Use 500R to be good for adding 2.5V-3.5V max depending on the JFET Idss. That 0-3V controllable addition should give you enough hand for making it easy. Do that for the 7.5V too. Little resistance, comparable noise to diodes. Easy to make.
For highers values, wich kind of zener, the same: 1N4148 0.65V?
+-15V = 7 Leds x 1.8V + 3 1N4148 x 0.65V + 0.6 standard = 15.15V
+-24V = 12 Leds x 1.8V + 3 1N4148 x 0.65V + 0.6 standard = 24.15V
Or I have to use other diode to match exact voltage needed, if yes please let me know wich type, or will be better if you let me know how can look for the needed diode or zener, thks.
In the schematic is C1 // Vref, so it's included or I have to add other more in // with the Vref?
Sorry for mine ignorance.
+-15V = 7 Leds x 1.8V + 3 1N4148 x 0.65V + 0.6 standard = 15.15V
+-24V = 12 Leds x 1.8V + 3 1N4148 x 0.65V + 0.6 standard = 24.15V
Or I have to use other diode to match exact voltage needed, if yes please let me know wich type, or will be better if you let me know how can look for the needed diode or zener, thks.
In the schematic is C1 // Vref, so it's included or I have to add other more in // with the Vref?
Sorry for mine ignorance.
Last edited:
Is it normal that the output voltage drops to 0.4V after 10-15 minutes of work? What happens with the others who made this power supply?
So, during start-up power the output voltage is + /-24.1V DC after 10-15 minutes the output voltage drops to + /-23.7V DC and does not change over the next 4 hours.
So, during start-up power the output voltage is + /-24.1V DC after 10-15 minutes the output voltage drops to + /-23.7V DC and does not change over the next 4 hours.
@merlin
For 15V: use 8 x LED. 8 x 1.8V = 14.4V + 0.65V(Vbe) = 15.05V
For 24V: use 13 x LED. 13 x 1.8V = 23.4V + 0.65V(Vbe) = 24.05V
For voltages 12V or lower is better to use LED's. For higher voltages LED's can be used, but it is not practical. Better to use Zener (less parts count but more noise as LED).
Use 1N4148 or resistors only to fine tune output voltage.
Example:
you want EXACTLY 8.5V output voltage.
Using 4 LED: 4 x 1.8V = 7.2V + 0.65V (Vbe) = 7.85V (too low)
Using 5 LED: 5 x 1.8V = 9V + 0.65V(Vbe) = 9.65V (too high)
Using 4 LED + 1N4148: 4 x 1.8V = 7.2V + 0.65V(1N4148) + 0.65V(Vbe) = 8.5V
Last edited:
Yes its normal it lapses after some thermal set. Its you use so many LEDS it will collectively be so as a value.
It is valid, if you touch them from cold and then, they could be rising more degrees? Also their tc can be stronger? And they are not alone. The JFET underneath lapses happily until final IDSS which is governed by a BJT's Vbe, and then is the universe and its zodiac sign.
Since it stops steady -0.4V after 15 mins, its tell tale some thermal set is taking place for it as a system.
tonight great jazz session with the Buffalo II to compare the Placid reg. vs Salas reg.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.