bc547 working for constant current regulation

[phobos1]

i am using bc547 with its base emitter connected across a current sense resistor.. whose collector output is fed to pwm controller through a opto.....



the problem is should i swing bc547 between cutoff and saturation to maintain constant current or should i operate it in active region......


if i should operate in active region suggest me any compensation technique.... for transistor stability................

refer circuit.........

the other end of optocoupler will be connected to primary side for changing the pwm width.....

 

[Audioguru]

If the transistor is cutoff or saturated then it isn't regulating anymore. It must be linear and active.

 

[godfreyl]

refer circuit.........

This is the picture you attached.


Please compress your pictures to GIF, PNG or JPG format to make the file size smaller.

 

[phobos1]

sry i could not edit my post but u attached some wrong image instead of mine...

 

[godfreyl]

No I didn't, that is your image.

If you don't believe me, click on the link in your first post.

 

[FvM]

I see this picture

 

[andre_luis]

...the problem is should i swing bc547 between cutoff and saturation to maintain constant current or should i operate it in active region......if i should operate in active region suggest me any compensation technique.... for transistor stability................

It is commonly neglected on employing BC54x transistor family device that its hfe property is defined by suffix character ( e.g BC547C ). and this was not informed on circuit above.

Other point is that once circuit above has not a emitter resistor Re it means that overall amplifier gain is defined mainly by transistor hfe, which is changed according to the variation of ambient temperature, becoming poorly stable.


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