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Need advice about 5V, 50mA power supply.

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belax

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Hello.
I need to make a small power supply (5V, 50mA) for microcontroller and other controlling circuit.

I have only two points: 300V and GND. 300V is from rectifier and ballast capacitor, so 300V is not stabilized.

I wanted to use this circuit

, where in my place Uvx will be about 300V. But in such circuit the power dissipation on the transistor will be about 295*0,05 = 14W. It is a lot.

So my question is: How to make a power supply which will not produce so much heat and will be relatively cheap(for example only resistors, capacitors, one or two transistors, zeners,...).

Thank you very much.
 

The only way f avoiding heat generation is a switching regulator .. here is on an example:
https://www.st.com/stonline/products/literature/an/1688.pdf

Otherwise you will have to use substantial heatsink on the HV transistor and maybe add a CPU-type fan ..
Also, becasue you are trying to drop 290-something volts you should consider output protection: a fuse on the 300V rail is a MUST !!!
Next, I would add 5W 1kΩ (Rk) resistor between the fuse and the collector of the HV transistor and Vout+1V zener diode on the output ..

Regards,
IanP
 

Thank you. But switching regulator will be too expansive.
Maybe there exist some switching circuit on one or two transistors, which will not let current to flow through the transistor all the time.
For example If I can switch the base on my circuit and put a ballast capacitor with rectifier diode on my emitter I will get some voltage on the capacitor and will not let the current flow through the transistor all the time. Then I just need to stabilize the voltage on the ballast capacitor (78l05).
But How to make a switching circuit. I even don't need a feed back. Just let it switch for example with 16kHz (20% signal, 80% zero) and I significantly decrease the heat.

Thank you.
 

Take a look at the attached picture ..
Maybe you can try something like that ..
As load use a zener diode - 10 to 20V - followed by 7805 voltage regulator ..

Regards,
IanP
 

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