HH2 -- first cut

[wam]

MOSFET Driver

I am using MAX4427 in my GoldPic3 - it keeps transistor cool.
I am using it for several years in professional applications as well - never got any problems. Priory to this we have experimented with variety circuits and suffered with large number of MOSFET’s damaged.
Regards.

[mts]

Thanks Wam,

As a follow up I ordered a couple of sample MOSFET drivers from Microchip. They were similar in nature to the MAX4427. Both of the chips I received can be purchased online for less than $1.50. I tested these drivers against Carl's push-pull BJT design and the results were very similar. I basically couldn't tell a difference in terms of turn off time, flyback voltage, and detector depth.

The only real difference I saw was that the BJT push-pull circuit doesn't turn off immediately. There is about a 6us delay before they actually switch the MOSFET off. This does not appear to hurt depth at all. You just need to start your sampling delay 6us later.

So overall I would definitely recommend using one of these MOSFET driver IC's instead of a bunch of discrete components. Carl's BJT circuit is fairly cheap and is made of off the shelf components. So it is a good alternative if you don't want to order special IC's. But buying discrete JFET's to create your own circuit is really not worth the money or time in my opinion. This is a solved problem so it seems right to use accepted solutions. These chips were made exclusively for turning off MOSFETS as quickly as possible.

[wam]

Synchro from pulse.

When it comes to delay, I like the idea of having interrupt taken from decaying signal. It is shown on this example. The other good idea from this circuit is digitally adjustable level for first gain amplifier. Honestly, presented concept is not my desire.
The electronic approach is not modern. I believe that it is available different circuit with greater ability to detect low level electronic signal pulse changes. The other concept of mine (…or some one else) is to recover pulse from separate high inductance coil then compare signal against original TX signal then extract phase difference between and signal strength at the same time with two build in lines of logarithmic electronically adjustable amplifiers and all this in one smart not expensive IC which operates in new generation electronics. I do not want to go to details but may be some one knows what it is about.
Regards

[wam]

Schematic

Sorry I have forgotten schematic for comments above.

[Carl-NC]

The only real difference I saw was that the BJT push-pull circuit doesn't turn off immediately. There is about a 6us delay before they actually switch the MOSFET off.

Are you using a Darlington PNP? I get <1us delay.

[mts]

No, I'm not using a darlington PNP. I'm using common switching transistors. That would probably account for the delay. I didn't think the schematic called for a darlington transistor on the push-pull driver?