Re: power supply issue

I took a new measurement and found out the the ac value was acutally 27V not
24. So when i muliply with the square of two i roughly get 37,5V peak to
peak.
But why do i see the peak to peak voltage after it has been rectified???
Even with load 40ohms load.

Anders


"Anders Nesheim Vinje" <a-vinje@xxxxxxxxxx> wrote in message
news:7RMde.8637$ai7.208762@xxxxxxxxxxxxxxxxx
> Hi.
> I have built this dual power supply.
> Transformer rating: 2 x 24 V 60VA
> Pretty standard with a bridge rectifier and ground connected to the center
> tap. So i got + 24 and -24.
> The i have two 4700uF 50v caps, one connected at each powerline to provide
> filtering. Then there is a 7815 and and a 7915 as regulators.
> Ok here is the issue. When i measure the voltage over the filtercaps i see
> +37,5V and - 37,5V! How is this remotly possible?. Even the peak to peak
> voltage isent that high. The 7815 and 7915 is only rated up to 35V so i am
> scared they might blow or something.
>
> Another problem is that since there is a voltage drop 37.5 -15 = 22 V over
> the regulators. It cant provide much current before they shut down
> because of the heat. I know from the data*** they can handle up to 10W
> with a decent heatsink and a max current of 1,5A. I dont need that much
> current anyway since the transformer can only deliver 30VA / 24 = 1,25A
> per secondery anyway.
> I have another question too. How much current goes through the primary
> side of the transformer with max load? I was thinking of having a fuse
> there instead of buying a fuse to each of the secondery outputs.
>
> Thanks in advance
>
> Anders Vinje
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