29-05-2011, 11:53 PM
Thank you Mark for your comments.
Yes, that is another area to which I will have to do a retrofit. And whilst I'm in that area, a voltage trim pot. for the -12v reg. is also required.
As regards the constant-current source, my thinking was along the lines of the current, I = (Vz - Vbe) / Re, where Re is the emitter resistor. By aiming at a Zener with a low temp-co., the idea was to minimise drift in the value of that current. But I now see your analysis: the constant current source, in effect, acts as a large resistance is series with the input voltage - hence the load on the source is largely isolated from Vin - and the ripple that goes with Vin.
The unit was specifically mechanically designed to make repairs and retrofits as easy as possible. Plus, since the 22v. reg. cct. appears twice, I can easily modify one cct. - replace the Zener with a LED - and compare one reg. O/P to the other. This, and the items mentioned above, I will get around to as soon as I can.
This all illustrates the value of submitting one's ideas to a peer group for review - something that the Internet now makes it very easy to do - especially when a Forum such as this is readily available. (Thank you, Jamie).
Al.
(29-05-2011, 01:12 PM)Mark Hennessy Wrote: I admit that I also didn't double-check with all the regulator ICs used, but certainly the LM340 recommends an external diode.
Yes, that is another area to which I will have to do a retrofit. And whilst I'm in that area, a voltage trim pot. for the -12v reg. is also required.
As regards the constant-current source, my thinking was along the lines of the current, I = (Vz - Vbe) / Re, where Re is the emitter resistor. By aiming at a Zener with a low temp-co., the idea was to minimise drift in the value of that current. But I now see your analysis: the constant current source, in effect, acts as a large resistance is series with the input voltage - hence the load on the source is largely isolated from Vin - and the ripple that goes with Vin.
The unit was specifically mechanically designed to make repairs and retrofits as easy as possible. Plus, since the 22v. reg. cct. appears twice, I can easily modify one cct. - replace the Zener with a LED - and compare one reg. O/P to the other. This, and the items mentioned above, I will get around to as soon as I can.
This all illustrates the value of submitting one's ideas to a peer group for review - something that the Internet now makes it very easy to do - especially when a Forum such as this is readily available. (Thank you, Jamie).
Al.
