Using a LDO Regulator on a ZXCore

[blittled]

I'm building a ZXCore and I have some LM2940 LDO 5V Regulators. I was thinking of using one to lower the input voltage requirement to 6V so I could possibly use batteries to power it. My question is if I use the original PSU for a ZX81 would I need to lower the max current requirement (300mA with heat sink)? I do have a universal 3-15V 300mA PSU I could use instead if the 9V PSU causes heat problems.

[1024MAK]

The current requirements do not significantly change between using a 7805 vs. using a 5V version of a LM2940.

When using a Sinclair "9V" PSU, the only difference between a 7805 and a 5V version of a LM2940, is the slight difference in heat output due to the different regulators having different quiescent currents (this is how much current is used by the internal circuitry).

If using 74LS logic, an NMOS Z80 CPU, NMOS EPROM and 1K SRAM chips, attach a heatsink to the LM2940, just as you would for a 7805 and you should be fine
If you are using modern CMOS chips (74HCT logic, CMOS Z80 and modern CMOS SRAM and EPROM/EEPROM/FLASH), then you do not need a heatsink

Alternatively, yes you can use a DC PSU that has a lower output voltage, but not a lower output current. The general rule of thumb is to allow a bit extra voltage above the sum of the regulator output voltage (5V) plus the regulator drop-out voltage (say 1V) to allow for the ripple (say 1v minimum). Keep in mind that the output voltage measured by a meter of a unregulated DC PSU will be higher when it is not connected to a load.

So on a switchable PSU try the 7.5V setting or if the current capacity is significantly greater than needed, the 6V setting.

Mark