[sdiy] VCO tempco R locataion

[Stewart Pye]

My plan is to feed the 5V reference to the comparator via a resistor so
that sync pulses can also be injected. Do you think the timing
components around the comparator would require tweaking if  5V reference
was used on the comparator input? Other than that it should only be the
reference current resistor that needs adjusting.
http://home.comcast.net/~ijfritz/sy_cir2.htm
The circuit on your website seemed to be a good base to work from as it
looked like more effort had been made for it to be precise than other
similar designs published on the web.


Regards,
Stewart.


Ian Fritz wrote:
> At 02:35 PM 7/30/2010, Stewart Pye wrote:
>> I'm planning on using OPA2134 op amps that have a max Vio of 2mV.
>>
>> I'm looking at your Sawtooth VCO design at the moment and planning on 
>> basing my circuit on that, but using REF02 for a 5V reference 
>> voltage, and possibly using the tempco resistor in the voltage 
>> divider to the base of the expo transistor.
>
> Hi Stewart --
>
> Sounds good -- that posted circuit is a bit long in the tooth now!
>
> I agree with using 5V references.  They don't even make the low drift 
> version of the 6.9V unit anymore.
>
> Nowadays I use an OPA 2227 for the expo summing amp and servo.  Better 
> specs, but I'm not sure I can really notice any difference from the 
> OPA2134. You might not want to go that route if you use the 
> voltage-divider method, though, because of the slew-rate limitation.
>
>   Ian
>