Hello,

My question is quite simple; can someone tell me how I can read the input capacitance of this transistor?

https://www.onsemi.com/pdf/datasheet/bd135-d.pdf



For some background if needed:

I have built this circuit and found through trial and error that C1 (Cf in formula) works best for my circuit at 10pF.

https://www.ti.com/lit/an/sboa325/s...35663&ref_url=https%3A%2F%2Fduckduckgo.com%2F

I am currently trying to explain the compensation techniques of a op-amp driving a capacitive load. The design is using a technique described by a reference guide by Texas Instruments.



The video can be found:

https://www.ti.com/video/series/precision-labs/ti-precision-labs-op-amps.html

I found one more reference for this:

https://www.proquest.com/docview/20...UxjsOWuCk=&pq-origsite=summon&accountid=11526

 

Welcome to AAC!

My question is quite simple; can someone tell me how I can read the input capacitance of this transistor?

https://www.onsemi.com/pdf/datasheet/bd135-d.pdf

They only give typical values:

 

Welcome to AAC!

They only give typical values:
View attachment 318914
View attachment 318915

Thank you so much! I am a bit confused why the graph gives the capacitance vs the reverse voltage.
if my emitter is GND, Base is 0.7v and collector is 2v. Would I read the graph for Cib at reverse voltage 0.7?

 

I am a bit confused why the graph gives the capacitance vs the reverse voltage.
if my emitter is GND, Base is 0.7v and collector is 2v. Would I read the graph for Cib at reverse voltage 0.7?

It sounds like you want information that the manufacturer didn't provide. In that case, you need to contact the manufacturer.

 

When the junction is forward biased, current flows steadily without building ip a charge, so it effectively has no capacitance.

 

You could always get a nanoVNA and measure it as a function of frequency. I hear they are quite affordable. Much more so that an actual VNA.

 

You could always get a nanoVNA and measure it as a function of frequency. I hear they are quite affordable. Much more so that an actual VNA.

Hello, I do have access to a lab with VNA etc. I am however not quite sure how you would approach measuring the capacitance. Would you approach it the same way as measuring a capacitor?

To me what bob said, would make the transistor act as a variable capacitor? (dependant on frequency)

When the junction is forward biased, current flows steadily without building ip a charge, so it effectively has no capacitance.

 

I am however not quite sure how you would approach measuring the capacitance. Would you approach it the same way as measuring a capacitor?

Unless your application is a one-off situation, measuring won't help.

 

Unless your application is a one-off situation, measuring won't help.

It is a on-off scenario

 

The term one-off means you are building only one of them. Not the same as on-off.

 

Hello, I do have access to a lab with VNA etc. I am however not quite sure how you would approach measuring the capacitance. Would you approach it the same way as measuring a capacitor?

To me what bob said, would make the transistor act as a variable capacitor? (dependant on frequency)

You fabricate a measurement jig where you can characterize the parameters of a part to show how a sample from the total population behaves.