Hi All,

Can I use MAX 232 with 5V power supply to get V+ 25V and V- 25V with 0.1uF capacitors. Will it generate any noise if so what measures i need to take.

I want to use it for the Ultrasonic transmitting sensor from T1out pin.

Thanks in advance

 

And where are you getting the source for the ±25V?

You might be able to use a boost circuit, if the resultant 80% loss in current is acceptable.

 

https://en.wikipedia.org/wiki/Charge_pump
The charge pump filters (VS-, VS+) can be used as low current power supply outputs but the voltage outputs are normally close to +/-9 to 10 volts.

 

Why torture the poor MAX232 for getting 5x its working voltage for your purposes. For your application, there are better circuits to do it. Most ended up with a small step-up transformer.

In the early 20s, I used the MAX232 to provide -5V for my display LCD in order to work properly. Nowadays they dont need the negative voltage which simplified things a lot.

Allen

 

Hi All,

Can I use MAX 232 with 5V power supply to get V+ 25V and V- 25V with 0.1uF capacitors. Will it generate any noise if so what measures i need to take.

I want to use it for the Ultrasonic transmitting sensor from T1out pin.

Thanks in advance

It would be best if you were to post a simple diagram of what you're trying to do. And yes, as others have already mentioned, there are more advanced chips out there which are variants of the MAX232 that are vastly improved.

 

It would be best if you were to post a simple diagram of what you're trying to do. And yes, as others have already mentioned, there are more advanced chips out there which are variants of the MAX232 that are vastly improved.

Thanks for the immediate response. I am trying to understand this schematic. Could you let me know why in this schematic how he used to generate 25v from 5v supply using 0.1 uF caps. Also for the Tout pins why high pass filter and 330 ohms are used and how can i calculate it.

Opearating frequency of the ultrasonic transmitter is 40 Khz.

 

Hello,

You will never get ± 25 Volts from a MAX232.
The maximum you will get is ± 10 Volts:



Bertus

 

Hello,

You will never get ± 25 Volts from a MAX232.
The maximum you will get is ± 10 Volts:

View attachment 188143

Bertus

Thanks for the response. Maximum charge pump is 10V.

but in the wiki - "Charge pumps can double voltages, triple voltages, halve voltages, invert voltages, fractionally multiply or scale voltages (such as ×3/2, ×4/3, ×2/3, etc.) and generate arbitrary voltages by quickly alternating between modes, depending on the controller and circuit topology" .

I do not know why he mentioned 25V in the schematic and how he got it. Are there any threshold levels to limit the voltage (charge stored in capactior). Also why high pass filter followed by resistor is used in the schematic ?

 

hi,
Please post the schematic or a link to it.
E

 

Hello,

The higher factor chargepumps are the Dickson charge pump.

https://en.wikipedia.org/wiki/Voltage_multiplier#Dickson_charge_pump

Bertus

 

From the schematic in post #6 I assume that the T1IN and T2IN inputs are driven in antiphase so the outputs will be in antiphase. I assume the transducer is connected between the two outputs so in one state one side will be about +10 volts and the other side will be - 10 volts. In the other state the polarities will be reversed so the peak to peak voltage seen by the transducer will be 40 volts.In practice it will be a little less than 40 volts.

Les.

 

hi,
Please post the schematic or a link to it.
E

Hi Eric, Schematic is posted in post #6

 

hi.

The only reference to 25V I can see on that schematic, is the maximum working voltage of the capacitors.??
E
BTW: T1 will only give a voltage out swing of +/-9V

 

hi.

The only reference to 25V I can see on that schematic, is the maximum working voltage of the capacitors.??
E
BTW: T1 will only give a voltage out swing of +/-9V

Hi,

May be he just specified voltage rating for capacitors. i think here max232 is used to make TTL 5V to +/- 5V swing. But what is the purpose of High pass filter followed by 330 ohm resistor. Is it to filterout low level noise ?

How to make caculations for this as the operating frequency is 40 Khz. With the capacitor 1uF and 10k cut off frequency is 15.9 Hz.

 

hi,
It appears to be electrical noise suppression, especially as he is using 60V ESD suppressors.

As you know TTL has a +5v/0V swing, which is not suitable for long distance transmission of data pulses, so the MAX gives a converted output of +/-9V

What is the specification of your 40kHz transducer and what ranges are you expecting.?
E

 

Detectable range is 0.2 ~ 4 meters with allowable input voltage 20Vp-p (40Khz) -continious signal. It has the capacitance 2550 +/-20 % (pF) with a resolution - 9mm.

 

hi,
With a MAX drive on T1 Out that will be a maximum of 18Vppk swing at 40kHz.
A 0.2mtr thru 4mtr distance is possible with that drive, a lot depends upon the sound reflective surface.
Which type of receiving amplifier do you plan to use.?
E

 

how did you conclude it is +/- 9V swing but not +/- 10V or +/-5V swing ?

I am planning to use LMV 854 Op-Amp for Receiver Section.

 

There are a number of charge pump circuits around, but for an application like this it seems more reasonable to use one of those small power converter modules. They work well and some of them have very low noise outputs.
For transmitting voltage it makes more sense to use a tuned transformer to drive the transducer, presuming that the transmitting frequency is supposed to be fixed.

 

Why am I under the impression that the circuit posted by the OP is intended to convert a PWM input signal into a linear output voltage?