Diode trigger transistor - help needed

[Help]

Diode trigger transistor

Dear All,

I would like to get some advice from you all.

I have 2 input signal to share with one transistor driver. I would like to know if this two input (EXIN1 and EXIN2) signal is Lo, is it the transistor BASE is fully shot to GND? I have using meter to measure the 'a' point it is 0V. But i'm worry it is hap logic condition will cause the IO signal not stable. I have use 430Ohm to pull it to GND, is it necessary?

Is it correct for this circuit?

Thank you,.

 

[IQBAL KHAN]

Diode trigger transistor

remove R1999

 

[FvM]

Re: Diode trigger transistor

There are two reasons to use a pull-down resistor at all:
- diode and transistor leakage currents, particularly at higher temperatures
- off switching speed

If you feel 430 ohm is too low, you can increase the value. To short leakage currents, 10 k is most likely sufficient. But the off switching
speed is much lower then.

 

[IanP]

Re: Diode trigger transistor

You need “something” to pull the voltage at point “a” down, but that something doesn’t need to be as strong pull-down as is 430Ω ..
Consider 4.7kΩ, 10kΩ or even 100kΩ, as I don’t think you are talking about situation where this transistor has to switch hundreds of MHz ..

Rgds,
IanP

 

[Help]

Re: Diode trigger transistor

Dear IQBAL KHAN,

Thanks for your reply and trying to give some help.

Dear FvM, Ianp,

Thanks for you all advice. I have learn new thing from this circuit. I will try change the pull down resistor to 10k or 100k.

Thanks alot.