in more detail. Considering Figure 4, we find that
The overcurrent signal from overcurrent detection 1124, typically 5 volts, is provided to the reset terminal of a reset/set latch 80 formed by a CMOS Nant gate (not shown). A signal applied to the reset terminal of latch 80 is applied to the set/reset latch 8 from gate control function 28.
A set of 0 disables any 5V signal from the microprocessor applied to the human power section. The output of set/reset latch 80 is processed by Bridriver circuit 82 and provided as an appropriate bias signal to gates G and G4 of switches SI and S4 (FIG. 1). The high potential side gates Gl and G3 are preferably supplied with a bias voltage approximately 12V higher than the supply voltage;
This voltage may be generated by a conventional voltage doubling circuit (not shown). On the other hand, the gates G and G on the low potential side,
On the other hand, a supply voltage of 12V is generally applied as a bias voltage. The bridriver circuit 82 cooperates with a corresponding bridriver circuit (not shown) of the gate disable circuit 32 (FIG. 1) to provide the bias voltage described above. The aforementioned Bridriver circuit has one logic input from the latch 80 that controls the control switch S and S3 as shown, and another logic input (not shown) that controls the other two switches. It can be designed to Apart from this, the Bridriver circuit has two logical human-powered toggle switches S and S2 or, conversely, toggle S3 and $
It can be designed to have other logic inputs similar to 4. The bridriver circuit 82 and its counterpart for switches S and S are configured to provide sufficient current flow to gates G through G4 so that sufficient current flows in one direction before causing current flow in the other direction to the load. It can also be designed to give a delay to the control signal. Apart from this, there is a gate control function 2 which is generally performed by a microprocessor.
8 and 34 (FIG. 1) may provide such a delay. FIG. 5 shows a more generalized form of the semi-invention, in which a -current switch SI' is provided on the high potential side of the load 14'. Overcurrent detector 24', gate invalidation circuit 26'
, and the gate control function 28' correspond to parts with the same reference numbers as in the °H" bridge type power divider described above. FIG. 6 shows yet another embodiment of the invention. , the same elements as in Fig. 2A are given the same numbers.
The figure differs from FIG. 2A in that a resistor 90 is connected between the bases of transistors 44 and 46 and ground;
The collector of transistor 46 is directly grounded. 6th
The circuit shown in the figure is found to have a change in current ratio with changes in voltage, current and transistor resistance due to temperature changes. These problems are largely avoided in the circuit of FIG. 2A. However, the circuit of FIG. 6 illustrates the principle of operation of the circuit of FIGS. 2A and 2B and is sufficient for some applications. In the circuit of FIG. 6, resistor 48 has a resistance value of 1000Ω, and resistor 90 has a resistance value of 50Ω.
It has a resistance of 1 to 100 Ω. [Effects of the Invention] A power distribution circuit for supplying load current to a load has been described. This power distribution circuit includes an overcurrent detection circuit for detecting an overcurrent condition of the load. The power distribution circuit of the present invention includes:
A circuit in the form of an "H" bridge may be included to provide current of selectable polarity to the load. Additionally, an accurate and reliable overcurrent detection circuit applying the so-called current mirror concept may be included. The power distribution circuit of the present invention can use discrete components that are inexpensive and easily procured. Although the invention has been described in conjunction with a preferred embodiment, many other variations will be apparent to those skilled in the art. Therefore, the invention is limited not only by the specification, but only by the scope of the appended claims.

[Brief explanation of drawings]

FIG. 1 is a partial block diagram schematically showing the present invention used in a so-called "H" bridge circuit, FIG. 2A is a partial block diagram of the current switch s1 and overcurrent detector 24 of FIG. 1, and FIG. 2B is a block diagram of a selective current sensing circuit that may be used in the overcurrent detector of FIG. 2A, and FIG. 3 is a block diagram of a multi-section current switch used to implement switch s1 of FIG. 4 is a block diagram of a subcircuit included in the gate disabling circuit 26 of FIG. 1; FIG. 5 is a block diagram of a general form of the present invention; and FIG. 6 is a block diagram of a general form of the present invention. FIG. 3 is a circuit block diagram of another embodiment. 10... H bridge circuit, 12... Control circuit, 14... Load, 16.18,2
0.22... Node, 24.30... Overcurrent detector, 26.32... Gate invalidation circuit, 28... Gate control function, 40.42... Auxiliary terminal, 43... Current detection circuit, 44.46...Transistor, 48.50...Resistor, 49...Capacitor, 62...Comparator, 64...Reference voltage level, 66...Voltage reference shifter 70...・Current detection circuit, 72...Transistor, L, or L4...Leg of load, Sl or s4...Current switch, G, or G1...Gate, CI or Cn...Cell

Claims (10)

[Claims] (1) A power distribution circuit for supplying load current to a load, which includes a power node for connecting to a power source, a load node for connecting to a load, and a control signal whose switch state is connected to a control terminal. a high potential current path for supplying current from a power node to a load node; and a controlled current switch responsive to an electrical condition of the high potential current path and detecting a current level in the high potential current path. a current sensing circuit for a device comprising a resistor connected between a first auxiliary terminal and ground and producing a voltage at one end approximately proportional to the main device current, and an impedance transformation controlled by a bias signal, such as a transistor; connected between one branch containing the series circuit of the device and a second auxiliary terminal and the grounding means;
and another branch providing a bias current for the impedance conversion device of the first branch. (2) The power distribution circuit according to claim 1, further comprising current interrupting means for turning off a current switch in the high potential current path when the current detection circuit detects a current exceeding a predetermined level in the high potential current path. . (3) The current switch in the current path of high potential includes a multi-cell device with a large number of terminals, the first main current terminal connected to the power means, a large number of device cells connected to the foot of the load. a second main current terminal that connects to individual node ends of the main current terminal, a first auxiliary terminal that has one end connected to a small number of device cells to provide a current that is generally proportional to the main device current; 2. The power distribution circuit of claim 1, further comprising a second auxiliary terminal having one end connected to a plurality of device cells, and wherein the current sensing circuit is responsive to electrical conditions of the first and second auxiliary terminals. (4) further comprising a second impedance conversion device coupled between the load node and the ground within the other branch, the second impedance conversion means being an impedance replacement device controlled by the bias signal; 2. The power distribution circuit of claim 1, wherein the power distribution circuit is coupled to. (5) an "H" bridge type power distribution circuit having two node ends and a load leg having means for connecting to the load, and a power source for connecting to a power supply for supplying current to the load; means for providing a path for the load current to return to the power supply; and a first current path for supplying the load current to the load in a first direction, the first current path between the power means and the load. a first high potential leg connected between a node end of the load leg and a first low potential leg connected between a second node end of the load leg and the grounding means; a second current path for supplying a load current to the load in a second direction, the second current path connected between the power means and a second node end of the leg of the load; a second current path comprising a high potential leg and a second low potential leg connected between the first node end of the load leg and the grounding means; Each leg is equipped with a current switch,
The switching state is controlled by a control signal coupled to the control terminal, and the power distribution circuit is further coupled to the respective electrical states in the first and second high potential legs to detect current levels in the legs. A power distribution circuit comprising responsive first and second current detection circuits. (6) when the respective current detection circuits associated with the first and second high potential legs detect an excess of a predetermined level;
6. The power distribution circuit of claim 5 further comprising current interrupting means for turning off at least a current switch in such foot. (7) The current switch in the first and second high potential legs comprises a multi-cell device with a number of terminals, as the number of terminals the first main current terminal connected to the power means, a number of devices a second main current terminal that connects the cells to individual node ends of the load legs; a first auxiliary, one end of which is connected to a small number of device cells to provide a current that is generally proportional to the main device current; 6. The power distribution of claim 5, comprising a terminal and a second auxiliary terminal having one termination connected to a plurality of device cells, and wherein the current sensing circuit is responsive to electrical conditions of the first and second auxiliary terminals. circuit. (8) further comprising a second impedance conversion device coupled between the load node and the ground within the other branch, the second impedance conversion means coupled to the bias-controlled impedance conversion device; The power distribution circuit according to claim 5. (9) The first and second impedance conversion devices described above both include first and second bipolar transistors, respectively, and further include a third bipolar transistor, and the emitter and collector of the third transistor are 5. The power distribution circuit of claim 4, wherein the power distribution circuit is connected between the common base of the first and second bipolar transistors and ground, and the base electrode of the third transistor is connected to a node between the transistor and the resistor in the second branch. . (10) The first and second impedance conversion devices described above both include first and second bipolar transistors, respectively, and further include a third bipolar transistor, and the emitter and collector of the third transistor are 9. The power distribution circuit of claim 8, wherein the power distribution circuit is connected between the common base of the first and second bipolar transistors and ground, and the base electrode of the third transistor is connected to a node between the transistor and the resistor in the second branch. .