That formula works well! Continuing to permute the various feedback possibilities, this also works at "about" same frequency, 1KHz- the 10V zener only conducts on start-up: View in a fixed-width font such as Courier.
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
The trouble with supplying Ig(pk) from a capacitor is that Ig(avg), (0.3mA in the above circuit), has to be supplied by the 2.2k+3.3k resistive pot down.
I'm ok with the crude zener dropper atm. The frequency stability is not that important, and the 18.8V is not related to the 20V supply voltage.
For a PUT circuit where high Iv is req'd, and with better stability, perhaps the circuit below would be generally more useful.
Using a saturating emitter follower allows easy setting of the required maximum short circuit gate current, and has the benefit that the Vbe tends to cancel the offset voltage of the PUT, (Vp-Vs). So V1 is approximately equal to Vp.
Start the design by deciding on the Vp. Probably not greater than about 0.75xVs in order to avoid a dV/dT that is too slow at the trigger point. Then choose R4+C1 to get the required timing. Then make R3 to be less than R4/45 (for a 2N6027 running at up to 50C ambient temperature). Then calculate R1+R2 to get the required V1, but with the proviso that R1//R2 is less than 20x R3. Note that (if required) a frequency trimming pot can be placed at the junction of R1 and R2. Choose R5 for an emitter current of about 50-100uA at the lowest value of V1.
I think that squeezes the most out of a PUT... all we have to do now is to find somewhere to insert Jim T's mandatory flashing LED (probably best where the sun doesn't shine). :)
I read in sci.electronics.design that Tony Williams wrote (in ) about 'PUJT valley current?', on Thu, 24 Feb 2005:
Facing outwards, it could be the next fashion craze. May appear at the Oscar ceremony, even. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.