Ron_H

The load is an ultrasonic probe and so it is always a combination of a resistive and a capacitive component. So, yes, 50 Ohm and 5 nF is a very common value.

 

And the 5nF is in series or in parallel with 50 Ohm?

 

The 50 Ohm is in series with 5 nF.

Ron_H, could you possibly post/attach the simulator code or just the circuit setup you used. As an embedded person, I am not that proficient in using Spice and have not been able to duplicate my situation.

Thanks

 

The 50 Ohm is in series with 5 nF.

Ron_H, could you possibly post/attach the simulator code or just the circuit setup you used. As an embedded person, I am not that proficient in using Spice and have not been able to duplicate my situation.

Thanks

The sim I ran dropped 25 volts across the 2k resistor. If that is significant, or close to your hardware results, I'll post the sim.
As a side issue, I believe you said the required peak current is 12 amps. Where did you get that number?

 

I measured the voltage across a high-power 1 Ohm resistor in series with the load..thereby calculating the current. The load was excited with a legacy instrument configured to obtain a desired response from the probe.

I am getting drops of around 30% of the voltage I use. which would definitely be more than the 20V you are getting, however the 2K and the low-value ( 1 Ohm) series resistor may be contributing. so I am not exactly sure if these are the only problems in my circuit.

Thanks

 

All,

I wanted to post an update on my problems. Turns out that there were these problems:

1) My probes were faulty, causing the appearance of slightly dropped voltage

2) My first PCB had an internal defect, (I found this only after I made a 2nd PCB) causing a small 'leakage' between power and ground. This made the voltage reduce even further

3) My resistors were replaced with high-power non-inductive resistors.

4) I upped the storage caps of my driver circuit

5) I found that my bootstrap caps were not getting enough charging time!!

----

After fixing all this, the circuit now works well. The max frequency I have been able to reach is 2 MHz. I am now trying to duplicate this on an IXYS design, which has been built to go to 10 MHz.

Will let you all know the results.