Can intrinsic standoff ratio be changed

It has a negative resistance region in the characteristics and can be easily employed in relaxation oscillators. The UJT relaxation oscillator is called so because the timing interval is set up by the charging of a capacitor and the timing interval is ceased by the the rapid discharge of the same capacitor.

From the name itself, the UJT or uni junction transistor is a semiconductor device that has only one junction. These end terminals are called B1 and B2.

A heavily doped P-type region is constructed on one side of the bar close to the B2 region. This heavily doped P region is called emitter and it is designated as E. The internal block diagram, simplified internal circuit model and circuit symbol of a UJT is given in the figure below. The diode symbol shown in the internal circuit model represents the P-N junction formed between the heavily doped P-region E and the lightly doped N-Type bar. In simple words, it is the resistance of the N-Type bar when measured lengthwise.

The typical range of intrinsic standoff ratio is from 0. For ease of understanding, the internal model of the UJT is used in the circuit Fig 1. Current starts flowing into the emitter only when the bias voltage Ve has exceeded the forward drop of the internal diode Vd plus the voltage drop across RB1 Vrb1.

UJT Relaxation Oscillator. The circuit shown in Figure 5 is applicable to low-level power-control applications with SCRs and triacs. The only modification to the circuit may be to use a pulse transformer. Figure 5 UJT relaxation oscillator circuit diagram. When the supply to the timing circuit is first turned on, the voltage across the capacitor will increase at a rate determined by the values of the resistor and the capacitor. The time may be modified by varying either the value of the resistor or the value of the capacitor.

In practice it is found that it is easier to alter the value of the resistor. The operation of a UJT relaxation oscillator is straightforward and may be summarized as follows:. Example 2. The frequency of the pulses from this circuit will depend on the time constant.

The actual calculation of frequency can be complex but if the standoff ratio is equal to, or near, 0. Example 3. In the circuit in Figure 5 , determine the output frequency if the standoff ratio is 0. Determine the frequency if RV 1 is set to 7. It is worth noting that in most cases when a relaxation oscillator is used as a trigger circuit for thyristors, the calculation of frequency is not important.

What is more important is the time delay from the start of a cycle to the point where a trigger pulse is delivered to the thyristor. This time delay will determine both the average value and the RMS value of load voltage , and hence the load power. Thin middle layer of the transistor is called. An Amplifier circuit of voltage gain gives 10V output, the value of input voltage is. Approximately how many number of gates are incorporated in SSL chip.

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