Op Amp VCC+ to 30V using 5V source?

You didn't specify the op-amp of your choice?

since that circuit can only produce low current. you should place a load resistor on the output and see how much of a drop you get.

Use a 1k ohm for example then take a reading.

This can help to determine if you have an excessive load in your op-amp circuit or you have an issue with the inverter circuit.

--
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I am using an LM324 - the datasheet seems to say that the VCC current is less than 2mA, and the circuit that I built to power it provides around 3mA, so I thought it would be ok... but my guess is that the current still isnt high enough.

So, that leaves me a the same place... how can I get 30V from 5V with a high enough current to provide to the amp?

** Floating inputs can be anywhere from ground to Vcc. Use the op-amp in a useful circuit. ** But you *ALREADY* stated you had a 30V supply, so you have no problem.

I do have a 30V supply, but apparently either 1) the output impedance is too low, or 2) the current drive of my 30V source is not high enough to act as VCC for the AMP.

When I said that the "input" goes to 1V, I actually meant that the VCC when connected to the 30V source actually has the OUTPUT OF THE 30V SOURCE GO TO 1V, so that would make the VCC just 1V, which is completely useless to me...

How much current does your OPAMP circuit need? If it's more than 1 or 2 ma, then your 30V power supply is not able to supply the current, thus the output goes down. You need a better power supply.

--
Dave M
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the

=========================================== Hello - I am new to this group so I hope this gets through

- I am unable to give a complete analysis because I do not know how the LM324 is configured or if there are any mistakes.

- The 30 volt power supply circuit seems like it should drive an op amp, but probably only as an instrument type of amplifier. There will not be enough current to do any real work, like drive speakers etc...

- I would building the op amp part of the circuit with a known good 30 volt supply, get it working the way that you want and then measure all currents and voltages.

- This should help determine what sort of power supply is needed for the final design

- at the very least you can string together some 9 volt batteries for testing purposes and this has the benefit of being a clean DC source.

- be advised that the ripple voltage goes up as current goes up when using the` power supply as described. signed Edward H. Bell ===================================================

Looks like your output impedance at DC is at least 1K. The R1 and C6 appear to be a noise filter that filters some of the switching noise. Every 10mA you pull from the supply will drop the output by 10V. I would bypass that resistor with an 100uH inductor and see if it gets better.

You also have to account for the resistive drop of the 74HC chip output when driving the inductor. As the current goes up the peek output voltage on them will go down as well. You might want to look at the 74AC14 version as they have a higher current rating (24mA vs 5mA). You had better have good supply bypassing as these chips are much more picky about supply bypasing then the HC series (larger supply current spikes)

These shoud improve the situation consierably.

Thanks for the good suggestions.

I am actually using a PC power supply, so I have a 12V rail that I can use as well... is there a better way to go from 12 - 30V, or should I just stick with the same method.

The whole application here is that I have an input voltage between 0 and 3 V, and I want to LINEARLY increase this voltage to between 0 and

30V... so thats why I figured an op-amp in a non-inverting mode with a 10X gain would be the best way to do this.

I will try to swap out that inductor and see what happens, but if as you say for every 10mA it draws that it reduces the voltage by 10V, then I might have a bit of a problem utilizing this circuit...

Do you want to build the op amp circuit or the 30V resonant converter? That 2mA current draw of the '324 is "per amplifier" and since the package contains four (4) of them , that means the loading is more like

8mA, which is way off the charts for that power supply. 24V modular plug-in line supplies are common, use one of them, and re-adjust your time wasteful activities and goals.

The circuit uses L1 and C3 as a series-resonant voltage booster. That's inherently unregulated, and assumes a multiplication ratio of about 7. It's very soft with the L and C values shown.

The LC booster mostly dominates the regulation problem.

You can buy a +5 to +-15 isolated dc-dc converter from Mouser or Digikey for around $10, and its output will be floating 30 volts. Or if you want to design it yourself, build a proper boost converter with feedback.

You could modify the Japanese circuit to use a small step-up transformer, at a much lower frequency, instead of the wimpy LC.

John

The "Japanese circuit" was devised by a "systems engineer." Need we say more.

LOL!!!! good one!

--
"I\'d rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

  SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
  THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

I stand corrected on that, they do say 3mA maximum total supply current at 30V or so, a departure from modern specification practices. You need to add in the current through your feedback divider, maybe another 1mA, and the load of course...

Actually, someone else pointed out on page 5 of the datasheet that the max "Isource" current is 70mA with Vin=15V... so I guess theoretically the VCC could draw about 280mA...?

I want to keep this circuit simple and hopefully as cheap as possible... I think that going to a circuit with a transformer and DC- DC converter might end up costing a bit too much (you can buy them for like $30 or so...)

SO, right now im between a rock and a hard place :(

It looks like the current circuit wont be able to drive enough current... I have heard about a "555 oscillator" but I dont know if that would be useful to me...

Anything else?

Read this, understand it, and adapt the 555 circuit to your 30V.

--
Yup, it\'s even worse than being between a rock and a hard place
since the LM324\'s opamps aren\'t rail to rail.

Worst case Vout is Vcc - 3V, and for 30V out that means Vcc needs to
be 33V.

Absolute maximum Vcc - Vee is 32V, so that just about puts the last
nail in the coffin.

What you need is an opamp which can take a higher supply voltage and
a 555 tripling your available 12V.

The question is... if I find an AMP that can have a VCC of like 40V, is the 555 100% THE SOLUTION THAT MAKES THE MOST SENSE TO USE...?

I have spent too much time and $$ on this already to try another solution that wont work...

Then buy a dc-dc converter.

Incidentally, those old klunky-process parts like LM324 will typically work to 60 volts or so.

John

ps- you can buy a 5 volt to +-15 converter cheap; that gives you floating 30 volts. Now stack that on top the +5, and you have +35.

John