I refer to the circuit in post #17.
I have used 2k2 for R2 and 47R for R6. These were the only changes. I do not know why is it so non-linear, any ideas?
For the cap I used 100nF. 30 Hz and lower is perfect for my application but I would like ot fo be linear.
Observing current being charged into C1, I noticed that around 1.2A of current (green line) is being injected into the cap. That is a lot of current going through the poor charging transistor (0.6A). To minimized this, I've added a cap at the base of the charging transistor, slowing the current charging into the cap down to ~5mA. Here are the outputs taken from the original and modified.
The same modification is to be applied to my circuit as well.
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As I said earlier, linearity can not be achieved using this method of discharging, because the VBE diff of the discharging transistor is constantly changing.
The NON-reverse sawtooth presented at post #1 is very linear by the way!
Linearity can only be obtained from a constant current source or sink, therefore the circuit posted and tested by the original author is a true linear ram generator, the bootstrapping method was suggested by someone else, which was the one that you prefer to have it inverted, was not tested.
Anyway, why not try mine?
That is what I said on post #3 but I was proposed for the schematic for the bootstraping version.
Are your circuit based on constant current method?
The fact that I see great linearity in tested conditions, at the first circuit of the author, if your method does not work as expected in practice than how could I convert the first schematic posted on #1 for inverse sawtooth?
(I guess I could use the same gurrent amplifier proposed.)
I think the gross non-linearity your are seeing is due to a wiring or part error. Did you double-check your circuit?I refer to the circuit in post #17.
I have used 2k2 for R2 and 47R for R6. These were the only changes. I do not know why is it so non-linear, any ideas?
For the cap I used 100nF. 30 Hz and lower is perfect for my application but I would like ot fo be linear.
Now about the hot transistor,
Ok I left the R6 connected durring tests on 50R and also 1M. This was not right and that was why the transtistor was probably getting hot. Maybe I should replace it with 1M, to match my scope's 1M input and to limit the current to the transtistor? 50 ohm is not really needed for this application. I do not like to have the internal load of the oscilloscope dissipating all the power of the amplifier so I think I am going to include this R6. But then R6 in parallel to the internal resistance of the scope will do 500K. Is that a problem?
I think the gross non-linearity your are seeing is due to a wiring or part error. Did you double-check your circuit?
As I stated any value for the load (R6 in parallel with any other load) of 200Ω or greater should be fine.
As promised, here is Alen Yate's Linear Ramp Inverted
Again, look at the current being charged into the cap, 600mA! To reduce this, use the same method I described earlier, use a 10uF cap to reduce it down to ~5mA
Here is the waveform from the last circuit without a buffer, as it is shown on the post #30.
I have used 2n2222 and 2n2907 for the transistors.
Not very linear. Also no oscillation fov vcc more than 4v
Please seem my post above, I have edited it.Which circuit is this? Is this the one that I converted?
Shall I try also circuit in #34 to see how it performs if it is more linear?
Yes, it is getting a little confusing. :-? The circuit in #34 is includes my modifications to iimagine"s circuit to solve a couple problems I noted and added the output buffer. Note that I also changed some resistor values which seemed to improve circuit performance and increase the output voltage with a 12V supply.So many circuits have been posted and it starts to get a bit confusing now. Is the circuit in post #34 the iimagine's final circuit?
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