triangle wave with single power supply?

[mabauti]

I want this waveform

**broken link removed**


so far I have this:
**broken link removed**


question(s)

What's an easier circuit to get this waveform with a single power supply (let's say using a 9V battery)? and w/o the negative offset?

 

[Blueteeth]

Well, for a start you could create a virtual ground by using a voltage divider on your 9v battery. So you have +4.5V, 0v, -4.5.

Just google 'single supply op amp circuits'

The output would be, from the opamps point of view, positive and negative. But if the rest of your circuit is with reference to the battery's negative terminal, then that will be roughly 0-9V out. Although...opamps do not reach the supply lines, so pick one like the LM358, its output can be 0v (ish) but it can only go within a few volts of VCC, about VCC-2. That will get you 0-5V output (use a voltage divider).

Failing that, just use a 555 timer and a transistor for a constant current source

Blueteeth

Update. check this schematic out. Its a PWM fan controller, which uses a triangle wave generator and a comparator (the last opamp).

http://www.cpemma.co.uk/graphics/erg_pwm_sch.gif

That uses a single supply (12V) but 4 opamps. Note R4 and R5 forming a voltage divider of 1/2. That is used as the 'virtual ground' for the opamps. The last opamp is just used as a comparator so you can ignore it for your purposes. The 3rd opamp just amplifies the triangle wave. But the first two opamps provide the traiangle wave.

Try it in your simulator thing.

 

[Roff]

When you have an integrator driven by a square wave generator like that, it must be in a feedback loop with the square wave generator, or the integrator will eventually run off and saturate the op amp at one of the supply rails, due to square wave duty cycle asymmetry and/or unsymmetrical voltage levels.
Look here to see how this is done. This is similar to the circuit Blueteeth posted. There are variations of this all over the Internet.

 

[eblc1388]

Good point, Roff.

The saturation will not be apparent if one uses a circuit simulator. Hence the beauty of a simulator, so comforting to the circuit designer.

 

[mabauti]

Thank you Blueteeth & Roff , I'll try those