I am trying to design a circut to power op-amps. I need a circuit to take 5 V input into a +12 V output and -12 V output. The output could be from +/- 8 V to 14 V.
I came across a charge pump circuit and a switching circuit. The charge pump was stable ( almost +/- voltage out ) but only give a low current out. I need at least 5 mA to 10 mA current out. The switching was unstable and unbalanced.
If I have to use an Arduino for pulse control, so be it.
I want this : Current : 5 mA to 10 mA
Voltage : +/- 8 V to +/- 14 V
Stable and Balanced
Here what I have so far.
Any help will be nice. I wonder an IC chip exist to do this job...
[digital bias showing]
Holy moly, you don't really intend to build that lot do you? Get a DC/DC converter for $10-15 and be done with it.
[/digital bias showing]
I will Google this up. A --- TRACO TMA 0512D <--- ???
I search the web about DC to DC converter inverter, and I stumble on the MAXIM site. I check it out, and I did find something. It is a charge pump IC chip. The MAX680 - http://datasheets.maxim-ic.com/en/ds/MAX680-MAX681.pdf
It fit my needs. I check the datasheet and a schematic of the chip, and I was close. I can make it using 4066 and a NOT gate and a 555 circuit set at 8 kHz. But it will be easier to get the chip. I hope I can order it on-line or better, get it locally. I will check my local suppliers web site. The charge pump is the same design for a MAX232 which is build in.
With this chip - MAX680, I can use op-amps in my design. A charge pump is OK, but they provided not much currents. A typical op-amp only need about 3 mA per op-amp according to the simulation using Circuit Wizard.
Thanks Graynomad for your input. I know, it is SOOO Analog ...
Thanks for the link. But that chip only has +5 in --> -12 V ONLY. I need Both. A + section and a - section. I may use this chip to control the negative section and another chip for the positve section, if I need more currents. That chip can give up to 250 mA.
I will download the datasheet. It maybe usefull after all.
the digikey breifing is all kinds of screwed up ... looking at the datasheet that will take 3 to 8 volts for the -12 volt part and is ajustable via a couple resistors. but give it a good read over, I just glanced at it
as far as ajusting the + side there are a ton of options, but yea I think its going to be a 2 part design.
It is a dual output switching design. The pdf is 4 M in size. I am downloading it as I write this.
A switching design can provide higher currents, but it is the making of the inductor, that is going to be not so easy to make. Well, easy to wind a wire around a ferrite, but to get at the right value is not that easy. And to get the right MOSFET and Scholky diode, will be tough to get.
Anyway, I just read the datasheet of the MAX743. @ 12 V mode, 125 mA. hmm ... not bad. You can power a few op-amps with it. Just need to make the inductor or buy it <-- that will be tough. and the "special" diode.
The 555 pump design will work <-- I did that, but it is the current is the problem. Not really stable design. I will just copy the MAX680 internal circuit design, using 4066 <-- 4 switch and 4069 <-- NOT gate will do the same.
I did try to find those chips at my local supplier, but with no luck. It got others type ( Motorola and Microchip ) but they are going to be tricky to use them. It lool like those chips are not available localy. I have to go online ordering.
Is there are particular reason you want to power the op amps from +/-12v? For many applications, there are alternatives:
If you are using the op amps to process AC signals then you don't need a negative supply at all, you can use single-rail op amps
If you are processing DC but the input never goes more than a few hundred mV below ground, you can use single-rail op-amps with a common mode range that includes ground
If you need to process negative inputs as well, then how about powering the op amps from +/-5v or something close to it? If you use low power op amps, then you may only need 1mA or even less at -5v. You can generate this using an Arduino PWM output pin (instead of a 555), resistor, 2 diodes and 2 capacitors. Even if you need more current than that, generating just -5v rather than +12v and -12v makes for a cheaper DC-DC converter or simpler charge pump circuit.
I've heard that a max232 chip does an ok job at this in the current range you are looking at.
I agree with you. But the voltage ( +/- ) are built-in. Can not be access. The MAX680 do exactly that, and it does have +/- output line. but it does not have a RS232 driver / receiver, the MAX232 do. The MAX232 make the 1488 and 1489 obsolete. Thoses chip are driver / receiver only. Just need the +/- power line.
Is there are particular reason you want to power the op amps from +/-12v?
The voltages are standart voltage in my opinion. I prefer +/- 9 V.
If you are using the op amps to process AC signals then you don't need a negative supply at all, you can use single-rail op amps
I did try that. It did not work at all. I use a LM339 for a single voltage rail, and NOP... not working... A 741, dual voltage, It work...
If you are processing DC but the input never goes more than a few hundred mV below ground, you can use single-rail op-amps with a common mode range that includes ground
Did not try that yet... But I am not so sure it is going to work.
If you need to process negative inputs as well, then how about powering the op amps from +/-5v or something close to it? If you use low power op amps, then you may only need 1mA or even less at -5v. You can generate this using an Arduino PWM output pin (instead of a 555), resistor, 2 diodes and 2 capacitors. Even if you need more current than that, generating just -5v rather than +12v and -12v makes for a cheaper DC-DC converter or simpler charge pump circuit.
That is a good idea. If I don't need a higher voltage ( plus side ).
But the voltage ( +/- ) are built-in [to the max232] and can not be accessed
That's just it. The voltages CAN be accessed. Either from the rs232 output side (with the inputs connected directly to appropriate levels), or from the leads connected to the (external) charge pump capacitors...
That's just it. The voltages CAN be accessed. Either from the rs232 output side (with the inputs connected directly to appropriate levels)
Hmm... I get you... from the outputs... I just put a proper 0 or 1 at the input of the drivers, and I am in the game... The output will be +10 for a 0 or -10 for a 1. That might work. I got to try it. I do have a MAX232 in my parts bins.
from the leads connected to the (external) charge pump capacitors...
