high current for pulsed nanosecond

Thread Starter

pooya_b

Joined Feb 25, 2021
53
Hello
I am am trying to run a nanosecond pulser circuit. This circuit is controlled by a flap. Therefore, a nanosecond pulse is generated and increased to 8 volts by an amplified transistor. Then, the transistor is connected to the MOSFET gate.
I designed this circuit to have a strong single pulse of light. Also operating-speed of the circuit is 100 nanoseconds.
My problem is with the Hebrew current through the ledge which a very little current passes through. But I want about 10 amps to pass through this led current.
Please let me know what is the problem with my circuit.a.JPG
 

Papabravo

Joined Feb 24, 2006
16,814
What is Hebrew current? I'm not familiar with that term.
Q2 is an inverter, so a high going pulse on the base is going to force the collector to about 0.2V and pulling 200 mA, and turning the N-Channel FET OFF!
When the input goes low allowing R2 to pull the collector and the gate to +9V. It will turn the FET ON
I'm going to go out on a limb and say I don't think your circuit will work very well at all.
You did not mention what value you have in mind for Vcc
The single BJT acts like an active pull down and a passive pullup. Very bad for driving the gate of a MOSFET

EDIT: the following simulation shows what might be required to meet your requirements using the IRF510
 

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Thread Starter

pooya_b

Joined Feb 25, 2021
53
By current I mean current passing through the led.
The voltage of the vcc is between 12 and 15 volts.
The input pulse is controlled by a fpga that I typed incorrectly.
What MOSFET driver do you think I can use?
 
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Bordodynov

Joined May 20, 2015
2,906
Here is the circuit I used to produce a laser pulse with a duration of about 100 ns and an amplitude power of 300 W. In the simulation I took into account the influence of parasitic inductances of the supply wires.2021-02-26_10-23-00.png2021-02-26_10-31-54.png
 

Thread Starter

pooya_b

Joined Feb 25, 2021
53
Here is the circuit I used to produce a laser pulse with a duration of about 100 ns and an amplitude power of 300 W. In the simulation I took into account the influence of parasitic inductances of the supply wires.View attachment 231444View attachment 231445
thanks a lot.
Do you think the circuit problem is in the MOSFET driver?
Can I use the MOSFET TC4420 driver?
What is the MOSFET problem I used?
 

Bordodynov

Joined May 20, 2015
2,906
I had my own problems and I solved them. But for a correct simulation it is necessary to consider the parasitic inductances even for a 10A LED driver.
The inductances can really screw up the fronts. You may have a problem with the LED turning off quickly. An LED is not a laser and its glow can dim slowly. You need to actively turn the LED off to speed it up.
I don't have a spice model of this driver. I have TC4422 and TC4421 models. Here's a look:

2021-02-26_15-52-14.png
 

Thread Starter

pooya_b

Joined Feb 25, 2021
53
I had my own problems and I solved them. But for a correct simulation it is necessary to consider the parasitic inductances even for a 10A LED driver.
The inductances can really screw up the fronts. You may have a problem with the LED turning off quickly. An LED is not a laser and its glow can dim slowly. You need to actively turn the LED off to speed it up.
I don't have a spice model of this driver. I have TC4422 and TC4421 models. Here's a look:

View attachment 231473
Thank you very much for your help
Can you introduce the simulation software you use?
 

AnalogKid

Joined Aug 1, 2013
9,355
Do you think the circuit problem is in the MOSFET driver?
Yes.

For the IRF540, the input capacitance is 2 nF. To charge that up to 9 V in 100 ns takes 200 mA. If 100 ns isn't the output risetime you want, and you want something much shorter to create a 100 ns pulse width, then the required gate current is more like 2 A.

ak
 

Thread Starter

pooya_b

Joined Feb 25, 2021
53
Yes.

For the IRF540, the input capacitance is 2 nF. To charge that up to 9 V in 100 ns takes 200 mA. If 100 ns isn't the output risetime you want, and you want something much shorter to create a 100 ns pulse width, then the required gate current is more like 2 A.

ak
thanks a lot.
 

DickCappels

Joined Aug 21, 2008
7,721
Quick notes: One method is to use an avalanche transistor pulse generator (they can be triggered) to generate the fast high current gate drive pulse, though the gate would need to be protected by a Zener from higher voltages.

Both the bipolar transistor and the MOSFET in your schematic are suitable for this use.

Check the rise and fall times of the LEDs you intend to use -I don't know exactly what you mean by "operating-speed of the circuit is 100 nanoseconds" but it sounds like you might be getting down to speeds that many LEDs are not very good at switching at.

I know you meant something other than "Hebrew current", I am just curious as to what you were thinking of.
 

Thread Starter

pooya_b

Joined Feb 25, 2021
53
Quick notes: One method is to use an avalanche transistor pulse generator (they can be triggered) to generate the fast high current gate drive pulse, though the gate would need to be protected by a Zener from higher voltages.

Both the bipolar transistor and the MOSFET in your schematic are suitable for this use.

Check the rise and fall times of the LEDs you intend to use -I don't know exactly what you mean by "operating-speed of the circuit is 100 nanoseconds" but it sounds like you might be getting down to speeds that many LEDs are not very good at switching at.

I know you meant something other than "Hebrew current", I am just curious as to what you were thinking of.
I am a physics student working on photoluminescence radiation.
I want to stimulate the substance I want by using the led.
To do this, I have to turn the led on and off at high speed, which means about 100 nanoseconds, and I mean "the speed of the circuit is 100 nanoseconds" means that my circuit has worked at 100 nanoseconds so far.
But my problem is in the light intensity of the led, which was very low and I want to increase the light intensity by passing a high current through the led.
 

Papabravo

Joined Feb 24, 2006
16,814
I am a physics student working on photoluminescence radiation.
I want to stimulate the substance I want by using the led.
To do this, I have to turn the led on and off at high speed, which means about 100 nanoseconds, and I mean "the speed of the circuit is 100 nanoseconds" means that my circuit has worked at 100 nanoseconds so far.
But my problem is in the light intensity of the led, which was very low and I want to increase the light intensity by passing a high current through the led.
You could look for a high current device with less gate capacitance, and given that the IRF540 is marked by the manufacturer as obsolete, such a search might not be an arduous undertaking. As for driving the gate fast for both turn on and turn off, as I mentioned in post #2, a push pull current source in the form of a Class AB audio amplifier might be just the trick.
 

Thread Starter

pooya_b

Joined Feb 25, 2021
53
You could look for a high current device with less gate capacitance, and given that the IRF540 is marked by the manufacturer as obsolete, such a search might not be an arduous undertaking. As for driving the gate fast for both turn on and turn off, as I mentioned in post #2, a push pull current source in the form of a Class AB audio amplifier might be just the trick.
thanks a lot
 

Bordodynov

Joined May 20, 2015
2,906
I did a simulation with a slow LED. The negative current dissipates the accumulated charge in the semiconductor structure. Because of this charge the luminescence time of the LED can increase. In this circuit there is an active switching off of the LED, and this reduces the time of the light pulse.PulseLED4.png
 

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DickCappels

Joined Aug 21, 2008
7,721
I am a physics student working on photoluminescence radiation.
I want to stimulate the substance I want by using the led.
To do this, I have to turn the led on and off at high speed, which means about 100 nanoseconds, and I mean "the speed of the circuit is 100 nanoseconds" means that my circuit has worked at 100 nanoseconds so far.
But my problem is in the light intensity of the led, which was very low and I want to increase the light intensity by passing a high current through the led.
One aspect I hope you are taking into account is that the average amount of energy is rather small because of the duty cycle. Even driving the LED with several amps how much energy can you emit in 100 ns? Then multiply that by the conversion efficiency of the luminescent material. Just a thought.
 
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