Voltage Regulator Project: Hysterisis, 9V, 15 Ohm Load

[LostEngKid]

hey guys, I've got to make a voltage regulator for a uni project. it has to use hysterisis and produce 9v out from a 16Vrms AC powerpack over a 15 ohm load. It also needs overload protection, I've drawn up the attached circuit, i think it will work and filled in some of the values i know but I am stuck for the others, any help would be great.

 

[Redbelly98]

I'm not qualified to analyze a circuit like that, but what about using a simple 9Vdc regulator after cap C6?

 

[mgb_phys]

I think that's cheating!

 

[berkeman]

hey guys, I've got to make a voltage regulator for a uni project. it has to use hysterisis and produce 9v out from a 16Vrms AC powerpack over a 15 ohm load. It also needs overload protection, I've drawn up the attached circuit, i think it will work and filled in some of the values i know but I am stuck for the others, any help would be great.

View attachment 15072

Couple comments:

-- Usually I would put the current sensing resistor in the + feed, right before Q1. Having it in the negative return complicates the grounding of this non-isolated buck converter.

-- I'm not sure about the snubber on the flywheel diode. I've never used one, and generally haven't seen them used in bucks. It will lower your efficiency at least. Why do you have it there?

-- It seems like you should consider putting a bit of hysteresis in your comparator circuit. I'm not generally comfortable with comparator circuits without at least some postitive feedback hysteresis.

 

[berkeman]

I'm not qualified to analyze a circuit like that, but what about using a simple 9Vdc regulator after cap C6?

I get the feeling that the assignment is to design a switching regulator, rather than a linear regulator.

 

[berkeman]

Couple comments:

-- Also, is there a reason that you are using a Darlington for Q1? That will impact your efficiency pretty significantly.


Quiz Question: Why?

.

 

[Redbelly98]

... what about using a simple 9Vdc regulator after cap C6?

I think that's cheating!

I get the feeling that the assignment is to design a switching regulator, rather than a linear regulator.

Whoops, my bad!

 

[berkeman]

Couple comments:

-- It seems like you should consider putting a bit of hysteresis in your comparator circuit. I'm not generally comfortable with comparator circuits without at least some postitive feedback hysteresis.

Another Quiz Question for the original poster (OP) -- Why do I say this about comparator hysteresis?