keefaz
Well-known member
barthman.de said:
Ok, I have wrongly read 22R on schematic!
35 - 13.2 = 21.8V drop through a 2.2k resistor seems more normal
Symmetrical PSU with different voltages and loads
- Thread starter barthman.de
- Start date
Help Support GroupDIY Audio Forum:
Ok, I have wrongly read 22R on schematic!
35 - 13.2 = 21.8V drop through a 2.2k resistor seems more normal
> R5 is 2.2 which means 2k2 in my opinion
> about 600 mA load
Do math.
600mA = 0.6A.
2.2K = 2200 Ohms
0.6A * 2200 Ohms = 1,320 Volts *dropped* in this resistor.
Which is obviously impossible with a 24V general level.
> about 60mA- 3 LED's switched on):
input lm 317: 4,5V
0.060 Amps in 2200 Ohms is 132V *dropped*. Again impossible.
Do you KNOW there's 60mA flowing? Or are you just assuming 20mA times three?
35V at first cap through 2200 Ohms can flow at-most 16mA. Yes, 16mA split across three LEDs will "light", but not as bright as should be.
Now take the 2.2 literally: 2 Ohms (about). 0.6 Amps in 2 Ohms is 1.2 Volts dropped. 1.2V lost from 3.5V is "small". So small we wonder "why have the resistor?" In this case it doesn't even protect the regulator. It (R5 C2) "might" reduce ripple into the regulator... but 2.2 Ohms 220uFd is 330Hz which is FAR above the 100Hz main ripple and hardly dents the 300Hz harmonic. Anyway a good regulator can take the raw voltage directly and get the ripple way-way down. I think R5 C2 are pointless.
Change R5 to a dead short. It WILL work. Probably very well. Remove C2 at your leisure and use it elsewhere.
> about 600 mA load
Do math.
600mA = 0.6A.
2.2K = 2200 Ohms
0.6A * 2200 Ohms = 1,320 Volts *dropped* in this resistor.
Which is obviously impossible with a 24V general level.
> about 60mA- 3 LED's switched on):
input lm 317: 4,5V
0.060 Amps in 2200 Ohms is 132V *dropped*. Again impossible.
Do you KNOW there's 60mA flowing? Or are you just assuming 20mA times three?
35V at first cap through 2200 Ohms can flow at-most 16mA. Yes, 16mA split across three LEDs will "light", but not as bright as should be.
Now take the 2.2 literally: 2 Ohms (about). 0.6 Amps in 2 Ohms is 1.2 Volts dropped. 1.2V lost from 3.5V is "small". So small we wonder "why have the resistor?" In this case it doesn't even protect the regulator. It (R5 C2) "might" reduce ripple into the regulator... but 2.2 Ohms 220uFd is 330Hz which is FAR above the 100Hz main ripple and hardly dents the 300Hz harmonic. Anyway a good regulator can take the raw voltage directly and get the ripple way-way down. I think R5 C2 are pointless.
Change R5 to a dead short. It WILL work. Probably very well. Remove C2 at your leisure and use it elsewhere.
barthman.de
Well-known member
@PRR and audio mixer:
This was very helpful! I took R5, C2, C7, D4 out and now it works. I thought too, that R5/C2 is to reduce ripple. But for LED's/relays a little hum is not so important. BTW my FLUKE shows no AC voltage/ frequency on output without R5/C2. Now with R7 nearly at 2k2 I get out 12,5V and all LED's are very bright. The regulator runs hot now too. I will mount it to the housing of my rack. I think I will not connect the 0V output of the 12V rail to ground. Only the 0V of the -20V rail for the preamps I will connect to ground. And I will use for both rails two separate transformer outputs.
Thanks a lot for helping me!
This was very helpful! I took R5, C2, C7, D4 out and now it works. I thought too, that R5/C2 is to reduce ripple. But for LED's/relays a little hum is not so important. BTW my FLUKE shows no AC voltage/ frequency on output without R5/C2. Now with R7 nearly at 2k2 I get out 12,5V and all LED's are very bright. The regulator runs hot now too. I will mount it to the housing of my rack. I think I will not connect the 0V output of the 12V rail to ground. Only the 0V of the -20V rail for the preamps I will connect to ground. And I will use for both rails two separate transformer outputs.
Thanks a lot for helping me!
audiomixer
Well-known member
Hi Sebastian,
glad we all could help.
you can adjust the brightness of the leds by changing their current limiting resistors. but thats not on the power supply, that would be on your device / project. leds brightness is governed by the current that flows, the led had a (sort off) fixed voltage across (depending mostly on led type...) you might adjust the current anywhere from 1mA to 20mA per led... usually 20mA is very bright. the regulator needs to be isolated when mounting, or you will release the magic smoke somewhere...
- Michael
glad we all could help.
you can adjust the brightness of the leds by changing their current limiting resistors. but thats not on the power supply, that would be on your device / project. leds brightness is governed by the current that flows, the led had a (sort off) fixed voltage across (depending mostly on led type...) you might adjust the current anywhere from 1mA to 20mA per led... usually 20mA is very bright. the regulator needs to be isolated when mounting, or you will release the magic smoke somewhere...
- Michael
barthman.de
Well-known member
Yes I think I will change the value of the resistors for the orange LEDs to limit the current to 10mA because they are very bright. The red ones are low current typs which needs only 2mA. Thats why they are darker. I know that the lm317 needs to isolate from housing.
barthman.de
Well-known member
To close the threat:
All works fine 8)
More detailed pictures of the mv810's you can find on my blog:
http://www.barthman.de/mv810.html
All works fine 8)
More detailed pictures of the mv810's you can find on my blog:
http://www.barthman.de/mv810.html
