DE1050930B - - Google Patents

Description

The invention relates to a device for generating sawtooth-shaped electrical pulses with a capacitor fed by a direct current source and a semiconductor as a switching element for discharging the capacitor when a certain capacitor voltage is reached. The semiconductor takes the place of a glow lamp in other known pulse generators, which when exceeded a certain capacitor voltage ignites, so that the capacitor over the glow lamp discharges.

Devices with semiconductors have the advantage over those with glow lamps Sensitivity to vibrations, longer service life and smaller construction.

The devices of this type that have become known with semiconductors as switching elements are double base diodes with a mode of operation similar to that of a Stromtor, which has been used for so long by a current coming from the capacitor are traversed, like a potential difference between the capacitor voltage and DC power source is present. Since the diode is continuously powered by one of the direct current source fed-in current flows through, a constant frequency sequence can occur due to the self-heating cannot be guaranteed. A deliberate change in the frequency sequence is in the known Arrangement not possible because the ohmic resistance in the 7? C circuit cannot be influenced from the outside Part of the diode is formed. Further are the amplitude voltage and the valley voltage (top and bottom limit of the voltage pulse) depending on the voltage of the Direct current source coupled and therefore only adjustable together.

There are also tube circuits with feedback for pulse generation become known, however either only sinusoidal oscillations of constant amplitude or sawtooth oscillations can generate rapidly changing amplitude.

It is also possible, with appropriately constructed known tube circuits, to use sawtooth-shaped circuits • generate pulses of constant magnitude; however, there is the disadvantage that when changing the Frequency at the same time inevitably a change in the individual sawtooth pulse takes place.

The object of the invention is to avoid the disadvantages described in the known devices. The solution is that for the separate setting of frequency, amplitude voltage and valley voltage of the pulses, the variable capacitor is connected on the one hand via a variable resistor to the direct current source and on the other hand a device for generating it
sawtooth-shaped electrical impulses

Applicant:
Siemens-Schuckertwerke

Corporation,
Berlin and Erlangen,
Erlangen, Werner-von-Siemens-Str. 50

Dipl.-Phys. Helmut Schwab, Nuremberg,

has been named as the inventor

is connected to a discharge circuit, which has a collector-earthed transistor in series with contains a transformer whose transformation ratio can be changed, its secondary voltage together with a variable DC voltage in the control circuit of the transformer during the Discharge process is effective.

Due to the separate setting options for the frequency, the aniplitude voltage and the valley voltage can be easily adapted to all such devices with one and the same pulse generator device set requirements can be achieved, as they are with none of the known facilities of this Kind is possible. Furthermore, the new facility is

4.0 , the frequency of the impulses is visibly independent of the intrinsic temperature, since the semiconductor only has current flowing through it for the duration of the capacitor discharge and is separated from the 7? C circuit.
The invention will be explained in more detail with reference to FIGS. 1 to 3. 1 shows an exemplary embodiment of the invention in which the capacitor 1 is charged from the voltage source 2 via a resistor 3 . In the discharge circuit of the capacitor 1 there is a transistor 4 in a collector-earthed circuit as well as the primary winding 5a of a transformer 5, the secondary winding 5b of which is arranged in series with a voltage source 6 in the controlling base circuit of the transistor. In this circuit, the voltage Uq across the capacitor corresponds to below

809 750/413

Claims (1)

Neglecting the voltage drop across the winding Sa of the emitter-collector voltage U _{e of} the transistor 4. As long as the voltage U _{e is} less than the voltage U _{v of} the voltage source 6, the transistor 4 is closed. If the voltage U _e becomes slightly greater than the voltage U _v as the capacitor voltage U _c increases, the base of the transistor 4 becomes negative with respect to the emitter, ie the transistor begins to open. The current flowing through the transistor now 4 and the primary winding 5a of the transformer 5 current induced in the secondary winding 5 b a voltage which is directed opposite to the base bias voltage _v U. The base voltage thus drops even more, the transistor opens more, a larger current flows through the winding 5 a, etc., until the transistor 4 is fully open, so that the capacitor 1 can discharge via the transistor 4. In Fig. 2, the emitter current-emitter voltage family of characteristics for different base voltages U _B is plotted as a parameter. It can be seen that the transistor begins to open as soon as the emitter-collector voltage U _{e is} a few tenths of a volt above the base bias voltage U _v set at the voltage source 6 . As long as the transistor is closed, UB-U _v . However, if the emitter current begins to flow, the secondary voltage U w2, which is _{connected in opposition} to the base bias voltage U _v , arises in the base circuit of the transistor, as described above, so that the base voltage of the transistor 4 applies U _b = U _{v -U w2} . If the transistor is open, almost the entire capacitor voltage U _{c is applied} to the winding 5 a of the transformer 5 ^ so that at this moment the secondary _voltage U w2 = m · U _c if m is the transformation ratio of the transformer 5 . However, since the voltage U _{c of} the capacitor 1 falls more and more during the discharge, the secondary voltage U _{w2 also falls} , so that the base voltage U _b increases. As soon as the emitter voltage U _{E is} equal to the base voltage U _b , the transistor begins to close, the voltage drop occurring at the winding 5 a decreases, the base voltage is increased further, etc., until the transistor 4 is completely closed. The formula thus results for the closing voltage U _C j, the so-called "valley voltage" U ₀ T = U _r - m U _ct = The formula for the transformation ratio of the transformer 5 is accordingly obtained with a prescribed valley voltage U _C r and a prescribed peak voltage U _v Ur Uci 1 . In summary, it follows that the size of the resistor 3 and the capacitance of the capacitor 1 are decisive for the pulse length, the base bias voltage U _v for the height of the pulse peak and for ίο the impulse valley is the transformation ratio m of the transformer 5. The device according to the invention can be constructed in the most varied of ways in terms of circuitry. For example, instead of the pnp junction transistor shown, a different type of transistor can be used. It is also possible to connect the voltage source 6 for the base bias voltage U _v and the voltage source 2 for charging the capacitor 1 in a single voltage source with a corresponding tap, as shown in FIG. 3, for example. The same designations as in FIG. 1 have been retained; the voltage source 2 serves in its entirety to charge the capacitor 1, while a tapped partial voltage 26 supplies the base bias voltage U _{v of} the transistor 4. Claim:
Device for generating sawtooth-shaped electrical pulses with a capacitor fed by a direct current source and a semiconductor as a switching element for discharging the capacitor when a certain capacitor voltage is reached, characterized in that for the separate setting of frequency, amplitude voltage and valley voltage of the pulses, the variable capacitor (1) on the one hand is connected via a variable resistor (3) to the direct current source (2 or 2 and 26) and on the other hand is connected to a discharge circuit which contains a collector-earthed transistor (4) connected in series with a transformer (5) whose transformation ratio can be changed, the secondary voltage of which is effective together with a variable DC voltage (6, 26) in the control circuit of the transformer during the discharge process. Considered publications:
"Electronics", August 1953, pp. 170 to 173; March 1955, pp. 198 to 202; Kerkhof and Werner, "Fernsehen", 1954, Philips' Technical Library, p. 147. 1 sheet of drawings