Hi,

I'm trying to create a Driver circuit for a laser diode stack (see attached diagram)

To adjust the power of the laser stack, on pin 3 of the operational IC3, using a voltage ranging from 0 to 4V, I adjust the maximum current that the driver can supply.

With the R1 trimmer I carry out the calibration.

+ Vo1 and + Vo2 = + 12Vdc
-Vo1 and -Vo2 = -12Vdc
On V + and V- there are 24Vdc
On LD + and LD- the laser diode stack is connected, it can have a maximum absorption of 60 amps for a few milliseconds e.g. 30ms.

If you kindly give me some advice on the value of the SHUNT resistances (R25, R24, R23, R22) to use ...

is 0.1 ohm 10Watt ok?

 

That might work. What can you tell us about the resistor you propose to use. Do you have a datasheet for it.

 

Thanks for your answer...

then what do you think of the following reasoning:

1. The voltage drop across the shunt resistor must be approximately 1% of the supply voltage, therefore:
Vs = 1% of V + = 1% of 24 V = 0.24 V (volts eliminated through the shunt resistor at maximum current)
2. shunt resistor value Rs = Vs / I = 0.24 V / 15A (60A max current divided by 4 because it is distributed over 4 MOSFETs) = 0.016 Ohm
3. Power dissipation required for Rs
P = I x I x Rs = 15Ax15Ax0.016Ohm = 3.6Watt

What do you think about it?

 

Looks good. The 1% of V+ looks like an arbitrary decision, which is no problem if the question isn't more complicated than I think. There is no doubt that the 10W resistor could handle that. Maybe you can find a 5W. Remember to make sure the heat can be dissipated from the resistors, particularly if the duty cycle is high.

 

Actually dont realize why so complicated circuit for so simple task?? Im elaborating one now for 2 GHz operations on laser called OPV314. Cheap, nice, furious. Just high impedance input cascade (my case BF998) or if the will is 50 Ohm then BFU910x, after it high-K(u) amplification on basis of two-bjt cascode cascade, then output cascade in current source mode (factually emitter follower BFP620. I evaluated the way to realize it better on opamp lik THS3202 but size (multiple Vcc need) and price comparison boldly pushed this solution toward the hell.