Astable Blocking Oscillator; With small variations of the Monostable Blocking Oscillator circuit, it can be provided to work into astable mode. The astable blocking. A blocking oscillator is a simple configuration of discrete electronic components which can .. ff and “The astable blocking oscillator” p. ff. Figure shows the diagram of an astable blocking oscillator with an. RC circuit in series with the base of the transistor. This circuit includes, in addition to the.

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Blocking Oscillators

This is the circuit situation shown in figure When the above condition occurs, the transistor turns OFF in the emitter timing circuit and so a stable output is obtained. Induction into the primary will be via the primary turns through which all the flux passes represented by primary inductance L p ; oscullator collapsing flux creates primary voltage that forces current to continue to flow either out of the primary toward the now-open switch or into a primary load such as an LED or a Zener diode, etc.


When a capacitor and resistor are used to absorb the energy, the repetition rate is dependent on the R-C time-constant, or the L-C time constant bloking R is oscilaltor or non-existent L can be L pL s or L p,s.

The circuit will remain in this condition as long as the base voltage of Q2 is positive. As shown, it has two alternations of equal duration and a square presentation for each complete cycle.

Blocking oscillator

A Pulse transformer is one which couples a source of rectangular pulses of electrical energy to the load. Hence the name diode controlled Astable blocking oscillator is given.

In any case, if there are no components to absorb the current, the voltage at the switch rises very fast. Its primary purpose oscollator to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer.


In a third case, the magnetic “core” material saturates, meaning it cannot support further increases in its magnetic field; in this condition induction from primary to secondary fails. The usual cure for turn-off transients, a diode across the offending inductance, does not work here because it destroys the necessary inductive action.

Control voltage or current to the switch is now free to “flow” into the control input and close the switch. Because of the bllocking polarities atsable the transformer, the collector voltage goes down, while the base voltage rises.

The astable multivibrator is said to oscillate. As the diode helps the transistor to change its state, this circuit is diode controlled.

Look at the output waveform from transistor Q2, as shown in figure A blocking oscillator is a simple configuration of astavle electronic components which can produce a free-running signal, requiring only a resistora transformerand one amplifying element. There are a seemingly endless number of combinations of voltages, transformers, capacitors, transistors and resistors that can be used to vary and model the circuit.

In some applications, the time period of higher voltage -V CC and the time period of lower voltage 0 volts will be equal. In the second case e. The bistable astzble has two stable states. The non-sinusoidal output is not suitable for use as a radio-frequency local oscillator, but it can serve as a timing generator, to power lights, LEDsElwireor small neon indicators.

The voltage blofking gets induced into the transformer primary windings induces some voltage into the transformer secondary winding, using which the capacitor starts charging. Explain how the jump voltage is produced in a trapezoidal wave generator.

For example, timing and gating circuits often have different pulse widths as shown in figure A linear voltage applied to the horizontal input will cause the electron beam to move horizontally across the CRT.

When the base of Q1 becomes negative enough to allow Q1 to conduct, Q1 will again go into saturation.

When only interwinding capacitance and a tiny secondary load is present to absorb the energy, very high-frequency oscillations occur, and these “parasitic oscillations” represent a possible source of electromagnetic interference.


At T1 this voltage abruptly falls essentially no time used to its previous static value. Electromagnetic cathode ray tubes use coils for the deflection system, and a osci,lator rise in current is required for an accurate horizontal display.

The time necessary for Q2 to become saturated is determined by the time constant R2C1. Fall time is the time required for the voltage to drop from 90 percent to 10 percent of the maximum amplitude point. Then the circuit can be triggered blockng as in the case of the transistor monostable.

Blocing h Atable varies with the transistor used. The following abbreviations are used in the analysis:. In the case when there is little or no primary resistance and little or no switch resistance, the increase of the magnetizing current I m is a “linear ramp” defined by the formula in the first paragraph.

An oscillator that uses a regenerative feedback to generate a nonsinusoidal output is called as Relaxation Oscillator. Instead of a resistor, a potentiometer placed in parallel with the timing capacitor permits the frequency to be adjusted freely, but at low resistances the transistor can be overdriven, and possibly damaged.

When the transistor turns off, however, there is a strong ringing.

Pulse Circuits – Blocking Oscillators

But Bistable operation is not possible. In all cases, the rate of rise of the primary magnetizing current and hence the fluxor the rate-of-rise of the flux directly in the case of saturated core material, drops to zero or close to zero. There is a rapid vertical rise of voltage from T0 to T1, which is linear straight.

The transformer used here is a Pulse transformer. Let’s analyze what is happening.