No. The circuit only draws as much current as it needs. Your car battery, unless you have a fuse in the circuit (which you should add, if you don't already have one) can supply much more than 6 amps - as much as a hundred amps or more under heavy load, like starting.ThirtyTwo said:could the op-amp be zapped by too high an amperage? The 12v on my car is at 6AMPS. When i was testing it on a computer power supply everything worked fine, but the 12v amps were really low
Sebi said:LM358 is a dual op-amp, so the supply pin 4 and 8.
RedCarzRFaster said:I wired it just like the attached image (post #4). I know this is from about a year ago or more but I was wondering if someone can chime in. My supply is only 5v but everything else is hooked up right. My input is 5v as well. The problem is if i clamp it at 0v i get an output of 1.6v and if I clamp it at 5v it only goes to like 3.something, not sure what i am doing wrong. I see in later posts to maybe flip a diode.
Blueteeth said:Hi, sorry for my large posts in the other topic, I didn't realise it was specifically for 'boost', the pure analogue (opamps) approch seems to be to best route.
As for your circuit, it is designed to be used with a +12V supply. So powering it by 5v (same as the Vref, your input form the sensor) will mean it won't funciton properly. Also, opamps have a 'maximum output voltage' rating. This means that with a 5v supply, the output cannot swing too close to the power voltage. For the LF358, the datasheet, it says with a supply of +/- 15V (thats dual power supply) the output can swing 13v above and below 0v. So, it can't output the same range of voltage as its power supply. Basically, you're powering it by 5v, so, no matter how the circuit is configured, it won't be able to output higher than about 4V, or lower than 1V. When its powered by 12V it is capable of putting out +11v and 1V (with reference the 'GND'/0V)
It uses the 5v supply for the sensor as its voltage reference, and the 12V supply as its power.
I'm not sure if you know about 'dual rail' supplies (don't want to be patronising here).
The link provided in this topic, http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm, discusses it, but it doesn't actually require it. Its a bit hard to explain :/
Ultimately, if you wish to use that circuit, it must be powered by +12V from your battery. The Vref should be connected to the sensors power supply (+5V) and Gnd, is, well, GND, your chasis (preferably where the sensor connects). 4 connections in total.
If you must have it powered by 5V, then things could get tricky, as few opamps can output that close to the power supply (0.3v - 4.7). Although you did mention you wanted it clamped at 4.3, leaving 0.7 between output and power....*might* be possible. I'll wait for your repsonse before I post anything else, sorry I could be of much help this time,
Blueteeth.
Blueteeth said:Hi again,
How are you testing this? Have you got a pot (voltage divider) connected to the input and the +5v supply (one lug 0v, one 5v, and the wiper as the input), so you can vary the input voltage form 0-5V just by turning it?
quote: Maybe that is my problem and I should put a potentiometer at the input as well and set the clamp to 5v but turn the input down all the way.
Yep. Although the pot at the input would 'simulate' the output of your sensor. So you set the clamp votlage pot, and slowly turn the input from 0v to 5v, and it 'should' hold the output at a certain threshold. if the input is unconnected, god knows what it will do...probably just pick up noise, so the voltage could be anything.
I think that the reason your circuit refuses to put out less than 1.6V is because of the opamp itself. As I said, opamps have an output voltage swing less than the supply voltage, it will never output 0V or Vcc (your power supply voltage), I guess, for your opamp, the lowest outptut with respect to ground is 1.6V.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/a741p2.html
for a different opamp, but has useful info
The LF358 apparently allows the output voltage to be very close to the negative supply (GND in this case) are you using this one? Theoretically, it should allow it to drop below 1v.
From that 'DIY FCD' page, he does explain it rather well, and I've been thinking about that circuit, but my analogue knowledge is not what it should be. All it seems to be is a voltage follower (a buffer) with a low pass filter on the input to attenuate noise pickup (but not eliminate), and a comparator. The comparator uses a diode in reverse bias so that the output swtiches from one input, to the other. Ie: from your signal, to your reference, set by the pot. (bit similar to my idea, but simpler, and rather clever)
If your app (your sensor) is identical to the one in the page mentioned above, then I don't think you need to worry, as the graph he has shows the lowest output of the sensor to be in the order of 2v.
Let me know how you get on.
Blueteeth.
audioguru said:The inputs of a TL072 are Jfets and they don't work and cause the output to suddenly invert when the input voltages get to within about 2.5V from the negative supply.
The inputs of an LM358 work fine down to the negative supply.
Ron H said:Use an LM393 as an op amp, and it will go almost to zero on the output, because you don't need the diode. The LM393 doesn't have a lot of bandwidth when used this way, but it will still be lots faster than you require.
According to the simaudioguru said:Hi Ron,
Doesn't the LM393 comparator oscillate when it has negative feedback?
Or does the 10nF with the 100 ohms compensate it?
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