Triangle wave generation for PWM

[larryg]

Is there an easy way to generate a triangle wave for use as a PWM clock using only an oscillator and a few components? I currently am using a astable vibrator circuit (with an opamp) and would like to improve the frequency accuracy.

Thanks

 

[nbucska]

1.) XTAL osc-- Single shot -- Constant current
charging C & open coll. or FET discharges it.

2.) Phase lock present circuit to xtal.

More ? Send specs. nbucska@pcperipherals.com

 

[glorgl]

it's gonna be a bit complicate to describe,so bare with me:

have two inverters in series, with a resistor from the end to beginning ; from the end, through another resistor, in a third inverter wich has a capacitor in parallel; a third resistor should be placed from one end to another of the hole scheme. You can collect the triangle wave from the end of the third inverter .
If I told you something you already knew, sorry, but that's the first thing(and easier, I say) that came in my mind.
If you think it's too complicated, what can I say, try finding some of them specialized IC's(I'm sorry, I'm don't have an appropiate catalogue).

PS: please excuse my bad english or my(eventually) poor thinking documentation. Hope to be a help...

glorgl

 

[jbartos]

What about just integrating ac rectangular wave from an rectangular wave oscillator?
va(t)=Integral from nT to (n+1)T/2 of A ~ At
vb(t)=Ingegral from (n+1)T/2 to (n+1)T of (-A) ~ -At
with appropriate integration time shift adjustments for n=0, 1, 2, ...

 

[Sunesis]

Or take the wafeform from a 555 time Cap. Just run it strait into a opamp with a high imput impedence (live a j-fet opamp). and youll get your charging ramp from the cap. this can be used for PWM.

 

[Jonas]

You can use the 555's 'Discharge' FET to produce a 'switching current' triangular wave. Charge a cap on any fixed reference voltage with a current 2*Io while discharging it with Io (-> charging with Io). The 555's switch add's another 2*Io to the discharge path (-> discharging with Io). Build the current source either with pairs of matched, fixed biased transistors (maybe use a cascode to improve output impedance) or with two opamps that control the current through an N- and P- type transistor(virtually any will do) over the voltage drop over matched resistors. Feed the triangle wave back to 555's comparator inputs...et voila. It produces a quite linear output. Frequency and duty cycle can easyli be adjusted. Need a schematic?