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  1. V

    Is a transistor a switch or an amplifier

    Transistor can be used as a current control switch, when you apply current (IB) to pin B, then it will allow hfe * IB to flow from C to E. In the circuit, the 1k resistor is used to control the IB (10V-0.6V)/1K Normally I will refer to datasheet for the hfe value (normally it's very wide)...
  2. V

    Surge Protection

    er... maybe the place that stored the pictures are not for all the public, anyway, I put them as attachments now
  3. V

    Surge Protection

    hi berkeman, thanks for your reply. I also considered will that be too high ripple current for the input capacitor, but I checked the input capacitor's ripple current rating is 0.9A @ 100kHz, 85degC, where my converter's output current is 1.2A. I think it should be fine... And 1 more point is...
  4. V

    Surge Protection

    Hi vk6kro, thank you very much for your reply. I mean a normal buck converter that same as your link, but I have a capacitor at input side and I have a feedback loop that done by the switching IC. Also I have more components between the input voltage and the buck converter for other purpose...
  5. V

    Surge Protection

    I had a circuit of buck convertor that converting 24V dc to 4V dc. 24V dc input is from a PSU (Meanwell's PLN series), once it go in, it connects to a Polyfuse, then polarity diode (in series), then Common mode choke, then it's my converter's input capacitor (35V 47uF AVX's TAJ series)...
  6. V

    Varnish or Potting, Which one is Better to Avoid Humming Noise from Inductor

    Thanks all your replys, it's informative for me and let me learned something more. I think I got my answer. The potting inductor that I posted is not really potted as I think (at least for the 1 that I disassembled), I disassembled 1 and found that's only EPOXY at the top gap of the...
  7. V

    Varnish or Potting, Which one is Better to Avoid Humming Noise from Inductor

    Someone just tell me that, "varnishing an inductor can reduce humming noise much better than encupsulating it", and this is what his friend told him where his friend worked in power supply field for over 10years. (But I don't know did his "encupsulating" means potting) Or did he mean varnish...
  8. V

    Tant. Cap VS E. Cap

    As I know, tant cap and e. cap are also the selection for high capacitance value under high voltage rating's condition. But due to the principle of e. cap, it requires some liquid inisde itself to provide capacitance. So if the circuit's ambient temperature is high, that may vaporize the...
  9. V

    Audible noise from SMPS

    Today, I tried to add another output capacitor on my buck converter, so the output capacitance changed from 200uF to 2400uF, and the humming seems gone. Maybe 200uF is not enough to handle the fast switching from 1.5A to 0.05A... Of course, I can't use 2200uF capacitor on it, but I think...
  10. V

    Audible noise from SMPS

    dlgoff, Thank you for your advice. I'm sorry that I didn't stay it clearly. What I mean is: 1. The buck converter's switching frequency is 150kHz. 2. The output's loading is driving by another switch and the switch is controlled by another PWM signal which is about 250Hz. That means the...
  11. V

    Audible noise from SMPS

    um... because it makes me feel unreliable on the circuit And I saw other similar circuit won't have this kind of humming and more information: I'm using 150kHz switching freq. and tried to change it to 250kHz, but the humming is still here.
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    Audible noise from SMPS

    Hello, I'm a newbie for this forum, and I don't have much practical experience on SMPS too. I found this forum when I'm searching for my solution from internet. My Circuit: I'm using a simple buck converter: Vin: 24V Vout:3.3V Iout: 1.5A (dynamic load) The loading is running in PWM...
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