Laser Diode Driver

Michael Borza

Other Parts Discussed in Thread: OPT8241

My question relates to topology of laser diode drivers, not LED drivers, but didn’t know where else to post it. I am trying to design a laser diode driver for TOF application and was thinking about using the capacitive discharge to generate a very short and fast rise current pulse. I also thought about the inductive discharge topology.

Then I read the SBAA209A app note and I thought the “shunt switching” circuit mentioned there is similar to the inductive discharge circuit I pictured above. However after watching this video by Larry Li: https://training.ti.com/3d-time-flight-illumination-subsystem-design-and-component-selection?cu=1127769 I started to have doubts this is the case. In the video the duty cycle is said to be 50%.

I am not sure what current waveforms to expect from the “shunt switching” circuit. Is there an app note describing this? I tried searching the TI website, but no luck. I would highly appreciate any feedback.

Thank you,

Michael

over 7 years ago

0 Alex Bhandari-Young over 7 years ago

TI__Mastermind 25855 points

Hi Michael,

I am looking into this and will get back sometime this week.

Best,

Alex

0 Subhash Chandra Sadhu over 7 years ago

TI__Expert 3800 points

Hi Michael,

Are you exploring ToF applications with OPT8241?

Regards,
Subhash

0 Michael Borza over 7 years ago in reply to Subhash Chandra Sadhu

Prodigy 70 points

I am only interested in driving the laser diode with a short (20-50nsec), fast rise time (1-2nsec) current pulse. Aiming for 30-50A.

0 Subhash Chandra Sadhu over 7 years ago in reply to Michael Borza

TI__Expert 3800 points

Can you tell us your duty cycle?

0 Michael Borza over 7 years ago in reply to Subhash Chandra Sadhu

Prodigy 70 points

Duty cycle would be 1% or even lower.

0 Subhash Chandra Sadhu over 7 years ago in reply to Michael Borza

TI__Expert 3800 points

Michael,

For very low duty cycles, I would recommend that you use a series switch with a very good capacitor network to feed the high frequency current requirement. Inductor energy storage with a shunt switch works well only for higher modulation duty cycles like 50%.

Regards,
Subhash

0 Michael Borza over 7 years ago in reply to Subhash Chandra Sadhu

Prodigy 70 points

Do you mean the capacitive discharge method, when you charge a small cap (hundreds of picoF) to several tens of volts and then quickly discharge it through the laser using a GaN fet?

0 Subhash Chandra Sadhu over 7 years ago in reply to Michael Borza

TI__Expert 3800 points

Michael,

Yes. Using the capacitive discharge method would give you better efficiency and probably a sharper response time(rise time and fall time). However, if you want a flat illumination waveform, you should use the series inductor "shunt switching" method. Owing to your high current values and low duty cycle, you would probably have a lot of conductive losses. If not, there would still be losses in charging and discharging the inductor to avoid the conductive losses.

Hope this answers your query.

Regards,
Subhash

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Laser Diode Driver