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Power Supply

By bassem ·
Nee to generate 5V DC @200 ma from 2v AC source. A 5v regulator get way too hot. Any ideas?

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by TheChas In reply to Power Supply

For most voltage regulators, you need a minimum of 2 volts differential between the raw DC and the regulated output.

With 2 VAC, the most DC voltage that you can get is 2.8 VDC.

How much do you know about electronics?
Most of the available solutions for your problem would require some circuit design and assembly.

How much current is available from the AC source?
For any solution that will generate 5 VDC from 2 VAC, you will need at least 600 mA available from the 2 VAC source to get 5 VDC 200 mA out.

There are 2 ways to get 5 VDC from 2 VAC.

1. Use a 3 to 1 ratio step-up transformer, rated for at least 500MA on the output.

Connect the output of the transformer to a 1 AMP rated bridge rectifier.

Connect a 500 UF capacitor to the output of the bridge.

Then connect a TO-220 package 5 volt regulator with a heat-sink to the Filtered DC.

2. Use a voltage converter.
Most of these require that you rectify and filter the AC source. Most of these are military grade units and are very expensive.

If there is any way to use a standard wall transformer style power supply, I recommend it.

Some of these are light weight switching type supplies and are very well regulated.


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by TheChas In reply to

That makes it a lot easier.

I would use a LM340-5 or LM78M05 TO-220 package regulator. With a heat-sink.
They are rated for up to 35 VDC in.

Use a single diode rectifier setup to limit the DC voltage derived from the 24 VAC.

A 1000 uF 75 Volt rated filter capacitor should be enough to do the filtering.

If the regulator still gets hotter than you like, add a 50 to 100 ohm 5 watt resistor in series with rectifier diode.

If you need a circuit diagram drawn up, e-mail me at thechas2000@yahoo.com

You could also use a switch mode power supply circuit. They run much cooler than linear regulators, but are MUCH more complex to design and build.


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by TheChas In reply to

Just another thought to reduce the voltage to the regulator input.

If you can find a small transformer with a turns ratio between 2 to 1 and 4 to 1, you could connect it to the 24VAC and lower the voltage applied to the regulator.

With a 2 to 1 transformer, the input to the regulator would be 17VDC.
With a 4 to 1, the rectified DC voltage would be 8.5 volts.

Taking 120VAC as the "normal" input voltage for a transformer, you want a transformer that has between 30 and 60 volts on the secondary.
I would choose a transformer rated for at least 400mA on the output to safely provide the 200mA that you need from the regulator.


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by bassem In reply to Power Supply

Sorry, I meant from 24v AC not 2v.
Thank you,

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