DE1072653B - Circuit arrangement for switching high electrical voltages with the aid of two or more switching transistors in a row - Google Patents

Description

The invention relates to a circuit arrangement for switching high electrical voltages with the help of transistors.

In electronics, transistors have proven themselves as on-off switches. Is particularly advantageous the low internal resistance of the transistor in the open state. By its nature it is However, transistor is only suitable for switching relatively low voltages. The reason for that lies in the relatively low collector reverse voltage of today's known transistors; depending on the type of transistor, this is between 10 'and 80 volts.

To switch to voltages that are higher than the collector reverse voltage of the transistor type used As is well known, it is now possible to put two or more transistors in series. Because those connected in series It is difficult to control transistors at the same time because their emitters are on different ones Potentials are, the arrangement has already been made so that only one of the transistors the series circuit is controlled, while the other transistors of this series circuit be controlled as a result of the control of the first transistor.

Because of the connection of the transistors to the voltage sources for the base or the collector caused by this series connection, z. B. with transistors of the pnp type in the blocked state a high positive base voltage, which for some Transistors is harmful.

Furthermore, in the known circuits, the use of a voltage divider for the task that controlled bases of the series-connected transistors in the blocking state to the potential of the associated To put emitter, disadvantageous, since the size of the partial resistances of the voltage divider of the Load, which is connected downstream of the series connection of the transistors, depends. With a low-resistance load the size of the partial resistance between the base and negative potential is therefore limited upwards.

The invention is based on the object of specifying a circuit which causes the Bases of the transistors a tolerable voltage for this is applied in the off state and which of is independent of the above limitation.

The invention relates to a circuit arrangement for switching high voltages with the help of two or more switching transistors in series, only one of which is at the base is controlled, while the other transistors with their bases so via voltage dividers at constant Voltages are that in the blocking state the base potential is equal to or more positive than the Po circuit arrangement for switching

high electrical voltages

with the help of two or more

switching transistors in series

Applicant:
Standard electrical system Lorenz

Aktiengesellschaft,

Stuttgart-Zuff enhausen,

Hellmuth-Hirth-Str. 42

Dr. rer. nat. Werner Schiebeler, Eutingen (Bad.),
has been named as the inventor

potential of the associated emitter, and that when the controlled transistor opens, the rest Transistors are also opened. According to the invention is the partial resistance of the voltage divider between base and negative potential terminal by a series connection of diode and low resistance Resistance bridged.

The switching arrangement according to the invention makes the use of a special voltage source superfluous for the bases of the non-activated transistors, which is then of particular advantage, if the required voltage source is otherwise not available in the circuit.

The invention is explained in more detail with reference to FIGS. 1 to 3, for example. The ones shown here Cases relate to transistors of the pnp type, as they are preferably used today find, apply mutatis mutandis to those of the npn type. It shows

1 shows a known series connection of transistors with control via just one transistor,

FIG. 2 shows a modification of the arrangement according to FIG. 1, to the effect that for the transistor that is not activated a separate base voltage source is provided,

3 shows a circuit arrangement according to the invention.

In the circuit arrangement shown in FIG. 1, the voltage t / ₃ , which is assumed to be −160 ¹ VoIt, for example, is the voltage to be switched. The collector reverse voltage of the available transistor type is assumed to be 80 volts. To the

909 708/197

Switching the voltage U ₃ therefore requires at least two series-connected transistors T ₂ and T ₃ . R represents the consumer.

As can be seen from the circuit, only the transistor T _{2 is driven} at its base, that is, the signal for opening or blocking is only supplied to it directly. For this purpose, the control transistor T _{1 is} provided, which is generally required for preamplifying the control voltage U ₁ , which in the present example can fluctuate between -12 and 0 volts. As long as U _{1 is} sufficiently negative, transistor T ₁ remains open and transistor T _{2 is} blocked. As a result, no base current flows through the resistor i? ₄ and the transistor T ₂ . If, however, the voltage U ₁ approaches 0 volts, the transistor T _{1 is} blocked, and via the resistor 7? ₄ and the transistor T ₂ , a base current can flow, which opens the transistor T _2.

The transistor T ₃ , the emitter of which is connected to the collector of the transistor T ₂ , has its base connected to the constant voltage U ₂ via the resistor R ₆ . As long as the transistor T _{2 is} open, ie has a low resistance, the emitter of the transistor T _{3 is} approximately at zero voltage. A base current can therefore _{flow through the transistor T 3} via the resistor R ₆ , which is thereby opened. Since both transistors are now open, the consumption resistance flows through i? _£ the full stream.

When the transistor T ₂ is turned off via the transistor T ₁ by sufficiently changing the control voltage U ₁ in the negative direction, the emitter of the transistor T is brought to a voltage _3, which causes the blocking of the transistor _T3.

So that the transistors T ₂ and T _{3 are} not loaded with unequal voltages in the blocking case as a result of unequal blocking resistances, they are bridged by the resistors R ₇ and R _{8, which are generally equal to one another.} R ₇ and R _s are much smaller than the smallest possible blocking resistances of the transistors, so that the blocking resistances have no noticeable influence on the voltage division.

In the circuit according to FIG. 1, the transistor T ₃ receives a base voltage U ₅ = −12 - (−80) = + 68VoIt in the blocked state. Some transistors cannot tolerate such a high positive base voltage. In order to avoid these difficulties, one can, as the arrangement according to FIG. B. provide a constant voltage source CZ ₄ = -75 volts. When the transistor T ₂ is blocked, the transistor T ₃ only receives a base _{bias voltage U 23} = -75- (-80) = +5 volts.

If, however, a separate voltage source U _{1 is to be} avoided, the high positive base bias in the blocking case of the transistor T _{3 can} , according to the invention, be avoided by the circuit arrangement shown in FIG. The circuit arrangement according to FIG. 3 corresponds by and large to the circuit arrangement according to FIG. 1. Identical parts are therefore provided with the same reference numerals. In addition to the known circuit arrangement, a diode D _{1 is} connected in series with the resistor R ₆ and this resistor-diode path is bridged by the resistor R _10. Furthermore, the base-emitter path of the transistor T ₃ is bridged by the resistor R _{a. When the transistor T 3} is blocked, the base voltage is therefore determined by the voltage divider R _g , R ₁₀ and is at the resistance values specified in the circuit

-12 - (- 80)
11

ί + 6 volts.

In the blocking case, the path via the resistor R ₆ through the diode D _{1 is} blocked. However, if the transistor T _{2 is} opened, the voltage at the emitter of the transistor T _{3 changes} from -80 volts to 0 \ ^r olt, so that a base current flows through the diode D ₁ and the resistor R ₆ and thus the transistor T ₃ can open. In the case of opening, the resistors R ₉ and R _{10 are} irrelevant.

If two transistors are not sufficient to switch a high voltage, this can also be used Trap three or more transistors connected in series.

Claims (1)

PATENT APPLICATION: Circuit arrangement for switching high voltages using two or more in Series lying switching transistors, of which only one is controlled at the base, while the remaining transistors with their bases are connected to constant voltages via voltage dividers, that in the blocking state the base potential is equal to or more positive than the potential of the associated The emitter is, and that when the controlled transistor opens, the remaining transistors are also opened, characterized in that the partial resistance of the voltage divider between Base and negative potential terminal through a series connection of diode and low resistance Resistance is bridged. Considered publications:
German Auslegeschriften No. 1 020673, 1 025 449. 1 sheet of drawings © 909708/197 12.59