QUCS UNIJUNCTION TRANSISTOR OSCILLATOR HOW TO
QUCS UNIJUNCTION TRANSISTOR OSCILLATOR GENERATOR

And, of course, the same can be true for a collector if enough voltage was applied to the collector and its breakdown Junction, the emitter-base junction breaks down and the transistor conducts current. This is because if enough voltage is applied to the emitter Once this voltage is exceeded, the transistor conducts current, almost as if a zener diode would once its breakdown voltage is reached.Īnother point about this circuit is that the base does not need to be connected in order for the circuit to work. So, for this circuit, we are really taking advantage of the reverse breakdown property of the Other than, the collector-base breakdown voltage is much higher. This means that if we apply any more than 6V to the emitter, it can cause the transistor region to break down and conduct current. Looking at the datasheet for the 2N4401 transistor, it hasĪn emitter-base breakdown voltage of about 6V. This is when the transistor is reverse biased, when we're apply positive voltage to the emitter of the transistor. The voltage which we're concerned about in this circuit is theĮmitter-base voltage. In fact, you can go to a transistor's datasheet and see these voltage points. This is because theĬollector region has a very large breakdown voltage. You were to connect the transistor forward biased, with the collector connected to the anode of the capacitor, the circuit will not work at all. If the voltage is too low, say, 5V, for instance, the transistor will not be reached, so that the LED will never light up. This is why we have to use a relatively large voltage of about 12V. If this breakdown voltage is exceeded, then the transistor junction at this region will break down and conduct electricity across from emitter to the collector. The emitter is connected to the anode of the capacitor. How this circuit works is based on the principle of the transistor being connected reverse biased. The current from the power supplyĪnd this creates the infinite sawtooth waveform.

Once the capacitor has discharged its current, then the process starts all over again. This makes creates current flow from the capacitor, through the LED, and through the transistor. Once the threshold is reached to turn on the transistor, the capacitor begins to discharge So at this voltage threshold, the capacitor stops charging up and begins to discharge. Once the transistor is turned on, it can conduct current across from collector Threshold level, the transistor is turned on. Once the voltage across the capacitor reaches a certain Slope that is present on the first half of the sawtooth waveform. This represents the positive, exponential It charges up and charges up and charges up. So as soon as power is supplied to the circuit, the capacitorĬharges up through the resistor. We will now explain how this circuit works. Then in parallel to the capacitor, we place an LED and 2N3904 NPN transistor in series. Next, in parallel to this voltage source, we place a 1KΩ resistor and a 3300μF electrolytic capacitor in But voltages much below 12V will not allow the circuit to work. Actually any voltage from 12V-15V will work. But we will show how you can make modifications to the circuit so that you canĬhange the frequency as well as the amplitude either up or down.įirst and foremost, we use 12VDC of power for this circuit. In this circuit, with the values we use, the frequency will be rather small, so that you can easily see The incline is nonlinear, or exponential.

QUCS UNIJUNCTION TRANSISTOR OSCILLATOR GENERATOR

A ramp generator is one in which the incline is linear. So what you'll see is a signal, such as shown above, in which Instead, a capacitor charges up exponentially according to the formula, Since a capacitor does not charge up linearly, it does Wavefrom is one in which the incline of the signal is non-linear. If you have an oscilloscope and you connect the anode of the probe to either to the collector of the transistor or the anode of theĬapacitor, which are both common, and the cathode to ground, you will see that a sawtooth waveform is generated. See that the LED flickers on and off, on and off, indefinitely. Since the output signal produces oscillations, you will In this circuit, we will connect an LED as output. The recharge and discharge time of the capacitor determines the time period and, thus, frequency of the signal. So basically the repetitive charging up of the capacitor and discharging of the capacitor creates the oscillations Other components such as a resistor and capacitor.Ī relaxation oscillator is an oscillator that repeats itself over and over again from the charging of aĬapacitor to some event threshold and then the discharging of the capacitor.

QUCS UNIJUNCTION TRANSISTOR OSCILLATOR HOW TO

In this project, we will show how to build a relaxation oscillator with a single transistor and a few How to Build a Relaxation Oscillator with a Transistor

Qucs unijunction transistor oscillator