Schottky for protecting SSM2164

elmegil · Posted: Wed Feb 27, 2013 8:30 am Post subject: Schottky for protecting SSM2164

I'm looking to confirm a substitution I want to make....

This explanation of protecting your SSM2164 chips from catastrophic failure:

http://www.electronic-sea.net/SSM2164.html

Recommends using a BAT85 schottky diode between pins 9 & 8 to protect the chip.

I don't have any BAT85's but I do have some BAT43's which appear to have the same voltage and current rating (30V, 200mA).

Does anyone know of a reason why I shouldn't use the BAT43 as a sub?

blue hell

elmegil · Posted: Wed Feb 27, 2013 1:37 pm Post subject:

Thanks Jan Smile

elmegil · Posted: Thu Feb 28, 2013 8:25 pm Post subject:

Over on Muff's Dr Sketch N Etch suggested 1N5818 and DavidRJ suggested 1N5817 as other viable alternatives. Figured I'd mention it here and cross pollinate a bit Very Happy

Osal · Joined: Aug 16, 2011 Posts: 147 Location: Here

This solution does protect the SSM2164 if the negative rail is disconnected or if it fails. It protects the chip from a negative rail failure.
BAT85 is the Schottky used in the original test. Any Schottky with low voltage drop does the job.

You can use also rectifier Schottkies like the 1N581X. They can stand more current and they can be used also for reverse polarity protection.

Reverse polarity happens when accidentally the power connector is reverse connected.

I think that the best solution to protect from reverse polarity is to use keyed connectors which make impossible that you connect them wrong.

Another solution for it, is to place diode rectifiers in the module's power input from -V to ground and from ground to +V. Parallel to the load. Always the cathode to the more positive part.
In this way, if the module is connected with the polarity reversed, the diodes will short the rails to ground and the power supply's regulator will limit its current. Everything is save. This technique is described by Walter G. Jung in its "IC Op-Amp Cookbook". The rectifiers should have greater current rating than the current limit of the power supply. So, 1N582X. (rated 3A), would be more appropriate for the LM317 power supplies, for-example.

Notice that the Schottky used in the protection from the negative rail failure is already placed from the negative rail to ground. Using a rectifier Schottky instead a simple Schottky and adding another one from ground to the positive rail will protect both, from the reverse polarity and from the negative rail failure.