TL783 ..need advice

[Sam_123]

Hi all,
I need to convert 230V DC to 12V DC (very large Voltage drop) so is it a good idea to use TL783? The load current is 22 m A.
Will I need input and output capacitors?

Thanks

 

[(*steve*)]

Get a plugpack (aka wall wart)

Or is there some reason you want to do it yourself.

A TL783 would be exactly the sort of thing I would NOT use.

A DIY soluion is a transformer to drop the voltage down to about 12VAC which is then bridge rectified, filtered, and regulated.

For that current you could probably use a simple zener shunt regulator.

But the DIY solution would probably cost (and weigh) multiple times that of a 12V 1A switchmode regulator in a wall wart.

 

[Sam_123]

No there is no reason for me doing it by myself. I tried searching online to find a better and safer way to do this but TL783 was the only method I came across.
I would love to use something off shelf. The adapter from walmart is AC to DC but I need DC to DC. (Input=130V DC and Output=12V DC)
Sorry I should have been more clear in my post.

Thanks,

 

[(*steve*)]

Many switchmode regulators will work perfectly fine from a DC source.

I didn't notice you specified 230VDC in your original post. And that is my mistake. I read 230V and assumed AC.

 

[Sam_123]

I think there are some DC power supplies but they are very expensive.
I don't see any other options other then using TL783
Do you have any experience with TL783?
Should I use it or should I find some other alternative?

Thanks,

 

[Resqueline]

So what is the high voltage? You mention first 230V & then 130V.. Any space or power loss restrictions? Is the current draw stable? Any noise considerations?
In valve radios it was common to drop the anode voltage through a ceramic resistor to run stereo decoders etc.. May I ask what your power source & sink consists of?

 

[Sam_123]

Oh my bad it is 130 V DC. The current draw is stable. Per my understanding I can use resistors to drop the voltage from AC to DC but for DC to DC, resistors won't work (May be I am wrong). power source is a 130 V DC power unit.

 

[Resqueline]

Ok, so you need to loose 118V then. At 22mA that is a dissipation of 2.6W. A resistance of 5364 Ohms would do this, but there is a question of how stable the 130V is.
The datasheeet reveals that the TL783 just about cuts it with its 125V rating. It also reveals that capacitors are not required, but a 1uF input capacitor is recommended.

A resistor can always be used to drop everything, and rectifying can take care of AC to DC. Capacitors and inductors can be used to drop AC only. DC to AC is harder.

So an alternative to the IC is a resistor and a zener. A 4700 ohm (3W) resistor delivers 25.1mA giving only 3.1mA headroom for the zener to deal with.
With this resistor value the HV can't drop to less than 115.4V for the 12V to keep stable.

 

[Sam_123]

I like your idea of using resistor and a zener diode. Ok, so then I can use a 4700 ohm 3W resistor and a zener diode. what zener diode should I get? I guess if we connect a diode and resistor in series with a DC voltage source then the voltage drop will be constant. correct?.

Thanks

 

[(*steve*)]

No, the voltage drop will not be constant. The voltage across the zener will be constant though. The resistor will drop the rest (which should be fairly constant)

The zener diode should be a 12V unit. It will be dissipating 0.3W when no load is attached. If the load is permanently connected, You could use a 400mW zener, But if the load can be disconnected, it would be far safer to use a 1W rated part.

I would use at least a 5W resistor, possibly even a 10W if I had the space (especially if it had no airflow or was at an elevated temperature). It won't reduce the amount of heat generated, but it will kelp spread it around and minimise the temperature buildup in the resistor.

You'll know if you connect the diode the wrong way because you'll get less than 1V across it rather than 12. It won't hurt anything (as long as the resistor is in series).
The zener isn't a perfect regulator. For currents between 3mA and 26mA, the voltage may vary a little.

 

[Sam_123]

Thanks a lot. You guys are very helpful.