DE1614825C3 - Circuit arrangement for automatically adhering to specified pre- and post-heating times for electron tubes - Google Patents

Description

The invention relates to a circuit arrangement for automatically complying with predetermined pre- and Post-heating times when operating electron tubes, their anode and, if applicable, grid voltages on the one hand, may only be switched on during commissioning if the cathodes of the tubes have a have been heated for a specified period of time (preheating) and, on the other hand, only after a power failure may then be switched on again if the cathodes are used for a different specified period of time, which depends on the duration of the power failure, have been reheated (reheating) at which on an operating voltage source which, if the anode voltage and possibly the grid voltage fails, for example fails simultaneously and of the same length, on the one hand a series connection of a voltage-controlled electronic switching element, e.g. B. a switching transistor, and one by the switching current of the Switching element controllable switching device, which the anode and optionally the grid voltage switches and the z. B. is a switching relay, and on the other hand, a series circuit of one with a discharge resistor bridged capacitor, a charging diode and a charging resistor connected and in which the capacitor is parallel with its discharge resistor lying parallel to it is connected to the control path of the voltage-controlled electronic switching element.

A circuit arrangement of this type is known from DT-AS 10 59 115, for example. As voltage controlled Electronic switching elements find electron tubes in the known circuit arrangement Use.

The invention is based on the object of the voltage across the capacitor of the known arrangement In the event of a power failure, it can be dismantled more quickly to ensure safe switching of the voltage-controlled electronic Switching element and thus the switching device controlled by its switching current guarantee. The solution to the problem is characterized in claim 1. Advantageous configurations of the invention are mentioned in the subclaims. The invention is described below with reference to four figures explained.

In the embodiment of the invention according to ⁷ i g. 1, the voltage-controlled switching element ms consists of a transistor T which, because of its required large input resistance, is expediently - as shown - an enrichment type field effect transistor. It works as a switching transistor.

In its circuit, the field winding of an electromechanical is in series with the transistor Relay Z provided, which in some applications by another, by a Switching current controllable switching device known per se Type is replaceable. Because of the relatively high currents that usually occur when switching on and off of electron tubes are to be switched with prescribed pre- and post-heating times, is for this switching device, which switches the anode and possibly the grid voltage, the use of an electromechanical Relays, however, are particularly useful.

The additional "series circuit consisting of a capacitor C ₁ , a charging resistor R ₁ and a charging diode CR is connected to the operating voltage source. The capacitor C is bridged by a discharging resistor R _{2 with a diode C 2} connected; together with this bridging circuit is capacitor C _{1 connected in} parallel to the control path of the transistor T.

In the invention, a direct voltage - U _B with respect to ground is used as the operating voltage, in contrast to the prior art mentioned in the introduction, in which the operating voltage is an alternating voltage.

_{The circuit arrangement according to FIG. 1} is parallel to the series connection of the charging resistor R and the charging diode C 1. 1 is a series connection of two diodes, one of which is the already mentioned diode CR , while the other diode of this series connection is designated CR _x. The diodes CR. ₂ and CR _x are polarized in opposite directions to each other. The diode CR _x , one pole of which is connected to the operating voltage - U _B , is polarized in the same direction as the charging diode CR.

A second capacitor C ₂ is located between the connection point of the diodes CR, CR _x and the operating voltage; it is thus connected in parallel with the diode CR ₃ .

If one sets the operating voltage in the polarity shown in FIG. 1 between the terminal labeled - L) _B and the circuit zero potential (ground), the first capacitor C charges _{exponentially via the series connection of the resistor R 1} and the diode CR ₁ , since the diode CR ^ in Forward direction is switched. At the same time, a current flows through the series circuit comprising the diode CR ₂ and the resistor R ₂ . The second capacitor C ₂ is short-circuited by the diode CR _x. The diode CR., Prevents additional charging of the capacitor C, via the diode CR _V. As is known, the field effect transistor Γ only becomes conductive when its so-called grid becomes negative with respect to its so-called source. As the grid voltage becomes negative, the resistance becomes continuously lower until the switching threshold voltage of relay 2 is reached as a result of voltage division.

By adjusting the preferably continuously adjustable resistor R ₁ , the switching point in time can be varied for a given switching threshold voltage of the relay Z and a given operating voltage - U _B.

In the arrangement according to FIG. 1, the time-determining capacitor is not discharged at the time of switching, but remains charged until the operating voltage is switched off or breaks down (power failure). When the operating voltage drops out, the capacitor C ₁ discharges with a defined time constant, which can preferably be changed by the adjustable resistor R ₂ .

When discharging and there is no operating voltage, the series connection of the transistor T, the excitation winding of the relay Z and the capacitor C, is automatically connected in parallel to the capacitor C ₁ and the diode CR _{2 is put} into its conductive state, so that the charge stored _{in the capacitor C 1} can be destroyed in resistor R _2. The capacitor C ₂ is used to accelerate the lowering of the voltage across the capacitor C ₁ to the switching threshold value. Its capacity is to be dimensioned according to the following relationship: C ₂ = C ₁ - AU / U with U = switching threshold voltage, AU = the voltage difference to be reduced.

The time constant for lowering the voltage across the capacitor C ₁ through the parallel circuit of the capacitor C, the capacitor C ₁ is derived from C ₂ · {R _Rc i + ^ r), the designated R _T of the effective internal resistance of the transistor T . In practice, this time constant is only a fraction of a second. The destruction of the energy _{stored in the capacitor C 1} and then distributed to the capacitors C ₁ and C ₂ in the resistor R. then proceeds with a time constant (C ₁ + C ₂ ) · R ₂ .

If the operating voltage is switched on again during the discharge period, the recharging of the capacitor C ₁ begins immediately, whereby the switching threshold value of the relay Z is reached earlier, the shorter the power failure time. By using RC combinations for charging and discharging, the switching behavior of the protective arrangement is advantageously adapted over time to the heating and cooling of the electron tubes to be protected, which also take place according to an exponential function.

If particularly long delay times of the order of 20 minutes for the preheating are desired, it is advisable, because of its particularly large input resistance, to use a MOS-FeI deffekttransistor as the transistor T and to ensure that the insulation resistances of the capacitors C ₁ and C used _{2 are} large compared to the resistors R ₁ and R ₂ , while the blocking resistances of the diodes CR _U CR ₂ and CR _{x must be} large compared to the resistors R ₁ and R ₂ .

Advantageously, all are with regard to their insulation resistance critical components in a manner known per se by pouring them into cast resin Protected against moisture influences; In addition, it is advisable to set the operating voltage in a known manner Way to keep it as constant as possible.

F i g. FIG. 2 shows an exemplary embodiment of the invention that has proven particularly successful in practice, which is associated with that according to FIG. 1 corresponds in principle. In Fig. 2, however, are the data and type designations specified. With this arrangement according to FIG. 2 became a pre-heating time and a post-heating time of 5 minutes each.

In the event of a very brief power failure lasting less than 10 seconds on the order of magnitude, is often an almost immediate reconnection of the anode voltage and, if necessary, the grid voltage is desired; in this case, only an extremely short reheating period is required. In this case the use one in FIG. 3 advantageous arrangement, which essentially consists of the combination of two Arrangements according to FIG. 1 exists.

The reference numerals of one of these circuit halves agree completely with those of FIG. 1, while the second circuit half of the arrangement according to F i g. 3 has a 'in addition to the respective reference number and the switching device is denoted by U in place of Z here. ζ and ü are the switching contacts belonging to the relays Z and U , by means of which a relay ReI can be connected to the operating voltage - Uβ . The relay ReI switches the anode and possibly grid voltages by means of its own contacts (not shown); thus these voltages in the circuit arrangement according to FIG. 3 are not switched directly by the relays Z and U located in the switching current paths of the transistors T and T.

The charging and discharging time constants of these circuit halves forming the combination are, however, selected differently according to the intended use, for example the time constant A ₁ C ₁ is 3 minutes, the time constant R ₂ ■ (C ₁ + C ₂ ) is 2 minutes, the Time constant A ₃ C ₃ to 10 minutes and the time constant /? ₄ C ₃ to 30 seconds to choose. In the arrangement according to FIG. 3, the relay ReI with its switching contacts (not shown) is used to switch the anode and, if necessary, grid voltages of the tubes to be protected on and off. The excitation development of the

ίο Relay ReI is switched via parallel contacts ζ and ü of relays Z and Ü in the switching circuits of the two transistors.

In the arrangements described so far, the full current flows through the transistor or through the transistors during the entire switch-on period of the switching relay. In order to reduce the economic effort required and to be able to get by with smaller power types in these transistors, it is often expedient to use the arrangement according to FIG. 4 to be used, which differ from the arrangement according to FIG. 1 essentially differs in that the transistor T with its internal resistance R _r, an ohmic resistor R is connected in parallel via a self-holding contact ζ of the relay Z, where R < R _{T is} selected so that after switching the relay at this resistor R is practically full Operating voltage is present.

For this purpose 2 sheets of drawings

Claims (6)

Patent claims: 1.Circuit arrangement for automatically adhering to specified pre-heating and post-heating times when operating electron tubes, the anode and possibly grid voltages of which may only be switched on when the tubes are put into operation when the cathodes of the tubes have been heated for a specified period of time (preheating) and, on the other hand, after a Netzausfan may only be switched on again when the cathodes have been reheated (reheating) for a different specified period of time, which depends on the duration of the power failure, in the case of an operating voltage source which, if the anode voltage and, if applicable, the grid voltage fails, approximately simultaneously and turns out to be of the same length, on the one hand a series connection of a voltage-ao controlled electronic switching element, e.g. B. a switching transistor, and a controllable by the switching current of the switching element switching device that switches the anode and optionally the grid voltage and the z. B. is a switching relay, and on the other hand a series circuit of a bridged with a discharge resistor capacitor, a charging diode and a charging resistor is connected and in which the capacitor is connected together with its parallel discharge resistor in parallel to the control path of the voltage-controlled electronic switching element, characterized in that the operating voltage is a direct voltage (-U _n ) that parallel to the series connection of the charging resistor (.R ₁ ) and the charging diode (CR ₁ ) a series connection of two further diodes (CR ₂ , CR ^) with opposite polarity is provided , of which the one (CA ₃ ), one pole of which is connected to the operating voltage, is polarized in the same direction as the charging diode, that a second capacitor (C ₁ ) is arranged between the connection point of the two further diodes and the operating voltage and that the discharge resistor ( R ₂ ) between the connection point of the two further diodes un d Ground is connected (Fig. 1). 2. Circuit arrangement according to claim 1, characterized in that the charging resistor (R,) and / or the discharging resistor (R.,) are continuously adjustable. 3. Circuit arrangement according to claim 1 or 2 with a field effect transistor as a voltage-controlled electronic switching element, characterized in that the insulation resistances of the two capacitors (C ₁ , C) and the blocking resistances of the three diodes (C / ?, " CR., And CR ₃ ) large compared to the resistances of the charging resistor (/ ?,) and discharging resistor (R.,) are selected. "" 4. Circuit arrangement according to one of claims 1 to 3, characterized in that all critical components with regard to their insulation resistance in a known manner by casting are protected against the effects of moisture in cast resin. 5. Circuit arrangement according to one of claims 1 to 4, characterized in that in the case of different possible preheating and post-heating times of the order of magnitude, the circuit arrangement is provided twice, that the charging and discharging time constants are adapted to these different times and that for switching the anode and optionally the grid voltage an additional switching device (ReI) is provided which can be controlled (z, ü) by the switching devices (Z, Ü) located in the switching circuit of the voltage-controlled electronic switching elements (T, T ') (Fig. 3). 6. Circuit arrangement according to one of claims I to 5, characterized in that the voltage-controlled electronic switching element is an ohmic resistor (R), the resistance value of which is selected to be smaller than that of the switching current path of the voltage-controlled electronic switching element when the switching current is flowing, can be connected in parallel (z) , as long as the operating voltage is applied (Fig. 4).