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# High current pulse train from supercapacitors?

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#### Flyback

##### Well-Known Member
Hi,
We wish to pulse a laser diode block with 20A for 250ms every 2 seconds.

(LTspice and jpeg as attached)

We cannot draw this pulsation from the 2S Lithium Battery that we have , so we will charge up supercaps with the battery instead, and draw the pulses from the supercaps instead.

We will use the VinaTech 25 Farad, 3V, 13mR ESR supercap…2 in series.

VinaTech 25 Farad, 3V, 13mR ESR supercap
https://www.vinatech.com/winko/data....3_85%B5%B5_%C1%B6%B0%C7%28R0%2C210201%29.pdf

Do you think the supercap can handle these pulses?…(datasheet doesn’t allure to pulse rating) its only some 0.7W of power in each supercap

#### Attachments

• Laser stack pulser.asc
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• Laser diode pulser.jpg
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What is the load impedance? That is what will be the RC time constant for the discharge? I'm somewhat dubious on the ability to maintain that current level for 250 msec.

Read the datasheet. it says 35 Amps Max. "Current : 1 sec. discharge to 1/2V"

Yes it can handle 20A no problem but with a +30%/10% tolerance you need a BMS to ensure each cap never exceeds 3.0V

1/2V_R means max current from 3V to 1.5V in 1 sec. but 37A * 13R= 0.481V reduces dV to about 1.0 V across C.

If you applied 20A for 250ms I*ESR= 260 mV or more. with Ic=20A, C= 50F, dV = Ic*dt/C = 100 mV sag for a **total drop of 360 mV after 250 ms.** With 2 caps in series the total drop from 6.0V is 720 mV assuming 0 tolerance error on C.

Since your requirements given are only 20A, this is inadequate to determine if your design will work.

Also, R8 should be a diode?

This design will never work because you have not specified the temperatures of each component and performed any current regulation or pulse width regulation of something like 100 ns max.

65W will fry this diode up in 250 ms even with an infinite heatsink

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