Clamp Diodes

[sakis]

a few days we had a very creative post about zobel networks and some many nice arguments were placed there .....

lets talk about output clamp diodes ......

it is a form of protection

against short circuit ????
against reactive loads ????
why yes ???? or why no ????

and finally why big comercial amps are always equiped with this diodes and almost none of the amplifiers shown in the forum hasn't any of these diodes ????

except a protection do they also have some effect in sound ????

regards sakis

[AndrewT]

If the output stage has some form of current limiting, then the fast switch off of output current creates a back EMF from an inductive load and this back EMF can overvoltage the output transistors.
The clamp diodes limit the back EMF voltage to supply voltage + 0.7V and save the output devices.
The distortion created by triggering the protection is still present.
Prior to triggering the amp should sound the same with/without the clamp diodes.
An additional pair of diodes (making 4 in all) from supply rails to ground are a further useful protection to help prevent reverse voltage building up on electrolytic capacitors during power down.

[peranders]

Originally posted by sakis
a few days we had a very creative post about zobel networks and some many nice arguments were placed there .....

lets talk about output clamp diodes ......

against reactive loads ????

Yes

Originally posted by sakis
...and finally why big comercial amps are always equiped with this diodes and almost none of the amplifiers shown in the forum hasn't any of these diodes ????

Lack of design experience plus the amps work in light duty probably.

[AndrewT]

the ESP site has a couple of articles about this.

[sakis]

andrew t and P-A ....

what sound most inderesting is that these devices will not effect sound quality ....

[sakis]

Originally posted by AndrewT
the ESP site has a couple of articles about this.

i will take look ...thanks to rod there is a lot of nice things arround there

i was actually looking at P68 that looks like one of the designs i like very much ( i have to listen though ) but eventhough is a design that is a high power thing ....there is a double zobel but no clamp diodes ......i wonder why

[AndrewT]

Originally posted by sakis
looking at P68 that looks like one of the designs i like very much ( i have to listen though ) but even though is a design that is a high power thing ....there is a double Zobel but no clamp diodes ......i wonder why

does the p68 have limiting?
If not, then clamping diodes are not mandatory.
But those 4 clamping diodes are nice to have, cheap to fit and gives peace of mind with no deleterious sound effects to worry about.

[teemuk]

Originally posted by sakis
and finally why big comercial amps are always equiped with this diodes and almost none of the amplifiers shown in the forum hasn't any of these diodes ????

It could be, as was mentioned, lack of design experience or the idea about this protection method even existing. I also have couple of alternative theories: In some cases those diodes are already integrated inside the output devices, e.g. such as in TIP142/TIP147 darlingtons. It has been said that trusting that these internal diodes exist or are even robust enough is bad practice, though. Some people simply do not care to make full-detailed schematics and trust that builders are wise enough to include all the neccessary protective or stabilizing elements to the design by themselves.

[sakis]

Originally posted by teemuk


It could be, as was mentioned, lack of design experience or the idea about this protection method even existing. I also have couple of alternative theories: In some cases those diodes are already integrated inside the output devices, e.g. such as in TIP142/TIP147 darlingtons. It has been said that trusting that these internal diodes exist or are even robust enough is bad practice, though. Some people simply do not care to make full-detailed schematics and trust that builders are wise enough to include all the neccessary protective or stabilizing elements to the design by themselves.

hmmmmm

"""designers that they dont include things like that in the schematics presuming that the constructor will any way ......""""

i will buy that ..... i kind of like it a lot .....

the truth is that i did try to dig some old story to find out if inductor was allready existing inside the citation 12 when modified by Nelson Pass to a mosfet amp cause in the schematic posted by NP there is no one .....

i wonder if this is simply a printing mistake ???? was inductor located some where else inside the amp so is no part of the amplifier schematic .....

or just simply missed it ???

asked some related people in the forum that seem to constructed citation 12 but no luck .....

[darkfenriz]

Keep in mind all MOSFETS have adequate diodes inside.