How to make adjustable dual +12V & -12V TO +30 & -30V

sghioto

Joined Dec 31, 2017
1,436
Use a positive and negative voltage regulator. An example is the circuit below from Texas Instruments. If you need plus and minus 30 volt regulated you will need plus and minus 35 volt input.
SG
EEE LM317 % LM337 dual regulator.png
 
Last edited:

dl324

Joined Mar 30, 2015
11,465
The power supply I got online is just fixed.
It's wrong too. You can't get more than 16V from that transformer without using a boost circuit.
  1. What secondary voltage are you planning to use?
  2. What current do you want?
  3. Do you care about power dissipation in the regulators?
 

bertus

Joined Apr 5, 2008
20,739
Hello,

You can make a "tracking voltage regulator" :

Tracking voltage regulator.png

The input voltage must be lower as +/- 15 Volts.
Using an OPA452 you can go upto +/- 35 Volts input.
Keep in mind that the negative line has no current limit protection.

Bertus
 

Thread Starter

dadadiouffy

Joined May 4, 2020
78
It's wrong too. You can't get more than 16V from that transformer without using a boost circuit.
  1. What secondary voltage are you planning to use?
  2. What current do you want?
  3. Do you care about power dissipation in the regulators?
I want to use 5-15vdc for signal generator, current 200mA. Power dissipation?... I am using LM324
 

Ian0

Joined Aug 7, 2020
445
Change of subject to sine wave oscillators?
is this meant to be variable frequency? If so, the time constants of the second and third op-amps will have to be adjusted at the same time.
And why the second op-amp to make the triangle wave. There’s already a triangle-ish waveform in pin 2 of the first op-amp.
if you want a sine wave from an op-amp what’s wrong with a Wien bridge? You need far less gain bandwidth product or slewrate than you do to make the intermediate squarewave. If you want to start from a squarewave generate it with a 555. Opamps will always have slewrate limitations when trying to output a square wave.
maximum frequency? There are some very fast opamps out there - how much do you want to pay?.
 

Thread Starter

dadadiouffy

Joined May 4, 2020
78
Change of subject to sine wave oscillators?
is this meant to be variable frequency? If so, the time constants of the second and third op-amps will have to be adjusted at the same time.
And why the second op-amp to make the triangle wave. There’s already a triangle-ish waveform in pin 2 of the first op-amp.
if you want a sine wave from an op-amp what’s wrong with a Wien bridge? You need far less gain bandwidth product or slewrate than you do to make the intermediate squarewave. If you want to start from a squarewave generate it with a 555. Opamps will always have slewrate limitations when trying to output a square wave.
maximum frequency? There are some very fast opamps out there - how much do you want to pay?.
Give me a link of online store or if you have function signal generator schematic, post it to me, better than trying out things that will never work
 

Thread Starter

dadadiouffy

Joined May 4, 2020
78
How good does it need to be? Minimum/maximum frequency? Distortion? Output level? Output drive current?
variable frequency is the best, at least with little distortion, medium power output. variable Voltage, is the current not depending on the voltage? About current I don't know but hope the a bit high the better
 

MrChips

Joined Oct 2, 2009
21,818
If you are trying to build a function generator with adjustable output amplitude you do not adjust the power supply voltage. You control the amplitude of the output signal.
 

Ian0

Joined Aug 7, 2020
445
It’s easy to get from sine to square, but do you really need triangle?
Tricky to get from sine to triangle. If you really need triangle then probably easier to make a separate triangle oscillator, which would also give square, but not sine.
I agree with Mr Chips. put a pot on the output and another op-amp as a buffer to get variable level. Keep the supply at +/- 12V with a pair of 7812/7912 regulators. (use +/-15V if you really want to)
 

bertus

Joined Apr 5, 2008
20,739

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Ian0

Joined Aug 7, 2020
445
It‘s a bit rubbish isn’t it? I know from designing audio amps that if you can see the distortion on the scope it’s too high, and the triangle wave has a flat top, and the square wave isn’t square, it’s trapeziodical, and asymmetric.
I thought Heathkit would be manage rather better than 2.5% Distortion.
 
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