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So this is a basic ramp generator built using transistors, resistors, and a capacitor. Occurs when the voltage of the capacitor reaches a certain threshold. To turn on the first transistor, sufficient positive voltage is needed at the collector of the first transistor. With the 4.5 V,īiasing power is provided to the base of the first transistor and the collector of the second transistor. Know thatīipolar junction transistors (BJTs) always need biasing to the base of the collectors in order to operate. This voltage is needed so that both transistors can turn on. Of the NPN transistor and the base of the PNP transistor. This voltage is the bias voltage necessary for the collector In half at the midpoint between the 2 resistors, creating 4.5V of power.
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Since the voltage supply is 5V, it divides the voltage The 2 10KΩ resistors in parallel form a voltage divider. This creates the constant ramp waveform of charging and discharging of the capacitor. The current source, charging up the capacitor again. The process starts over with the leftmost transistor, Therefore, the 2 rightmost transistors no longer conduct current.
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Once all the chargeįrom the capacitor has been discharged from the capacitor, then there is not enough voltage to turn on the PNP transistor. Now thatĬurrent can flow through the transistor, the capacitor discharges its current through the transistor. To turn on the transistor, the transistor goes from cutoff (not conducting) to saturation (fully conducting). Being that the voltage at the capacitor is now high enough Both transistorsĪre now operating in saturation mode and are fully conducting. Once it turns on the PNP transistor, this PNP transistor turns on the NPN transistor. Once the voltage reaches a certain threshold, the peak of the ramp waveform, it is high enough to turn on the second As the current flows into the capacitor, its voltage increases. Is proportional to the amount of current that charges it up. As it gets charged, the voltage across the capacitor increases. The capacitor gets charged up by the PNPĬurrent source. Leftmost part of the circuit) acts as a current source for the capacitor. Once we turn on the power, the first PNP transistor (to the To the circuit, no current can flow because there is no power. Once the voltage rises to a level high enough on the capacitor that turns on the PNP transistor that it isĬonnected to the anode the ceramic capacitor, then the capacitor begins discharging. As the capacitor charges up more and more and the charge gets larger and larger, the This is the same current that gets dumped into the 10nF ceramic capacitor, charging it up. The current flowing through this transistor is aboutģ0 microamperes. This allows for the PNP transistor to turn up and allowsĬurrent flow from the emitter to the collector of the PNP transistor. Resistors in parallel set up a bias voltage for the PNP transistor. The datasheet for the 2N3904 NPNP transistor is found here:Īll the way to the left of the circuit, are a 1KΩ resistor and a 10KΩ resistor in parallel. The datasheet for the 2N3906 PNP transistor is found here: Other type of PNP and NPN transistor that you have. So in this circuit we use 2 PNP transistors and 1 NPN transistor.Īlthough we've designated to use the 2N3906 as the PNP transistor and the 2N3904 as the NPN transistor, you really could use any If you do not haveĪn oscilloscope, then you can simply connect to an output device such as an LED to see the fade in, fade out process. If you have an oscilloscope, you can check the output waveform that the circuit produces.
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Making a ramp with cheetah3d how to#
The details of how to build this circuit and how exactly it works is described in detail below. The process then repeats itself over and over again. As the ramp hits its peak and starts to descend inĪmplitude, the LED fades out until it turns off. The amplitude of the ramp increases, the LED will get brighter. If you connect to an output device such as an LED, it will turn the LED first with low brightness and as This waveform increases steadlyĪs the capacitor is being charged until it hits its peak and then decreases even more dramatically as the capacitor isīeing that this waveform repeats over and over again, this generator can be seen as an oscillator. This circuit requires no integrated chips.Ī ramp generator is a signal generator which generates a ramp waveform. In this project, we will show how to build a ramp generator circuit using transistors and a few other simple How to Build a Ramp Generator with Transistors