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Recent content by Sebastie

  1. S

    Need help to model op amp current source in block diagram

    Hello, I need to convert a little schematic for a current source with an op amp and a BJT to a block diagram in order to study the stability. My concern is that I don't know how to model the transistor in the feedback loop. Does someone know how I can do ? regards
  2. S

    transistor biasing circuit : need help to calculte it

    Hello LvW, Thanks for your reply. Well, I can send you the link (but it's in french), he only mentions that the transformation for the Rb resistor is made by Thevenin or norton. https://www.gipsa-lab.grenoble-inp.fr/~christian.jutten/mescours/Conception_circuits.pdf (page 27 and 28). and he...
  3. S

    transistor biasing circuit : need help to calculte it

    Hello Goldsmith, Many thanks for your help. Well, I have the answer but I don't understand how they found the expression : for RB they have : RB=R1+(R6R7)/(R4 +R5+R6+R7) do you know how they found this ? regards
  4. S

    transistor biasing circuit : need help to calculte it

    Hello all, I would want to know he someone could help me to simplify the first schematic to the second one. i would want to know what is the method to calculate the Rb resistor ... ? (I suppose I have to use thevnin, but I don't success to do it). Could you help me ? thanks
  5. S

    Need help to choose a cap for low noise application

    Hello all, I'm working on a low noise voltage reference (1.25V) and would want to know what is the best capacitor type to reduce noise ? Since this is an embedded equipment I tested a MLCC capacitor (100µF/X5R) but the problem is the piezzo effect... so I need to change it. What is the parameter...
  6. S

    Small transistor signal analysis

    Hello and thansk a lot for your replies. I'm going to hazve a look on calculation. I made an error with the small signal schematic : the R1 and R4 are referenced to the ground not to the emitter of T1
  7. S

    Small transistor signal analysis

    Hello FvM, Thanks for your reply. For the 1/y11 parameter, I found on the net this expression : 1/y11=Beta*VT/Ic the problem is that the Beta of the transistor is specified in the datasheet with a value comprise between 100 to 630... How can I found the good value ? 1/y22=(VA+VCE)/IC what is...
  8. S

    Small transistor signal analysis

    Transistor small signal analysis Hello all, I would want to study a low noise preamp with small signal analysis, but I don't really know I can do. I would want to calculate the gain of the amplifier. I tried to deduce the equivalent schematic in small signal analysis, but I don't know how I...
  9. S

    Need help to better understand the role of the integrator

    Hello, Thanks for your help, You're right albbg, I forgot that I have to consider the loop and not only the integrator stage... but on the relation that I have found, if I consider the first case with V1 and V2 which are exactly same, if my theorical expression is correct, we will have...
  10. S

    Need help to better understand the role of the integrator

    Hello thanks for your replies. Ok, the integrator permit to have the average of the variation between V1 and V2 and correct it. I tried to to evaluate the output and I have this : **broken link removed** I don't see the relationship beetwen the theorical result and the simulation When there...
  11. S

    Need help to better understand the role of the integrator

    Hello I would want to understand the integrator function on this schematic : **broken link removed** What is the aim of it instead of a simple inverter circuit ? I tried to calculate the expression of the integrator stage in Laplace : Vs(s)=V2(s)+(V2(s)-V1(s))*1/(R4*C3*s) Does it correct ...
  12. S

    Need help to calculate values of BJT switch function

    Hello Jony130, Thanks a lot, it's more clear for me now :)
  13. S

    Need help to calculate values of BJT switch function

    Hello Jony130, Thanks a lot for you reply. RB2 doesn't seem to be very important, I suppose the relation RB2=10*Rb1 that is a convention ... I don't understand the relation ib > Hfe_min*Ic, do you mean Ib > Ic/Hfe_min ? why do you take Ic/Ib=10 ? (since the beta min is specified at 35 in the...
  14. S

    Need help to calculate values of BJT switch function

    I forgot to tell you that my application need a IC=5mA.
  15. S

    Need help to calculate values of BJT switch function

    Hello I have to calculate the value of resistor of a simple switching stage. My question is what is the method to calculate the value of resistor ? Since the value of the beta is dependant of the VCE voltage and collector current (and as the voltage of my application doesn't match with the...
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