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Yes, I understood, this is very strange idea from newbie, but whatever... I want to make sawtooth waveform generator, based on capacitor charging by constant current. With specified frequency, capacitor will be short-circuited, producing sawtooth on the output. So, voltage controlled constant current source is needed. Yes, I understood that there is more convenient solutions, like Howland current pump. But! I have found XTR115 - current loop transmitter.enter image description here

As I understood, this IC could supply constant current in range 0.25-25mA depending on input voltage Vin. Is this extremely silly idea to use this IC as voltage controlled current source?

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  • \$\begingroup\$ Sawtooth requires constant-current charge and constant-current discharge. Looks like this one is unidirectional, whereas you need bidirectional current. Try a 4046 or HC4046 chip \$\endgroup\$
    – glen_geek
    Commented Oct 23, 2017 at 22:20
  • \$\begingroup\$ I think that for sawtooth requirement is to discharge as fast as possible. For triangle - yes, we need constant-current discharge. \$\endgroup\$
    – artsin
    Commented Oct 23, 2017 at 22:25

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It would be a silly idea to build a sawtooth generator this way if you were trying to make a commercial product. But as you're educating yourself, I'd say go for it.

On the surface, it is not a silly idea to use a voltage controlled current source IC as a current source. However, it will be a bit tricky to apply to a sawtooth generator, and you would learn a lot about more general electronics by the time you've done it successfully.

The problem with this current source is that it is powered from its output current on pin 7. In a sawtooth oscillator, that current is being drawn from the timing capacitor, so you end up with unnecessarily high currents in the timing circuit. It's not impossible to make it work, but it's rather a square peg in a round hole.

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  • \$\begingroup\$ Actually, this is an attempt to make DCO for audio purpose(in parallel, learning of the analog electronics:). And this way of sawtooth generation is very common even in nowadays, I mean for this audio purpose. And thank you for great advice, I'll try this! \$\endgroup\$
    – artsin
    Commented Oct 24, 2017 at 7:07

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