ace.neerav
New Member
**broken link removed**
can someone explain me this circuit?
can someone explain me this circuit?
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ace.neerav said:hello friends, thanks for you efforts. the working is not exactly clear in my mind.
i dont quite understand what the transistor is doing there. is it in cut of or sat or active region initially? and what happenes when opamp o/p goes +Vsat to the Base collector junction?
Its a pnp transistor, When pin 6 is High +V its OFF, when pin 6 is low 0V its ON
i would also have to do some reading on relays. i have no clue what they are. can u provide me a link?
basically we got this project made from someone else and now its explaination time in college. in our project, based on the same circuit, an led glows when we provide heat to the thermistor. now i am not sure if the led is IN 4148.
this is the difficulty we are facing for not doing it ourselves.
The 1N4148 is a regular diode used to suppress the relay inductive spike. There is no LED shown in the schematic. You could add one in parallel with the relay coil, if desired, along with the 1N4148. (Place cathode to ground and add the appropriate resistor in series to limit the LED current)ace.neerav said:i dont quite understand what the transistor is doing there.
The transistor operates as a switch to provide sufficient current to operate the relay. The op amp doesn't have enough output drive to power most relays.
is it in cut of or sat or active region initially? and what happenes when opamp o/p goes +Vsat to the Base collector junction?
When the op amp output is high, the transistor is off. When the op amp output is low the transistor is on
now i am not sure if the led is IN 4148.
alright! i did some reading on relays and have understood majority of the circuit. just a few questions...
1.when the opamp o/p is 0 what is the state of the be jn and the bc jn and why?
Vbe=0.7v, due to the current flowinhg thru R3 and R4 and the transistor base/emitter junction.
2. when the opamp o/p is high what is the state of the be jn and bc jn and why?
Vbe=0, there is no current in R3/4 so NO Vbe
ace.neerav said:cause i read in relay articles that the transistors is to be operated in saturation region. and that means ic would be in opposite dirction. and that would also mean when the opamp o/p is 0 and transitor is on, the relay should be energised but would not cause the forward biased diode would nearly short the relay. things are getting confusing.
hi ace,ace.neerav said:OMG! there is a huge confusion. when does the opamp turn on? when the temperature rises or when the temperature falls?
ace.neerav said:(which we have already got made from some one and which now only requires to be explained to our professors)
when we touch the thermistor the LED would glow.
Your circuit does not show an LED???
and that would happend only if the opamp o/p tunred high when the the
voltage drop accross the thermistor increases and that would also mean that the thermistor has +temp coefficent.
Your circuit is showing a NTC thermistor, reducing resistance with increase inTempr
if ur talking about the feed back then as i have not yet come up to the topic of opamp in my self study
There are basically two types of feedback:
negative, this is where a portion of the output signal is fed back to the input in antiphase to the input.
positive this is where a portion of the output signal is fed back to the input in phase to the input.
i m not quite sure what hysterisis is
I would suggest as a starting point that you look [Google] for hysteresis.
Look at magnetic hysteresis also schmitt inputs.
and how the f/b works