power supply

[peter g]

hi, i'am looking to build a 100vdc, variable, regulated power supply. does anyone have a circuit they will share with me? thanks.

 

[BradtheRad]

The most convenient device to dial from 0 to house voltage is a variac (variable transformer). I purchased a 1.75A unit on Ebay.

Add a full diode bridge and hefty electrolytic capacitor. Wherever you set the voltage, it varies just slightly.

If you provide more details you can expect more informative replies. Example, current requirements, initial power source?

 

[peter g]

The most convenient device to dial from 0 to house voltage is a variac (variable transformer). I purchased a 1.75A unit on Ebay.

Add a full diode bridge and hefty electrolytic capacitor. Wherever you set the voltage, it varies just slightly.

If you provide more details you can expect more informative replies. Example, current requirements, initial power source?

current required 50ma. powered from ac line.

 

[KlausST]

Hi,

powered from ac line.

A proper design starts with deciding it's requirements. In numbers with units.

Remember that this is a worldwide forum. There are several different types of mains voltage and frequency.
We don't know where you live. We can not input "AC voltage" into our calculators.
--> better give numbers

Also we don't know what's your understanding of "100V DC variable" is:
* for the one it is 0..100V
* for the other it is 100V +/-5% (95V .... 105V). Not unusual for power supplies.
--> give numbers

"Regulated" usually means: high precision, low ripple, low (thermal drift). Is this the case for your application?
For the one a +/-1V ripple is good, the other needs a ripple/drift less than 10mV
--> give numbers

Also give more informations. Maybe linear/switch mode .... isolated or not ...
Does the load draw up to 50mA, or does the supply need to limit to 50mA?
Is the load constant? Is it purely resistive?

Traditional linear power supplies with 0..100V DC / 50mA out and 230V AC in have a DC rail of about 300V, thus may generate up to 300V x 50mA = 15W of heat. --> A big heatsink or even a fan is needed.

Especially when working with other people "numbers" are really useful, so we all can give focussed assistance.
It's your benefit (and less work and less guessing for us).

If you do an internet search, you get thousands of hits. Different solutions for different requirements.
Schematics, ready to buy devices, tutorials, videos ...
What suits you, what not? And why?

Klaus

 

[BradtheRad]

current required 50ma. powered from ac line.

Capacitive drop is popular because it's transformer-less. The capacitor introduces reactive impedance, thus it doesn't generate heat the way ohmic impedance does.

However it's not isolated thus it has a high voltage hazard.

R1 is for the purpose of limiting inrush current on power-up.
Here's a simple 100V supply. Unregulated. It needs further effort to make output voltage variable and regulated.

 

[peter g]

Capacitive drop is popular because it's transformer-less. The capacitor introduces reactive impedance, thus it doesn't generate heat the way ohmic impedance does.

However it's not isolated thus it has a high voltage hazard.

R1 is for the purpose of limiting inrush current on power-up.
Here's a simple 100V supply. Unregulated. It needs further effort to make output voltage variable and regulated.

View attachment 180816

my line voltage is 120v. need 0-100vdc, either linear or smps. isolated. 30-50ma. i need this supply to test for leakage in electro caps.

 

[BradtheRad]

I think you'd like a cost-effective solution. Consider putting two power transformers back-to-back. The first transformer steps down mains to low voltage. Feed that into a second transformer installed in reverse, so it steps up voltage. It's isolated.

They can be low power. 5W going by raw math (100V * .05A=5W). But perhaps you should go for greater Watt rating to make up for inefficiencies. Notice your output stage is really a primary winding. The primary consists of many turns of thin wires, designed to present high impedance to the electric company. However you're using it to drive a 50mA load. You'll need to test a variety of transformers.