Bootstrap Circuit

[Godfather]

Hi to all,

My name is Alex,I'm Romanian and I am a student in third year on electronics(RTV).I have to make a project about Bootstrap circuit ,but since I haven't used it I don't know anything about it.I will sure learn about it on school but later on.So can you give me a general perspective on Bootstrap circuit?What does it do,on what it is used?Olso can you give me an electronic scheme?

Thx you..>!!

 

[audioguru2]

Hi Alex,
Welcome to our forum. ;D
Are you talking about bootstrapping the collector load of a transistor so it is more linear, has more gain and has a wider voltage swing?

 

[Godfather]

Yea,I want to find out ,please tell me how does it work?and if you have a scheme I would apreciate very much..

 

[audioguru2]

This link shows how bootstrapping reduces distortion by 10 times:
http://www.dself.dsl.pipex.com/ampins/discrete/twoq.htm

The capacitor causes a constant current to flow during signal changes in the transistor's collector resistance. Constant current means the resistor has a higher impedance, so its voltage gain is higher allowing for more negative feedback that reduces distortion.
The capacitor also allows the collector's voltage to rise above the supply voltage on its positive swings, for max output voltage swing from the circuit.

View attachment 38515

 

[Godfather]

thx you,I apreciate this

 

[Godfather]

Okay...now from what I'v understand the amplifiers with high imputy resistance , the value of this resistance depends very much on the bias resistance Rb.But stability requires that Rb cannot be very high , therefore it is necessary to use the bootstrap circuit so that high value of input resistance can be obtain with

 

[Godfather]

I'v put Rb 900 k

 

[audioguru2]

Okay...now from what I'v understand the amplifiers with high imput resistance , the value of this resistance depends very much on the bias resistance Rb. But stability requires that Rb cannot be very high , therefore it is necessary to use the bootstrap circuit so that high value of input resistance can be obtain withView attachment 38773

 

[Godfather]

Thx you audioguru...you really know a lot  and you are very helpfull.
Now I understand ...

PS:The program you use to simulate circuits it's free ware?If yes ,can you send it to me?

 

[SM2GXN]

Hi Godfather!

You can download it directly from LT website, here's the link to the download page just click on LTSpice/SwitcherCAD III

 

[Godfather]

Hi SM2GXN!
The link is not working...I am using Opera. :'(

 

[audioguru2]

I got this link from Google:
http://www.linear.com/company/software.jsp

 

[Godfather]

Thx ...a lot of  interesting programs there...

 

[SM2GXN]

Sorry I forgot to place the link in my post, there's nothing wrong with your opera Godfather
Thanks audioguru