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  1. R

    Why a pull down resistor for transistor base

    Yes, it should be this, I have corrected it. My concern is that the transistor T1 is switching on at 1.1V and off at 0.56V. Where are my calculations wrong? Can you help?
  2. R

    Why a pull down resistor for transistor base

    Hi, I have just noted that the circuit switches on at 1.1V and off at 0.56V. I need to switch on at 3V and off at lower then 0.56V. I have measured the current through the relay and green LED to be 72mA.
  3. R

    Why a pull down resistor for transistor base

    Hi thanks for your reply. Please remember the relay module is not my design, it was an brought via a website (not by me). I just want to know that my additional circuit looks fine and confirm with calculations. I made R3 a 10K, so Ic woul be 5/10K = 0.5mA.ib calculated at 2.34mA. everything...
  4. R

    Why a pull down resistor for transistor base

    Hi, I have attached a image of the schematic. I have only added the section on the left i.e. R1,R2, R3 and T1. R3 added to keep T2 off. The relay coil is 600R, and driven from 5V. T2 is S8850 PNP transistor. I have added the circuit to give base current of 2.3mA i.e. 3-0.6/1K. I am only...
  5. R

    Why a pull down resistor for transistor base

    Ok, I will provide a better schematic. Please bear with me and thanks
  6. R

    Why a pull down resistor for transistor base

    Sorry for the confusion. The relay module has the PNP, relay, fly back diode etc. I have added only the 1K (R2) to base of T2, The 10K pull down at R1, the transistor T2 and a 10K pull up at R3. R3 ensures that the PNP is off when T1 is off as the base of the PNP and it's emitter are at 5V...
  7. R

    Why a pull down resistor for transistor base

    Hi all, Just to be clear I am only ensuring the PNP is in the off and on condition. I am not driving the relay coil. The 10K pull up keeps it off as base emitter are both at 5V. The additional transistor with 1K base resistor and 10K pull down is what I have added. So when this is driven...
  8. R

    Why a pull down resistor for transistor base

    Thanks, I am starting off in Electronics, so unsure of a few things. I will post up my calculations so that people can see if I have done everything correctly. Thanks for the advice.
  9. R

    Why a pull down resistor for transistor base

    The 1K and 10K combination switch on the transistor. This is turn drives the. NPN on. The relay contacts then switch over.
  10. R

    Why a pull down resistor for transistor base

    I have, it works fine. Thanks.
  11. R

    Why a pull down resistor for transistor base

    Thanks for the help. The micro has a 100R series resistor that will be in series to the 1K base resistor. That will probably cause no problem I think? I think it probably will not hurt to have the 10K to OV. Rhanks
  12. R

    Why a pull down resistor for transistor base

    Hi I have attached a image I saw on the web. The transistor is used to drive a relay module by inverting the logic, which ensures that the relay PNP is switched off too. Why is the 10K required pull down from base of transistor? How is this value calculated? If the input of the transistor...
  13. R

    LC parallel tank circuit

    Thanks. I simulated the circuit (my circuit) in simetrix and at resonance the voltage was high, current low. However doing this practically resulted in the voltage being at a minimum. I will show pics of my set up. Thanks again.
  14. R

    LC parallel tank circuit

    Hi, Thanks for the reply and the pdf documents. Really appreciate you taking time out to help. I have just wired the LC Parallel circuit (as in my message). The scope was placed at the output i.e. across the LC Circuit. However, I saw no change in voltage as I changed the frequency. I sweeped...
  15. R

    LC parallel tank circuit

    Hi, I have just tried putting the resistor in series (see attached schematic and output - LC Parallel Circuit.pdf). It shows voltage at a max and current at a minimum as you mentioned. I took this a bit further by adding a transistor (see attached schematic - LC Parallel with Transistor). I am...
  16. R

    LC parallel tank circuit

    Hi Just to confirm the resistor should be placed in between the lc parallel circuit and the sine wave generator? I will try this. However, i have seen the configuration that i have shown in a text book, hence the confusion. I will give it a try. Thanks
  17. R

    LC parallel tank circuit

    Hi all, I have attached a simulation in Simetrix, as you can see the voltage is at a minimum on the resonant frequency. What have i done wrong? The 1K was added to create a voltage to be monitored. thanks in advance
  18. R

    LC parallel tank circuit

    Hi Thanks, I will post what I have done in Pspice, LC in parallel with a resistor to the parallel connection all connected across a 1V pkpk Sinewave. I have added a voltage probe across the LC part and see a dip in the voltage at a resonant freq of around 189KHz. The inductor is 7mH and the cap...
  19. R

    LC parallel tank circuit

    Hi Should the voltage be at a max for resonance? The current minimum and impedance maximum. Is there anyway I can verify this by calculation? Thanks
  20. R

    LC parallel tank circuit

    Hi all, Please can someone show me how to verify that the current is low, impedance is high and voltage is low for a parallel lc tank circuit. Also how can i verify this using pspice. Thanks
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