PROTECTION DIODE on HexFET Amp, HELP!

[abeteer]

HI all,

I am showing here for the second time the HexFET amp from Elektor for the following reasons-

Quoted from the previous help thread on this amp;

*connect a 1N4004 or similar and a 12V zener protection diodes to Gate - Source terminals

*A of zener1 to G of T12
K of zener1 to S of T12
A of zener2 to S of T13
K of zener2 to G of T13

Looking further at the circuit, both channels means S to VAS rail and D to mid-v (out). If the symbol used for the output was precise then to my understanding the suggested placement for the protection diodes would become -

A of zener1 to D of T12
K of zener1 to G of T12
A of zener2 to G of T13
K of zener2 to D of T13

Is this correct?

From the previous help thread there was a mention of using 6.8v, and 12v for the zeners. Was there a difference?

One constructor mentioned of replacing P2 I wonder what rating would that be... Sorry some links no longer exist from the previous thread can't view your modified versions

Your guidance will surely clear things out for me....


Thanking you in advance



(sorry mooly, no can do, I guess your design will have to wait, lateral mosfets will only become available upon ordering in this place. I don't do this..too risky and most likely you'll get fake ones...always happen.)

[Junm]

hi abeeter, where you located in PH?

refer to the attached schemetics on how to connect the protection diodes. You can also try this schematic which uses N channel mosfets which are abundant here in PH.

you can purchase lateral Mosfet in RAON in manila but in higher price compared to IRF's.

[abeteer]

Easternmost in Region V, I work here in a geothermal facility, fact is Kapampangan runs my blood Mekeni ku naman...surprised? I live here na

I'm still confused 'bout the pin assignment of the drain & source. Upon encountering various mosFET circuit, to most of them the source was tapped to mid-voltage(out) and the drain to voltage supply. The gate is always fixed. This one here was different though... I had the parts, well at least for one channel (no turning back eh). I'm currently doing a revision of the pcb, that is why I need to figure-out the proper circuit for the protection diodes.


Thanks & Regards

[abeteer]

Here's a quick draft for you to see if I doing it the right way

[meanman1964]

Why would you install those zener and diodes?

[djk]

So you don't blow the gates when clipping into a low impedance load.

A small resistor needs to be inserted between the collectors of the driver transistors and the diode strings

[meanman1964]

The main problem of this amp is oscillation.

[bigpanda]

I am not trying to discourage you but I hope you are not expecting it to give you 120w (not even 60w) with a power rail of +-35v and a pair of outputs like that.

[abeteer]

Originally Posted by djk

So you don't blow the gates when clipping into a low impedance load.

A small resistor needs to be inserted between the collectors of the driver transistors and the diode strings

You're quite right both collectors of the driver transistors were tied to VAS rail, will it do if I move the diode string and place it after the resistors at the gates?

[WuYit]

Hi,

will it do if I move the diode string and place it after the resistors at the gates?

Yes. You don`t need the external diodes across drain and source.