Greetings,
I'm in the process of researching (a design for) a transformer that must fit insize a cylindrical volume measuring 1" diam by 1.75" long. I thought I would pass it by this forum because so many of you have experience far beyond me; I thought you might come up with some clever ideas I haven't thought of.
The supply must convert 120VAC mains to 40VDC, and carry 700mA (minimum) ~ 1A (maximum).
I am exploring three avenues:
1. Transformerless - Though the 15uF cap is large, measuring .9" x 1.84", it is well within the limits of the container. I can make this work, but I don't know that I need such a large capacitor, since:
700mA @ 120V (I = 2 x pi x C x f x Vrms)
is not the same as 700mA @ 40V. Or is it? I don't know, since I'm getting the voltage across a shunt zener diode. I figured since I'm only using 40V, the power is less for the same current. My gut tells me it's not the power, but the current I should worry about, in which case, the cap value is correct. Comments, please.
Please do not bug me about the implications of transformerless supplies unless it pertains to the question. The design will be well protected against electrocution. Thank you.
2. Linear supply - I figured I might be able to get a cylindrical ferrite rod and fabricate a step-down transformer. Size is the big question. If someone has done this before, I'd be interested to hear their opinion.
3. Switching supply. I'm not at all versed in SMPS theory, but I can imagine that I may be able to reduce the size significantly since I don't have to compenstate so much for variables of input and output that are normally considered in commercial supplies. My input voltage is fixed, and my load is fixed. Again, comments on this matter are appreciated.
4. Some other idea that I haven't thought of, but you have. Please tell!
One more note on the transformerless design. I've been simulating multiple loads in series (e.g. If each load normally drops 10V, then I put four of them in series, each with with their own parallel 10V zener), but the simulation is wonky.
Can you think of any reason why four 10V zeners (in parallel with their loads), in series aren't the same as one 40V zener with four loads in series?
Torin...
I'm in the process of researching (a design for) a transformer that must fit insize a cylindrical volume measuring 1" diam by 1.75" long. I thought I would pass it by this forum because so many of you have experience far beyond me; I thought you might come up with some clever ideas I haven't thought of.
The supply must convert 120VAC mains to 40VDC, and carry 700mA (minimum) ~ 1A (maximum).
I am exploring three avenues:
1. Transformerless - Though the 15uF cap is large, measuring .9" x 1.84", it is well within the limits of the container. I can make this work, but I don't know that I need such a large capacitor, since:
700mA @ 120V (I = 2 x pi x C x f x Vrms)
is not the same as 700mA @ 40V. Or is it? I don't know, since I'm getting the voltage across a shunt zener diode. I figured since I'm only using 40V, the power is less for the same current. My gut tells me it's not the power, but the current I should worry about, in which case, the cap value is correct. Comments, please.
Please do not bug me about the implications of transformerless supplies unless it pertains to the question. The design will be well protected against electrocution. Thank you.
2. Linear supply - I figured I might be able to get a cylindrical ferrite rod and fabricate a step-down transformer. Size is the big question. If someone has done this before, I'd be interested to hear their opinion.
3. Switching supply. I'm not at all versed in SMPS theory, but I can imagine that I may be able to reduce the size significantly since I don't have to compenstate so much for variables of input and output that are normally considered in commercial supplies. My input voltage is fixed, and my load is fixed. Again, comments on this matter are appreciated.
4. Some other idea that I haven't thought of, but you have. Please tell!
One more note on the transformerless design. I've been simulating multiple loads in series (e.g. If each load normally drops 10V, then I put four of them in series, each with with their own parallel 10V zener), but the simulation is wonky.
Can you think of any reason why four 10V zeners (in parallel with their loads), in series aren't the same as one 40V zener with four loads in series?
Torin...