From: ehsjr@verizon.net
On 3/5/2026 11:09 PM, Jeff Liebermann wrote:
> On Thu, 5 Mar 2026 17:34:25 -0500, ehsjr wrote:
>
>> On 3/5/2026 12:12 PM, Christopher Howard wrote:
>>>>
>>>> parallel protection1 parallel protection2
>>>> -+-[>>> | | | |
>>>> -+-[D3>]-[D4>]-+- -+-[D5>]-[D6>]-[D7>]-[D8>]-+-
>>>>
>>>
>>> Thank you, would you mind please explaining a little more about these
>>> parallel protection circuits, i.e., how the protection works?
>>>
>>
>> Sure. The diodes act as simple voltage limiters.
>>
>> General purpose diodes conduct when the voltage across them rises
>> to about .7 volts. 2 diodes in series will conduct when the voltage
>> across the series pair is about 1.4 volts. Therefore a speaker with
>> a series pair of diodes across it won't be exposed to more than
>> roughly 1.4 volts, provided of course, that the diodes are installed
>> in the "right direction". Since a speaker usually is exposed to
>> an AC voltage, you need two diodes in one direction and two in
>> the other direction, so no matter what polarity signal is applied
>> to the speaker one or the other pair of diodes will limit the voltage.
>> 1A rated diodes can easily handle all the current a 386 is able
>> to provide.
>> Ed
>
> Two pairs of Si diodes will limit the audio (sine wave) to the speaker
> to 1.4 V peak to peak or 1.0 V RMS. Into an 8 ohm loudspeaker, that's
> a fabulous:
> Power = E^2 / 8 = 0.13 watts RMS
> My home entertainment system claims it can deliver 50 watts[1], which
> will probably vaporize a simple diode voltage limiter.
The limiter I described addresses the OP's application, not yours:
"I feed in a small
signal, from my signal generator or from my analog computer, into my
LM386 amplifier (20x gain) and then to the speaker."
>
> Hint: I haven't seen any commercial hi-fi amplifier schematics that
> include such diode clipper speaker protection.
Nor I, but irrelevant to the OP.
Ed
>
>
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