this circuit in the figure below, consists of an oscillator stage followed by an amplifier stage, is simple and has a status indicator uses few components and easy to find. So we use the oscillator to generate the frequency that allows us to determine whether the transistor under test is capable of amplifying the signal, if so transistor in good condition, otherwise, buy another.
Operation:
As foreshadowed, the circuit tester is an astable oscillator formed by the two gates ICA-ICB investors in the scheme and the frequency of oscillation is determined by the values \u200b\u200bof R1 and C1, in this case a frequency near 120 Hz to avoid possible the annoying flash.
If you want to change the frequency, can be done by setting potentiometer R1, arranged for this purpose. The frequency can be calculated by: f = 1 / (0.7 x R1 x C1), where R1 is in Ohms and C1 in farads.
C1 should be less than 10uF to avoid as much as possible the "high leakage currents" to be presented, comparable to the initial charging current of the capacitor in many cases. The capacitor acts like a short circuit. Because the investor has 6 CI4049B have been used in parallel pairs as you can see, so you get more intensity and chargeability, ensuring the necessary current to drive the LED's. Oscillation obtained
attacks the input of a pair of separators investors to not load the oscillator and heads the terminals of the transistor FET, but with a lag of 90 °, in another couple of investors, ensuring a flow of current DS (drain-sink) in each half of the oscillation and SD in the half cycle following when they stay active pusher This will excite the corresponding LED indicating its polarity (Canal N or P channel) and if in good condition.
Subject: ESS.
Student: Pedro Jose Contreras Urbina
Source: http://www.fortunecity.es/felices/barcelona/146/3ds/tutores/mosfet_test.html
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