THS3001: THS3001

Well +/-12.5V into 5ohm is 2.5Amp. also, you need to check you slew rate - what is your maximum frequency. 

The THS3001 has an internal design problem, use something else like the THS3491 - but once you put in the Class AB stage, you will need to comp the whole thing back to handle its phase delay, no reason to go further without max frequency. 

The max frequency = 6 MHz. The maximum RMS current = 1.77A (12.5V x 0.707 / 5ohm).

The max slew rate = 0.5 V/ns

Hi Ilya,

do you already have a schematic?

Kai

Yea, that might be possible, do you have a TINA file for the Class AB buffer with the transistors you intend to use? 

So yes, there are several CFA parts that could be used for gain of 20 and >500V/usec slew rate - of course the buffer will also have to have > than that slew rate. I wonder if there are any > 3A power amps with that much slew rate to use instead of the transistors. 

I only have LT Spice simulation with THS3001 and bipolar push-pull at the output inside the loop. The simulation does not run well

Why don't you attach that file, I can work with LTspice files, 

Hi Michael. I was planning to use THS3001 with ON Semi 2SC6144SG and 2SA2222SG BJT push-pull stage at the output, but inside the loop. I have SPICE models for all of them that work with ORCAD or LT SPICE. Unfortunately I have never used TINA.

You have mentioned THS3491. I can build something like on Fig. 67 of the data sheet. I have few questions: 1) The MOSFET push-pull stage is outside the loop. So what is the bandwidth?  2) What kind of MOSFET-s are used in this schematics? If this amplifier is for ultrasound applications as mentioned in the spec, i.e. driving piezoelectric transducer, its bandwidth should be at least few MHz.

I meant to attach the LTSpice .asc file. and the models if those have .include statements. Outside the loop of course you lose all your accuracy.

Hi Ilya,

to post the asc-file here you must "zip" it first.

Kai

Actually Kai, I think if we wanted just the .asc file might ok to just attach as a normal file, I usually zip if I need to send the device models also. 

And Ilya, my real starting point here is to just see your schematic starting point - you could just snip that on your LTSpice screen and paste that in a reply here. Many details in these composite power boost stages and no reason to be guessing on our end. 

I looked at Figure 67 in the THS3491, I am not sure anyone built that - kind of a risky looking circuit in my opionion. Has to be AC only as the balun primary is a dead short to the supply in each cycle. 

Hi Michael,

Michael Steffes said:

Actually Kai, I think if we wanted just the .asc file might ok to just attach as a normal file, I usually zip if I need to send the device models also. 

The "insert" feature of this input box doesn't allow me to attach .asc files. It only works when I "zip" it first.

Kai

Booster amp 20dB THS3001.zip

Hi Kai, Michael. Please see enclosed the LT SPICE file

Thanks Ilya, 1st of all lets move to a better CFA part, I would suggest the THS3091 on +/-16V supplies. I did run your sim on +/-18 at 10kHz, something is clearly clipping and of course is was oscillating, need to increase the Rf to say about 2.5kohm. The THS3091 has much higher peak output current which you need for the base current peaks. 

Booster THS3091.zip

Hi Michael. I've tried THS3091 with regular and with Darlington output stage (see enclosed). Both do not work properly though the latter shows higher output voltage swing.

Yea, I am running that sim - looking at the current through that 3ohm base resistor - those are hitting >300m peaks. Sure you don't want to use power Mosfets in the boost stage?

Do you mean power MOSFET stage as on Fig. 70 in THS3091 data sheet, or power MOSFET push-pull stage inside the loop?

yes