ruffrecords
Well-known member
I have been thinking about heater supplies for the EZTubeMixer project. It finally dawned on me that the regulators I have been using and looking at, LM338, LM317 and TL783, all have identical pin outs in their TO220 versions. Looking at the datasheets it is clear they also have near identical application schematics. So it occurred to me that a single PCB could be used for all of these regulators. Most of what is needed is already on my phantom power PCB, including rectification, smoothing and provision for a modest heat sink. Calculations show this heat sink should be sufficient for a 12V heater regulator passing just over 1 amp; enough to power a couple of EZTubeMixer Eurocards.
For a sub-rack we need over 3 amps which the TO3 version of the LM338 can handle with a suitable heat sink. The spacing of the mountings for the small heat sink on the phantom board is less than the spacing between the fixings of a TO3. However, if you drill an extra hole you can fit either. The TO220 heat sink fixings just happen to be off centre so when you add the extra hole, the TO3 ends up pretty near centre of the PCB. The idea is that with this extra hole you can add a couple of pillars and mount a TO3 LM388 on a heat sink to the back of the PCB. There's a standard 2.3 degree C/W TO3 heat sink that is almost exactly the same size as the phantom PCB and calculations show this should be able to provide over 4 amps at 12V. The largest 35V capacitor that will fit on the phantom PCB is 22,000uF which gives a calculated 2V pp ripple at 4 amps. The regulator should be able to reduce this to less than 2mV.
For large currents the 1N5400 series of diodes is not able to carry the required continuous forward current so I will need to make provision for bridge rectifiers up to 10 amps to be fitted to the PCN
The TL783 is used for 48V phantom supply. There's no reason it should not be configured to provide HT voltages. In fact I have tried this - it works but it is very easy to blow up the chip by accidentally shorting the output - the solution is to add a 75V zener across the TL783 to limit the voltage across it to a safe level. I think about 100mA of regulated HT would be possible wwith the existing heat sink.
Bottom line is I think I could come up with a single PCB that could be used for 12V heater supplies at various currents up to over 4 amps, or phantom power, or even regulated HT using the TL783. Oh no! it's the Universal Regulator!
Cheers
Ian
For a sub-rack we need over 3 amps which the TO3 version of the LM338 can handle with a suitable heat sink. The spacing of the mountings for the small heat sink on the phantom board is less than the spacing between the fixings of a TO3. However, if you drill an extra hole you can fit either. The TO220 heat sink fixings just happen to be off centre so when you add the extra hole, the TO3 ends up pretty near centre of the PCB. The idea is that with this extra hole you can add a couple of pillars and mount a TO3 LM388 on a heat sink to the back of the PCB. There's a standard 2.3 degree C/W TO3 heat sink that is almost exactly the same size as the phantom PCB and calculations show this should be able to provide over 4 amps at 12V. The largest 35V capacitor that will fit on the phantom PCB is 22,000uF which gives a calculated 2V pp ripple at 4 amps. The regulator should be able to reduce this to less than 2mV.
For large currents the 1N5400 series of diodes is not able to carry the required continuous forward current so I will need to make provision for bridge rectifiers up to 10 amps to be fitted to the PCN
The TL783 is used for 48V phantom supply. There's no reason it should not be configured to provide HT voltages. In fact I have tried this - it works but it is very easy to blow up the chip by accidentally shorting the output - the solution is to add a 75V zener across the TL783 to limit the voltage across it to a safe level. I think about 100mA of regulated HT would be possible wwith the existing heat sink.
Bottom line is I think I could come up with a single PCB that could be used for 12V heater supplies at various currents up to over 4 amps, or phantom power, or even regulated HT using the TL783. Oh no! it's the Universal Regulator!
Cheers
Ian