The point is, if you switch off the primary side, that side may fall faster than on the regulated side. That means that the output voltage could actually become higher than the input voltage, iow the reg is reverse biased, and it may be damaged. The reverse diodes make sure that the reverse voltage stays below 1V. What effectively happens is that the output caps spill over through the diodes into the input caps.
Whether this actually happens depends on the relative capacitances, the load and a couple of other things that are difficult to predict, so it is like an insurance.
Jan Didden
Whether this actually happens depends on the relative capacitances, the load and a couple of other things that are difficult to predict, so it is like an insurance.
Jan Didden
Example: rectifier bridge + 10000 uF + LM317 + 22-100 uF This will never create any problems.lopan said:
rectifier bridge + 470 uF + LM317 + 2200 uF This _may_ create any problems.
So what Jan means is that if you don't have control over your load (know how it is), use always proetcion diodes.
Finished!!!
I changed the layout to include a rectifier and screw terminals as this will be for testing opamps so I needed easy connectivity.
Custom mirror PCB
Costs:
transformer $26
Both Regs $8
PCB etc about $4
Caps, resisters, connectors and diodes about $17
Total approx: $55NZ = $39US
Now I just gotta make something for it to power
I changed the layout to include a rectifier and screw terminals as this will be for testing opamps so I needed easy connectivity.
An externally hosted image should be here but it was not working when we last tested it.
Custom mirror PCB
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Costs:
transformer $26
Both Regs $8
PCB etc about $4
Caps, resisters, connectors and diodes about $17
Total approx: $55NZ = $39US
Now I just gotta make something for it to power
costiss said:hope those nasty yellow caps are not tantalum... otherwise try some starget/ panasonic instead....... good work
They are tantalum as specified here:
http://tangentsoft.net/elec/teps/pguide.html
I dont know enough to know what is better but I know that starget would be overkill given how much they are in New Zealand
So you think small electrolytics would be better? how come?
might be... but: tantalum are low ESR at relatively high freqs... what is needed IS A SMOOTH ESR and impedance capacitor throughout the audio spectrum.. caps like starget cerafine etc are designed for this... you could see why generic low esr caps arent suitable using them in a psu with quite a current demand at ~100-200 Hz.. (a power amp maybe).. after a while theyll be hot... joules law.. esr in low freqs is high enough consume to consume power and raise the temperature.. how much are cerafines in n.z.? here the 100u 35V is about 2 euro (quite expensive..)...
costiss said:hope those nasty yellow caps are not tantalum... otherwise try some starget/ panasonic instead....... good work
a while back I posted on the use of tantalum caps with voltage regulators -- I used the Linear Tech LT1964 and LT1761 ULN regulators and the circuit just wouldn't work correctly with surface mount alum electrolytics, but when I substituted through-hole tantalums in their place (since that's all I had) made the devices work to spec.
this could have been a problem unique to my application..
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