1us 2A pulse generator? - Page 1
Forum section: electronics / projects

author: rfengg
author_rank: Regular Contributor
timestamp: April 03, 2025, 08:46:18 pm
content: Hi there,We need to generate a 1us pulse to deliver 2A of current into a small inductor of 30nH. What would be the best way to approach this design? Since the inductance is very low, is it possible to drive this current with fast switching MOSFET's?

author: moffy
author_rank: Super Contributor
timestamp: April 03, 2025, 09:07:55 pm
content: This discussion might be of interest:https://www.eevblog.com/forum/projects/fast-1-mhz-1-amp-pulse-current-driver/msg5827809/#msg5827809

author: Benta
author_rank: Super Contributor
timestamp: April 03, 2025, 11:45:07 pm
content: That's pretty easy. But what kind of current pulse rise time do you need?That's important for the voltage compliance of the source. Or in other words: how high a voltage will be needed?

author: David Hess
author_rank: Super Contributor
timestamp: April 04, 2025, 09:25:43 am
content: With 2 amps and such a low inductance, just switching 2 volts through a low inductance 1 ohm resistor will be enough.Alternatively if a high impedance is required, I would use a 2 amp current source driving the tail current of a differential pair. Now switching the differential pair via its base or gate connections will very quickly switch the 2 amps from one side to the other side. This configuration can switch within 10s of nanoseconds or faster with some effort.

author: rfengg
author_rank: Regular Contributor
timestamp: April 04, 2025, 03:25:21 pm
content: Hi Benta,I am looking for a rise time of around 10ns thru the 30nH......would you mind explain how to set this up?

author: rfengg
author_rank: Regular Contributor
timestamp: April 04, 2025, 03:37:15 pm
content: Hi David,If I look at the L/R time constant of "switching 2 volts through a low inductance 1 ohm resistor" with 30nH, one tau would be 30ns.I am not sure which MOSFET to incorporate that can give a rise time of 10ns.thanks

author: uer166
author_rank: Super Contributor
timestamp: April 04, 2025, 04:22:57 pm
content: Quote from: rfengg on April 04, 2025, 03:25:21 pmYou can't get much faster than a GaN FET with an integrated gate driver such as:https://epc-co.com/epc/products/gan-fets-and-ics/epc2112I don't think it's hard to do if you have some experience with power and high dV/dT switching

author: David Hess
author_rank: Super Contributor
timestamp: April 04, 2025, 07:54:25 pm
content: For that kind of switching speed, I would look at RF MOSFETs, RF bipolar transistors, and GaN MOSFETs, and use a differential pair to do the switching.It is not that common power MOSFETs or bipolar transistors are not fast enough, but non-RF packages have too much lead inductance. Some common surface mount packages might be good enough without going to ball grid arrays.Input and output capacitance will be a problem because it will conduct the fast base or gate signal into the other leads, so look for low capacitance parts.For proof of concept, I might start with an inexpensive and easy to use RF power MOSFET:https://www.mouser.com/ProductDetail/NXP-Semiconductors/AFT05MS004NT1The current source does not need to be as fast.