Quick Diode Question

[TrevorP]

Ok I'm reading a datasheet for a 1N4148 Diode and its Vf is 1V. If is 10mA.

Am I right in assuming then that if I have a 1.1V Peak to Peak 440hz AC signal going through it that assuming the current was less than 10mA that it wouldn't damage it but simply cut off the current at that point? Essentially create distortion?


I'm just trying to get a grasp of electronics and the use of certain parts.

 

[Sceadwian]

The Vf is the forward voltage across the diode, that voltage was measured with a current of 10ma's. Different forward currents are going to result in slight changes in the voltage dropped by the diode. That diode can actually pass 400ma's of current repetativly, as long as the average forward current is only 200ma's. It will even allow 1 amp pulses for 1 second (non repeating) or 4amp pulses for 1 micro second, again only if these pulses do not recur frequently.

 

[audioguru]

Its max voltage is 1V at 10mA. Most will have less voltage. The graph in the datasheet shows that its typical forward voltage at 10mA is 0.73V at 10mA and 0.92V at 100mA.

What are you trying to do with the diode?

 

[TrevorP]

Well I was looking over an old schematic which I had made up for a distortion pedal and it used two diodes to clip in the feedback stage of the amp. But at the time I was rushing to finish it for a project (in high school not legit) so I didn't actually know what I was doing.

So I assumed that how it worked was that obviously one cuts off almost entirely the signal except for a small reverse voltage. Therefor my thoughts are that it must have some sort of threshold at which the voltage is limited in order for it to clip the top of a signal.

Basically am I write in assuming that it does provide clipping capabilities for past a certain voltage?

 

[audioguru]

The negative feedback of an amplifier usually has low currents. Two back-to-back diodes from the output to the (-) input clips the output to about 1.4V peak-to-peak.
When a diode conducts it drastically reduces the voltage gain of the amplifier.
It is called "soft clipping". A solid-state amplifier with an input signal too high has "hard clipping".