I am trying to design a MOSFET constant current generator controlled by a 0 - 5VDC signal (non pwm). I have had no problems getting a nice resistor divider and an op amp to control the circuit. I am looking to get 5A through either a HBLED or a Laser Diode.
My issue is this. For the application, the 0-5V needs to be linear. The "0" volt setting needs to be adjustable as the LEDs & Laser diodes do NOT start emitting light at .01mA. I need to be able to set a "bias" or threshold current with a pot so that when the signal is introduced into the circuit, I have set the "actual current", the device will need to begin emission. Next, I need a pot to vary the top end of the circuit to stop at the max current when 5V is reached. I use a Zener diode for over-voltage and reverse voltage protection. Overshoot in this application I really can do without. I hope I phrased this correct using the word bias.
This circuit (seen here in forum before) is a great V to I section:
For example, the laser diode has a "threshold current" of say 120mA and will max out at say 2.5A
I need the "0" volt or NO input to be right under the 120mA. so when we start ramping up the voltage from 0, the circuit immediately starts feeding 120mA. When the voltage approaches the Max setting with 5V input, I need 2.5A output. Each HBLED and Laser diode have a varying threshold & Operational current, thus the need for multiple potentiometers. Once again, I hope my question is clear. I am disabled and my brain doesn't allow the ideas to flow correctly sometimes. Sorry, look forward to any help!! Happy Turkey Day
To obtain 2 offsets, one high one low, both corresponding to the 0-5V signal. It seems like I can imagine it, but not put it on paper.
One potentiometer sets the I threshold current when no voltage applied, second potentiometer sets the Imax at 5V. I feel like an idiot since it does not just "POP"