Weird. It takes me to post 1893 page #190. NBC's Lost we became.
I was psychic to initially reference by page # only it seems.
Yes you can use 2V green LEDS. It will only pass more current for same Rset. You can find how much by measuring the voltage drop on Rset and divide by its value. In practice each Mosfet has a different Vgs which is a significant variable in that system. Don't worry, you will be in the ballpark if initially calculate roughly ICCS=2.2V/Rset
The first CCS 3 LEDS will run at IDSS of the JFET on their tail.
The Vref LEDS will run at about 70% IDSS of the JFET under them.
Select and measure your JFETS first and you will know.
The first CCS 3 LEDS will run at IDSS of the JFET on their tail.
The Vref LEDS will run at about 70% IDSS of the JFET under them.
Select and measure your JFETS first and you will know.
Thanks! Yesterday I got working 2 positive regs from Dac End2 psu board and they worked from the first. As you might know for Vref it uses 2 leds + pot to get the desired voltage. It works perfectly as I can change from 4.6V to 5.6V, and I set to sharp 5V.
I noticed an unwanted thing however: on power up and power down the voltage rises for a split of a second to the unregulated voltage ~14-15V. I doubt that it is supposed to be like this
I used Rset 27R, loaded the output with a 2K resistor (25mA consumption), 200nF MKP2 over Vref, Idss of first CCS SK170 ~6.5mA, Idss of the other SK170 ~7mA, BC550C, leds Vf are ~1.97V and an Oscon SP 180uF at the output.
What do you suggest?
Thanks!
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I'm trying to dig a little deeper into the design and have read all the posts onwards from the schematics of V1.2.
I have made a little comparison between the two positive designs Salas posted and marked the differences.
The left one is for +15V - the right one for +46V.
One basic difference is the choice of MOSFET. I looked up both datasheets, but don't really know why the IRF96xx/95xx is chosen over the IRFP9240.
The next thing is that I read so many good points about using LEDs as reference - why does the left design substitute the LED reference?
Is there a formula to calculate the value of the "output" C3 in relation to the output voltage? Is output voltage a parameter anyhow?
How are the different values for R6 (4,3k in the left one) and R10 (10k/1W) calculated?
Why is R7 added in the left schematic?
The "sensing circuitry" on the left and right differ in the values of the resistors, too. There is probably a well-thought out reason behind it, but I couldn't grasp it from what I have read so far. Could you elaborate on that?
If all that was already explained and I was unable to find it, I really apologize for taking your time, but I couldn't find it (at leats not reading from page 190 onwards).
Best reagdrs
THKL
I have made a little comparison between the two positive designs Salas posted and marked the differences.
The left one is for +15V - the right one for +46V.
One basic difference is the choice of MOSFET. I looked up both datasheets, but don't really know why the IRF96xx/95xx is chosen over the IRFP9240.
The next thing is that I read so many good points about using LEDs as reference - why does the left design substitute the LED reference?
Is there a formula to calculate the value of the "output" C3 in relation to the output voltage? Is output voltage a parameter anyhow?
How are the different values for R6 (4,3k in the left one) and R10 (10k/1W) calculated?
Why is R7 added in the left schematic?
The "sensing circuitry" on the left and right differ in the values of the resistors, too. There is probably a well-thought out reason behind it, but I couldn't grasp it from what I have read so far. Could you elaborate on that?
If all that was already explained and I was unable to find it, I really apologize for taking your time, but I couldn't find it (at leats not reading from page 190 onwards).
Best reagdrs
THKL
Attachments
1. Both reg examples can work with all those Mosfets. I wrote it was made TO-220 also to verify they can work too, and that the IRF9610 can make it a bit better CCS in bandwidth, although the cascode tail brings even IRFP9240 very near and has the TO-247 reliability and mounting sturdiness thing going for it. The 9540 is no better than 9240, just makes for TO-220 choice. IRF9610 must NOT be used for shunt Mosfet. Only IRF9540, IRFP9240 and the like for Ciss, gfs. Plus you got to find something TO-220 if going for a neg reg, and IRF610 I am not sure is that available, maybe IRF710 is.
2. The 15V reg has a JFET cascode, its top's -Vp opens the low one. The BJT cascode on the 46V needs an active reference to set current, thus the LED. The thing with the 46V is that 2n5459 is only 25V max, so I used 45V BJTs making it a few more components.
3. Its not a about a formula, its about loop gain margin as a whole. Substitute a 22uF-47uF medium ESR instead of the film cap and 1R Zobel, so to be covered for many loads, a bit slower but more generally compatible, its an option.
4. They are different because the voltages are different, so if I wanted a certain current through the emitter follower it's load got to go from 4k3 to 10k.
5. R7 is added because it gave a certain contribution to the loop margin and shape for this particular higher Vout range example.
6. What sensing circuitry? Maybe you mean the RC step feedback network? The one with the 33p? That's lead lag feedback compensation and the resistor is tuning it a bit different between those regs, the semiconductors have beta curves etc. that are not the same in all voltages.
2. The 15V reg has a JFET cascode, its top's -Vp opens the low one. The BJT cascode on the 46V needs an active reference to set current, thus the LED. The thing with the 46V is that 2n5459 is only 25V max, so I used 45V BJTs making it a few more components.
3. Its not a about a formula, its about loop gain margin as a whole. Substitute a 22uF-47uF medium ESR instead of the film cap and 1R Zobel, so to be covered for many loads, a bit slower but more generally compatible, its an option.
4. They are different because the voltages are different, so if I wanted a certain current through the emitter follower it's load got to go from 4k3 to 10k.
5. R7 is added because it gave a certain contribution to the loop margin and shape for this particular higher Vout range example.
6. What sensing circuitry? Maybe you mean the RC step feedback network? The one with the 33p? That's lead lag feedback compensation and the resistor is tuning it a bit different between those regs, the semiconductors have beta curves etc. that are not the same in all voltages.
P.S.
Use 7mA IDSS 2N5459s for cascoding 2SK170BL right, by the way. Also any NJFET that has Vp -1.5V upwards, and can give over 7mA IDSS. If it is 40V VDS max you can use the JFET cascode tail simpler example for higher Vin Vout too, up to 43V in. Its the 2N5459 that imposes the 28V in max. But most people would want a +/- 10-20V thing and 2N5459 is easy to get. Performance is the same between the NJFET and BJT cascode examples. I gave them for ease of choice, given easiest available parts and voltages needed.
Use 7mA IDSS 2N5459s for cascoding 2SK170BL right, by the way. Also any NJFET that has Vp -1.5V upwards, and can give over 7mA IDSS. If it is 40V VDS max you can use the JFET cascode tail simpler example for higher Vin Vout too, up to 43V in. Its the 2N5459 that imposes the 28V in max. But most people would want a +/- 10-20V thing and 2N5459 is easy to get. Performance is the same between the NJFET and BJT cascode examples. I gave them for ease of choice, given easiest available parts and voltages needed.
Thx a lot, Salas.
I'm not an electronics pro and it is sometimes hard for me to distinguish whether posts are referring to 1.2 or 1.0 builds.
Referencing your answers:
3.) I'm not a electronics pro, so I just ask right away:
Say I wanted to drive a 5V logic system consisting of a microcontroller, a CLPD and a clock-generator - could I somehow power that system with a 7805, measure something and then calculate the output c3?
What would I have to measure?
4.) Just speaking about the left circuit which Rs would have to be adjusted to make the wohle thing 5V? How are those calculated?
6.) Is it neccessary/beneficial to adjust those values when changing the voltage from 15V to 5V? If so, how would they be calculated or looked up in the datasheets?
Best regards
THKL
I'm not an electronics pro and it is sometimes hard for me to distinguish whether posts are referring to 1.2 or 1.0 builds.
Referencing your answers:
3.) I'm not a electronics pro, so I just ask right away:
Say I wanted to drive a 5V logic system consisting of a microcontroller, a CLPD and a clock-generator - could I somehow power that system with a 7805, measure something and then calculate the output c3?
What would I have to measure?
4.) Just speaking about the left circuit which Rs would have to be adjusted to make the wohle thing 5V? How are those calculated?
6.) Is it neccessary/beneficial to adjust those values when changing the voltage from 15V to 5V? If so, how would they be calculated or looked up in the datasheets?
Best regards
THKL
Some help needed
Yesterday I finished 2 positive regs from Dac End2 psu board (V1.1 I think) and they worked from the first. AC in is 12V, DC out is set to 5V with Vref: 2 leds + R adj.
I noticed an unwanted thing however: on power up and power down the voltage rises (sometimes) for a split of a second to 14-15V. I doubt that it is supposed to be like this.
I used Rset 27R, loaded the output with a 2K resistor (25mA consumption), 200nF MKP2 over Vref, Idss of first CCS SK170 ~6.5mA, Idss of the other SK170 ~7mA, BC550C, leds Vf are ~1.97V and an Oscon SP 180uF at the output.
Thanks!
Yesterday I finished 2 positive regs from Dac End2 psu board (V1.1 I think) and they worked from the first. AC in is 12V, DC out is set to 5V with Vref: 2 leds + R adj.
I noticed an unwanted thing however: on power up and power down the voltage rises (sometimes) for a split of a second to 14-15V. I doubt that it is supposed to be like this.
I used Rset 27R, loaded the output with a 2K resistor (25mA consumption), 200nF MKP2 over Vref, Idss of first CCS SK170 ~6.5mA, Idss of the other SK170 ~7mA, BC550C, leds Vf are ~1.97V and an Oscon SP 180uF at the output.
Thanks!
yes, funny thing. Output voltage can rise only if shunt element is not working and only CCS MOSFET is conducting. Maybe is there small delay before shunt MOSFET start conducting, just enough to let some voltage spike go through?
@vzs
As far as I understand, you are using 2 LED + trimmer as voltage reference?
Is this is your case, I will suspect trimmer for bad contact. Better to replace it with fixed value. Digital IC's and DAC chips will tolerate higher voltage as 5V, but 14V or 15V is way too much. Try to "clamp" output with Zener diode as safety measure.
@vzs
As far as I understand, you are using 2 LED + trimmer as voltage reference?
Is this is your case, I will suspect trimmer for bad contact. Better to replace it with fixed value. Digital IC's and DAC chips will tolerate higher voltage as 5V, but 14V or 15V is way too much. Try to "clamp" output with Zener diode as safety measure.
3. No, irrelevant. Just use a 22uF-47uF across output normal ESR lytic cap and forget C3+1R. More secure for you.
4. Leave it 4k3, R emitter that is. Also, its the current that runs through the 27k determining Vdrop+0.6V=Vout. The trimmer controls the current. Make that trimmer a 5k one because it may need to go set over 1k for 5Vout and 27k.
6. No, forget tweaking that, its crucial for compensation and works OK for 5V too.
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