voltage dropper help

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aruna1

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Hi, I want to make a power supply that will reduce 230V AC voltage to 5V DC voltage. Do do this I want to use a buck converter. Easiest buck converter I can get is MC34063. it has input up to 40V.
what I want to know is how to reduce 230V rectified DC voltage to 30V DC voltage so I can use MC34063 to drop 30V to 5V.
I have added a diagram below. my question is to solve the middle box named as "voltage dropper". I'm looking for a simple circuit for this. since i dont know current requirement of the load I guess i cant use a resistive dropper. any idea would be great.

EDIT: cant use a transformer due to space constraints.

thank you
 

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Hi
I'm trying to find a way to use MC34063 for this coz MC34063 is the only one I can find here.

and I dont want to use a transformer coz it makes the unit bulky. I want to finish it with minimum space requirement.
 
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@dougy83

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capacitive power supplies can supply very low current right? so might not useful for this
 
Last edited:
aruna1 said:
capacitive power supplies can supply very low current right? so might not useful for this
Click to expand...
The current is proportional to the size of the capacitor.

Can you not just buy a premade converter for US$2.39: e,g. **broken link removed**

Another option is to make a circuit that only conducts when its input voltage is <30V - if you have this after the bridge rectifier, and before the filter cap, you can get the 30V DC (peak) from the 220V rectified AC.
 
hi
I was thinking about MC34063 because it allows me to adjust output voltage. In future I might have to increase output voltage from 5V to 12V but if i buy something like that i will e stuck with 5V
 
You can just adjust the output resistor divider in those things (and replace the capacitor with a higher voltage one) in up the output voltage.
 
hmm
i checked a mobile charger circuit that gives 5V 500mA from 230V. it didnt has any resistive divider. output was simply taken from the transformer.
 
how about this

I was running some simulations and thought this could do some thing. see below circuit.

230v to 7.5V transformer less. any ideas on this method? zener use is a 8.2V one.
you can see the voltage values on multimeters attached
 

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aruna1 said:
I was running some simulations and thought this could do some thing. see below circuit.

230v to 7.5V transformer less. any ideas on this method? zener use is a 8.2V one.
you can see the voltage values on multimeters attached
Click to expand...

Sorry, but a completely useless idea

It will be HUGE, use loads of electricity, and double as a toaster!.

You need a switchmode transformer based supply, small, efficient and provides mains isolation as well.
 
aruna1 said:
hmm
i checked a mobile charger circuit that gives 5V 500mA from 230V. it didnt has any resistive divider. output was simply taken from the transformer.
Click to expand...
The device I linked to is a SMPS; it has a SMPS controller IC, a tiny transformer & a normally they have an optocoupler providing feedback (related to the output voltage - which has either a regulator - e.g. TS431 - & resistor dividers or a zener diode) to the controller. You obviously checked the wrong sort of device.

Your regulator circuit won't work without a large heatsink and/or a cooling fan either - if you draw 747mA from that, the transistor has to dissipate >100W.
 
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