TECHINCAL FIELD
Embodiments of the present disclosure relate to short circuit protection systems. More particularly  the embodiments relate to output driver short-circuit protection for automotive applications.

BACKGROUND OF DISCLOSURE
In general  for controlling an electrical component a semiconductor switch such as a transistor can be used. A semiconductor switch typically controllably transform between a conducting state and a non-conducting state to turn the electrical component ON and OFF respectively.

One concern in the control of electrical components is in short circuit protection of semiconductor switches involved. Consider  for example  if a semiconductor switch is used at the high side of an electrical component. There is a chance that a short circuit to ground which may occur at the high side of the electrical component can cause the semiconductor switch to “over dissipate” when the semiconductor switch turns ON. Thus  the result can be excessive power dissipation within the semiconductor switch  which can potentially damage or destroy the semiconductor switch.

One prior art provides the concept to detect the short circuit of the high side driver as shown in Fig. 1. The system as shown in Fig. 1 includes a capacitor having a charge state. When the capacitor is charged  the electric load is ON via a transistor. The system automatically latches the electrical load ON until short circuit occurs or until the capacitor discharges. When a short circuit occurs  the system automatically turns the load OFF. Under normal operating conditions  microcontroller 12 provides logic high output for a predetermined amount of time  thereafter reconfigures terminal 22 as an input and starts sensing the voltage  if the voltage sensed is high then there is no short circuit.

If short circuit happens  ground voltage will appear at load. Capacitor 46 is charged to approximately 5 V by voltage applied by transistor 26 being divided by the series combination of resistors 48  44 and 34  due to short circuit resistor 34 and 49 act to limit the current that is supplied by transistor 26. Therefore the voltage at the electric load will drop to essentially zero volts. Once the voltage drop to zero occur  the capacitor 46 discharges after turning electrical load 14 ON. Thereupon  the microprocessor 12 reconfigures terminal 22 as an input terminal and will detect the low voltage.

The prior art system as shown in Fig. 1 has few disadvantages  such as no isolation between the input and output circuit  and the circuit cannot be used for low side driver.

Another prior art for short circuit protection circuit is shown in Fig. 2. The circuit includes a power supply  and an opto coupler. The optocoupler includes a light-emitting diode (LED) and a phototransistor  R1 is connected between D1 cathode and the LED. Cathode of light emitting diode connected to ground  the collector of the phototransistor is connected to the cathode of diode D1 through R2  emitter of phototransistor is grounded via a load circuit.

The disadvantages of the short circuit protection circuit as shown in Fig. 2 are that  in case of short circuit condition the phototransistor will burn due to excessive current flow and there is no provision to switch OFF the LED during the short circuit condition.

Conventionally automotive ECU use costly smart-switches for driving high-current output loads. Also  smart switches consume two CPU pins for interfacing; viz. output pin for operating the switch and an input pin for detecting short-circuit status. This implementation uses a single CPU pin for both these purposes.

Thus  there is a need of a solution to provide effective short circuit protection with minimal complexity. In addition  solution needs to be simple and provide a low cost implementation for short circuit protection using off-the-shelf components.

OBJECTIVES OF THE DISCLOSURE
The objective of the present disclosure is to provide a cost- effective and reliable short circuit protection system for a high side as well as low side driver.

SUMMARY
The shortcomings of the prior art are overcome and additional advantages are provided through the provision as claimed in the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

One embodiment of the disclosure provides a driver circuit with short circuit protection. The driver circuit comprises at least one solid state switch connected in series with a resistor to receive an input voltage. The solid state switch is turned ON based on the input voltage to provide an output current to a load. Also  the circuit comprises an optocoupler transmitter connected in parallel combination with the load. The optocoupler transmitter illuminates based on the output current provided by the switch. Further  the driver circuit comprises an optocoupler receiver connected to the input of the switch to provide predetermined current to operate the switch in ON condition. The optocoupler is turned ON based on the illumination received from the optocoupler transmitter. Further  the driver circuit comprises a voltage regulator connected between the input of the switch and ground to provide regulated voltage across the switch. A control unit is configured to trigger the driver circuit by providing predefined voltage through the pin which acts as one of either output pin to trigger the driver circuit or input pin to sense voltage in the driver circuit to detect the short circuit. The pin of the control unit senses the short circuit condition based on variation in voltage sensed. Thus  the control unit notified or signals the short circuit condition.

One embodiment of the disclosure provides a method for short circuit protection of a driver circuit system in automotive applications. The method comprises providing a voltage to activate the driver circuit system using a pin of a control unit acting as an output pin. The voltage biases at least one solid state switch that in turn switches ON optocoupler transmitter and optocoupler receiver to generate an output voltage on a load. Also  the method configuring the pin of the control unit for sensing voltage in the driver circuit periodically for detecting short circuit condition in the load thereby switching OFF the at least one solid state switch to switch OFF the driver circuit system.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects  embodiments  and features described above  further aspects  embodiments  and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself  however  as well as a preferred mode of use  further objectives and advantages thereof  will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described  by way of example only  with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Fig 1 shows an electrical schematic of a prior art short circuit protection system for high side driver.

Fig 2 shows an electrical schematic of a prior art short circuit protection system using optocoupler.

Fig. 3 shows an electrical schematic of an automotive high side driver with short circuit protection  in accordance with an embodiment.

Fig 4 shows an electrical schematic of an automotive low side driver with short circuit protection using single transistor  in accordance with an embodiment.

Fig. 5 shows an electrical schematic of an automotive low side driver with short circuit protection using MOSFET  in accordance with another embodiment.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure  both as to its organization and method of operation  together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood  however  that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

Referring now to the drawings wherein the drawings are for the purpose of illustrating an exemplary embodiment of the disclosure only  and not for the purpose of limiting the same.

To overcome the drawbacks mentioned in the background  the disclosure provides short circuit protection circuit for a series voltage regulator  which is also a cost effective solution.

An exemplary embodiment of the present disclosure provides a short circuit protection system for driving high current automotive loads. The system makes use of off-the-shelf solid state switch such as power transistor  field effect transistor (FET) or metal oxide semiconductor field effect transistor (MOSFET) for driving high current automotive loads. The short circuit protection is provided by employing an opto-isolator technique or scheme. A control unit triggers the solid state switch on by means of an edge signal on an output pin. Thereafter  the output pin is reconfigured as input for monitoring the short-circuit condition. The control unit is one of central processing unit (CPU)  microcontroller  microprocessor  field programmable gate array (FPGA) and application-specific integrated circuit (ASIC). The opt-isolator technique detects and protects the driver from short-circuit as well as notifying the CPU input pin about the short circuit  by means of voltage changes on the input pin. The CPU may employ a short-circuit recovery application by retrying the switch ON operation periodically.

Fig.3 shows a circuit diagram of short circuit protection system for driving high current automotive loads (i.e. a circuit diagram automotive high side driver with short circuit protection. The driver comprises two solid state switches i.e. transistors (Q1  Q2)  resistors (R1 to R5)  zener diode (D1) and optocoupler (U1) or OPTO coupled to load (RL). The solid state switch is one of a bipolar junction transistor (BJT)  field effect transistor (FET) and metal oxide semiconductor field effect transistor (MOSFET). The optocoupler includes optocoupler transmitter i.e. light emitting diode (LED) and an optocoupler receiver i.e. a photo transistor. The three components used in the driver circuit diagram to obtain the logic of low cost high side driver are NPN Transistor (Q1)  PNP Transistor (Q2) and optocoupler (U1). Also  a CPU triggers a switch on by means of an edge signal on an output pin. The CPU is one of a processing unit or control unit or a microcontroller.

In one embodiment as shown in Fig. 3  initially the microcontroller pin is configured as an output and provides a logic high level to make Q1 which is an NPN transistor turn ON. When the microcontroller pin is turned as input  the Q1 will be maintained in ON state through photo transistor. The Q1 is to make the Q2 or PNP transistor ON  which in turn will ON the optocoupler. The transistor Q1 is the main transistor to turn ON the optocoupler which helps to turn ON the load (RL).

The optocoupler is powered ON through the transistor Q2. When the LED of the optocoupler is ON then it will trigger the photo transistor of the optocoupler. If the microcontroller pin is turned as an input  then phototransistor will provide supply to the transistor Q1 which thereby keeps the load RL ON.

In one embodiment  the microcontroller port pin connected to resistor R1 as shown in Fig. 3. The other end of resistor R1 is connected to emitter of the phototransistor  cathode of zener diode D1 and one end of resistor R3. Anode of zener diode is connected to ground (GND). Collector of the phototransistor is connected to one end of resistor R2. Base of transistor Q1 is connected to another end of resistor R3. Emitter of NPN transistor Q1 is connected to GND. Resistor R4 is connected between collector of NPN transistor Q1 and Base of the PNP transistor Q2. The other end of resistor R2 and emitter of PNP transistor Q2 is connected to 12V. Anode of light emitting diode is connected to collector of PNP transistor through resistor R5  the cathode of the light emitting diode is grounded.

In one embodiment of the present disclosure is an optocoupler technique along with a single microcontroller  whose pin is used as output as well as input  detects the short circuit and drives the load. Initially the microcontroller pin acts as output and issues a logic high  which will make the NPN transistor (Q1) turn ON. The NPN transistor (Q1) provides the necessary current to the PNP transistor (Q2)  which turns ON thereby provides the required current to the optocoupler photo diode or optocoupler light emitting diode (U1) to turn ON. When the LED of the OPTO is made ON then it will trigger the photo transistor of the optocoupler and provides supply to load RL.

To detect short circuit of the load  the same microcontroller pin is changed to input and reads the feedback voltage from the load. The Q1 still remains on  since U1 transistor provides supplying current to the base drive. If no short circuit is detected  then microcontroller pin which is in input condition will get high voltage and remains as input to read feedback voltage from the load further.

In another embodiment  if a short-circuit condition i.e. load is shorted to ground  would lower the voltage sensed by the microcontroller input pin. The microcontroller may periodically conjure itself as output and try recovering the short-circuit condition  if external short-circuit fault is rectified. Until the short circuit is removed the controller pin may be toggling from output to input in order to read the high voltage from the load as a feedback. This method will execute the circuit in closed loop manner to detect the short circuit.

Fig. 4 shows the electrical schematic for automotive low side driver with short circuit protection using only single solid state switch  in accordance with another embodiment of the present disclosure. The solid state switch is one of a bipolar junction transistor (BJT)  field effect transistor (FET) and metal oxide semiconductor field effect transistor (MOSFET). The solid state switch used is a bipolar junction transistor Q1. The control unit or microcontroller pin is responsible to give output high to drive the load  as well as the same pin is configured as an input to detect the short circuit. The pin of the microcontroller is connected to the resistor R1  another end of resistor R1 is connected to the zener diode D1 cathode  optocoupler receiver or photo transistor emitter and resistor R3. The resistor R3 is connected to the base of the solid state switch i.e. transistor Q1. Collector of the photo transistor is connected to 12 V through resistor R2. A logic high voltage supplied from microcontroller will saturate transistor Q1. The collector of transistor Q1 is connected to the cathode of optocoupler transmitter or Light emitting diode (LED) and Load RL. The anode of the LED is connected to the 12V through resistor R4. The transistor is saturated with the logic high voltage applied by the microcontroller; the LED will turn ON  which will trigger the photo transistor to turn ON. Thereafter  the microcontroller pin is changed to an input to read the feedback voltage from the load RL. The transistor Q1 still remains ON  since U1 transistor keeps supplying the base to drive the load RL.

In one embodiment  if no short circuit is detected  then the microcontroller pin which is in input condition will get high voltage and remains as input to read feedback voltage from the load.

In another embodiment  if a short-circuit condition i.e. shorted to +12V exists then it would lower the voltage sensed by the micro-controller input. The micro-controller can now attempt to periodically conjure itself as output and try recovering the short-circuit condition  if external short-circuit fault is rectified. Until the short circuit is removed  the controller pin will be toggled from output to input in order to read the high voltage from load as a feedback. This process will execute the circuit in closed loop manner to detect the short circuit.

Fig. 5 shows an electrical schematic for automotive low side driver with short circuit protection using MOSFET as a solid state switch  in accordance with an alternate embodiment. The microcontroller port pin connected to resistor R1  other end of the resistor R1 is connected to emitter of photo transistor i.e. optocoupler receiver  cathode of zener diode D1  one end of resistor R3 and gate of MOSFET Q1. The terminals anode of the zener diode  other end of R3 and source of MOSFET Q1 are connected to GND. Collector of photo transistor is connected to 12V through resistor R2. Resistor R4 is connected between anode of light emitting diode (LED) of optocoupler U1 and 12V. Cathode of the LED is connected to drain of MOSFET Q1 and load (RL). The working principle of microcontroller and optocoupler in low side driver with short circuit protection with MOSFET is same as low side driver with single transistor as shown in Fig. 4  except that the solid state switch is MOSFET Q1 is used to give active low signal to drive the load RL as shown in Fig. 5.

The advantages of the driver circuits with short circuit protection are that  the circuit works using a single microcontroller pin. Also  this reduces the CPU utilization and memory usage since there is no need of checking feedback periodically. Further  this technique can be used for high side driver as well as low side driver with minor changes in circuit  which is cost effective in comparison with automotive driver chips or conventional short circuit protection schemes.

The present disclosure is not to be limited in terms of the particular embodiments described in this application  which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope  as will be apparent to those skilled in the art. Functionally equivalent methods and devices within the scope of the disclosure  in addition to those enumerated herein  will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims  along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only  and is not intended to be limiting.

With respect to the use of substantially any plural and/or singular terms herein  those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

In addition  where features or aspects of the disclosure are described in terms of Markush groups  those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

While various aspects and embodiments have been disclosed herein  other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting  with the true scope and spirit being indicated by the following claims.

We claim
1. A driver system with short circuit protection comprising:
at least one solid state switch connected in series with a resistor to receive an input voltage, said solid state switch is turned ON based on the input voltage to provide an output current to a load;
an optocoupler transmitter connected in parallel combination with the load, wherein the optocoupler transmitter illuminates based on the output current provided by the solid state switch;
an optocoupler receiver connected to the input of the solid state switch to provide predetermined current to operate the solid state switch in ON condition, wherein said optocoupler is turned ON based on the illumination received from the optocoupler transmitter; and
a voltage regulator connected between the input of the solid state switch and ground to provide regulated voltage across the switch;
2. The system as claimed in claim 1, wherein the solid state switch provides a variable resistance based on the current flowing, said resistance varies with operating conditions of the voltage regulator circuit.
3. The system as claimed in claim 2, wherein the solid state switch is one of a bipolar junction transistor (BJT), field effect transistor (FET) and metal oxide semiconductor field effect transistor (MOSFET).
4. The system as claimed in claim 1, wherein the voltage regulator is a zener diode.
5. The system as claimed in claim 1, wherein the system comprise a control unit configured to trigger the driver circuit by providing predefined voltage through a pin, said pin acts as one of output pin to trigger the driver circuit and input pin to sense voltage in the driver circuit to detect the short circuit.
6. The system as claimed in claim 5, wherein the control unit is one of central processing unit (CPU), microcontroller, microprocessor, field programmable gate array (FPGA) and application-specific integrated circuit (ASIC).

7. The system as claimed in claim 5, wherein the pin of the control unit is re-configured as input for monitoring short circuit condition when the optocoupler receiver starts conducting.
8. The system as claimed in any one of the preceding claims, wherein the control unit generates an output signal upon detecting the short circuit condition based on variation in the voltage sensed by the pin.
9. A method for short circuit protection of a driver circuit system in an automotive applications comprising:
providing predetermined voltage to activate the driver circuit system using a pin of a control unit acting as an output pin, wherein said voltage biases at least one solid state switch that in turn switches ON optocoupler transmitter and optocoupler receiver to generate an output voltage to a load; and
configuring the pin as an input pin by the control unit for sensing voltage in the driver circuit periodically for detecting short circuit condition in the load thereby switching OFF the at least one solid state switch to switch OFF the driver circuit system.
10. The method as claimed in claim 9, wherein the at least one solid state switch output current provides necessary bias current to the opto-coupler transmitter to generate illumination.
11. The method as claimed in claim 9, wherein the optocoupler transmitter becomes reverse biased to turn OFF the optocoupler receiver when the load is short circuited to ground.