Wide range input 5V power supply

[hkBattousai]

If Rc is only 100R how is it supposed to dissipate all the power?


The 2N3904 has a maximum voltage rating of 40V, if the input voltage is 600V, the voltage across Rc will need to be 555V so the current will need to be 5.55A so the the power dissipation will be 3.1kW.

Did you read my note under the circuit shcematic? I made a mistake forgeting the name label of that BJT transistor I randomly chose. After previewing my message before posting I realized that and added the note below in my message to avoid any confusion.

...I put the model 2N3904 symbolically, I know it is not able to stand as high as 600V...

mmm portable sun. Excellent.

And my "portable-sun" friend...
I think you are the type who only stares at pictures and doesn't read any text...
Go on, have you fun, I was stupid enough to design a portable sun.

 

[Sceadwian]

Think what you want Battousai, I wasn't even talking to you, I was responding to Hero999's comments.
I am not a type. I am a Sceadwian. You can call me Jake if you want, but don't think my brief comment was against you in any way.

Everyone screws up every now and then. Please feel free to not lash out against other people you find convenient targets the next time it happens, and no one is laughing, you should however BE laughing, take this stuff too serious and it'll get you nowhere.

 

[hkBattousai]

Think what you want Battousai, I wasn't even talking to you, I was responding to Hero999's comments.
I am not a type. I am a Sceadwian. You can call me Jake if you want, but don't think my brief comment was against you in any way.

Everyone screws up every now and then. Please feel free to not lash out against other people you find convenient targets the next time it happens, and no one is laughing, you should however BE laughing, take this stuff too serious and it'll get you nowhere.

Ok then, if it wasn't against me I have no problem with your post.

 

[Hero999]

Did you read my note under the circuit shcematic? I made a mistake forgeting the name label of that BJT transistor I randomly chose. After previewing my message before posting I realized that and added the note below in my message to avoid any confusion.

And my "portable-sun" friend...
I think you are the type who only stares at pictures and doesn't read any text...
Go on, have you fun, I was stupid enough to design a portable sun.

A schematic speaks much louder than words. If you used large bold text immediately below the schematic, then we might've noticed.

Anyway, I think the idea to include Rc was a good one, I would probably increase the value so the voltage across it is 590V at the full operating current. Obviously the transistor will still need to be rated to 600V because it will have to stand it when no load is connected.

As you have 600V available you could consider using a 5V SMPS designed to run from a 440V three phase supply which should be able to work from 600VDC.

 

[hkBattousai]

A schematic speaks much louder than words. If you used large bold text immediately below the schematic, then we might've noticed.

Anyway, I think the idea to include Rc was a good one, I would probably increase the value so the voltage across it is 590V at the full operating current. Obviously the transistor will still need to be rated to 600V because it will have to stand it when no load is connected.

As you have 600V available you could consider using a 5V SMPS designed to run from a 440V three phase supply which should be able to work from 600VDC.

I decided to use this IGBT.

Since the since this IGBT is supposed to work in switching mode, it won't produce any heat. All the energy will be consumed on Rc. The lower the value of Rc, the lower energy will be wasted. I should check the datasheet of this IGBT to find the minimum possible value of this Rc resistor...

 

[Hero999]

So you've decided to build a switching regulator?

You'll need to add an inductor, an oscillator and a flyback diode.

I hope you're not falling into the trap of the holy grail of an inductorless switching regulator?

 

[vlad777]

Hi people.

I am not really shure about my solution but I will
post anyway.

So here is how its suppose to work.

Diak is closed so cap is charging but when it reaches
certain voltage diak opens and closes the mosfet.
So now cap is discharging and (correct me if I am wrong)
when the voltage on diak is less then 0.7V it closes
and cap is charging again. Since there is a resistor
in series with diak the voltage on cap didnt drop too low.
My understandig of diaks is poor so if this is a waste
of bytes I apologize.

Even if this doesnt work to the requirements it can be used
as input stage and the second stage would do the rest.

 

[hkBattousai]

vlad777, thank you very much for this alternative circuit.

It is a quite simple circuit comparing with mine, and I think it works theoratically. Though there are two points to discuss about it. I will wait for other people's comments on this one.

First,
The voltage on 100uF capacitor is supposed make very small ripple's aroung 5V DC level. Both diac and BJT doesn't have sharp transition regions between saturation and cut-off states. It cause a time delay while turning on and off the MOSFET. I need a design which immidiately switches the MOSFET, if it doesn't there will be a lot of power dissipation on it. That's why I used a comparator in my design.

Second,
You didn't use a current limiting resistor for charging the 100uF capacitor. Without using such a resistor the time constant τ=R.C will be too too small which woulc probably create overshoots on the capacitor voltage level. I didn't calculate this case, but I don't think it is a robust solution to charge the capacitor so fast. Still I may be wrong on this one, I didn't make any calculation on it.

Any way thank you for this circuit.

 

[Hero999]

You need to add an inductor to limit the current.

Adding a resistor won't help because it will just waste power leaving you with a circuit as inefficient as a linear regulator but worse because of all the ripple generated by the switching.

Using an inductor to limit the current doesn't waste energy because the inductor stores energy so it can be released slowly, rather than dissipated it as heat.

I think you should just stick with a proven topology such as a buck or a forward converter. I'd recommend the latter since you really need a transformer to keep the duty cycle to an acceptable level.

 

[hkBattousai]

Using an inductor is a brilliant idea, how couldn't I think it before?
But I think there is still a problem. Step response of an L-C will contain overshoots and oscillations. Using a second order system like this may be dangerous, isn't it?

 

[Hero999]

No, it's not dangerous at all, buck regulators have been used for many years and are safe. You just need to change the transistor to an PNP because it needs a high side switch.
Buck converter - Wikipedia, the free encyclopedia

It's possible to build one with a couple of transistors.

2-transistor Black Regulator

I'd recommend a Darlington or Sziklai pair rather than a single transistor for Q1 in this case because it will reduce the base current and make it more efficient. The transistors will need uprating to 600V and you'll need to increase some resistor values to reduce the current.