hello,
I am working on a circuit that needs three different voltages at different parts. I have a 150 volt dc power supply and i need -20V,+20V and +110 V pins to run my circuit. Currently I am using 3 resistors in series with my power supply to produce these voltages. Currently my circuit only needs to draw 15 mA to run. But I need it to be able to draw 300 mA and I don't think that using a resistive voltage devider is the right way of doing it. Trouble is that i don't know how to go about this problem.
Any suggestions or help is much appreciated. Thanks

 

First of all, you can't obtain -20V from a positive source without some other circuitry other than resistors. The ground you drew in between RS4 and RS2 is incorrect. Your current divider will produce 30V across both the 3K resistors (RS4, RS1) and 90V across the 9K resistor (RS3). I know of no Voltage regulators that will accept 150V as input.

 

First of all, you can't obtain -20V from a positive source without some other circuitry other than resistors.

This is not true if the supply is "floating", or isolated from ground.

The ground you drew in between RS4 and RS2 is incorrect.

If the supply is not grounded, then the ground reference could be applied anywhere one would like to place it.

 

This is not true if the supply is "floating", or isolated from ground.


If the supply is not grounded, then the ground reference could be applied anywhere one would like to place it.

I was thinking about that after I posted, but was fast asleep before I could alter it. Thanks.

 

150V @ 300mA = 45 Watts. Can your supply deliver this?

 

Yes the supply is rated for 420 mA at 150 mA
I have found a positive regulator that accepts 150 V as input but I'm not sure how to use it to get the voltages I need
Any suggestions?
Thanks

 

Yes the supply is rated for 420 mA at 150 mA

You mean at 150V right?

I have found a positive regulator that accepts 150 V as input but I'm not sure how to use it to get the voltages I need
Any suggestions?
Thanks

Care to post it´s name?

 

You mean at 150V right?
Care to post it´s name?

Sure it's from a company called acopian :
http://www.acopian.com/store/productdetail.aspx?q=i557

 

Yes the supply is rated for 420 mA at 150 mA
I have found a positive regulator that accepts 150 V as input but I'm not sure how to use it to get the voltages I need
Any suggestions?
Thanks

I'm lost. All I see is a Power supply that can output 150V, and for more than $200. You said in your first post that you have the power supply.

 

I think Kubeek meant to ask what's the name and part number of the 150v regulator that was found, not the 150v power supply that you already have.

 

sorry i misunderstood. this is the regulator : http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20778-2-ND

 

sorry i misunderstood. this is the regulator : http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20778-2-ND

The datasheet really doesn't specify use @ 150V except in fig. 18. and I can't be sure if that will work or not.

Here is the Application Schematic for others to look at:

Datasheet

 

Well, after a quick look through the data sheet it appears applicable.

 

There's just that elephant in the room called "power dissipation".

Our OP says he needs 300mA current - although I don't know if that's total or each voltage needs 300mA available.

Just for grins, let's start with the 110v output. And let's say we're going to call the negative terminal of the supply ground.

So, the power dissipation in the regulator would be roughly (150v-110v)*300mA = 12 Watts, which might be do-able with a good-sized heat sink.

How about the +20v output?
(150v-20v)*300mA = 39 Watts.
That is a heck of a lot of heat to get rid of.
For the TO220 package, junction to package is 3°C/Watt, so in order to keep the regulator from overheating at 125°C, you would have to keep the package at 8°C/46.4°F or lower (8°C+3°C*39W=125°C, alternatively 125°C-3°C*39W=8°C).
Also, 130V differential from in to out exceeds the 125v maximum.
It's also at the maximum output current for the junction temp being high; which it'll be.

 

You just verified my reluctance to commit to this circuit. Too much heat and at the extremes of the IC's limits. Maybe if he cools it with liguid nitro, he might make it last for a few months!

 

Good point =/
Alright given this information I've decided to go a different route. I will be using a second power supply to provide the -30V and +30V and I will use the 150V power supply to provide the high voltage I need.

On a related note does anyone know of any opamps that operate with up to 150 voltage difference as supply?
using another opamp seems to be the easier way to go. FYI the opamp will be used to drive a sinusoidal signal from 0 to 100 Volts at maximum frequency of 200 Hz and the load will draw roughly 25 mA on average so power dissipation should be managable I think.

Thanks for the responses everyone.

 

You just verified my reluctance to commit to this circuit.

There's a job waiting for you in politics. How else do you expect to accumulate a good resume of miss-speaks?

Glad to hear that nimaajbphs has opted for the minimal waste approach though.

 

MSKennedy makes high-voltage opamps.
Just for example, here's one datasheet:
http://www.mskennedy.com/client_images/catalog19680/pages/files/130rc.pdf
Main page: http://www.mskennedy.com

Actually, that seems to be their best-suited opamp by supply voltage alone for what you're doing.

It's not going to be cheap.

You'll probably find it much less expensive to use a switching PWM controller to drive a transformer, supplying the sine wave to the reference and using some sort of optocoupler feedback from the secondary side. It'll take a good bit of work to come up with a decent design, though.

 

You Just verified my reluctance to commit to this circuit.

There's a job waiting for you in politics. How else do you expect to accumulate a good resume of miss-speaks?

Glad to hear that nimaajbphs has opted for the minimal waste approach though.

Perhaps I should offer my resume to Sarah Palin!!!

The word I really wanted was not reluctance or even reluctant, but rather reservation. ...more political spin, I know! Ye Haa, I might have a real chance!