# The transistor lat as SCR trigger

This circuit works similar to a SCR. When the trigger input is high, Both transistors Q2(PNP transistors) and Q1(PNP transistor) will work. Therefore, a current flow to the base pin of Q2, it has voltage 0.7 volts at resistor R1.

When cutting the activation voltage, the transistors can continue to perform, because the base current. The reset circuit will do this by cutting the power supply circuit. Which this circuit we press the switch Reset button only.

# Current-controlled Sawtooth Generator Circuit

This Sawtooth wave generator circuit include of the frequency oscillator is controlled by current. Which can generate the sweep frequency in wide range. Suitable to be applied in the field of music equipment and a narrow pulse output. Also we are able to be a random circuit, and Hold.

This circuit include of current variable power supply circuit (T1, T2-BC557) and trigger (N1, N2 of CD4011) and switch (T3-BC547). When apply voltage to the circuit, C1 will be charged by current sources. Then, voltage across C1 to threshold level of N1. The T3 is conduct current, through N1 and N2, and C1 is discharged. After all, the cycle will start automatically. The sawtooth waveform at the output will be buffer by FET(E300). The T4 is the peak-to-peak signal of about 1.3 volts.

The value of the equipment specified in this circuit, it is frequencies about 5 to 500KHz, by adjusted by P1, although the circuit is able to output at high frequencies. But it would have distorted waveforms. If C1 = 5.6 nF and R1 = 1K frequency is in the range of 0.5 to 500 KHz, And may be used the inverter replace the nand gate.

# Low-volts Crystal Frequency Generator Circuit

We can easily use FET and Crystal to generate the frequency and In particular, this circuit use very low voltage. It can operate at a supply voltage to 1.5 volts only and at crystal frequency 100 KHz to 10 MHz.

The crystal is connected to between the drain and gate of FET-T1 BF256. It runs in resonance mode in parallel coil form. The inductor L1 makes better frequency stability and can use crystal in the wide frequency range, Although the crystal is not appropriate, it also works.

The capacitor C1 is connected with the crystal to act as “padding” for the return phase 180 degrees, to the input of FET. The output will be buffer by T2. This designed circuit is tested to operate at frequencies 100 Khz, 1 MHz, 4 MHz, 8 MHz and 10 MHz at lowest 1.5 volts only.