Author Topic: What is RSC  (Read 1913 times)

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Offline queennikki1972Topic starter

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What is RSC
« on: October 09, 2019, 12:23:21 pm »
What is RSC ? I know its probably obvious but Im still new. Also at the bottom it says -10v Can someone explain a little further?
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: What is RSC
« Reply #1 on: October 09, 2019, 12:28:32 pm »
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline queennikki1972Topic starter

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Re: What is RSC
« Reply #2 on: October 09, 2019, 12:30:49 pm »
But how do I calculate the sense resistor needed for the 0-30vdc supply in the diagram.
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline soldar

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Re: What is RSC
« Reply #3 on: October 09, 2019, 12:50:46 pm »
But how do I calculate the sense resistor needed for the 0-30vdc supply in the diagram.

That resistor limits current. Nothing to do with voltage which is handled by the second LM317.

Look at fig. 23.
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Offline queennikki1972Topic starter

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Re: What is RSC
« Reply #4 on: October 09, 2019, 02:03:12 pm »
Ugh still lost.. :(
Siglent SDS 1202X-E - Heathkit IO-4105 - Dr. Meter 0-30v 5a power supply - 862d+ combo unit - Weller WLC100 - Kunkin KL283 DC load. Not much gear yet.
 

Offline RoGeorge

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Re: What is RSC
« Reply #5 on: October 09, 2019, 02:58:43 pm »
In the datasheet http://www.ti.com/lit/ds/symlink/lm317.pdf , figure 8.3.3 says how to calculate Rsc

Imax = 1.2/Rsc, so Rsc = 1.2/Imax.  In your schematic Imax is 1.5A, so Rsc = 1.2V/1.5A = 0.8 ohms.  The dissipated power for a 0.8 ohm resistor at 1.5A is P = I*I*R = 1.5A*1.5A*0.8ohm = 1.8W

In conclusion Rsc is 0.8 \$\Omega\$ / 2W.  A 2W resistor at least, 3W or more will be even better.

Later edit:
About the -10V, it's a negative voltage.  To power that schematic, 2 voltages will be needed.  One is +32...40V, the main power voltage.  The other voltage is -10V, for the Q1 and Q2 biasing circuits.  Q1 and Q2 are constant current generators, in order to get a constant current on each of their diodes pairs (D1, D2 and D3, D4 respectively) and thus a constant 1.2V on each pair of the series diodes.

Both +32...40V and -10V are with respect to the GND (measured relative to the GrouND).

The positive voltage will need to be able to provide at least 1.5A, while for the negative voltage there is not much need for a lot of current, a 0.1A maximum for the -10V will be more than enough.
« Last Edit: October 09, 2019, 03:24:52 pm by RoGeorge »
 
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