Transformerless power supply with Viper12A

Published by MKDas on

One of the very useful transformerless power supplies using Viper12A IC can be used in many applications. It is sufficient to run micro-controllers, sensors, displays, relays, and so on. With very few numbers of components, we can get a reliable transformerless power supply using Viper12A.

Disclaimer: Electricity is always dangerous. Skill required to work with electricity. Do work with your own risk. Author will not be responsible for any misuse or harmful act. This website contents is also copyright protected. Anything copied and directly posted in your website and claiming it as yours is prohibited and nonsensical. Author published all the articles as opensource to help you making your project and learning purpose only. Learn and make one for yourself. If need any help feel free to ask the author. Author will be helpful to you. Thanks.

***Warning: An electrocution hazard exists during experimentation with transformerless circuits that interface to wall power. There is no transformer for power-line isolation in the following circuits, so the user must be very careful and assess the risks from line-transients in the user’s application. An isolation transformer should be used when probing the following circuits.

About Viper12A:

This is actually a PWM controller with high voltage power MOSFET inside. Usually used in low power standby power supplies, battery chargers, auxiliary power supply etc.

Datasheet of Viper12A.

Circuit diagram:

Here, R1 is used to limit the inrush current and L1 and C1&2 are used to rectify the AC with a filter to get DC voltage. The L2 is the main inductor in this circuit. In this circuit, the inductor should not be used less than 1mH. Diode D2 is supplying the power to VDD and D3 & D4 are generating the feedback voltage. If you need another voltage rather than 12, change the value of this Zener diode D4. C5 and C6 are used to filter the noise from the feedback signal. And finally, C4 is used as the main filter capacitor for the low voltage side. A safety Zener diode D6 of 15V (higher than the output voltage) is used to limit the initial voltage spike during startup. And D5 is the freewheeling diode. Must be used any Ultra Fast diode.


This article was a serial post of the previous post (Transformerless power supply design guide). As this circuit performs much better than the capacitor or resistor based power supplies and I’ve been using this circuit in many applications and field running (24/7) devices for a long time so I decided to share the diagram. If you can design the PCB carefully keeping sufficient PCB space as heatsink, this circuit will last a long time. Average power delivery is 100mA. And most interesting this is this circuit works from 15V to 300V wide (may be extra wide) range.

I hope this project was helpful to you. If you make one for yourself, it will be a great pleasure for me. Anywhere you need help, let me know. Please share this project and subscribe to my blog. Thank you.


Mithun K. Das; B.Sc. in EEE from KUET. Blog:

1 Comment

Joy · February 12, 2021 at 11:51 am

Thank you… Nice Project..

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