ringing with high speed switching
ringing with high speed switching
(OP)
hello all.
Im working on reconstructing a circuit that someone else made. Im by no means an expert. Im having a little trouble understanding a ringing effect Im seeing.
So I have one mosfet driver driving 4 other mosfet drivers at approximately 2MHtz. These chips have 40MHtz band limit (EL7158) and Im pretty sure they are not the problem. I have the all 5 chips in a line staring with the one driving the 4 others. The output of this first chip is directly connected to the input of each of the others via wire wrap (size30). As I progressively get further away from the chip driving the others, a ringing becomes more pronounced on the inputs to the chips and this is amplified in the outputs that they produce. I rebuilt the circuit twice with the same effect.
Id like to understand what is going on. Is it some type of inductive effect that takes place at higher frequcines in the longer length wire. Is there a way to fix it? I tried disconnecting the wires and using thicker size 22 solid wire. Maybe stranded? I dunno.
Ill attach some photos of the 5 pin drivers (front and back) as well as the inputs to the pin driver (same node), as well as the driver outputs
Im working on reconstructing a circuit that someone else made. Im by no means an expert. Im having a little trouble understanding a ringing effect Im seeing.
So I have one mosfet driver driving 4 other mosfet drivers at approximately 2MHtz. These chips have 40MHtz band limit (EL7158) and Im pretty sure they are not the problem. I have the all 5 chips in a line staring with the one driving the 4 others. The output of this first chip is directly connected to the input of each of the others via wire wrap (size30). As I progressively get further away from the chip driving the others, a ringing becomes more pronounced on the inputs to the chips and this is amplified in the outputs that they produce. I rebuilt the circuit twice with the same effect.
Id like to understand what is going on. Is it some type of inductive effect that takes place at higher frequcines in the longer length wire. Is there a way to fix it? I tried disconnecting the wires and using thicker size 22 solid wire. Maybe stranded? I dunno.
Ill attach some photos of the 5 pin drivers (front and back) as well as the inputs to the pin driver (same node), as well as the driver outputs





RE: ringing with high speed switching
Standby for others with more experience in this exact area.
You might want to upload the schematic of the section in question.
RE: ringing with high speed switching
its not perfect.
but there were really two problems
if i scoped the ground, there was some ringing on it and it should have been ground potential.
On the supply voltage was a ringing that appears on the high end of the pulse
So i had to put 2 more different value caps on each chip to decrease the ringing, i already had 2 and assumed it was not the problem but it was.
then also adding a lot more ground wires in for redundancy and reducing also helped.
RE: ringing with high speed switching
OK, additonal grounds and bypass capacitors are a start. Keep leads short - solder them point-to-point on the bottom of the board (none of this through-the-hole-rightangle-bend-make-it-look-neat stuff). Add short leads to SMT capacitors if you have them. Keep the electrolyitc and bigger capacitors - since these are drivers, they supply the bulk energy for the pulses, but later since they have more ESR than ceramic caps.
For grounds go for low inductance. Copper foil or tape cut to 1/8 to 1/4" width. If you don't have that, use solder braid.
Also, you can get distorted signals with the scope depending upon where the scope ground lead is connected, and how long it is.
Finally, if there is still some ringing, then try dampening it by using a series resistor in the range of 10 to 33 Ohms. Your connection distance is short, so you should not need terminations on both ends. Put the resistor on the output of the first driver with the lead as short as possible.
RE: ringing with high speed switching
RE: ringing with high speed switching
RE: ringing with high speed switching
Its true that its not ideal way to make a prototype board. Ie the soic to dip adapters and wirewrap sockets, something i knew ahead of time as very bad a high frequency. I do appreciate your input though, its just something it was hard to get around with the tools I have at hand. These matched high frequency (3mhtz) high voltage (100V) matched mosfet pairs are the only chips that fit this application and only come in this package. They are unique chips although a ixys is making a new dip chip for higher power (200V) matched arrays which is soon to come out. The wirewrap looks pretty bad too but it gets the job done although messy... Its a good step before using pcb express. Im not sure about the wire wrapping tool adding hundreds of uH as i can measure inductance and get 1-5uH on each connection. Probably has to do with the core being the same dielectric as the wire.
There is one problem i really dont understand. With the 1Mhtz (1072nF)transducer, the waves are very powerful, rippling through the water bath but they get much smaller after about 5 seconds. If I shut the power off and then back on, the waves stay at low power. During this time, If i scope the power output, there is no change in frequency, amplitude, or phase. If I let the device/transducer rest untouched for a while and then start it up again, it goes for about 1- 5 seconds again and then returns to the small output. The same type of transducer in 2Mhtz (1582nF) does not have this problem and I can let it run perpetually (hours) with very high output. I did notice there seems to be a capacitance change on the transducer when it chokes and that the capactice is very different when it is in water (DI or not DI). What is going on?
I attached a few photos of the transducer and the circuit
RE: ringing with high speed switching
RE: ringing with high speed switching
Looking at photos - bad prototype.
This EL7158 driver chip has rise/fall time in 10ns range.
Piece of wire =10nH for every inch, so few inches of thin wire may give you 50nH inductance.
Few Amps (say 5A), and 50nH, and 10nseconds will give you lots of ringing (now I'm too lazy to calculate).
just remember - when you go into nanoseconds and nanohenries field - there is no more ZERO ohm/Henries wire. Every piece of copper should be viewed as resistance and inductance.
advice:
for every 'hi speed' connection use wide, flat piece of copper (low inductance). Short as possible (low inductance).
2MHz is not very high frequency, but what makes is difficult is rise/fall time of your driver.
Capacitors - ceramic (or film) with very low ESR and low ESL. Sometimes you will have to connect few caps, not to get higher C, but to lower ESR.
For switching few Amps (and more) - forget about tantalum or aluminum.
Scope - connect probe (and GND!!!) at the point you want to check. CAN NOT connect probe at the chip output pin, and GND at supply wire from main PS.
thx