Products > Test Equipment
Inside the new Korad KA3305P linear PSU
torch:
--- Quote from: mos6502 on September 20, 2015, 06:53:38 pm ---Another trick is to use a very small filter cap and higher transformer output voltage and rely on the pass element to dissipate the extra heat.
--- End quote ---
The filter caps are 6800µF each. If I did the math right, that should work out to 3% ripple with a load of 10A at 30v. From what I've read, that's a reasonable figure for a linear supply. Or would you consider that "small" for the application?
mos6502:
--- Quote from: torch on September 20, 2015, 07:25:27 pm ---
--- Quote from: mos6502 on September 20, 2015, 06:53:38 pm ---Another trick is to use a very small filter cap and higher transformer output voltage and rely on the pass element to dissipate the extra heat.
--- End quote ---
The filter caps are 6800µF each. If I did the math right, that should work out to 3% ripple with a load of 10A at 30v. From what I've read, that's a reasonable figure for a linear supply. Or would you consider that "small" for the application?
--- End quote ---
6800uF for 5A is fine. I was merely explaining what some Wun Hung Lo manufacturers do. The Korads actually seem to be well designed. :-+
bitseeker:
I remember seeing this new model on pre-order for a while. Thanks for the teardown photos. What all changed from the prior triple-channel model?
torch:
--- Quote from: bitseeker on September 21, 2015, 03:42:41 am ---I remember seeing this new model on pre-order for a while. Thanks for the teardown photos. What all changed from the prior triple-channel model?
--- End quote ---
Not a lot, as far as ripple/regulation specifications go. The 3-channel 3amp predecessor was called KA3003D-3S. It looked just like they took two single-channel supplies and stuck them in a double-wide case. They even retained separate on/off buttons and separate keyboard lock buttons for channel 1 and channel 2. There was no obvious serial/parallel operation, (although one review I read suggested it was possible, so it may have been added mid-production). It had separate fans and reviews I read mentioned they are running all the time and a bit on the noisy side.
Supposedly there was a KA3005P-3S version providing 5 amps and programming capability, however that may have been vapourware as I never did find one actually for sale anywhere.
This one seems better integrated (to me) and perhaps more importantly, available.
Kleinstein:
As transistors a cheap today, the real weak spot is often the transformer - but sometimes even a few cents saved on the output transistors are still tempting.
Having a rather small filter cap helps to reduce the current peaks, but you than also need more reserve in voltage. So you can not gain that much by reducing the cap size, unless you risk that ripple might be apear at the output at high voltage and high current. This might only happen if the caps are at the lower end (tolerances are quite large) or mains voltage is less than nominal.
Using a relay to switch transformer taps also calls for the cap not to be very large, as this gives extra current peaks when swithing to a higher voltage.
Transformers can stand more than nominal load for quite some time. They get hotter however and thus age faster. Having the fan might also help to ensure cooling of the transformer.
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