Pulsed laser diode driver - how it works?

  • Thread starter McKendrigo
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  • #1
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Main Question or Discussion Point

Hi everyone,

I've been looking at the data sheet for a pulsed laser diode driver that I've been using, and I've managed to convince myself that there's a mistake. I was hoping that if I post my explanation of how the circuit shown in the data sheet works, that you guys can either confirm that the data sheet is wrong, or (embarrassingly) tell me that I'm wrong :redface:

I've attached the circuit as shown in the data sheet. My explanation is as follows (which is more or less what the data sheet says):

When S1 is open, the capacitor Cpfn charges by the high voltage input, HV_IN, through the clamping diodes D1 and D2. The output laser diode is reverse biased in this case, so no current flows through it. When S1 is closed, D1, D2 and the output diode are effectively connected in parallel with the capacitor Cpfn. Because D1 and D2 are now reverse biased, and the output diode is now forward biased, all the charge that accumulated in Cpfn is discharged through the output diode, producing the output pulse from the laser diode.

Where I disagree with the data sheet is the direction of the arrow showing "electron flow". It shows the flow of electrons as moving from the output diode's cathode to it's anode. They seem to be depicting electrons flowing towards the negative terminals of the output diode and capacitor! Surely this arrow is pointing in the wrong direction.....or have I got the wrong end of the stick?

Thanks in advance for your input!
 

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Answers and Replies

  • #2
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At least in a regular diode the actual flow of electrons is from the cathode to anode, and that's also in agreement with your description of how the circuit works; i.e. the cap discharges through D3, with current flow in the direction of the arrow.
 
  • #3
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Hi,

thanks for your reply. Glad to have someone agree with me! I'm still naive enough to have this voice in my head tell me that if it's in something like a data sheet, it must be right! ;)
 
  • #4
Hi,

Is there some commercial product according to this data sheet?
 
  • #5
26
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Hi,

Is there some commercial product according to this data sheet?
Yes. It's from a commercial laser diode driver. The company is www.directedenergy.com and it's from a PCO-7110 Laser Diode Driver Module.
 

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