12V -> 170V DC/DC smps, what's wrong?

markusA · 9th March 2011, 09:44 PM

I found this 170V'ish DC/DC smps and since I'm always looking for new ideas I decided to give it a try with LTspice. I have a 19VDC@3.2A Lap top adapter that would be a good start.

I have a circuit that need 150VDC so it looks to be a match made in heaven.

I read the text, looked through the schematics and did the sim.

Either I'm missing something important or this is one faulty design?

What do you think of it?

http://greygum.net/sbench/sbench101/...plies/lvps.txt

http://greygum.net/sbench/sbench101/...plies/lvps.gif

In my sim:
1. The "power on" delay is necessary to start the oscillator but it's no delay?
2. No regulation until it hits the over voltage protection?
3. It's got almost twice the current draw compared to what's listed?

luka · 10th March 2011, 07:48 AM

why don't you just use some IC?

markusA · 10th March 2011, 08:00 AM

I just stumled across this circuit and thought it looked simple enough.
A IC solution would be as good as any I guess?
Since I'm a n0ob I probably need some help to point me in the right direction.

luka · 10th March 2011, 08:04 AM

IC is more safe option, since it was design for that kinda operation... not saying that this above wouldn't work, but on the other hand...

I think I would use
http://www.classiccmp.org/rtellason/chipdata/uc3844.pdf

darkfenriz · 13th March 2011, 08:29 PM

It is a boost converter, I don't recommend that for so high convertion ratio. Try a transformr coupled converter, like pushpull or fullbridge.

mag · 28th March 2011, 09:02 PM

Using a boost converter with so high vout/vin conversion ratio is not recommended. On top of that
irf640 is a 200v mosfet and using it at vout=170v there is no safety margin.
Maybe this circuit will work but it is much easier to use a controller like the uc3842 or similar.
Instead of doing a boost converter make a simple flyback with properly desinged transformer turn ratio. If you don't need in/out isolation you can connect the transformer secondary gnd to the primary gnd simplifying also the feedback loop.
A flyback converter is also inherently short circuit protected, a boost is not and can not be easily protected.

Ciao

-marco

9th March 2011, 09:44 PM	#1
markusA diyAudio Member Join Date: Dec 2009 Blog Entries: 8	12V -> 170V DC/DC smps, what's wrong? I found this 170V'ish DC/DC smps and since I'm always looking for new ideas I decided to give it a try with LTspice. I have a 19VDC@3.2A Lap top adapter that would be a good start. I have a circuit that need 150VDC so it looks to be a match made in heaven. I read the text, looked through the schematics and did the sim. Either I'm missing something important or this is one faulty design? What do you think of it? http://greygum.net/sbench/sbench101/...plies/lvps.txt http://greygum.net/sbench/sbench101/...plies/lvps.gif In my sim: 1. The "power on" delay is necessary to start the oscillator but it's no delay? 2. No regulation until it hits the over voltage protection? 3. It's got almost twice the current draw compared to what's listed?

10th March 2011, 07:48 AM	#2
luka diyAudio Member Join Date: Sep 2005 Location: in Slovenia :)	why don't you just use some IC? __________________ home page @ http://www.classdaudio.co.cc @ 24/7 all year long I FEEL SLOVENIA

10th March 2011, 08:04 AM	#4
luka diyAudio Member Join Date: Sep 2005 Location: in Slovenia :)	IC is more safe option, since it was design for that kinda operation... not saying that this above wouldn't work, but on the other hand... I think I would use http://www.classiccmp.org/rtellason/chipdata/uc3844.pdf __________________ home page @ http://www.classdaudio.co.cc @ 24/7 all year long I FEEL SLOVENIA

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10th March 2011, 08:00 AM	#3
markusA diyAudio Member Join Date: Dec 2009 Blog Entries: 8	I just stumled across this circuit and thought it looked simple enough. A IC solution would be as good as any I guess? Since I'm a n0ob I probably need some help to point me in the right direction.

13th March 2011, 08:29 PM	#5
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	It is a boost converter, I don't recommend that for so high convertion ratio. Try a transformr coupled converter, like pushpull or fullbridge.

28th March 2011, 09:02 PM	#6
mag diyAudio Member Join Date: Jan 2008 Location: Chiasso	Using a boost converter with so high vout/vin conversion ratio is not recommended. On top of that irf640 is a 200v mosfet and using it at vout=170v there is no safety margin. Maybe this circuit will work but it is much easier to use a controller like the uc3842 or similar. Instead of doing a boost converter make a simple flyback with properly desinged transformer turn ratio. If you don't need in/out isolation you can connect the transformer secondary gnd to the primary gnd simplifying also the feedback loop. A flyback converter is also inherently short circuit protected, a boost is not and can not be easily protected. Ciao -marco

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