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| Canis Dirus Leidy:
--- Quote from: rebelrider.mike on October 16, 2018, 11:30:50 pm ---I don't want to reverse engineer this unit, but just reference it and learn to recognise the components. Another thing that will help pick the topology is that I want to go from AC to DC. Seems there are still a lot to choose from, and I don't really know the difference. --- End quote --- As a rule of thumb: SMPS overview, comparsion and selection guide. P.S. There is another way: transformer with switched (manually with rotary switch in most simple case, more advanced designs use relays or triacs with some voltage detection circuits) secondary wingdings. Pro: It's the same good old 50Hz transformer with linear regulator circuit. Contra: It's the same bulky and heavy 50Hz transformer. Plus, most likely, you will need to do it yourself or pay for manufacturing single non-standard transformer. |
| bloguetronica:
Hi, Since you wish to learn, have you tried to build your own linear regulator circuit? You can do it with a few parts: an op-amp, a pass transistor (I suggest a NPN Darlington), a few resistors and capacitors, a Zener to serve as voltage reference and a pot to serve as your variable voltage divider. You can even add a simple short circuit protection with another transistor and two more resistors. I think this would be an interesting project for you to build, before you move on to SMPS topologies. You can apply some principles of linear regulation there too. Kind regards, Samuel Lourenço |
| rebelrider.mike:
Well, I've been reading and researching, and I haven't made a lot of progress. I have learned a little though. Here's a rudimentary diagram of what I think the circuit will have: I've read that the control chip runs off the rectified input Voltage, except that is being switched off and on rapidly by the control chip. So there are capacitors that keep enough Voltage so the chip will function. The chip runs on way less Voltage than the input from the wall though, so a Voltage divider is employed. Hot diggity, I actually know what that is! I've also read that this type of topology is called flyback as every time the input is switched off, the collapsing magnetic field from the transformer creates a negative Voltage. Though the current induced remains a forward current, and has to go somewhere. Somehow, they got the word flyback out of all that. Anyway, it seems there is a clamp needed to prevent bad things from happening if the induced forward current has nowhere to go. This is accomplished with diodes, resistors and capacitors that I haven't added to the above diagram yet. I've also heard this part called a snubber. Though these may be two different things. I still haven't been able to find a control chip that I can use in this setup. I must be searching wrong, but I don't know how. Surely such chips should be common. There are millions of these things charging cell phones, right? I was able to read the label on the chip from that circuit board I have. It reads: AP8012H. I found the datasheet on it, and it features an internal switch. Makes sense, as there's no switch on the circuit board that I have. So at worst, I can get these for 0.90$ each from AliExpress. Maybe I should reverse-engineer that circuit board after all... |
| prasimix:
--- Quote from: rebelrider.mike on November 15, 2018, 02:43:10 pm ---I still haven't been able to find a control chip that I can use in this setup. --- End quote --- Choose any of your preferred IC vendors and simply search for flyback controller or AC/DC converters. In case of TI you can find it here. On ST site you can search here. In general there is two category: with integrated and without integrated power switch (i.e. MOSFET or BJT). Very straightforward solutions comes from PI (Power Integrations). They are offering TinySwitch series (III and 4), etc. |
| technix:
--- Quote from: rebelrider.mike on November 15, 2018, 02:43:10 pm ---Well, I've been reading and researching, and I haven't made a lot of progress. I have learned a little though. Here's a rudimentary diagram of what I think the circuit will have: I've read that the control chip runs off the rectified input Voltage, except that is being switched off and on rapidly by the control chip. So there are capacitors that keep enough Voltage so the chip will function. The chip runs on way less Voltage than the input from the wall though, so a Voltage divider is employed. Hot diggity, I actually know what that is! I've also read that this type of topology is called flyback as every time the input is switched off, the collapsing magnetic field from the transformer creates a negative Voltage. Though the current induced remains a forward current, and has to go somewhere. Somehow, they got the word flyback out of all that. Anyway, it seems there is a clamp needed to prevent bad things from happening if the induced forward current has nowhere to go. This is accomplished with diodes, resistors and capacitors that I haven't added to the above diagram yet. I've also heard this part called a snubber. Though these may be two different things. I still haven't been able to find a control chip that I can use in this setup. I must be searching wrong, but I don't know how. Surely such chips should be common. There are millions of these things charging cell phones, right? I was able to read the label on the chip from that circuit board I have. It reads: AP8012H. I found the datasheet on it, and it features an internal switch. Makes sense, as there's no switch on the circuit board that I have. So at worst, I can get these for 0.90$ each from AliExpress. Maybe I should reverse-engineer that circuit board after all... --- End quote --- I have a few samples of ST VIPer22A. That chip has almost everything on the primary side integrated up to and including the power transistor. You just need to supply the transformer, optocoupler, rectifier and some passives for it to work. |
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