Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Adjustable voltage controlled current source with negative values

Status
Not open for further replies.

leilamontazeri

Newbie level 1
Joined
Jul 11, 2017
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
13
I have a MEMS mirror which can tilt based on the input current. The current can vary between -15mA to +15mA in order to change the angle of the mirror from -15 to +15 degree. Now, I need to have an adjustable voltage-controlled current source that can also provide negative values. I prefer to use Raspberry pi or Arduino. I appreciate any help.
 

You need a Current Charge Pump that sources and Sinks a current. I believe this current pump will change the current linearly between -15 to 15 mA Right ?
In this case, you should find a solution Voltage-to-Current Converter to drive this Charge Pump.
 

Depends on the input resistance of this MEMS (is it linear? I have never used one), but you could use maybe a resistor and a variable voltage source to create the necessary current values.
The voltage source needs negative value too, with dual supply it is easy. If you don't have dual supply maybe a bridge-circuit from stereo potentiometer or a differentially variable voltage source could solve it.
It would help I think if you shared more data about the MEMS and your application, how accurate tuning you need, etc.
 

You could likely use a Howland op amp current source, since it can generate plus and minus currents.
What is the resistance of the load?
What power supply voltages do you have available?
 

Here's the LTspice simulation of a representative Howland current source that generates ±15mA pk constant-current into a load:
Notice that the load current (yellow trace) remains constant as the load resistance increases (red trace) until saturation.
For the op amp and supply voltage shown, it saturates at a load resistance of 1k ohm and above.
The input is fully differential, and either input can be connected to ground, as desired.

Capture.PNG
 

If you need to derive a -5v supply from an existing +5v supply then this is a popular method:

555 iC positive pulses to negative V quadrupler makes +-5V biploar supply 15mA.png

For the load you install your circuit which needs between +5 and -5v (referenced to 0v ground).

The low-ohm resistor at the 555 output is optional although it is a good idea in order to reduce spikey jolts in the system.
 

Attachments

  • 555 iC positive pulses thru negative V quadrupler makes +-5V biploar supply 15mA.png
    555 iC positive pulses thru negative V quadrupler makes +-5V biploar supply 15mA.png
    35.5 KB · Views: 84

Here's a corrected schematic with a higher voltage op amp.
The LMC6484 is only rated for 16V max.

Capture.PNG
 
Last edited:

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top