I am trying to improve a device previously made by a past colleague by getting a higher voltage and current output between the leads labeled CE and WE. This circuit is currently powered by the 5V rail and ground on an Arduino, but I'm looking to increase the power by adding a battery pack. I tried simply replacing the 5V and ground with a 6V battery pack but the output from the circuit was ruined by this. I would appreciate any advice on how to fix this, and I'm looking to double the voltage output by this device. Thanks.

 

Looks like CE is an output and WE is an input. CE output voltage will only go as high as the voltage on the op-amp. Output current may be limited (usually to around 20-30mA) by the op-amp.

What opamps are you using? It would help to know what's connected to WE and CE.

 

What connects between CE and WE?
What voltage are you currently getting at CE?
Are you trying to get greater than 5 volts or is the output voltage range too small?
What is the duty cycle of the PWM? If you have a low duty cycle then you can get higher voltage by using a higher duty cycle.

 

Looks like CE is an output and WE is an input. CE output voltage will only go as high as the voltage on the op-amp. Output current may be limited (usually to around 20-30mA) by the op-amp.

What opamps are you using? It would help to know what's connected to WE and CE.

20-30mA is high enough for my current as it is usually only a few mA. The Op-amp is LMC6484. WE and CE are electrodes that are connected through an electrolyte solution.

 

What connects between CE and WE?
What voltage are you currently getting at CE?
Are you trying to get greater than 5 volts or is the output voltage range too small?
What is the duty cycle of the PWM? If you have a low duty cycle then you can get higher voltage by using a higher duty cycle.

CE and WE are connected through an electrolyte solution. The voltage I am recording between WE and RE is from -2.4 to +2.4 V. I should mention that this is for a potentiostat and the RE is connected to WE and CE through the electrolyte.
The duty cycle varies over time. The goal of the device is to scan the voltage between two set points and measure the current.

 

The Arduino is basically a 5V part. Its max is 6V, but characterized at 5.5V.
So really 5.5 should be considered upper limit.

If you split the supply to the Arduino from OpAmps so that you can increase
V out of OpAmps you have to be concerned with injection current by the OpAmp
follower thru its 68 ohm output R back into AVR CPU.


Regards, Dana.

 

20-30mA is high enough for my current as it is usually only a few mA. The Op-amp is LMC6484. WE and CE are electrodes that are connected through an electrolyte solution.

This part is good up to 15V power, going up to 6V shouldn't hurt this part at all, but your Arduino might explode. This part is really only good for about 10mA without significant voltage drop on the outputs. You'll have to look at the datasheet to determine what these numbers really are in your situation.

If I were to guess, CE is one electrode and RE is another electrode across your electrolyte solution. WE is just a control electrode at some point between CE and RE used to control the voltage across the electrolyte - it's probably physically close to CE based on the circuit depiction. RE is held at 2.5V, and CE can vary between ~1 and 4V (at 10mA loads). This gives +/-1.5V across the electrolyte. Note the bipolar nature - current can flow both ways. WE simply measures the voltage at some point in the solution and provides a feedback signal to the Arduino to let it know to raise or lower the voltage across the electrolyte, which is done by altering the PWM. The set point voltage is controlled by some other means not depicted in your circuit.

Can you move the physical location of WE to adjust the power output? If you move it farther away from WE, the voltage across the electrolyte should go up - if it's not already railed out. If this doesn't work, I'd suggest measuring the voltage across the 68 ohm resistor on the CE electrode and deciding if you're hitting the short circuit current threshold. Perhaps reduce the 68 ohm resistor a bit to see if you can get more power out of the part may be prudent as well. 10 mA across 68ohms is over half a volt! I wouldn't have any problem shorting out the 68 ohm resistor. It's only wasting power and the opamp is already current limited.

If you need more voltage to the electrolyte you can perhaps reduce the lower resistor of the 5V divider on the input of the lower opamp to give yourself more positive voltage. If you change the resistor to 2kohm your reference will then be ~1V and you'll be able to get up to 3.5V out of your part - again current limited by the short circuit current of the driver opamp. You'll lose the bipolar operation, and your firmware in your Arduino may need changed to allow the higher voltages, and minimize the negative voltage.

Finally, that op-amp is ancient - it may be worth trying to find a more modern opamp with better rail-to-rail characteristics and more output current. You can maybe find a drop-in replacement.

A few thoughts anyway.