triangle wave

[trihieu]

Hey Hdoggz,

Can you tell me the values of the resistors?
Thank you very much.

[trihieu]

Hey sovadk,

In the circuit that you have, the other end of C26 connected to ground? Or is it something else?
Thanks

[sovadk]

C26 is a part of a high pass filter, used to shift the DC level of the triangle wave, before feeding the pwm comperators. It plays no role in the triangle generator.

[sovadk]

I've done some simulations on my schematic. I've added a outbuffer to improved linearty and output impedance.

This is the result:




I've alos attached the orcad/pspice files for those of you who want to play arround with it.

[hdoggz]

trihieu,

The two equations in my previous post determine the value of the resistors and caps based on the frequency and amplitude ofthe triangle wave you want. I think once you solve them, you have more unknowns than equations which is a good thing cuz that means you can start off by choosing the value of one of the resistors. I'd start with something like 10k for 'R' to keep the current low. also, you may want to simulate thewhole thing in P-Spice before actually building it to doublecheck everything. again, use really highspeed components

[trihieu]

Thank you so much guys.

[trihieu]

sovadk,

What components are E4 and U1? I'm trying to buy those 2 components to build the circuit, but dont know what those are. Could you please help me out?
Thanks

[sovadk]

E4 together with R9 and C3 is just working as a comperator. I've placed a picture earlier in this thread, showing the actual configuration. You can brobably use LM119, LM219, LM319 or some other cheap comperator. Be aware that those comperators need a pullup resistor to work, since they have a open drain configuration. I don't know why so many conperators are made with a open-drain configuration. It really limits their rise time, and increese the current if you go for a small pullup resistor.

U1 and V3 are used to trigger oscillation in pspice and are not needed IRL. Pspice starts a simulation by calculating DC bias points. If the circuit isn't triggered by something, I'll stay in that initial state forever.

If you are going to buy some resistors for this circuit, you won't have to go for the exact values. I believe that I've chosen values from the E24 range.

The ratio between R7 and R8 controls the hysteresis voltage on the comperator. In other words the amplitude of the triangle wave.

Q1 and Q2 are current generators. The resistors arround these transistors contorls the current, which controls the slope of the triangle wave.

C1 is charged by alternately by Q1 and Q2, where dU/dt=I/C. Thereby C1 also contorls the slope of the triangle wave.

The frequency of the triangle wave is a function of the slope and the hysteresis voltage.

Q5 together with R13 is just a simple voltage follower. The triangle wave is only linear if there are no resistive loads to C1, which will give the slope an exponential character.

V2 can be made with a simple decoupled resistive voltage divider.

I believe that Orcad has a free limited version of capture and pspice, if you would like to simulate the circuit that I've attached.
That should be about all there is to say for now.

Good luck with it.

Kaspar Sinding Meyer