JPH0571968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention generally relates to voltage regulator circuits;
More particularly, the present invention relates to integrated circuit voltage regulators capable of withstanding temporary high voltages such as those found in automotive applications.

[Background of the invention]

Electronic devices often include voltage regulators that receive current at an unregulated supply voltage and provide a regulated voltage to an electrical load.

In modern equipment, many of the load circuits that require power are integrated circuits. Integrated circuits and the sensors used in conjunction with them operate at relatively low voltages,
Typically requires a voltage of 6 volts or less. In connection with such circuits and sensors, it has become common to use integrated circuit voltage regulators to regulate the voltage, either on a separate chip or on the same chip as the integrated circuit being powered.

Monolithic integrated circuits are increasingly being used in automobiles. In automobiles, voltage regulation requirements are particularly demanding. 80 to 90 volts of either polarity with respect to ground due to interaction between the alternator and the mains voltage regulator in the event of an engine stop, start, or disconnection of the battery cable or disconnection of some other electrical connection. A temporary voltage of appears on the feeder line. Automobiles also need to operate over a wide temperature range.

Therefore, voltage regulators for many automotive electronic circuits must output relatively tightly regulated low voltages from a supply voltage that is subject to positive and negative voltage fluctuations many times larger than the regulated voltage. Moreover, such adjustments must be made over a wide temperature range. After all, cost and reliability are very important in automotive applications.
Cost must be minimized, thus requiring a simple and reliable circuit design that is easy to manufacture.

A problem encountered with circuits containing bipolar transistors is that conventional manufacturing methods for monolithic integrated circuits make it difficult to create transistors that can withstand transient voltages of the magnitude expected in automobiles. Therefore, automotive integrated circuit voltage regulators must include protection against some type of transient voltage. Various circuit designs and techniques for protection against transient voltages are known.

One method is described in U.S. Patent No. 3, 9, 1982, issued to Double
It is disclosed in No. 4319179. This approach includes a high voltage tolerant transistor between the regulator pass device and the error amplifier that controls the device. High voltage withstand capability can be obtained by a circuit that lowers the impedance between the base of the transistor and ground when the temporary voltage on the power supply line is of a moderate magnitude. In the event of a large transient voltage, the base is effectively shorted to ground.

Although such circuits increase the voltage resistance capability of the transistor, the maximum allowable voltage is still limited to being slightly less than the breakdown voltage of the transistor when the base is shorted to ground.
This voltage limit is not high enough in many automobiles. If a voltage higher than the breakdown voltage is applied for a considerable period of time, the transistor will be destroyed and the regulator will fail. Furthermore, if a voltage is applied that short-circuits the base electrode to ground, voltage adjustment becomes impossible. If regulation is not possible for even a moment, the logic circuit powered by the regulator will fail. After all, if certain transistors of the regulator are relatively unprotected, under certain conditions they will be subject to destructive voltages.

Because the voltage regulator of the present invention provides a significantly increased breakdown limit for the entire regulator and regulates the voltage up to that breakdown limit, the voltage regulator of the present invention has the protection design against conventional transient voltages. Many of the constraints are circumvented. Under transistor breakdown conditions, the current flowing through the regulator is limited by the internal impedance. Thus, exceeding the breakdown voltage of the transistor does not necessarily lead to breakdown of the regulator.

[Summary of the invention]

The present invention is an integrated circuit voltage regulator with an NPN pass transistor. This pass transistor consists of a PNP transistor as a preregulator and a reverse bias diode.
Protected against temporary overvoltages of either polarity.
The PNP transistor supplies current to the pass transistor, and the connection point between the pass transistor and the PNP transistor as a preregulator is connected to a reference potential via a reverse-biased diode.
The base electrode of the pass transistor is supplied with a substantially constant voltage from the first base drive means, and the base electrode of the PNP transistor is supplied with a substantially constant voltage from the second base drive means. A PNP transistor exhibits a high impedance when subjected to a negative temporary overvoltage to protect the pass transistor from the negative temporary overvoltage. The diode also protects the pass transistor from positive temporary overvoltages when subjected to positive temporary overvoltages.

〔Example〕

FIG. 1 is a circuit diagram of a first embodiment of the voltage regulator of the present invention, and FIG. 2 is a circuit diagram of a second embodiment of the voltage regulator of the present invention.

In FIG. 1, input terminal 11 is a terminal that receives an unregulated voltage that is subject to significant positive and negative transient voltages. This voltage is regulated and supplied to the output terminal 12 as a constant voltage. The regulator circuit is designed to be advantageously manufactured as a monolithic integrated circuit using conventional epitaxial manufacturing techniques.

In the regulator circuit, final regulation is performed by a regulator pass transistor 13, shown as an NPN transistor whose emitter is connected to the output terminal 12. Input terminal 11 is connected to the collector of transistor 13 via preregulator 14 . A constant base drive voltage of the transistor 13 is provided by a Zener diode 15 whose cathode is connected to the base of said transistor and whose anode is connected to ground or another reference potential source 16.
given by. Diode 15 is biased into breakdown by bias circuit 17. As will be explained in detail later, the preregulator circuit 14 and the bias circuit 17 are designed so that excessive positive and negative temporary voltages are not applied to the regulator pass transistor 13.

The preregulator circuit 14 includes a PN transistor 20 whose emitter is connected to the input terminal 11 via a resistor 21 and whose collector is connected to the collector of the regulator pass transistor 13. For purposes described below, resistor 21 is preferably a P-type diffused resistor in an electrically insulated N-type well. A phase connection point between the collectors of transistors 13 and 20 is connected to ground 16 through a diode 22 whose cathode is connected to this phase connection point and whose anode is connected to ground. The base of transistor 20 is connected to the drain electrode of field effect transistor (FET) 23. this
The gate electrode of the FET 23 is connected to the ground 16, and the source electrode is connected to the collector of the NPN transistor 24. The transistor 24
It is interconnected with the NPN transistor 25 to form a current mirror. More specifically, the bases of transistors 24 and 25 are connected in phase, and the emitters of the transistors are connected to ground 16. The collector of the transistor 25 is connected to the base of the transistor and is also connected to the output terminal 12 via a resistor 26. The drain of the FET 27 is connected to the base of the transistor 20, and the source and gate of the FET 27 are connected to the ground 16.

In a practical example, preregulator circuit 14 is designed to limit the positive voltage at the collector of regulator pass transistor 13 to approximately 34V, thus:
Transistor 13 was protected from excessive positive supply voltages. This clamping action is provided by diode 22, and transistor 20 serves to limit the current when diode 22 breaks down. Transistor 20 and resistor 21 limit the current when the supply voltage goes negative with respect to ground.
More specifically, the transistor 20 and the resistor 21
forms a reverse biased diode when subjected to a negative supply voltage. Therefore, neither the transistor nor the resistor normally conducts current under voltage conditions of such polarity.

Base drive for transistor 20 is provided via resistor 26 and the current mirror (consisting of transistors 24 and 25). The emitter current of transistor 25 is determined by the regulated voltage at output terminal 12 and the resistance value of resistor 26. Transistors 24 and 25 have suitable parameters and are formed such that this emitter current is amplified in transistor 24 by a desired factor (for example, 5 times).
The collector current of transistor 24 is supplied to the base of transistor 20 via FET 23.
FET 23 serves to limit the voltage across the collector of transistor 24, protecting it from the effects of temporary large positive supply voltages. FET 27 provides sufficient base drive current for transistor 20 to ensure starting of the regulator circuit.

Biasing circuit 17 provides a suitable current to maintain Zener diode 15 in breakdown while protecting the base of transistor 13 from excessive transient voltages. The emitter of this bias circuit is connected to the input terminal 11 via the resistor 32.
Includes a current mirror consisting of PNP transistors 30 and 31. Transistors 30 and 31 and resistor 32 block negative transient voltages in the same way that transistor 20 and resistor 21 do. The collector of transistor 30 is connected to the drains of FETs 33 and 34 whose gates are connected to ground. The source electrode of FET 33 is connected to the base of NPN transistor 35 and the collector of NPN transistor 36. The source electrode of FET 34 is connected to the collector of transistor 35. The emitter of transistor 35 is directly connected to transistor 3.
6 and to the ground 16 via a resistor 37. transistor 36
The emitter of is also connected to ground 16.

〔motion〕

The collector current of transistor 30 is FET33
and the current flowing through 34. transistor 3
The emitter current of 0 is amplified by a predetermined factor (for example, 4 times) by the transistor 31,
It is supplied as a bias current to the Zener diode 15. Transistor 30 flowing through FET33
A portion of the collector current enables transistor 35 to start, causing the current supplied to FET 34 to pass through resistor 37 to ground 16. Transistor 36 limits the collector current of transistor 35 according to the base-emitter voltage of transistor 36, which is divided by the resistance of resistor 37. Due to the characteristics of FET 33, the current flowing through FET 33 is effectively limited to the current flowing when its gate and source are shorted. Thus, a constant current is provided to bias diode 15.
FET 34 protects transistor 35 from positive temporary overvoltages. As the current through transistor 30 is precisely regulated, the current supplied to the cathode of diode 15 is also precisely regulated. The voltage at the base of transistor 13 is then protected from the effects of positive and negative temporary overvoltages.

In the embodiment of FIG. 1 described above, the Zener diode 15 provides a reference potential to the pass transistor 13. In such a typical example, the values of the circuit components were selected to produce a regulated voltage of approximately 5.4 volts. In the example circuit of FIG. 2, a band gap criterion was employed to produce a temperature stabilizing regulation voltage of approximately 3.2 volts. Except for the voltage reference generation circuit, the first
The circuits of FIG. 2 and FIG. 2 are substantially identical. Identical components of the circuits in these two figures are designated with the same reference numerals. The description of the embodiment of FIG. 2 will be limited to the bandgap voltage reference circuit.

The bandgap voltage reference circuit shown in Figure 2 is an NPN whose collector is connected to the output terminal and whose base receives a signal from a voltage divider circuit (consisting of resistors 41 and 42 connected in series between output terminal 12 and ground).
A transistor 40 is included. The emitter of transistor 40 is connected to the collectors of a pair of transistors 43 and 44 via resistors 45 and 46, respectively. The resistance values of resistors 45 and 46 do not have to be the same. The collector of transistor 43 is connected to the bases of transistors 43 and 44. The collector of the transistor 44 is connected to the base of an NPN transistor 47 whose collector is connected to the base of the pass transistor and whose emitter is connected to the ground 16. The emitter of transistor 43 is directly connected to ground 16, and the emitter of transistor 44 is connected to ground 16 via resistor 48. Transistors 43, 44 and resistor 48 form a logarithmic current source.

Next, the operation will be explained. The base voltage of transistor 13 is determined by the state of transistor 47, which is controlled by transistor 40. transistor 4
A base voltage of 0 is the temperature stabilization reference voltage. This reference voltage is applied to the bases of transistors 40 and 47.
It is the sum of the emitter voltage drop and the voltage drop across resistor 46. The current flowing through resistor 46 is determined by a logarithmic current source. Therefore, the voltage drop across resistor 46 has a positive temperature coefficient that compensates for the negative temperature coefficient of the base-emitter junctions of transistors 40 and 47. A voltage divider circuit consisting of resistors 41 and 42 is for adjusting the reference voltage.

In the circuit of FIG. 2, the bandgap reference provides a lower regulated voltage than the Zener diode 15 of FIG. Diode 15 in FIG. 2 serves as a protection against too much positive transient voltages that are too fast for a reasonable response by this bandgap criterion.

〔Effect of the invention〕

From the foregoing discussion, the integrated circuit voltage regulator of the present invention is characterized by much higher breakdown limits than conventional integrated circuit regulators. Adjustments are not lost until the destruction limit is exceeded. If the transistor fails, the internal circuit impedance continues to limit the current flowing through the regulator, so it will not be damaged under any conditions it may encounter.

Although two embodiments have been disclosed and described to illustrate the invention, it will be apparent to those skilled in the art that various modifications may be made within the scope of the invention.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of an embodiment of the voltage regulator of the present invention. 11: Input terminal, 12: Output terminal, 13: Pass transistor, 14: Preregulator, 15:
Zener diode, 17: Bias circuit.

Claims (1)

[Claims] 1. A supply terminal that receives current from a positive voltage source that may include a large superimposed voltage of positive or negative polarity with respect to a reference potential; and an NPN regulator having a base electrode, a collector electrode, and an emitter electrode. a pass transistor, wherein the voltage exceeds a first predetermined magnitude that is less than the magnitude of the voltage fluctuation that may be present at the supply terminal; When an excessively negative voltage exceeding a second predetermined magnitude smaller than that is applied between the base electrode and the collector electrode,
an NPN regulator pass transistor that is electrically destructive; a first base driving means for supplying a substantially constant voltage to the base electrode of the pass transistor; an anode connected to the reference potential, and a cathode connected to the pass transistor; a diode connected to the collector electrode of the pass transistor, the diode limiting the positive voltage of the collector electrode of the pass transistor to less than the first predetermined size; a PNP transistor having a base electrode, a collector electrode, and an emitter electrode; a PNP transistor, the collector electrode of which is connected to the collector electrode of the pass transistor; connecting means for connecting the emitter electrode of the PNP transistor to the supply terminal; and a substantially constant current in the base electrode of the PNP transistor. and a second base driving means for supplying a voltage to the collector electrode of the pass transistor, the PNP transistor limits the negative voltage applied to the collector electrode of the pass transistor to less than the second predetermined magnitude, and causes the diode to have an electric current at its electrical breakdown. An integrated circuit voltage regulator with a protection function against superimposed voltages, characterized by limiting the current flowing. 2. The integrated circuit voltage regulator according to claim 1, wherein the connecting means comprises a P-type diffused resistor provided in an N-type well. 3. In the integrated circuit voltage regulator according to claim 2, the first base driving means comprises:
a Zener diode having an anode connected to the reference potential and a cathode connected to the base electrode of the pass transistor; current supply means for supplying a current to the cathode sufficient to maintain the Zener diode in an electrical breakdown state; An integrated circuit voltage regulator comprising: