UA7812C Replacement Advice

Hi @mtlatc,

  I make no claims about being smarter .... 🤔

  Replacing a linear part with a switch mode part is one of those "Often, but not always" answers.

The first things to ensure the voltage input and output, plus current ratings match up ... if they don't it tends towards a definite no!

Using data sheet for UA7812C found at https://datasheetspdf.com/pdf/1480907/etcTI/UA7812C/1 as a reference

Input voltage range of Traco part of 15 - 36 VDC ...  compared to 14V - 35V max of 7812. 14V min for 7812 is expressed as 2V dropout. In theory, the 7812 will keep going in the range 14-15V, whilst it is out of spec for the Traco part. My guess is the actual input voltage will be higher than 15V, but obviously I don't know that, so in theory at least, the there could be a problem here - but you will be unlucky to see it.

Output voltage of 12V in both cases, one would hope!!

Current capability ... 7812 seems to be 1.5A max continuous, 2.2A peak ... which in practice, can be reduced by heatsink limitations. I couldn't find a max continuous rating for the Traco device .... unlikely to be a problem, given its claims as a replacement, but ...

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The other issue is more tricky ... switch mode devices tend to produce more electrical noise. For many applications, this is of no consequence .. e.g. most digital logic circuits are relatively insensitive to noise. But some applications, e.g. low level audio amplifiers and small signal level instrumentation can be more fussy.

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For many applications, linear regulators have been replaced by their more efficient switch mode cousins, which can now be cheap and small, but linear regulators are still manufactured in large numbers. You may find the part numbers have changed, as newer devices with slightly improved characteristics to replace 7812 have become available. In view of the present crazy chip market, plus availability in different countries vary, I am reluctant to suggest a specific part number, but hopefully you could find a linear device if you prefer.

Alternately, there is a good chance the Traco device you identified will be fine ... I think you will be very unlucky to have any 'catastrophic' problems, but the electrical noise issue could degrade the performance of the load, if it was something like a microphone pre amp, which may exhibit buzzing or other strange noises.

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Unfortunately, the only 100% test is 'suck it and see' ... the final responsibility is all yours!

Best wishes and good luck, Dave

@Davee Thanks for the awesome response.  Since it will be placed on a AC to DC converter board I don't think "noise" will be an issue.  I'll see if I get anymore responses before I "suck it and see" 😎.

Posted by: @mtlatc

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@Davee Thanks for the awesome response.  Since it will be placed on a AC to DC converter board I don't think "noise" will be an issue.  I'll see if I get anymore responses before I "suck it and see" 😎.

Hi @mtlatc, I was was just reviewing your thread with @Dave and I decided to take a look at the specs as you have indicated that you'd like some more opinions on the subject matter..

While @Dave has given you, I believe, a very good indication of the compatibility of the two devices, I see no reason why you couldn't use the TSR-1 as a replacement for the UA7812C.. as you have mentioned that it's use is in a AC to DC converter board. Hope this helps you with your project.

regards,

LouisR

@inst-tech thank you very much for your response. 

Hi @mtlatc,

   Just to clarify what I meant by noise in case there was any confusion. An ideal 12 Vdc power source, would produce a steady 12Vdc, with no variations of voltage.

Real voltage regulators, even linear ones, produce an output with tiny variations, typically at the millivolts level, superimposed on the otherwise steady 12V (say), which is often described as 'noise'. If that noise is coupled into the input of an audio amplifier, you would be able to hear hissing or buzzing.

Whilst all regulators produce at least some noise, switch mode suppliers internally rely on very strong switching currents to function, whilst linear regulators usually only produce a low level 'hiss'.

The Tracor device lists "50 mVp-p typ.", which is typical for this type of device, whilst the 7812 device lists 75 microvolts (roughly 1000 times lower), and it offers a considerable rejection of noise that may be on the incoming (unregulated) power.

Whilst good quality switch mode regulators include filters to minimise the amount of internal activity affecting the output, they are far from perfect. And small low cost regulators, minimise the filtering components to reduce cost, weight and size, with the result of higher levels of switching noise on the output.

So it really depends on what type of equipment the power supply is going to power ... a very high proportion of equipments will not be affected by low level noise on the power lines ... but some will.

Best of luck, Dave 

@davee — Like I said someone way smarter than me. 😆 

I was considering putting it on the power supply board for a TI 994/A computer. The board brings in 18V and 7.5V AC and converts it to 5,12, and -5V DC. 

Hi @mtlatc,

 A computer should be fine with a little switching noise. I was being cautious as I didn't know what the load was.

Dave