Hello Team,
Can you have a look at the following customer inquiry? Please let me know if you need the schematic and I will send it to you offline.
Circuit is oscillating at audible frequency.
The circuit is connected to 6 times one channel with 3x 4700 µF each. These are decoupled by diodes in series.
Thus, 18 capacitors with 4700µF each (~84600 µF) are charged at the moment of switch-on.
The sound is audible at about 3.9 kHz.
With 2 ohms in series in the primary 24V supply, no sound is heard and the oscilloscope does not show large overshoots.
Measured with a current clamp channel 2 in the primary 24V supply.
Channel 1 is the switchpoint at V1/L1/D8
Please contact me for further questions or missing measurements.
About the circuit:
Terminal X28 +24V
Terminal X29 GND
1st try
R205 : RT 412 kOhm ~ 322 kHz
D8 : Si7465DP-T1-E3
V1 : V20PWM60C
Rsense 10 mOhm
R204 : Radj 1k6
L1 15 uH Würth 744373965150
R202 42k2
"Whistle" ~ 0.4 seconds
2nd attempt
R205 : RT 412 kOhm ~ 322 kHz
D8 : Si7465DP-T1-E3
V1 : V20PWM60C
Rsense 33 mOhm
R204 : 4k7
L1 15 uH Würth 744373965150
R202 42k2
no change to 1. try
"whistling" ~ 0.4 seconds
3rd try
R205 : RT 180 kOhm ~ 700kHz
D8 : Si7465DP-T1-E3
V1 : V20PWM60C
Rsense 33 mOhm
R204 : Radj 3k6
L1 15 uH Würth 744373965150
R202 : 24k
Deterioration "whistle" ~3 seconds
It has also been connected directly, without filter from L2 and L12 voltage, no change.
4th try / like 1st try
R205 : RT 412 kOhm ~ 322 kHz
D8 : Si7465DP-T1-E3
V1 : V20PWM60C
Rsense 10 mOhm
R204 : Radj 1k6
L1 15 uH Würth 744373965150
R202 42k2
In 24V line was connected primary 2 ohm resistor in series.
Here no whistling is to be heard and inrush current course would be in such a way in order.
What I have tried so far, increased the storage choke to 47µF, this has given a small improvement so that the regulator oscillates shorter on power up.
Increasing the sense resistor to 33mOhms and adjusting Radj has not resulted in any improvement.
When the Ripple Reduction circuit (R202/C1/C6) is removed, no audible oscillation is measurable at power up, but the output voltage oscillates strongly.
Switch pint and current input prim, turn on
Switch point after 1s
Current input prim 24v, turn on
Current input prim, f=3.9kHz
With 2 Ohm in series of the input line, 24V
Best regards,
Franz
