# Increasing DC Voltage

Discussion in 'Electronic Design' started by Dan Mills, Feb 11, 2004.

1. ### Dan MillsGuest

Well, you will need a oscilator of some form to pull this off, no way around
it. But you might also want to look at the energy balance given above,

10.6 * 150 mA = 1.59W, 16v @ 100mA = 1.6W so you would in any case need an
efficiency slightly greater the 100%. Let the Nobel comittee know if you
pull it off.

Regards, Dan.

2. ### EEngGuest

Does anyone know of a way to increase DC voltage WITHOUT using any
kind of oscillator? Can't use any DC-DC converters that rely on
oscillators of any kind.... transformers, buck boosts, etc....
because it goes on a high density PCB wtih lotts of Audio and RF.

I'm trying to convert a DC input that unreliably varies from 10.6V -
16V @ 150mA up to any voltage greater than or equal to 16V and can't
drop under 100mA . FYI, I'm using a 15Vzener to limit anything
greater than that.

Currently we're using a simple op amp with gain to provide the higher
voltage but it causes the necessity for several dynamic circuits to
develop bias voltages throughout the circuit that change with the
input. What I'm trying to do is eliminate all the extra circuitry
that accounts for varying biases. If I can accomplish this, it will
reduce component count by 20% and PCB real estate by 30%.

This ones a poser....several engineers at a Fortune 50 company and I,
have been scratching our heads over it. If I haven't been absolutely
clear on what I need, please let me know which parts need explaining.
Thanks in advance, this NG has always rocked.

3. ### Roger HamlettGuest

Without using an oscillator (or having AC available to you from some other
part of the circuit), you are not going to succeed.
If there is any point where there is an AC signla available, there are a
number of solutions. Otherwise you will _have_ to use an oscillator.
Proper design, and careful board layour will allow such devices to be used
in 'noise critical' enviroments. As an example, I have a board here used as
part of a sensor head, that presents of 10^12 ohm input impedance to the
sensor, and is reading signals in the uV area, yet has such an inverter, and
gives no problems. It comes down to careful design.

Best Wishes

4. ### Ian StirlingGuest

LED + solar cells.
Should have an efficiancy of over 5%, picking the right LED.

5. ### EEngGuest

That's the conclusion we've come to as well. I just wanted to see if
anyone else had an idea we hadn't thought of. Looks like the op amp
will have to remain, and the variably considered bias voltages dammit.

Thanks for trying. Great minds not only think alike, they also pain
alike.
LED + solar cells is not an option.

6. ### Tim WescottGuest

I've seen this done, too, with great success. We were measuring to 16-bit
accuracies with no problem with step-down regulators on the board. Linear
Technology and National both have app notes on ultra-quiet switched
regulator design. If you're really going to lose 30% of your component then
the layout and shielding attention is probably worth it.

7. ### Jan PanteltjeGuest

Take 2 caps, charge them from the voltage you have.
Now disconnect and put them in series.
But you will have to do this repeatedly, so you assign someone to do
it for you (cheap labor country).
To toggle the switch....
But an OSCILLATOR could switch some transistors....
In stead of oscillator you can use usenet bitstream.
I DID IT WITHOUT OSCILLATOR

8. ### JamieGuest

going from what your describing here i would say that your merly using
the DC input as a refence to activate a function ?
why not use a voltage comparator ?
you can set the - input of an op amp around 10 volts and the supply
voltage of the OP to be 16 volts.
using the + input of the OP you can then have a steady 15 volts
when ever the input is >= the - input..

I thought of the LED-and-photocell thing too. There's something
that might have a little more efficiency, that "technically" meets
your specs (it's "not an oscillator"), but is even less practical: A
dynamo (motor-generator). So, now that you've totally dismissed me...

Presuming you're concerned about audio and RF interference
generated by the voltage converter, some sort of sinusoidal (so almost
all of its current pull variation and radiation is at the fundamental
frequency) RF oscillator (in the 20kHz to 200kHz range, low enough
that it radiates very little) is your best bet. There's a model of
studio condenser microphone (I forget what model, it was discussed on
rec.audio.pro) that uses an RF oscillator and transformer to generate
its 50-odd volts bias voltage (if you haven't guessed, that's a
demanding, low-noise application). A well-designed (probably Class A,
or for better efficiency, push-pull Class AB) converter circuit should
not generate significant signal interference to nearby circuitry.
Great, send us our consulting fee.

10. ### Clifford HeathGuest

Add a battery in series with the supply?

11. ### N. ThorntonGuest

Well, it depends on your app but another perhaps could be to use an
already existing signal amplified to drive the convertor power stage.
This sneaky way of getting round interference problems is just to save
design time, if you have a suitable f already present.
One of us isnt making sense of this, but I dont know who. You cant get
a higher Vout from an opamp than its Vsupply: perhaps you could
explain clearly?

Also why must you convert an unstable dc voltage? With the V figures
you give, and what youre asking, I'm guessing its a lead acid powered
item. Why arent you designing the circuit to run on whats given? What
does the circuit do and why must it have >16v?
Could you explain this varying biasing? It is a mystery to me, hence
it is impossible to suggest anything.

Regards, NT

12. ### Frithiof Andreas JensenGuest

So!? But Whatever as long as they pay....
So this is *not* a power supply - because the supply of that op amp must be
higher - why is it a problem then? You can apply any transformation you
like.

PS: If it is a power supply, the circuit should be redesigned to eat
whatever it is fed!

13. ### R.LeggGuest

It's got RF but you can't allow (another) oscillator on the board?

Use the RF section to generate the milliwatts required for a higher
integrity rail. Your RF guys should be up to it. Believe me, if it's
RF, you've got AC on board.

Partition critical sections only to run on the higher integrity rail
(minimum power drain).

RL