Hello there,
So this is something that I would like to build in a few weeks, It is essentially a variable power supply that will go from +/ 15v to +/ 25v, and one 0v connection, while being capable of supplying up to 1.5A if need be.
So this power supply provides two 30v rectified smoothed inputs into the regulators on the positive and negative sides, I have used a positive voltage regulator on the negative side which regulates the negative voltage. Have a look at the SPICE model included.
Anyway, my problem seems to be when I change the test loads connected across the outputs. If I choose I low resistance then the current being drawn will be large, thats fine, however the ripple increases by quite a bit. For example in the SPICE model, if the regulator supplies +/25v and there is 1.25A drawn to the 20 ohm load. The ripple is then equal to about 11.5v.
However if I do the calculations using I = (C*dv ) / dt , where dv is the ripple voltage and dt = 1/100Hz, and C = 4700uF.
Then the ripple is 1.25*0.01 / 4700uF = 2.65v , nowhere near as large as 11.5v !
These calculations seem to work when the current being drawn is low. Even If I choose an even larger capacitor and run the simulation for a longer time, the ripple is still large, if not slightly larger.
So how can I reduce this ripple when drawing a larger current ? it also seems to happen when I adjust the output to be 15v and use a small resistance, say 15 ohms, the voltage waveform looks quite odd with quite a bit of ripple.
See my SPICE model, To adjust the regulator output voltage change Rvariable for both regulators (1900 for 25v and 1 for 15v, and change the smoothing capacitor to a larger value to see what im talking about.
Any help would be greatly appreciated
thanks.
So this is something that I would like to build in a few weeks, It is essentially a variable power supply that will go from +/ 15v to +/ 25v, and one 0v connection, while being capable of supplying up to 1.5A if need be.
So this power supply provides two 30v rectified smoothed inputs into the regulators on the positive and negative sides, I have used a positive voltage regulator on the negative side which regulates the negative voltage. Have a look at the SPICE model included.
Anyway, my problem seems to be when I change the test loads connected across the outputs. If I choose I low resistance then the current being drawn will be large, thats fine, however the ripple increases by quite a bit. For example in the SPICE model, if the regulator supplies +/25v and there is 1.25A drawn to the 20 ohm load. The ripple is then equal to about 11.5v.
However if I do the calculations using I = (C*dv ) / dt , where dv is the ripple voltage and dt = 1/100Hz, and C = 4700uF.
Then the ripple is 1.25*0.01 / 4700uF = 2.65v , nowhere near as large as 11.5v !
These calculations seem to work when the current being drawn is low. Even If I choose an even larger capacitor and run the simulation for a longer time, the ripple is still large, if not slightly larger.
So how can I reduce this ripple when drawing a larger current ? it also seems to happen when I adjust the output to be 15v and use a small resistance, say 15 ohms, the voltage waveform looks quite odd with quite a bit of ripple.
See my SPICE model, To adjust the regulator output voltage change Rvariable for both regulators (1900 for 25v and 1 for 15v, and change the smoothing capacitor to a larger value to see what im talking about.
Any help would be greatly appreciated
thanks.
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