Blocking oscillator

A blocking oscillator, the electronic circuit of a feedback Kippschwingungsgenerators used as one equipped with a transformer electric oscillator circuit for generating pulses. In its simplest form it consists only of a magnetically coupled double coil or a pulse transformer, and a reinforcing device such as a transistor, formerly the electron tube. A distinction is made between the blocking oscillators that operate self-oscillating or can be, and those that are triggered once or periodically. Eponymous feature of the non-linear operation of the reinforcing element at the transition to the stop band (e.g., barrier voltage of the electron tube ).

General

By choosing the component parameters, the time often short spikes in a very wide range of duty cycle and period can choose. The electrical coupling of the pulse signal can be effected via the pulse transformer by means of an additional winding. The vibrator is provided by a positive feedback via the pulse transformer.

Depending on the arrangement, the blocking oscillator can also be used to produce relaxation oscillations as a form of the output signal. Since such a sawtooth wave contains all harmonics of the fundamental frequency of this oscillator type has been used in older electronic organs for sound generation in particular.

Applications

Electric clocks

When technological transition mid-20th century of mechanical movements towards today's conventional quartz watches were on the market, electronic watches, which had a blocking oscillator as a driving device. Unlike quartz watches watches quartz, where the electronic circuit is a correspondingly accurate time base for itself and the watches mechanism only serves to move the pointer, the electronic circuit in this case is not to improve the accuracy of the mechanical clock, but only to to replace the mechanical energy store. This is necessary to compensate for friction losses in the movement among others.

In purely mechanical watches, the drive device together with the associated lift usually consists of a spring-loaded. By replacing with an electric drive and electric energy storage device, consisting of the blocking oscillator, and an energy storage device such as a battery, so long periods of operation can be achieved. A "peel " of the spring accumulator as in mechanical clocks by most only a few days is not necessary. There is no mechanically highly stressed anchor escapement, which increases the service life. The accuracy is set as with mechanical watches, by a mechanical device in the balance.

The blocking oscillator provides in this application, not a separate oscillator circuit, but takes vibratably only by the interaction with the mechanical clock system as an electromechanical system as a whole. The balance wheel is provided with a permanent magnet of high coercive force, which is mounted directly next to two magnetically coupled air coil L1 and L2. The coils are of a bipolar transistor T, as indicated in the adjacent circuit diagram, driven. To avoid too large amplitudes at the balance additionally located in this addition to the permanent magnet eddy current brake. To put the electromechanical oscillator to vibrate, for example after a battery change, the balance must be set in motion by a device with a mechanical impulse.

The capacitor C represents the approximate operating frequency of the blocking oscillator, depending on the model, at about 2 Hz to about 5 Hz. The system is mechanically designed such that by the interaction with the permanent magnet close to the zero crossing of the balance ( position of rest ), a short drive pulse emanating from the blocking oscillator, which ensures the movement of the balance to the exhaustion of the battery. Typically, such movements are supplied by a AA cell with a voltage of 1.5V.

Locked oscillator

Blocking oscillator can be synchronized to another by coupling pulse signal that they oscillate at the same frequency (see below for TV use) or at a fixed frequency relationship to the input signal ( frequency divider ).

They have been used in older television sets for generating the relaxation oscillations of the vertical and horizontal deflection are synchronized by the synchronizing pulses in the received television signal. In the horizontal deflection of the blocking oscillator, however, was soon replaced by circuits which allow a higher safety of the synchronization with the transmitter-side tilting vibration (so-called flywheel synchronization).

In older electronic organs (eg Dr. Böhm organ) they were used as a frequency divider with a ratio of 1 to 2 for tone.

Radar technology

A self-oscillating blocking oscillator used in the old radars as a generator for the pulse repetition frequency.

Triggered blocking oscillator was used as a frequency divider in a ratio of 1: 2 to 1: 5, for example, for the generation of distance marks in radar devices.