If I would be interested in replacing the existing speaker protection relay (in my personal home audio amplifier) with the mosfets while taking the steering signal from amplifier's existing protection circuit then I would need 2 mosfets per channel and two photovoltaic drivers?
I.e. the output part of this board schematic?
I.e. the output part of this board schematic?
Yes. The photovoltaic driver needs 20mA current through the diodes, and then connect the output to your mosfets as shown in the schematic. Here is a document I made in 2012 about it:-
https://hifisonix.com/wp-content/uploads/2013/01/Simple_solid_state_relay_Updated.pdf
Here are the Gerber files SSLR.
(The TLP191 is no longer available from what I can tell, but the VOM1271 is directly pin-compatible)
https://hifisonix.com/wp-content/uploads/2013/01/Simple_solid_state_relay_Updated.pdf
Here are the Gerber files SSLR.
(The TLP191 is no longer available from what I can tell, but the VOM1271 is directly pin-compatible)
Thanks, I think I will use a perf board as startup 😉
My idea is to use 4 sets (pairs) of mosfets to act as A and B speaker switches. So both speaker switching and protection circuit breaking would be done by same devices and speaker signals would not be routed via rather thin wires through the rather shabby selector switches behind the front panel.
That leaves protection of the headphone output to be solved but that can be done via additional auxiliary relay.
To make this easy understandable for newr's i will repost more analytic.
The amplifier is 400W into 4 Ohms.
We need to know the current(I).
We know the power(W) and the load(Ohm)
P(w)=I*.R that is I*=P/R that is 400/4=100 that is I*=100 that is I=√100 that is I=10A RMS or 10x1.41=14.1A peak.
Or use this.I=√P/R direct.
Thanks Andrew!🙂
The amplifier is 400W into 4 Ohms.
We need to know the current(I).
We know the power(W) and the load(Ohm)
P(w)=I*.R that is I*=P/R that is 400/4=100 that is I*=100 that is I=√100 that is I=10A RMS or 10x1.41=14.1A peak.
Or use this.I=√P/R direct.
Thanks Andrew!🙂
Last edited:
''Eggburt, the post of mine above is incorrect, so let's do it again. The amp is 400W into 4 Ohms, so that is 10A RMS into the load at full power, 14A peak. With 8 pairs that is 1.75V peak across one of the emitter degen resistors (not both as I incorrectly stated in my earlier post). The opto emitter diode is typically 1.1V and we want 10 mA through that so (1.75V-1.1)/0.01 = 65 Ohms. Use 68 Ohms and adjust Rtrim per the earlier post.''
Sorry,i think something is wrong here.
Sorry,i think something is wrong here.
That's correct - I did not show the working. Remember you them have to divide the total output current by the number of output device pairs because you have to sense across just one of the pairs, making the (acceptable) assumption the pairs all share the total output current equally.
. The amp is 400W into 4 Ohms, so that is 10A RMS into the load at full power, 14A peak. With 8 pairs that is 1.75V peak across one of the emitter degen resistors
Is this correct?
I think that ...with 8 pairs that is 1.75A peak through pair of emitter degen.
Suppose that degen resis is 0.1 Ohm ,that is 1.75X0.1= 0.175v.
Is this correct?
I think that ...with 8 pairs that is 1.75A peak through pair of emitter degen.
Suppose that degen resis is 0.1 Ohm ,that is 1.75X0.1= 0.175v.
Last edited:
How do I determine the voltage needed for that?
From the datasheet graph (e.g. for VOM1271) it seems to be ca 1,4V needed?
I need to calculate the series resistor for placing the driver into a 24V relay drive circuit.
Edit: TLP3906 has also been recommended as replacement for 191 - will it work?
Cause of question is that 3906 price is remarkably lower than that of VOM1271.
Last edited:
if you look at the paper I posted a link to, there’s a formulation in there. Run your VOM1271 diode at 20mA.
The datasheets show a diode across source and drain - since the devices are connected "back to back" then it does not prevent using them?
Apologies for a beginner's question but I have not dealt with mosfets before...
Apologies for a beginner's question but I have not dealt with mosfets before...
1. In my design shown below, I put the diodes in series and added a DC blocking diode - that's why it is three volts. If you are doing a stereo set up, wire the diodes in series as shown, but just use one VOM1271 for each channel. If you want high-speed switching, then use two VOM1271 per channel as shown. I don't think it's strictly necessary, but one of my commercial amps, the Model 1721 used two in series and can switch >60A in just 100 or 200 us.
2. Re your question about back-to-back drain-source diodes. It's the two mosfet sources that are connected together, so the diodes are always reverse biased and never conduct - maybe the diagram below should have made that clearer by labeling them - when I do an update in the future, I'll add that.
2. Re your question about back-to-back drain-source diodes. It's the two mosfet sources that are connected together, so the diodes are always reverse biased and never conduct - maybe the diagram below should have made that clearer by labeling them - when I do an update in the future, I'll add that.
Typically, here, you would look at where the 20mA current intersects the 25C line, and then read off on the Y axis that the diode forward drop is a shade under 1.5V and then base your calculation on that. However, if you are driving the diodes from a high voltage (which means 10V or more in this context) via a dropper resistor, 200 or 300mV either way makes little difference. The forward drop really only becomes critical when you are driving the diodes off a low voltage - for example, if you are driving them from a 3.3V supply as might be the case if a microcontroller is involved.
You do not have any such boards as pairs or quads?
Which could be screwed to the back panel of the amplifier...
Full wave rectifier, then it doesn’t matter? Perhaps even a 20 mA 2 terminal current limiter (using two transistors), allowing one to run up to the Pdiss limit of said limiter. 48 volt supply do-able with TO-126 VAS/driver transistor. TO-220 would get you to about 75V before getting too toasty. Idiot proof relay.
One could make the SSR idiot proof by full wave rectifying the input so it sends the current the right way through the photocouplers regardless of how the user connects it. Better than just a reverse protect diode because there would never be an error to correct. Works either way. And one could install a current source in the loop setting the LED current at 20mA, regardless of amp power supply voltage or if an auxiliary supply is there or not. No dropping resistor to calculate. Plug and play.
Geez, why just not post the technical solution for this instead of verbal overflow?
Edit:
In plain English - put up or shut up.