but you're using a linear regulator. With a linear regulator you can't get more current out than you put in. If you want the output current to be higher than the input current, you need to use a switch mode regulator....a circuit to convert ~48V DC @ 350mA to 5V DC @ 700mA...
I'm not sure what you meant here. The power supply should deliver a constant voltage to the load, but it's up to the load how much current it wants to draw.Do I need to add anything to make sure the current doesn't drop below 700mA?
What is the purpose of the two bridge rectifiers?
Another idea was to use a voltage divider, but everything I read said it's a bad idea to use that configuration in a power supply.
One thing I'm still not clear on is how the current is increased. Is that a function of the inductor?
That topology looks like a flyback, but what is the reasoning for the rectifier? I reconfigured it to this ['URL'] and the output seems very similar.
One thing I read yesterday is this pdf. On page 15 it says you can add an output to a buck through a transformer, but I only need one output so I was wondering how to hook it up without the buck output capacitor.
It seems to me that the transformer becomes the load and it is driven directly from the regulator, but when I configure that topology through the java circuit simulator, I get only a very small output on the load resistor.
I was previously looking at the TL2575HV-05 voltage regulator, so I made a new circuit diagram to show how I thought it could work with the coil before the regulator (as my flyback circuit simulation above), but I'm not sure if its possible for the regulator to operate this way.
Finally, the TL2575HV-05 switching frequency is 52kHz, but the simulator doesn't allow anything over 25. When I set the frequency to 25kHz I was unable to find a combination of parameters for the transformer that would produce a reasonable output.
It seems to me then, that the transformer choice has a huge impact on the output. How can i find out how to choose the right transformer?
I decided on the SG3524N which seems a bit old, but it's really cheap.
The first major question is: Can I power the controller from the bias winding of the transformer - does it present a chicken-and-the-egg problem?
The first part, according to the data sheet, is calculating the oscillator frequency controlled by the RT and CT pins. The equation the data sheet gave yielded .052kohms for RT, but that was below the minimum also listed in the data sheet. Using the equation for minimum and maximum recommended values, it appears they are off by two decimal places which means I think I really need 5.2kohm for RT while using the maximum value for CT to get 250kHz. I'm using a 5.1kohm resistor instead though for cost reasons. Calculating it back out gives me 255kHz for my oscillator.
The second part was calculating the resistor values to compare to the 5V reference. Since my output will be 5V, I just used the same value all around. The data sheet said 5kohm, but I opted for a cheaper 5.1kohm. I thought about using 51kohm resistors because of this write-up, but they converge at 1A, so I don't expect it to make much difference.
From there I just mimicked the configurations from the data sheet, but I still had some leftover questions.
In the data sheet it says the two transistors are alternately turned on, but the flyback design has them connected in parallel. Wouldn't this cause the circuit to be perpetually on instead of switching?
I'm not really worried about low frequency noise. Do I really need to connect the COMP pin?
I'd like to use the SHUTDOWN pin as an under-voltage lockout, but it shuts down when there is voltage, and not when there isn't. Is there an easy way to replace my Z1, R2, R3, and Q1 with something that works with the SHUTDOWN pin?
Does this design look like it will work?
Edit: One last thing, I was thinking I could use some tweezers and dip some SMT capacitors in some already-melted solder then attach a wire to them, but I'm afraid that may be unrealistic. How likely am I to be successful with that idea?
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