Mosaic
Well-Known Member
Hi All:
I've been simulating the SMPS improvement (mc33063a LTspice model) as documented here:
https://www.onsemi.com/pub_link/Collateral/AND8284-D.PDF
for the NCP3063 (about $0.45 ea) 40Vmax, buck/boost regulator.
Here are the data comparisons for a buck I am making:
Cout = 100µF , 0.2Ω ESR. L = 1mH, 1.7 Ω DCR. Vin = 36V, Vreg = 12.65V. 100Khz clock.
Case 1: Light Load
400 Ohm load @ 12.65Vout (32mA): Stock design (no feed forward) => 103 mVpp ripple at an audible 4Khz .
133K Feed forward resistor => 31mVpp ripple @ 24Khz (not human audible).
Case2: My max Load
40 Ohm @ 12.65V (320mA): Stock design (no feed forward) =>62 mVpp ripple at 25Khz.
133K Feedforward => 47 mVpp @ 48Khz.
The addition of a single resistor appears to resolve the long 'off' periods and resultant ripple and audible whining. I chose a 133k as the closest BOM item to 120K which seemed to give the best results. Too low a value loads down the V.out regulation.
This can be optimized further with the use of a zener & 10K series arrangement for the feed forward where the zener is about 0.6V under the target Vout. 12V in this case.
I've been simulating the SMPS improvement (mc33063a LTspice model) as documented here:
https://www.onsemi.com/pub_link/Collateral/AND8284-D.PDF
for the NCP3063 (about $0.45 ea) 40Vmax, buck/boost regulator.
Here are the data comparisons for a buck I am making:
Cout = 100µF , 0.2Ω ESR. L = 1mH, 1.7 Ω DCR. Vin = 36V, Vreg = 12.65V. 100Khz clock.
Case 1: Light Load
400 Ohm load @ 12.65Vout (32mA): Stock design (no feed forward) => 103 mVpp ripple at an audible 4Khz .
133K Feed forward resistor => 31mVpp ripple @ 24Khz (not human audible).
Case2: My max Load
40 Ohm @ 12.65V (320mA): Stock design (no feed forward) =>62 mVpp ripple at 25Khz.
133K Feedforward => 47 mVpp @ 48Khz.
The addition of a single resistor appears to resolve the long 'off' periods and resultant ripple and audible whining. I chose a 133k as the closest BOM item to 120K which seemed to give the best results. Too low a value loads down the V.out regulation.
This can be optimized further with the use of a zener & 10K series arrangement for the feed forward where the zener is about 0.6V under the target Vout. 12V in this case.