[SOLVED] 220V pulse DC to 12v DC

[scottlad]

Hi! I have a circuit which I'm designing which consists of a resistive load fed from a 220V DC output of a bridge rectifier. This part of the circuit is isolated from my micro-controller by a TLP-250 FET driver. I'm wondering what my options are of providing an approximately 12V DC voltage with little ripple voltage to my driver. I have the circuit operating correctly (FET switching) when the TLP-250 is fed from a power supply and another 24V power supply simulating the 220V DC feeding the load switched by the FET with the grounds of both power supplies linked.

My options (Are these even options?)
1) A voltage divider feeding into a 7812 regulator
2) A voltage divider feeding into an LM2576-4-12 regulator

Thanks in advance, I'm sure I've left out information needed so ask away!

 

[Audioguru]

The output of the bridge rectifier is pulses with 0V between them. A 7812 voltage regulator will not work properly when fed pulses because it has a minimum input voltage rating of +14.5V. So the rectifier must be filtered with a pretty big capacitor which increases the high DC voltage to near the peak voltage of the 220VAC which will be about +309VDC.

You will discover that a voltage divider to reduce 309V to about 15V will make VERY MUCH HEAT! Why can't you reduce the 220VAC to about 12VAC with a transformer?

 

[scottlad]

Thanks for the reply, indeed you are correct, I got it working there correctly used a 220v-12V transformer into a diode bridge and joined the negative terminal with the negative terminal of my 220V AC to 220V DC diode bridge for a common ground. Thanks for your help, I was going around in circles over complicating the situation!

 

[BradtheRad]

I was going to suggest sending the pulses through an inductor. This will put out an averaged voltage, bringing it down to a lower level as you wish.

Say you make the duty cycle 6 percent. This will bring 220 VDC down to 13V DC (give or take).

As it turns out, that describes a buck converter. It can be made efficient. Low output ripple.