current pulser

I want to build a circuit that generates current pulses of 50mA peak value .The pulse width is 15ms and occurs every 400ms. I found a reference circuit that produces pulses using 555 timer.

https://www.jensign.com/opto/ledlaserdrivers/
Ideally, I need the pulse peak value to settle within 99% of maximum, as shown in fig 2 in attached sketch.

How can this be achieved?
Can the existing circuit in above reference be improved further?
Is there any alternate method to produce current pulses that's very stable ?

Previously I have made voltage pulser, which was noisy. Then I connected a comparator to the voltage pulser output to obtain very clean and stable voltage pulses.
Thank you
nzb109

Welcome, nzb109!

nzb109]
Ideally, I need the pulse peak value to settle within 99% of maximum, as shown in fig 2 in attached sketch.
How can this be achieved?
Can the existing circuit in above reference be improved further?...

Click to expand...

The circuits look fine.

From what you have provided, the "noise" displayed riding on the top edge of the pulse I would attribute to power supply ripple (+ noise). Making absolutely sure your Vcc source is as clean as you can get it would help ensure your 1% tolerance requirement.

thanks for your feedback

https://www.jensign.com/opto/ledlaserdrivers/
I can understand in above reference, 555 timer is wired as astable.
The reference says the transistor is boosting the current drive capability.
Now could you please explain how the transistor is doing so? Is it common collector?
I want to understand the role of transistor.

I hope this makes some sense: http://www.elperfecto.com/2011/01/04/calculate-resistor-values-for-driving-leds/

Usually, you don't drive from the emitter, but the author of your link had reasons to do so (miller capacitance: http://en.wikipedia.org/wiki/Miller_effect). This would make the equations different.

Basic equations for a transistor are: Ie=Ib+Ic
There is a voltage drop depending on temperature from base to emitter: Vbe which is around 0.6V for silicon.
There is a saturation voltage from Collector to Emitter of Vce(sat). The voltage won't be lower than that.
Transistors have a current gain called hfe, It also has another gain when used when saturated. Hfe has a huge variation. Both per transistor type and overall. Hfe from about 20 to 20,000. The 20,000 is for a darlington transistor configuration.
Ic=Ib*Hfe

When designing an amplifier, the idea is to make the circuit work for various values of Hfe. This is really not an amplifier,. It's a switch.

LEDs have a voltage drop depending primarily on color. This is on the order of 1.2 ro 3V