DE4229329C1 - Voltage stabilization circuit - Google Patents

Description

The invention relates to a voltage stabilization circuit, where the stabilized output voltage is dependent of the voltage drop at a temperature compensated Se Rienkreis is generated, the at least one in Durchlaßrich connected diode and one to compensate the result serving diode temperature coefficient serving first Resistance includes.

Such a voltage stabilization circuit is known from DE-Elektronik, 1976, Issue 1, page 68. In addition to two silicon transistors, two germanium diodes are used in this known circuit. This combination of silicon components and germanium components prevents the circuit from being produced in the form of an integrated circuit. Thus, if a voltage stabilization circuit is required in an integrated circuit based on silicon technology, the known stabilization circuit cannot be used. Furthermore, in the known stabilization circuit, temperature compensation (ie a low TC) can only be achieved if a certain voltage U _{z is} present. By calculation it can be shown that the desired temperature compensation is only achieved at U _z = 1.3 V.

To stabilize DC voltages, Zener Diodes used that differ from the other diodes in the first Distinguish the line in that the breakdown voltage, at which is a steep increase in reverse current, exactly specific is adorned. The stabilizing effect of such a zener Diode is based on the fact that a large current change only causes a small change in voltage. The stabilization the better the steeper the current / voltage curve running, d. that is, the smaller the differential internal resistance is.  

In semiconductor elements manufactured in bipolar technology to realize such a Zener diode usually the Avalanche effect exploited. With such, on the Avalan che effect based Zener diodes with positive temperature breakdown voltage is usually between between 6 and 8.5 V.

In practice, however, it is often much smaller breaking stress required. To achieve this small Breakdown voltages have already been proposed, an ent speaking number of diodes operated in the forward direction connect in series and the resulting negative Temperature coefficients of these diodes through one in series to compensate with the diode switched resistance.

With such a series circle you get a kind of zener Low breakdown voltage and temperature diode compensation. Such a voltage stabilization circuit has the disadvantage, however, that especially at high a weakly curved knee point there and the slope of the current / voltage curve to a high degree depends on the operating temperature. A relatively weak one curved knee point is synonymous with a relative high dynamic output resistance of the simulated Ze ner diode, which also depends on the respective operating temperature is dependent. Furthermore, a complete temperature comm pensation only given at a certain voltage value, the on the number of diodes and the value of the temperature coefficient efficiency of the resistance depends.

To get a steeper rise in the current / voltage curve hold, has already been proposed such a Se circle between the collector and the base of one aisle side, between the collector and emitter the stabili Switched transistor supplying output voltage.

After only a small part of the breakthrough or forward current through the resistance of the series circuit  flows, there is no longer any question of temperature compensation his. Although there is a relatively constant slope of the subject current / voltage curve ensured. The disadvantage is however, that the breakdown voltage is highly dependent on the depending on the temperature.

The aim of the invention is a voltage stabilization to create circuit of the type mentioned at the beginning simple construction a relatively sharply curved knee area and has a constant dynamic output resistance and at the same time is temperature compensated.

This object is achieved by the characterizing features in claim 1.

Because of this training, not only is a small one stabilizing effect increasing and over a large tem temperature range is essentially constant tial output resistance achieved, but also at the same time an optimal, comprehensive temperature compensation provides so that the breakdown or forward voltage practically independent of the respective operating temperature is. The respective breakdown voltage can be within wide limits can be varied by in particular a corresponding number connected in series by diodes and for the first resistor an appropriate temperature coefficient is selected. The respective breakdown voltage is both from the number of diodes as well as depending on this temperature coefficient.

The second resistor is preferably parallel to the base Emitter path of the transistor output stage switched. Here the temperature coefficient is that of this second Resistance falling voltage equal to the temperature coefficient the base-emitter voltage of the transi in question to choose stors.  

The diode or the diodes can each by a Transi stor be realized, its collector-base section short is closed.

At least that of the temperature-compensated series circuit too ordered first resistance can be through multiple resistors preferably be of different types, so that within the range between the highest possible and the smallest possible value any temperature coefficient by interconnecting different resistors reali is sizable.

Further advantageous embodiments are in the subclaims variants of the invention specified.

The invention is illustrated below with the aid of an embodiment game explained in more detail with reference to the drawing; in this shows:

Fig. 1 to the diodes umfasssenden temperature compensated series circuit of erfindungsge MAESSEN voltage stabilizing circuit shown in Fig. 5,

Fig. 2, at different temperatures reproduced current / voltage characteristics of the temperature compensated erge series circuit shown in Fig. 1,

Fig. 3 shows the series circuit shown in Fig. 1 with secondary transistor is switched without temperature compensation,

Fig. 4, for different temperatures reproduced current / voltage characteristics erge the circuit shown in Fig. 3,

Fig. 5 shows an embodiment of the voltage stabilization circuit according to the invention with a Se rienkreis according to FIG. 1 and a downstream, temperature-compensated transistor, and

Fig. 6 which erge for different temperatures reproduced current / voltage characteristics shown Spannungsstabilisie 5 according to the invention approximately the circuit in Fig..

The embodiment shown in Fig. 5 of the voltage stabilization circuit according to the invention comprises a temperature-compensated, one or more diodes Q₁-Q _N and at least one first resistor R1 comprising series circuit SK according to FIG. 1. The diodes Q₁-Q _N are each by a bipolar transistor realized with short-circuited collector-base section. In principle, however, normal diodes can also be used.

Referring to FIG. 1, three series-connected diodes Q₁-Q _N and a switched with these series resistor R1 before are seen. However, this series circuit SK can comprise any number of diodes and also several resistors.

The temperature coefficient TC _{D of} the forward voltage U _{D of} the diodes Q₁-Q _N connected in the forward direction is in each case negative and is approximately -2 mV / K. In contrast, the temperature coefficient TC _R1 of the resistor R1 provided to compensate for the resulting diode temperature coefficient TC _N is positive.

The resulting diode temperature coefficient TC _N results from the following relationship:

TC _N = N · TC _D (1)

With
N = number of diodes Q₁-Q _N connected in series,
TC _D = temperature coefficient of the forward voltage U _{D of} a respective diode (≈ -2 mV / K),
TC _N = resulting diode temperature coefficient.

In order to ensure compensation of this resulting diode temperature coefficient TC _N by resistor R1, the following conditions must be met:

With
T = temperature,
R1 _{25 °} = value of resistance R1 at 25 ° C,
TC _R1 = temperature coefficient of resistance R1,
I _Opt = optimal operating current in the temperature-compensated SK series circuit.

From the relationship (2A) it follows that, for example, given a temperature coefficient TC _R1 for the resistance R1, the desired temperature compensation is only given at a certain optimal operating _current I _Opt for the series circuit SK. This can also be clearly seen in the diagram according to FIG. 2, in which the respective current / voltage characteristics (I _LIM , U _LIM ) are shown for three different temperatures (-40 ° C, 25 ° C, 85 ° C).

The optimum operating voltage across the series circuit SK, which is assigned to the optimum operating _current I _Opt of the series circuit SK, can be determined as follows:

With
U _Opt = optimum operating voltage across the SK series circuit
= Voltage across a respective diode (base-emitter voltage) at 25 ° C
= Voltage across resistor R1 at 25 ° C.

The following values are provided for the example of a series circuit shown in FIG. 1, which is identical in the exemplary embodiment of the voltage stabilization circuit according to the invention shown in FIG. 5:

N = 3
R1 _{25 °} = 100 kΩ
TC _R1 = 6000 ppm / K,

which theoretically results in the following for the SK series circuit optimal operating values result:

I _Opt = 10 µA (see 2A)
U _Opt = 3.1 V (see 3A)

Based on the characteristics of such a series circuit SK shown in FIG. 2, it now emerges that for a certain operating point I _Opt , U _Opt temperature compensation is given, but in particular at the high temperature of 85 ° C. there is only a slightly curved knee area. The I _LIM / U _{LIM characteristic} curve has a greater slope at -40 ° C than at 85 ° C. If one were to use the voltage drop across the series circuit SK as a stabilized output voltage U _LIM , there would be a certain temperature compensation, but a relatively high dynamic output resistance would have to be accepted, which is also dependent on the temperature.

FIG. 3 shows a circuit in which the series circuit SK according to FIG. 1 is connected in parallel with the collector-base section of a transistor T supplying the stabilized output voltage U _LIM between the collector and emitter.

As can be seen from the I _LIM / U _LIM characteristics of this circuit shown in FIG. 4, this measure allows a sharper curved knee area and an essentially constant dynamic output resistance to be achieved. However, after only a small part of the breakdown or forward current flows through the compensation resistor R1, the desired temperature compensation of the circuit is no longer guaranteed. The breakdown voltage always changes with the temperature.

In Fig. 5, a preferred embodiment of the voltage stabilizing circuit according to the invention is shown. In this circuit too, the stabilized output voltage U _{LIM is} generated as a function of the voltage drop U _SK at a temperature-compensated series circuit SK according to FIG. 1.

The series circuit SK accordingly comprises at least one diode Q 1 -Q _N connected in the forward direction and a first resistor R1 serving to compensate for the resulting diode temperature coefficients TC _N. The temperature compensation of the series circuit SK and the dimensioning of the respective components takes place in exactly the same way as was described in connection with the identical series circuit SK shown in FIG. 1. The number N of the Dio the Q₁-Q _N can in particular be selected depending on the forward voltage desired. In principle, it is possible to provide only a single diode instead of several diodes.

The temperature-compensated series circuit SK is followed by a transistor output stage with a transistor T, which on the input side comprises a base-emitter path BE, the temperature coefficient TC _{BE of} which is compensated by a second resistor R2. This second resistor R2 is connected in parallel to the base-emitter path BE of the transistor T. In contrast, the temperature-compensated series circuit SK is connected in parallel to the collector-base section CB of the transistor. Accordingly, the temperature-compensated series circuit SK and the compensation for the temperature coefficient TC _{BE of} the base-emitter voltage U _{BE of} the transistor T serving resistor R2 form a voltage divider SK, R2, the center tap M located between the series circuit SK and the second resistor R2 the base B of the downstream transistor T is connected. The stabilized output voltage U _LIM is present between the collector C and the emitter E of the transistor T.

In the embodiment shown in Fig. 5, three diodes Q₁-Q _{N are again} provided in the series circuit SK, each of which is formed by a bipolar transistor with a short-circuited collector-base path. The downstream transistor T is preferably also a bipolar transistor.

At least the first resistor R1 can be divided by several parts resistances R1 ′; R1 '' preferably of different types ge be educated. For example, according to the LBC2 (Lin-Bi CMOS 2) process different resistance types (poly, Base, Nwell) are produced, with within the range ches between a maximum achievable and a minimum achievable value by any temperature coefficient a serial interconnection of two or more cons stands of different types can be realized.

The temperature coefficient TC _{BE of} the base-emitter voltage U _{BE of} the conductive transistor T is negative and is approximately -2 mV / K. For a given current I R2 flowing through the second resistor R2, the voltage U _R2 dropping across the resistor _R2 has the same temperature coefficient as the base-emitter voltage U _{BE of} the transistor T. This compensates for the fluctuations in the base-emitter voltage of the transistor T that occur with changing temperature.

After the base current of the transistor T downstream can be neglected, the current flowing through the second resistor R2 current I _R2 can practically the current flowing through the series circuit also tempe raturkompensierten SK current I _Opt (see FIG. [2A]) be equated.

In order to ensure not only the temperature compensation of the series circuit SK, but also the compensation of the temperature coefficient TC _{BE of} the base-emitter voltage U _{BE of} the conductive transistor T, the following conditions must be met:

With
R2 _{25 °} = value of the resistance R2 at T = 25 ° C
TC _R2 = temperature coefficient of the second resistor R2
I _R2 = current through the second resistor R2

After the series circuit SK comprising the elements R1 and Q₁-Q _N must be temperature-compensated in the manner described above (cf. relations [2] and [2A]) and the base current of the transistor T is practically negligible, the following relationship applies:

I _R2 = I _Opt (5)

in which
I _Opt = with regard to the temperature compensation of the series circuit, the current flows more optimally through the series circuit SK.

From (5) in (4A) it follows:

R2 _{25 °} TC _{R2I Opt} = -2 mV / K (6)

At a temperature T of 25 ° C applies to the base emitter Voltage of the downstream transistor T:

 = 0.7 V (7)

After the second resistor R2 to the base-emitter diode of the Transistor T is connected in parallel, the two must be on voltages falling across these elements are of equal magnitude, From which follows:

 = = 0.7 V (8)

= I _{OptR2 25 °} (9)

From (8) in (9) it follows:

I _Opt · R2 _{25 °} = 0.7 V (10)

The value of the second resistor R2 therefore results from the following relationship:

The following value can be calculated from the relationships (10) and (6) for the temperature coefficient TC _{R2 of} the resistor R2:

TC _R2 = -2850 ppm / K

With such a temperature coefficient of the resistor R2, the voltage stabilization circuit according to the invention shown in FIG. 5 is also temperature-compensated with regard to the downstream transistor output stage.

The value of the second resistor R2 can be determined by the fol determine the relationship:

In the voltage stabilization circuit according to the invention shown in FIG. 5, the stabilized output voltage U _LIM between the collector and the emitter of the transistor T is composed of the voltage U SK falling across the series circuit _SK and the base-emitter voltage U _{BE of} the transistor T. . In comparison to the circuit shown in Fig. 1, the base-emitter voltage U _BE must therefore also be taken into account, which, like the forward voltage U _{D of} a respective diode Q 1 -Q _N , can be set to 0.7 V, for example. Accordingly, in the voltage stabilization circuit according to the invention according to FIG. 5, the optimal value for the temperature compensation of the series circuit SK for the stabilized voltage U _LIM lying between the collector and the emitter of the transistor T is as follows:

By a corresponding variation of the number N of the diodes Q 1 -Q _N contained in the series circuit SK and the temperature coefficient TC _R1 , any breakdown voltage U _Opt can thus be set.

The circuit shown in Fig. 5 with three diodes Q₁-Q _N (N = 3) and the additional base-emitter path of the transistor T was tested in a simulation. The elements of the series circle SK were dimensioned exactly as specified in connection with FIG. 1. The value of the second resistor R2 was 70 kΩ. The temperature coefficient TC _{R2 of} this resistance was set at -2800 ppm / K.

As can be seen from the characteristic curves shown in FIG. 6 for the temperatures -40 ° C, 25 ° C, 85 ° C, there is a sharply curved knee area for all temperatures. In all cases there is a relatively steep increase in the characteristic curve, which is equivalent to a small differential output resistance r _z which improves the stabilization and for which a value of about 1.4 kΩ was measured at 25 ° C. In addition, this differential output resistance r _z also remains constant. Finally, the desired temperature compensation is also given at an optimal operating point OA. The breakdown or forward voltage therefore always remains the same even at different temperatures.

Claims (3)

1. Voltage stabilization circuit in which the stabilized output voltage (U _LIM ) in dependence on the voltage drop (U _SK ) on a temperature-compensated series circuit (SK) is generated, the at least one diode connected in the forward direction (Q₁-Q _N ) and one for Compensation of the resulting diode temperature coefficient (TC _N ) serving first resistor (R1), characterized in that the temperature compensating th series circuit (SK) is followed by an output stage formed by a transistor (T), to the base-emitter path (BE ) a second resistor (R2) is connected in parallel and the series circuit (SK) is connected in parallel to its collector-base section (CB), the series circuit (SK) forming a voltage divider with the second resistor (R2), the voltage divider on the series circuit ( SK) resulting voltage drop to the transistor output stage as an input voltage, and the stabilized output voltage (U _LIM ) between hen the collector (C) and the emitter (E) of the transistor (T) of the transistor output stage can be tapped. 2. Voltage stabilization circuit according to claim 1, characterized in that each diode is formed by a transistor (Q₁-Q _N ) with a short-circuited collector-base path. 3. Voltage stabilization circuit according to one of the preceding claims, characterized in that at least the first resistor (R1) by several Partial resistors (R1 ', R1' ') preferably formed different types is.