PWM to mosfet - using isolator or ?

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Gerlu

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Joined 2004
I try to build a converter, but I am not sure how the connection is made from the output of PWM to mosfet. Would it require an isolator ? Can someone show me in diagram ?

The mosfet I used should be p-channel. And I need some suggestions on what mosfet I need, is RFP30P06 ok ? The incoming supply is 28V with switching frequency 100kHz.

The diagram is as below, any problem with that ?

I am new to this design and here too. Hopefully I am posting in the right place. Appreciate and expecting any suggestions. Thanks.
 

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Petter

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Joined 2001
Nobody is answering because your question is not answerable.

There simply isn't enough information to provide a meaningful answer.

May I suggest you use a reference design from one of the manufacturers instead?

Please note that there is limited competency in SMPS on this board - true some individuals are highly skilled but the traffic on SMPS is very limited.

Petter
 
G

Gerlu

Member
Joined 2004
Circlotron said:
Have a look at an IR2121 or an IR2125. Not sure which one but they are similar.
Click to expand...
Ok, will check it out. :D

Circlotron said:
Seeing your converter will have a negative output voltage, will the error amplifier input on the controller chip work ok with this?
Click to expand...
Yup, by first inverting it with another error amplifier (inverting amplifier -- positive input to ground)
 
G

Gerlu

Member
Joined 2004
Re: pwm

Thanks for the replies :)

raypsi said:
Your schematic shows 2 grounds, ya?
Click to expand...

Yup, 1 power ground and 1 signal ground. But .. why using isolator :confused: Both the grounds will be connected at a single point after all.

sivan_and said:
If u are looking for a step down conv,,,Try a single chip solution like MAX 724.
Or SG3524 (both o/p added for max duty cycle.and IR2110 or any high side driver.
Click to expand...

Single chip solution is good :angel: .. but .. .. :cannotbe:
SG3525 featuring soft-start ..
Yup, I think I need a high side driver :D


sivan_and said:
Even the outputs can be connected directly to MOSFEt w/o isolator,if u r using SG3524 or TL494.Since the IC output transistors collectors and emitters are easily accessible,can be configured freely...
Click to expand...

Really !!!?!! Can you show me ?
 
G

Gerlu

Member
Joined 2004
Still not figure out the application for it yet, +/- 12V should be useful. Just try to build some converter myself. :D :D And to gain some experiences with it.

Input voltage is +25V .. might need zener diode or diode here.
Output voltage is -12V (require soft start ?). +12V is ok too.
Resistive load 15ohm. So, load current = 0.8A.
Mosfet p-channel IRF9540 ?

The values above are not fixed.
Vi = 12V Vo = 5V R = 10 ohm or 15 ohm
are fine too.

And, thanks for your responces :)
 
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