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Help needed with power supply for circuit

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Brass

New Member
Hi,

I have a Speech Syntheses Unit which was produced in Canada by a company called Pacific Education Systems. I am trying to figure out what type of power supply (AC/DC) and rating in Volts & Amps would be appropriate. The connector on the rear looks like a connector for a DC power jack.

1 Pole of the power connection goes to a 1N4001 the other end of which travels to a variable pot with an on/off switch capability. The other pole goes to a 16v3300uf Radial Electrolytic capacitor. I have looked up some of the chips on the net: 27c64-25,TSP5220CNL,MC145406P. I have noted voltages range from 4.75v through to 12v and some of the parts that I did check are TTL tolerant. I can not see a rectifier anywhere but can see 3 pole Voltage regulators marked uA7812,8730 LM340TS,8644 LM7905CT.

I am presuming the Electrolytic's rated at 16v are deliberately high and the circuit maybe 12 or even as low as 5v. If I remember rightly its ok to give a circuit like this a 12v supply with say 2amps of current ( probably overkill ) as the circuit should only draw what it needs. Is this correct?

Lastly something I can not find on the internet looking at an electrolytic capacitor rated at 16v3300uf which has an arrowy stripe down one side with 0 written in it would this be the negative or positive pole?

Thanks to all who respond in advance.
 

Diver300

Well-Known Member
Most Helpful Member
If I remember rightly its ok to give a circuit like this a 12v supply with say 2amps of current ( probably overkill ) as the circuit should only draw what it needs. Is this correct?

Yes, but the 1N4001 is only rated at 1A so the power supply will not need to be bigger than that. That is likely to be there to prevent damage if the power is the wrong way round. Unless there are 4 of them, the power input is probably DC.

I am presuming the Electrolytic's rated at 16v are deliberately high and the circuit maybe 12 or even as low as 5v.

Correct. Even running a 12 V unregulated supply with 16 V capacitors would be dodgy.


I can not see a rectifier anywhere but can see 3 pole Voltage regulators marked uA7812,8730 LM340TS,8644 LM7905CT

The 7812 is a +12 V regulator so would normally run from 15 - 18 V. The 16 V capacitors could be on the output or on lower voltage rails.

The 7905 is a -5V regulator. There are lots of ways that could be connected.

I would supply it with 15 V or so. If you use a supply that is fused, or current limited, and see if the unit works.
 
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