Universal Regulator

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ruffrecords

Well-known member
Joined
Nov 10, 2006
Messages
16,155
Location
Norfolk - UK
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
 
I'm sure for the HT and phantom that it will "work" as envisioned, but so you can already get the cheap'o velleman k1823 kit and tweak it to your liking (and how do you think I know that "secret").

What I suggest is you rethink the HT and phantom "combo" slightly and drop-in a simple "pre-reg" which could be a mosfet or some TO-220 darlington (perhaps some clever part juggling could enable use of either on the same PCB). These things can be remarkably simple but quickly add to the "booteeq" vibe - and will in case of the HT reg actually add some safety margin wrt. operation safety.

Hey, manng, I tried ...
 
The Vellemam kit is OK as far as it goes but it lacks a couple of essential protection diodes. Also, the smoothing capacitor is a little on the small side. With a 1 amp load, the ripple across the 2200uF will be close to 4.5 volts. If the regulator does manage to achieve 80dB ripple reduction that becomes a minuscule 0.45mV. That's fine for heaters but not good enough for HT. In fact I am not happy with the TL783 in the current phantom board supplying HT at 100mA as that would give an output ripple of about 160uV.  (the HT350 PCB under the same conditions provides over 130dB of ripple reduction). Also the diodes are OK only up to 1 amp so doing 5A is not an option. A pity really as it is a neat little kit. I particularly like the idea of the regulator at the side of the PCB so you can fit almost any sized heat sink.

Cheers

Ian
 
First, this is getting mondo offtopic, so delete if you wish. Second, this while true wasn't the point I was trying to make. Generic psu kits, even with higher amperage (velleman again f.e.) are abundant and cheap, and it's so easy to swap in better components (couple of MURs, low-esr caps etc, et voila, you're surfin' in "audiophile" territory).

The point I was trying to make was that you have a specific idea for a specific crowd, and I was suggesting to focus further and split your effort in two entities - one targeted for heaters supply and the other targeted to HT and/or phantom supply (or with certain overlap in features). So I'm sorry if this didn't come accross as clear as it was intended.
 

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