True for portable equipment but untrue for equipment hardwired into the mains, in which case the switch is required to precede the fuse :-)
There is no schematic notation for Line and Neutral, but then we don't even know V1 is mains, could be some low voltage a/c system.
It's something else.
In practice I'd just grab a big cap from the lab. A Sprague 39D 2300uF
50VDC (to throw a knowing wink at recent _Art of Electronics_ threads). :) Doing the math as specced may prove entertaining. ### "I'm going to spell it out because I'm thick. Watch my arithmetic. It's nowhere near as good as yours. Watch my every move." Recalling Lacon, he held up a white hand and spread the fingers as a prelude to counting on them. _Smiley's People_ ### Let's calculate the time constant: Rload = 5V / 0.1A = 50ohms Rload * C1 = 50ohms * 10uF = 500uS 1/f = 1/120Hz = 8.3mS The time constant is small relative to V1 Rload * C1
TR and BR are improper reference designators.
C1 is a little small, too.
Most electronic mags make lots of errors on their published schematics, so maybe they accidentally got this one right.
I'm just now doing the final pre-Gerber checks on a small (13 page) schematic, and it's impressive how many silly errors people have found on this one.
Methinks that's wrong. The fuse is ALWAYS first:
Since there's no power cord or plug shown in the schematic, I guess one could wire a 5V power supply directly into the mains, as in a USB power jack installed on an AC power wall receptacle. Not exactly the standard configuration, and these never include an on/off switch, but it's possible.
Notice that the AC power hot terminal is strapped to one terminal of the fuse. When a similar outlet is supplied with an on/off switch, all the connections are brought out to terminals so that the external fuse could be connected directly to the AC hot terminal.
The AC generator symbol and transformer look like something borrowed from a schematic generated by LTspice. When was the last time you modeled something with SPICE and added a fuse and on/off switch?
When the ridiculous, absurd, inane, and dubious have all been eliminated, that what remains, no matter how unlikely, is the problem. (Apologies to Sir A.C. Doyle).
I submitted my contest entry. We'll see after Feb 20th whether I win, or just receive the usual postal mailings and spam.
It's nothing complicated like that, all they did was move the circuit GND away from the IC GND.
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Not going to check pin assigments but the P on '-' and N on '+' really stan ds out as being wrong somehow. The bias resistors on the 7301 seem really s mall for something with 250pA input current. And the D17 diode for fast dis charge doesn't seem to go well with a 2.2u C51 gate cap.
The comparator is oddly marked--P goes with - and N goes with +.
Does Q5 oscillate during its very slow ramp-up?
Cheers
Phil Hobbs
C1, too small, for this 1Amp rated linear regulator's [78XX], must be at le ast 1000uF or sort of.
Is that a *very* small pull up resistor on the LM7301?
George H.
I took the P and N to be supply connection annotations.
But the output connected to +15V won't help.
Cheers
I guess we'll have to use the HC (high current) version of the 7301.
I saw this as weird, but is it actually wrong by any standard?
Well, let's see.
The 7805 is rated for 35V max input. The dropout voltage is 2V and the output voltage is 5V.
So, taking the components shown at face value, the minimum input voltage value is 7V and the maximum value is 35V.
That gives a max ripple voltage of about 28V. Approximating the delta V over 8ms gives a max drain of about 35mA.
So, AFAICS, it will work up to about 35mA.
Other than that, I see no problems.
That seems most likely, but the intended currect rating is not given. It would work OK at low current.
why weird? common to not have crossing lines on a schematic
-Lasse
I was thinking the 10uF so limited the current yet it has 7805 not L05, doe sn't jive. But if it were run off 35v max to get upto 35mA, Pdiss would be
35mA x 30v = 1.05w, so it would need the bigger packaged reg. So its poss ible, but far from likely that C1's correct.NT
I think you are mixing up pin labels. The + and - are on the signal inputs and the P and N are on the power supply pins.
Sometimes you want the inverting input up, and sometimes you want it down. So the first person to create the opamp library part gets it the way he wants it. The power supply pins, P and N, go top and bottom respectively.
So, when another person uses that opamp symbol, they may flip the symbol to make the inputs look nice, which moves the V+/P supply to the bottom and V-/N on top, another great way to blow things up. We've learned to always check that.
I suppose we could create two symbols for each opamp, but we don't.
I doubt that Q5 oscillates, what with the source bypassed and on a big power pour. And it is only linear during the powerup transient, and soon saturates. It's bringing up the power to the FPGA i/o banks.
The regulator is not spec'ed for such a large cap on the output. One would need to take a look at the chip internals to make sure stability is not compromised.
ChesterW
Could just add the title "Digitally Controlled 75 mW Heater".
ChesterW
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