1) I simulated this, and the maximum peak collector current on Q1 is 240µA, with or without the 200 ohm resistor. Isn't it ultimately limited by the base current that can flow through the 1M emitter resistor?
2) Can you elaborate? I'm not sure what the output not going fully to ground has to do with Q1? Do you mean the trigger input won't go fully to ground?
2) Can you elaborate? I'm not sure what the output not going fully to ground has to do with Q1? Do you mean the trigger input won't go fully to ground?
1) The discharge current runs through the collector-emitter of the saturated transistor. "Theoretically" this current can be infinite, but I'm sure you know the constraints on this. I'm not sure if your simulator is showing this.
I always put the resistor in there, but it's up to you.
2) It could interfere with fully cutting off the transistor. Common wisdom says you can't use an NPN emitter follower on the output of the 555, but of course you can with an appropriate workaround.
You can always build a prototype and see if it has any glitches.
I always put the resistor in there, but it's up to you.
2) It could interfere with fully cutting off the transistor. Common wisdom says you can't use an NPN emitter follower on the output of the 555, but of course you can with an appropriate workaround.
You can always build a prototype and see if it has any glitches.
1) Heard. This is in LTSpice, but yeah that spike could be too sharp for it to capture. I do actually use a resistor for this same purpose in my GFA-555 Soft-start design, and I thought I was being paranoid to include it, so thanks for confirming that's not misplaced!
In that case I used a 220R hanging off the collector instead of in series with the timing cap as you suggest, but accomplishes the same purpose, as far as I can see, please correct me if not.
2) Base cutoff: Are you referring to the relay switching transistor Q2? I was thinking of Q1.
If you mean Q2 the relay switching transistor...
Interesting, I was playing around on the breadboard with the EF switch, and I'm not a fan of the approx 0.8V C-E I was getting, dropping relay voltage to 11.2V. I mean, that's how EF is supposed to work, and it's nice that it keeps parts count down... But I've always done the old open-collector approach, emitter grounded, with a base resistor. <0.2V C-E, but then I also need the reverse-protection diode around the relay. (Don't I?)
I don't think that arrangement would have any base cutoff issues, but I'm not fully understanding what what you mean about the EF.
Here's the base currents of Q1 and Q2, alongside the relay switching in and out. Where could there be trouble?
Thanks for your help with this, I'm learning.
Q1 Base Currents
Q2 Base currents
In that case I used a 220R hanging off the collector instead of in series with the timing cap as you suggest, but accomplishes the same purpose, as far as I can see, please correct me if not.
2) Base cutoff: Are you referring to the relay switching transistor Q2? I was thinking of Q1.
If you mean Q2 the relay switching transistor...
Interesting, I was playing around on the breadboard with the EF switch, and I'm not a fan of the approx 0.8V C-E I was getting, dropping relay voltage to 11.2V. I mean, that's how EF is supposed to work, and it's nice that it keeps parts count down... But I've always done the old open-collector approach, emitter grounded, with a base resistor. <0.2V C-E, but then I also need the reverse-protection diode around the relay. (Don't I?)
I don't think that arrangement would have any base cutoff issues, but I'm not fully understanding what what you mean about the EF.
Here's the base currents of Q1 and Q2, alongside the relay switching in and out. Where could there be trouble?
Thanks for your help with this, I'm learning.
Q1 Base Currents
Q2 Base currents
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