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elementary electronics 3 / drive a transistor by DC

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These videos are made for beginners and all people interested in these matters. Here you see how to drive a NPN transistor (or a NPN Darlington) by means of a DC voltage/current on the basis. First set a "critical point" by means of the variable resistor on the basis. The DC Voltage/current applied to the basis drives the transistor over its critical point (approx. 0,8 Volt for a Silicium type, called treshold voltage) so that the transistor is going to conduct and the lamp is going to burn, the relay switches etc. The schematic works far better with a Darlington, consisting of 1 small signal transistor with a high current amplification (250-300) and a medium power transistor with a current amplification about 40-150. The circuit will be extremely sensitive with a Darlington. The variable resistor on the basis is in case of a Darlington 470 K, in case of one transistor 25K-50K (values for a 12 V power supply). You can combine this schematic for instance with a light or temperature dependant resistor, so that the lamp burns/relay switches at a given temperature or certain light volume. The schematic is also possible with PNP transistors, reverse the feeding voltage in that case and make the basis of the transistor or Darlington negative to let the circuit switch, reverse the LED when you use a LED.

Channel: Science & Technology
Uploaded: December 31, 1969 at 6:59 pm
Author: radioam232

Length: 04:49
Rating: 5.00
Views: 7221

Tags: by  current  drive  lamp  LED  NL11561  or  radioam232  relay  switch  transistor  voltage  

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Video Comments

radioam232 (December 31, 1969 at 6:59 pm)
Take between A and B a resistor of 1K (1000 Ohm) and connect the emitter (3) to ground. From collector (2) to ground you will find a changing Voltage dependent on the input.
tinku6565 (December 31, 1969 at 6:59 pm)
hi can u please send a video about how a transister works as a voltage amplifier?
oprechtvanmensen (December 31, 1969 at 6:59 pm)
hmmm thats look easy, but its just that all that calculation stuff looks so horrible to me and my brain just cant fit that into the right location... i guess the "elementary = false".
radioam232 (December 31, 1969 at 6:59 pm)
It fascinates me too and I have done a lot of experiments with this schematic. In the charge meter on my channel I used 3 PNP transistors (300x) in a Darlington. Amplification is so extreme that it detects elec./magn. fields.
AllAmericanFiveRadio (December 31, 1969 at 6:59 pm)
It has always fascinated me that when two transistors are in a Darlington configuration, that you don't add their gains together, you multiply them together.

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