I am looking for low power power supply without transformer.

Input \$110V-230V\$,

Output plan to use 7805 regulator IC.

Application demand \$5V/3.V, 150-250mA. \$

In input side I should be able to give 110VAC /230V AC I know transformer based design give good isolation. Whether bridge rectifier with Zener diode serve purpose?
Kindly suggest me some power supply design

Information about some design

  • 2
    \$\begingroup\$ "low power power supply without transformer". Only a transformer provides good isolation. If the power supply is for a consumer product and accessible to the end-user, a transformer should be used to protect the user from shock hazards. A switched-mode power supply can be used to reduce the size of the transformer. A transformerless design should only be used when the system is not accessible to the user, such as an electric lamp on the ceiling, or when it's part of some industrial machinery that is not a consumer product. \$\endgroup\$ – 比尔盖子 Feb 27 '20 at 3:51
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    \$\begingroup\$ If you are asking these questions then you do not know enough to safely build and use a supply without a transformer. Use a transformer. \$\endgroup\$ – DKNguyen Feb 27 '20 at 4:02
  • 1
    \$\begingroup\$ Use a phone charger. more than about 10mA it too much for a practical transformerless supply. \$\endgroup\$ – Jasen Feb 27 '20 at 4:35
  • \$\begingroup\$ Here's a bunch of google images of possible cheap solutions. Also see this performance test and review of mains to 5V 0.6A Hi-Link HLK-PM01. \$\endgroup\$ – jonk Feb 27 '20 at 4:43
  • \$\begingroup\$ if i wanted to use transformer . what is min construction of transformer \$\endgroup\$ – Ajit Feb 29 '20 at 3:50

Use a phone charger. more than about 10mA is too much for a practical transformerless supply

To get 150mA from 250V you need a 600uF X capacitor that's going to cost over $100 at digikey. (you have to put several smaller capacitors in parallel)

For a tenth of that price you can buy a 1W AC-DC converter module (and probably cheaper if you shop elsewhere.)


If you use just a rectifier and Zener diode, then the Zener will go "bang" in a spectacular fashion. The first circuit in the accepted answer in the question you linked to is a common way to produce a lower voltage without a transformer.

But you need to understand how to calculate C1 and R1. For the currents you want, R1 would be much lower. C1 is set to pass the largest current you want.

I would expect to see a high value resistor connected across C1. Perhaps 330k ohms.

Be aware that the circuit provides no isolation from the mains supply. It can be lethal if anyone touches any part of the circuit. Such supplies are only to be used if completely enclosed, and should not be used as power supplies for anything that plugs in to them.


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