the puls from avanlanche transistor

[chunjonas]

Hi,
if by using the avanlache transistor to generate high current puls, what is dependece of the output pulswidth? is it depend on the trigger pulswidth at bias or not? e.g. if 1 ns pulswidth wanted must the triggerpuls also be 1 ns?

i appreicite for ur answers!
chun

 

[ronsimpson]

I may have answered this on your other question about fast MOSFETs.

 

[ericgibbs]

Hi,
if by using the avanlache transistor to generate high current puls, what is dependece of the output pulswidth? is it depend on the trigger pulswidth at bias or not? e.g. if 1 ns pulswidth wanted must the triggerpuls also be 1 ns?

i appreicite for ur answers!
chun

hi,
The method I used in my lasers, was a ZTX transistor in avalanche mode.
A 10nF capacitor was charged to approx 150v via a 10K resistor
The ZTX was 'triggered' ON using a 5V pulse via a 47R.

You could use a lower value cap for a shorter pulse.
Look at this image.

 

[chunjonas]

hi,
The method I used in my lasers, was a ZTX transistor in avalanche mode.
A 10nF capacitor was charged to approx 150v via a 10K resistor
The ZTX was 'triggered' ON using a 5V pulse via a 47R.

You could use a lower value cap for a shorter pulse.
Look at this image.

thanks it is worth a trying. if i try i will post the result. thanks!

 

[chunjonas]

hi,
The method I used in my lasers, was a ZTX transistor in avalanche mode.
A 10nF capacitor was charged to approx 150v via a 10K resistor
The ZTX was 'triggered' ON using a 5V pulse via a 47R.

You could use a lower value cap for a shorter pulse.
Look at this image.

a question more how big the current you got on laserdiode with this setup?

 

[ericgibbs]

a question more how big the current you got on laserdiode with this setup?

I would suggest you start with a low value cap say 1nF, this will reduce the energy of the laser pulse, then increase the cap value until you reach the light pulse radiant power you require.
Use caps with a very low inductance.
The FD [fast diode] is essential for damping any reverse over voltage swing when the laser is pulsed.

I used the circuit to pulse LD130, 25Watt laser diodes, radiant energy was approx 5 to 10Watts...

REMEMBER. You MUST wear eye goggle protection for 905nM lasers at this radiant energy level and the instrument should have the correct Laser Warning labels attached.

 

[chunjonas]

I would suggest you start with a low value cap say 1nF, this will reduce the energy of the laser pulse, then increase the cap value until you reach the light pulse radiant power you require.
Use caps with a very low inductance.
The FD [fast diode] is essential for damping any reverse over voltage swing when the laser is pulsed.

I used the circuit to pulse LD130, 25Watt laser diodes, radiant energy was approx 5 to 10Watts...

REMEMBER. You MUST wear eye goggle protection for 905nM lasers at this radiant energy level and the instrument should have the correct Laser Warning labels attached.

thanks...

 

[chunjonas]

I would suggest you start with a low value cap say 1nF, this will reduce the energy of the laser pulse, then increase the cap value until you reach the light pulse radiant power you require.
Use caps with a very low inductance.
The FD [fast diode] is essential for damping any reverse over voltage swing when the laser is pulsed.

I used the circuit to pulse LD130, 25Watt laser diodes, radiant energy was approx 5 to 10Watts...

REMEMBER. You MUST wear eye goggle protection for 905nM lasers at this radiant energy level and the instrument should have the correct Laser Warning labels attached.

Hi,
i have tested with your suggested circuit. at the moment the charge cap is 4.7pf the load is a 47 Ohm resistor. i can measure the voltage on the resistor with neg. peak -16.4V and pos. peak 7V and pulswidth ≈2ns.(by now without fast diode)
i believe it can drive the laser now. But there is a problem about the pos. pulse. it should be disappeared, so i used the shottky diode MBR1100. when it was on the pos. pulse has been well eliminated. but the pulswidth has been wider(4ns) and neg. peak became only ≈7V.
i want to ask u what FD have u choosed?
thanks...

 

[ericgibbs]

hi,
Look at these types for the modern versions, keep the track inductance and capacitance VERY low.
https://uk.farnell.com/jsp/search/b...cale=en_UK&catalogId=&prevNValues=2031+203046

 

[chunjonas]

hi,
Look at these types for the modern versions, keep the track inductance and capacitance VERY low.
https://uk.farnell.com/jsp/search/b...cale=en_UK&catalogId=&prevNValues=2031+203046

Hi,
i just now used the diode BAS16H with max. cd 1.5pf and trr ≤4ns. in your circuit i have added a resistor(3Ω) below the laserdiode. i meaused the voltage on this resistor and found there still were strong positive signal(max.6V). bsides i have meaused the signal on the ground (two random points) and found there also strong disturbing signal! i think this disturbing signal was induced signal. i wanna know does it happen also when u took a mearement? if u got this how did u removed them to watch the real signal?
thanks

 

[ericgibbs]

Hi,
i just now used the diode BAS16H with max. cd 1.5pf and trr ≤4ns. in your circuit i have added a resistor(3Ω) below the laserdiode. i meaused the voltage on this resistor and found there still were strong positive signal(max.6V). bsides i have meaused the signal on the ground (two random points) and found there also strong disturbing signal! i think this disturbing signal was induced signal. i wanna know does it happen also when u took a mearement? if u got this how did u removed them to watch the real signal?
thanks

hi,
You need tinned thick copper tracks and very short leads from the power supply driving the laser and avalanche transistor.

Its a very fast high current pulse so it will induce 'strong' noise in the surrounding tracks, good decoupling is essential.

What is the laser diode type, datasheet.?

 

[chunjonas]

hi,
You need tinned thick copper tracks and very short leads from the power supply driving the laser and avalanche transistor.

Its a very fast high current pulse so it will induce 'strong' noise in the surrounding tracks, good decoupling is essential.

What is the laser diode type, datasheet.?

for test i used the laserdiode SPL PL90_0. but the driver is designed for another laserdiode which is a DBR laserdiode from Ferdinand-Braun-Institut.
the datasheet for SPL u can google to get.