Search results

  1. R

    Voltage Drop across NPN BJT C&E?

    I hope we are not mixing up the selection of a switch component with the circuit design after it has been selected. Since I don't know exactly what you are doing, and you have received help from several members, I don't think I can help you further. I only observe that it is easy to make a...
  2. R

    Voltage Drop across NPN BJT C&E?

    What makes you think I don't know how to read a transistor datasheet? Ratch
  3. R

    Voltage Drop across NPN BJT C&E?

    All I can say in general is that the BJT must be saturated to be on. How it performs depends on the components you select and put together. Perhaps a BJT is not the best component to use. Don't manufacturers sell solid state switch modules? Ratch
  4. R

    Voltage Drop across NPN BJT C&E?

    You can't. You have to know the component values of your circuit. A BJT is not an inherent switch, anymore than it is a inherent current amplifier. But, it can be made into either by the right circuit and component values. Ratch
  5. R

    Voltage Drop across NPN BJT C&E?

    There is another problem with having a high base resistance. It is thermal instability. Whenever the reverse bias voltage on the base collector circuit is applied, the Icbo generator fires up and sends its current into the base terminal. Then the current splits, with some of it going into the...
  6. R

    Voltage Drop across NPN BJT C&E?

    Of course not. But, just enough forward voltage to saturate the transistor reliably. You will have to calculate it. It will depend of Vc, Rc,Rb, and Re. Ratch
  7. R

    Voltage Drop across NPN BJT C&E?

    Controlling a BJT by Vbe is difficult, if not impossible. I was not advocating designing that way. But by knowing what controls a BJT, one can apply alternate design techniques. Did you look at the link I sent? Ratch
  8. R

    Voltage Drop across NPN BJT C&E?

    A switch is easy. Zero volts on the base, and no current will be present in the emitter/collector. Applying some forward voltage on the base to saturate the BJT (not much is needed), will turn on the switch. Ratch
  9. R

    Voltage Drop across NPN BJT C&E?

    I don't have to mention that the relationship between base and emitter/collector current (Beta) is not precise between two different BJTs, do I? Beta can have quite a range. Designs that depend on beta either use an excessive amount of feedback or are prone to unreliable performance. See...
  10. R

    Voltage Drop across NPN BJT C&E?

    Everyone here knows that I have been playing Whack-a-Mole with every BJT base current control freak that pops up here. They just can't seem to understand that base current is an indicator of the emitter/collector current, not the control of it. The physics of the BJT determine what is in...
  11. R

    please can someone help me out with this:-

    Sure I can, but can you? The powers that own this website don't want me to give you a direct answer. Hint: Use differential calculus. Ratch
  12. R

    please can someone help me out with this:-

    Actually, you can transfer more power to the load if you reduce the source impedance. That is not always possible, but if you can to it, so much the better. Let me demonstrate. Suppose you have a 12 volt source with a 4 ohm impedance feeding a 8 ohm load impedance. The power transferred to...
  13. R

    Voltage Drop across NPN BJT C&E?

    No, Vbe controls the Ic of a BJT. The base current is an indicator, not a control of Ic. A BJT by itself is a transconductance amplifier (voltage Vbe controls current Ic). If you load the base with lots of resistance to make it a current generator, then you have a current amplifier circuit...
  14. R

    Voltage Drop across NPN BJT C&E?

    For your information, BJTs do not operate using "channels". The operate using diffusion. Also they are bipolar (charge carriers are both holes and electrons), so the designation of N-channel or P-channel does not apply or make sense for BJTs. Ratch
  15. R

    Buying components from China.

    Need I say more? Ratch
  16. R

    What is special about solderable enamelled copper wire?

    What website?? Check your post better. You should know that materials like wood, paint, paper, plastic, and many non-metallics do not bond to solder. Evidently, someone has invented an enamel that either disintegrates when heated or turns into flux. Ratch
  17. R

    How do constant current loads work and how to make one

    If you cannot understand the explanation of how to do it, and have minimum electronic construction skills, how do you expect to achieve the goal of building what you want. Perhaps a study of elementary electrical theory knowledge and hardware basics is in order first. Ratch
  18. R

    testing voltages across components in an AC circuit

    You first determine what component is defective by how the circuit malfunctions. THEN, you can remove or disconnect the suspected component and test it out of circuit. Ratch
  19. R

    Signal flow fundamentals

    No, the capacitor shunts the AC current around the emitter resistor,. This increases the AC current in the emitter leg for a given base voltage, thereby increasing the amplification more than if the capacitor were absent. A transistor is a transconductance device, meaning that input voltage...
  20. R

    Signal flow fundamentals

    Confusion arises when you don't specify whether the signals are current or voltage. Ratch
Top