90V DC-DC converter IC?

[[email protected]]

I am hoping to find a DC-DC converter IC/and or simple circuit that
can take 90VDC and provide 5VDC @ ~ 20 mA. I note that the LT1339CSW
from Linear Tech is a relatively inexpensive surface mount part,
however, input voltages are limited to 60VDC. Can anyone suggest an
alternative, workaround, or confirm that I am barking up the wrong
tree? Thanks.

 

[Andrew Holme]

I am hoping to find a DC-DC converter IC/and or simple circuit that
can take 90VDC and provide 5VDC @ ~ 20 mA. I note that the LT1339CSW
from Linear Tech is a relatively inexpensive surface mount part,
however, input voltages are limited to 60VDC. Can anyone suggest an
alternative, workaround, or confirm that I am barking up the wrong
tree? Thanks.

That IC requires 12V at (typ) 14mA for the 12V_IN supply.

 

[linnix]

That's the easy part.

You (OP) may need to look at a dual conversion - 90V to some
intermediate value with a discrete solution (doesn't have to have
particularly good ripple performance) and then an IC based solution.

The easy part above is to use a high voltage transistor with a zener at
the base to provide some Vreg at the emitter. Make sure that Vreg is
lower than the output of the supply so that once the supply starts up,
the supply output provides chip power, not the transistor.

A linear drop would burn up 1W (78V * 14mA). I suggest some simple
switching circuit to lower the duty cycle.

 

[PeteS]

That IC requires 12V at (typ) 14mA for the 12V_IN supply.

That's the easy part.

You (OP) may need to look at a dual conversion - 90V to some
intermediate value with a discrete solution (doesn't have to have
particularly good ripple performance) and then an IC based solution.

The easy part above is to use a high voltage transistor with a zener at
the base to provide some Vreg at the emitter. Make sure that Vreg is
lower than the output of the supply so that once the supply starts up,
the supply output provides chip power, not the transistor.

Cheers

PeteS

 

[PeteS]

A linear drop would burn up 1W (78V * 14mA). I suggest some simple
switching circuit to lower the duty cycle.

I did not suggest a linear drop for the intermediate system. A linear
drop *during startup* for the final system would burn minimal power.
I assume you understand switched powering systems.

Cheers

PeteS

 

[neon]

for 50 ma you can use three lm117 in series they are good for 35v each so use a divider to to get 30 volts chap too

 

[Mike Harrison]

I am hoping to find a DC-DC converter IC/and or simple circuit that
can take 90VDC and provide 5VDC @ ~ 20 mA. I note that the LT1339CSW
from Linear Tech is a relatively inexpensive surface mount part,
however, input voltages are limited to 60VDC. Can anyone suggest an
alternative, workaround, or confirm that I am barking up the wrong
tree? Thanks.

Look at Power Integrations Linkswitch-TN series. Aimed at mains, but should be adaptable.
Cheap and stocked by Digikey.

http://www.powerint.com/linktnproduct.htm

If you're feeling adventurous you might want to try adapting this :
http://www.romanblack.com/smps/smps.htm

 

[Paul Mathews]

Look at Power Integrations Linkswitch-TN series. Aimed at mains, but should be adaptable.
Cheap and stocked by Digikey.

http://www.powerint.com/linktnproduct.htm

If you're feeling adventurous you might want to try adapting this :http://www.romanblack.com/smps/smps.htm

You'll find Power Integrations DPA series very easy to use in either
flyback or forward modes:
http://www.powerint.com/dpaproduct.htm
Paul Mathews

 

[Fred Bloggs]

If you're feeling adventurous you might want to try adapting this :
http://www.romanblack.com/smps/smps.htm

That kluge has been exposed time and again for being a bad design...

 

[Traver]

That kluge has been exposed time and again for being a bad design...

TI/Unitrode has a UCC3889 for low power offline apps. I'm not sure
it's guaranteed to work down to 90V. 90 to 5v is a huge step down
ratio. I recommend using a transformer. Look at the LM5020 (National).
Runs up to 100V and has some good flyback applications. Unfortunately
the conversion ratio makes it difficult to do something simple.

 

[Fred Bloggs]

I am hoping to find a DC-DC converter IC/and or simple circuit that
can take 90VDC and provide 5VDC @ ~ 20 mA. I note that the LT1339CSW
from Linear Tech is a relatively inexpensive surface mount part,
however, input voltages are limited to 60VDC. Can anyone suggest an
alternative, workaround, or confirm that I am barking up the wrong
tree? Thanks.

There is no ready made solution other than a DC-DC converter module end
product.

Other than that you have a 1:18 step-down ratio and fairly high voltage
which will require more engineering than you're used to :
www.national.com/appinfo/power/files/national_power_designer117.pdf

 

[Mike Harrison]

That kluge has been exposed time and again for being a bad design...

Anyone who brands something 'bad' or 'good' is an idiot.

There is only more or less appropriate for any given situation. All applications are different, and
have different requirements.

one man's 'bad' is another's 'the only thing that makes a design financially possible'

 

[Fred Bloggs]

Anyone who brands something 'bad' or 'good' is an idiot.

The circuit is trash. I posted an analysis of it a few months back, the
feedback is wrong among other things. It's a clueless hack.

 

[Mike Harrison]

The circuit is trash. I posted an analysis of it a few months back, the
feedback is wrong among other things. It's a clueless hack.

Analysis notwithstanding, it works.
May not be as 'good' as an LM2574, but you don't always need all the bells & whistles.

 

[linnix]

The circuit is trash. I posted an analysis of it a few months back, the
feedback is wrong among other things. It's a clueless hack.

How about adding the modified Larkin oscillator? See

http://linnix.com/polk

Note the L2 C2 tank at the emitter. L1 L2 are 80% mutual inductors.
Don't forget R2 D2 too.

 

[John Larkin]

I am hoping to find a DC-DC converter IC/and or simple circuit that
can take 90VDC and provide 5VDC @ ~ 20 mA. I note that the LT1339CSW
from Linear Tech is a relatively inexpensive surface mount part,
however, input voltages are limited to 60VDC. Can anyone suggest an
alternative, workaround, or confirm that I am barking up the wrong
tree? Thanks.

Why not throw away the first 30 volts in a zener, and then use the LTC
regulator? The power dissipation would be small.

You could do a switcher with 10 or 12 parts, but it's probably not
worth the effort.

John

 

[Michael A. Terrell]

Analysis notwithstanding, it works.
May not be as 'good' as an LM2574, but you don't always need all the bells & whistles.

But fred likes bells and weasels.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[John Devereux]

Why not throw away the first 30 volts in a zener, and then use the LTC
regulator? The power dissipation would be small.

There is also the LM5574 - goes up to 75V so you only need to throw
away 15 . I've used it recently.

 

[Terry Given]

The circuit is trash. I posted an analysis of it a few months back, the
feedback is wrong among other things. It's a clueless hack.

yep! with a bit of effort it can be improved from "appalling shit" to
merely "bad".

I built one just for fun. Try starting it into a shorted load. By the
time you add enough bits (in USian: components) to fix the glaring
defects, you have more than enough bits to build a proper SMPS.

that being said, its a pretty good effort from someone who knows not
what they do

Cheers
Terry

 

[Mike Harrison]

yep! with a bit of effort it can be improved from "appalling shit" to
merely "bad".

I built one just for fun. Try starting it into a shorted load. By the
time you add enough bits (in USian: components) to fix the glaring
defects, you have more than enough bits to build a proper SMPS.

So it isn't suitable for starting with shorted loads.

As I said, there is no such thing as 'bad', just more or less appropriate for any given situation.
This circuit is not appropriate for situations where the load may be shorted at startup.