Level42
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I've always seen the extra resistor (R20 and R21) mounted over the 7824 and 7924 as a poor hack to get more current from the power supply.
Apart from the fact that they get freaking hot (and thus waste energy), it also greatly reduces the functions of the 7824 and 7924.
Now there's a much better solution (I think), using a transistor instead of a resistor. This kind of set-up is mentioned on several datasheets too but here's a schematic I found:
And here's the negative version:
This set-up can deliver 5 Amps (compared to 1 amp for a unmodified 78xx set-up)....
Any idea's if we could incorporate this (safely) into the HV board ? Any reason not to do it ?
The good thing is that the transistors needed can be mounted on the cooling body that's already present on the HV board (which doesn't get very hot).
I've uploaded a scan of the HV PCB schematic that came with my manual, this actually includes the resistors R20 and R21 which I haven't seen on any of the schematics that are available on-line.
Apart from the fact that they get freaking hot (and thus waste energy), it also greatly reduces the functions of the 7824 and 7924.
Now there's a much better solution (I think), using a transistor instead of a resistor. This kind of set-up is mentioned on several datasheets too but here's a schematic I found:
And here's the negative version:
This set-up can deliver 5 Amps (compared to 1 amp for a unmodified 78xx set-up)....
Any idea's if we could incorporate this (safely) into the HV board ? Any reason not to do it ?
The good thing is that the transistors needed can be mounted on the cooling body that's already present on the HV board (which doesn't get very hot).
I've uploaded a scan of the HV PCB schematic that came with my manual, this actually includes the resistors R20 and R21 which I haven't seen on any of the schematics that are available on-line.
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