NL8401648A - INTEGRATED VOLTAGE CONTROL CIRCUIT WITH TRANSIENT PROTECTION. - Google Patents

Description

Tr N.O. 32440

Integrated voltage control circuit with protection against transients .__

The invention generally relates to voltage control circuits, and more particularly relates to an integrated circuit voltage regulator which may have high transient voltage deviations, such as occur in motorized transport applications.

Electronic systems often have voltage regulators or control circuits that draw electrical current at an unregulated supply voltage and deliver a regulated voltage to an electrical load. In modern systems, many load circuits, 10 requiring electrical power, are integrated circuits. Integrated circuits and sensors used in conjunction with them require relatively low voltages, typically of six volts or less. In conjunction with these circuits and sensors, it has become common to provide voltage control using integrated circuit voltage regulators that are powered on a separate chip or on the same chip as the integrated circuit.

Monolytic integrated circuits are increasingly used in motorized transport applications. The motorized transport environment places particularly strict voltage control requirements. Voltage transients of 80 or 90 volts of either polarity to ground may occur in the supply conductors due to the interaction of the alternator and the main voltage regulator, when the engine is turned off or started quickly, or when a battery lead is removed or some other electrical disconnected. In addition, motorized transport devices must be able to operate over a wide range of temperatures.

Therefore, a voltage regulator for many electronic damage must be! Motorized transport applications provide a relatively tightly regulated low voltage from a supply voltage that is subject to positive and negative voltage deviations many times the size of the controlled voltage. Furthermore, the voltage regulator must be able to provide such regulation or regulation over a wide temperature range. Ultimately, in motorized transport applications, cost and reliability are of great importance. Costs must be kept to a minimum which therefore requires a relatively simple circuit design that can be easily fabricated.

A problem encountered in circuits equipped with bipolar transistors is that such transistors, which may have voltage transients of the size expected in motorized transport applications, are difficult to fabricate using the conventional processes for manufacturing monolytic integrated circuits. Accordingly, integrated circuit voltage regulators in motorized transport applications must have some form of protection against transient voltages. Various circuit designs and techniques for providing protection against transient voltages are known.

One approach is from U.S. Patent 4,319,179 to W. Jett Jr. of March 9, 1982. In this approach, a transistor, which can tolerate or have a high voltage, is applied and interposed between a control pass device and an error amplifier driving the pass device. The ability to tolerate a high voltage is obtained through a circuit that reduces the impedance between the base of the transistor and ground in the case of a moderate transient voltage on the power supply conductor. When a high transient voltage occurs, the base is essentially shorted to ground.

Although such a circuit increases the transistor's ability to withstand voltage, the maximum allowable voltage is still limited to a little less than the breakdown voltage of the transistor when it is short-circuited to ground. This voltage limitation may be insufficient for many motorized transport applications. The application of a voltage higher than the breakdown voltage for an arbitrarily estimated duration results in the destruction of the transistor and a malfunction in the regulator.

Furthermore, the application of a voltage that short-circuits the base electrode to ground results in loss of voltage control voltage. Even a momentary loss of control can result in an erroneous operation of the logic circuits fed by the regulator. Ultimately, certain other transistors in the regulator 35 are relatively unprotected, and may be subject to destructive voltages under certain conditions.

Many of the limitations of known designs for protection against voltage transients have been avoided in the present voltage regulator, which regulator provides a significantly increased breakdown limit for the entire regulator and voltage regulation up to breakdown limit 8401648 J t 3. In transistor breakdown conditions, current through the regulator is limited by internal impedances. Therefore, exceeding the transistor breakdown voltage will not necessarily result in destruction of the regulator.

The invention provides an integrated circuit voltage regulator comprising a first transistor type pass transistor which is protected against transient voltage deviations of both polarities by a bias transistor which supplies an electric current to the pass transistor and a reverse voltage transistor. 10 voltage diode connecting the junction of the forward and biasing transistors to a source of reference potential. First and second base driving means provide constant base driving signals to the pass and bias transistors whereby the bias transistor and its base drive means protect the bias transistor against transient voltages of a first polarity and the diode protects the bias transistor against transient voltages of a second polarity.

The biasing transistor may have a resistor in series therewith to limit the current through the transistor when it enters an electrical breakdown state due to an excessive voltage of the second polarity. The resistor may be a diffused resistance of a first conductivity type in an electrically insulated well of a second conductivity to further block transient voltages of the first polarity. The base drive means for the pass transistor may include a zener diode and a current source which provides sufficient current to sustain breakdown of the diode. Protection of the base of the forward transistor against excessive voltage variations of the first polarity can be provided by a diffused resistor and a transistor in the same manner as the protection obtained by the biasing transistor and diffused resistor. The zener diode protects the base of the forward transistor from excessive voltage deviations from the second polarity.

The invention will be further elucidated with reference to the drawing, in which Fig. 1 shows a diagram of a first embodiment of a voltage regulator according to the invention; and Fig. 2 shows a diagram of a second embodiment of a voltage regulator according to the invention.

40 In FIG. 1, an input terminal 11 for picking up 8401648 4 is an unregulated voltage which is subject to significant positive and negative voltage transients. This voltage is controlled and applied as a constant voltage to an output terminal 12. The control circuit is designed to be advantageously manufactured as a monolytically integrated circuit using conventional epitaxial manufacturing processes.

In the control circuit, the final control or regulation is obtained by means of a control pass transistor 13 which is indicated as an NPN transistor, the emitter of which is connected to the output terminal 12. The input terminal 11 is connected via a pre-control circuit 14 to the collector of the transistor 13. A constant voltage for the basic control of the transistor 13 is obtained by means of a zener diode 15 of the cathode which is connected to the base of the transistor and of which the anode is connected to ground or other reference potential source 16. The diode 15 is biased to breakdown by means of a biasing circuit 17. As will be explained in detail below, both the pre-control circuit 14 and the bias circuit 17 are designed to prevent excessive positive and negative voltage transients from reaching the control pass-through transistor 13.

The pre-control circuit 14 has a PNP transistor 20 whose emitter is connected via a resistor 21 to the supply terminal 11 and whose collector is connected to the collector of the control-pass transistor 13. For purposes explained below, resistor 21 is preferably a diffused resistor of P-type material in an electrically insulated N-type well. The junction of the collectors of the transistors 13 and 20 is connected to ground 16 via a diode 22 whose cathode is connected to the collector junction and whose anode is connected to earth. The base of the transistor 20 is connected to the drain electrode of a field effect transistor (FET) 23 whose gate electrode is connected to ground 16 and whose source electrode is connected to the collector of an NPN transistor 24. Transistor 24 is interconnected with an NPN transistor 25 to form a current mirror. More specifically, the bases of transistors 24 and 25 are connected to each other and the emitters of the transistors are connected to ground 16. The collector of the transistor 25 is connected to the bases of the transistors and through a resistor 26 to the output terminal 12. From a field effect transistor 27, the drain is connected to the base of the transistor 20 and the source and gate are connected to ground 16.

40 In actual implementation, the pre-control circuit 14 was 8401648! (5 throws to limit the positive voltage at the collector of the control pass transistor 13 to approximately 34 volts, protecting this transistor 13 from excessive positive power transients. This clamping action is provided by the diode 22 where 5 serves the transistor 20 limiting the current when the diode 22 trips. The transistor 20 and the resistor 21 limit the current when the supply voltage to ground is negative. More specifically, both the transistor 20 and the resistor 21 form biased diodes when connected to a negative supply voltage are therefore subject, therefore neither the transistor nor the resistor will conduct current under these voltage polarity conditions.

The hasis drive for the transistor 20 is obtained by means of the resistor 26 and the current mirror consisting of the transistors 24 and 25. The emitter current in transistor 25 is determined by 15 the regulated voltage at output terminal 12 and the resistance value of resistor 26. Transistors 24 and 25 are configured with suitable parameters to provide this emitter current with a desired multiple (e.g. 5 times) in the transistor 24 to increase. The collector current in the transistor 24 is applied through the field effect transistor 23 to the base of the transistor 20. The field effect transistor 23 serves to limit the voltage to which the collector of the transistor 24 is subjected to the transistor against the protect the influence of large positive supply voltage transients. The field effect transistor 27 ensures a sufficient base driving current 25 for the transistor 20 to initiate the start of the control circuit.

The biasing circuit 17 provides a current sufficient to keep the zener diode 15 breakdown while protecting the base of the transistor 13 from excessive voltage transients. The biasing circuit contains a current mirror consisting of the PNP transistors 30 and 31, the emitters of which are connected via a resistor 32 to the power supply terminal 11. Transistors 30 and 31 and resistor 32 block negative power transients in the same manner as transistor 20 and resistor 21. The collector of transistor 30 is connected to the drains of the field effect transistors 33 and 34 whose ports are connected to ground 16. The source electrode of the field effect transistor 33 is connected to the base of the NPN transistor 35 and the collector of an NPN transistor 36. The source electrode of the field effect transistor 34 is connected to the collector of the transistor 40. The emitter of the transistor 35 is directly with the base of the 8401648 6

1 I

transistor 36 and connected to ground 16 via a resistor 37. The emitter of transistor 36 is also connected to ground 16.

In operation, the collector current in transistor 30 is equal to the sum of the currents through the field effect transistors 33 and 34. The emitter-5 current of transistor 30 is multiplied in transistor 31 by a predetermined factor (e.g. 4 times) and as bias current for the zener diode 15 is supplied. The portion of the collector current in transistor 30 which flows through the field effect transistor 33 turns on the transistor 35 which conducts the current applied to the field effect transistor 34 through the resistor 37 to ground 16. FIG. The transistor 36 limits the collector current of the transistor 35 to a value determined by the base emitter voltage of the transistor 36 divided by the resistance value of the resistor 37. The current through the field effect transistor 33 is effectively controlled by the characteristics of that device limited to the current it conducts when its gate and source are shorted. Therefore, a fixed current is supplied to the biasing diode 15. The field effect transistor 34 serves to protect the transistor 35 from positive power transients. When the current through transistor 30 is tightly regulated, the current applied to the cathode of diode 15 is also tightly controlled and the voltage at the base of transistor 13 is protected from the influences of positive and negative power transients.

In the embodiment of Figure 1 explained above, the Zener diode 15 provides a voltage reference to the forward transistor 13. In such a typical embodiment, the values of the circuit components were chosen to provide a controlled voltage of about 5.4 volts. In the circuit embodiment of Figure 2, a band interval reference is used to generate a temperature stabilized regulated voltage of about 3.2 volts. Except for the voltage reference device or circuit, the circuits of FIGS. 1 and 2 are essentially identical. The same components in the circuits of the two figures are denoted by the same reference numerals. A description of the embodiment of Figure 2 will be limited to the reference circuit for the band interval voltage.

The band interval voltage reference circuit of FIG. 2 includes an NPN transistor 40 whose collector is connected to the output terminal 12 and at the base of which a signal is applied 40 from a voltage divider consisting in series between the output terminal 8401648 r 7 12 and ground 16 included resistors 41 and 42 # The emitter of transistor 40 is connected via resistors 45 and 46 to collectors of a pair of NPN transistors 43 and 44, respectively. The resistance values of resistors 45 and 46 may be unequal. The collector of transistor 43 is connected to the bases of transistors 43 and 44. The collector of transistor 44 is connected to the base of an NPN transistor 47 whose collector is connected to the base of the pass transistor 13 and whose emitter is connected to ground 16. The emitter of transistor 43 is directly connected to ground 16 and the emitter of transistor 44 is directly connected to ground 16 via a resistor 48. Transistors 43 and 44 and resistor 48 together form a logarithmic current source.

In operation, the voltage at the base of transistor 13 is determined by the state of transistor 47 which is in turn driven by transistor 40. The voltage at the base of transistor 40 is a temperature-stabilized reference voltage equal to the sum of the base-emitter voltage drops of transistors 40 and 47 and the voltage drop across resistor 46. Current through resistor 46 is determined by the logarithmic current source . Therefore, the voltage across resistor 46 has a positive temperature coefficient that compensates for the negative temperature coefficients of the base-emitter junctions of transistors 40 and 47. The voltage divider consisting of resistors 41 and 42 provides an adjustment of the reference voltage.

In the circuit of Fig. 2, the band interval reference provides a lower regulated voltage than the zener diode 15 in Fig. 1. The diode 15 in Fig. 2 serves to protect against arbitrary excessive positive voltage transients that are too fast for an adequate response by the band interval reference voltage .

According to the above-mentioned explanation, the integrated circuit voltage regulator according to the invention is characterized by a considerably higher breakdown limit than with the known integrated circuit regulators. The control is not lost until the breakdown limit is exceeded. In the case of transistor breakdown, the internal circuit impedances continue to limit the current through the regulator so that it remains undamaged under all likely conditions to be expected.

Although two embodiments of the invention have been indicated and illustrated, various modifications can be made without departing from the scope of the invention.

0401648

Claims (10)

Integrated voltage regulating circuit, to which a current is supplied by a supply voltage source, the voltage output having positive and negative voltage transients with respect to a reference voltage, characterized by first and second transistors (13, 20) of opposite conductivity which are between the power supply source (11) and an output are connected in series; a current limiting element (21) between the supply voltage source (11) and the two transistors (13, 20); a diode (22) between the reference-10 voltage (16) and two current-carrying for the two transistors (13, 20. common connection electrodes in order to conduct voltage differences with a polarity at these common connection electrodes at a value below the breakdown voltage of the first transistor (13) and first and second basic control circuits (15, 17; 23-25) for supplying substantially constant signals to the bases of both transistors (13, 20). Integrated voltage control circuit according to claim 1, wherein the controlled voltage at the output is positive with respect to the reference voltage, characterized in that the first and second 20 transistors (13, 20) are formed by NPN and PNP transistors, which is the current limiting element (21) is disposed between the emitter of the second transistor (20) and the supply voltage source (11), and the emitter of the first transistor (13) forms the output (12); and that the diode (22) is connected with its cathode to the common collectors of both transistors (13, 20) and with its anode to the reference voltage (16). Integrated voltage control circuit according to claim 2, characterized in that the current limiting element (21) is a p-type conductivity resistor diffused into an electrically insulated n-type conductivity well. Integrated voltage control circuit according to claim 3, characterized in that the second basic control circuit comprises: a first current mirror (24, 25) with first, second and third terminals, which connect to the second at a current of a predetermined size 35 produces a proportional current to the third terminal and the first terminal of which is connected to the reference voltage (16); switching means (26) between the output (12) and the second terminal of the first current mirror (24, 25); and a first field effect transistor (23) included with its drain / source junction between the base of the second transistor 40 (20) and the third terminal of the first current @ 401648 it mirror (24, 25) and which is control electrode is connected to the reference voltage (16) # Integrated voltage control circuit according to claim 4, characterized in that the first control circuit has a zener diode (15) driven by a current source (17) and arranged in the base circuit of the first transistor (13), the current source (17) comprising : third and fourth transistors (36, 35) of the npn type conductivity, the collector of the third transistor (36) with the base of the fourth transistor (35), the emitter of the fourth transistor (35) with the base 10 his of the third transistor (36) and the emitter of the third transistor (36) is connected to the reference voltage (16); a resistor (37) connecting the base of the third transistor (36) and the emitter of the fourth transistor (35) to the reference voltage (16); a second current mirror (30, 31) with first, second and third terminals which produces a proportional current at the third terminal at a current of a predetermined size at the second terminal; a resistor (32) between the supply voltage source (11) and the first terminal of the second current mirror (30, 31); second and third field defect transistors 33, 34) whose gates are connected to the reference voltage 20 (16), whose outputs are connected to the second terminal of the second current mirror (30, 31) and whose sources are connected to the collectors of the third and fourth transistors (36, 35) are connected; and connecting the third terminal of the second current mirror (30, 31) to the base of the first transistor (13) and 25 to the cathode of the zener diode (15). Integrated voltage control circuit according to claim 5, characterized in that the resistor (32) between the supply voltage source (11) and the first terminal of the second current mirror (30, 31) is a p-type conductivity resistor which is electrically insulated. The learned n-type conductivity well is diffused. Integrated voltage control circuit according to claim 6, characterized in that the zener diode of the control circuit (15, 17) is connected between the base of the first transistor (13) and the reference circuit (16). Integrated voltage control circuit according to claim 7, characterized in that the first control circuit further comprises a reference voltage source comprising: a fifth transistor (47) of the npn conductivity type, the collector of which is connected to the base of the first transistor (13) and whose emitter is connected to the reference voltage (16) 40; a logarithmic power source (43, 44, 48) with first, 8401648 4 th second, third and fourth terminals, which in the case of a current of a first magnitude at the third terminal produces a current of unambiguously involved magnitude at the fourth terminal, the fourth terminal is connected to the base of the fifth transistor (47); 5 a resistor (48) for connecting the first and second terminals of the logarithmic current source to the reference voltage (16); a sixth npn transistor type (40) of which the collector is connected to the emitter of the first transistor (13) and whose emitter is connected via resistors (45, 46) to the third and fourth terminals of the 10 logarithmic current source (43, 44 , 48) is connected; and a third driver circuit (41, 42) for supplying an essentially constant voltage to the base of the sixth transistor (40). Integrated voltage control circuit according to any one of claims 6, 7 or 8, characterized in that the second control circuit further has a fourth field-effect transistor (27), whose drain is with the base of the second transistor (20) and whose source and port to the reference voltage (16). Integrated voltage control circuit according to claim 9, characterized in that the third control circuit consists of a voltage divider 20 (41, 42) between the output (12) and the reference voltage (16). -Η Ι Η -Ι I 8401648