Transformerless 5V DC Power Supply
This board takes AC mains input from 100V to
250V AC and output regulated +5V DC providing
current up to 50mA. Great for running small
and almost zero heat generation.
In most non-battery applications, the power to the
mounted transformer, which is then rectified,
filtered and regulated. In most applications, this
method of generating the regulated voltage is
cost effective and can be justified. However,
there are applications where the main controller
and low voltage is not required by other
components except the microcontroller in
application. In these instances, the cost of the
transformer becomes the sizable cost factor in
the system. For example, most fire alarms &
round the clock monitoring alarms are powered
Transformerless power supplies, thus, have a distinct advantage in cost as well as in size. The
disadvantages of using a transformerless power supply are low current supply and no isolation from
The microcontrollers usually draw a maximum of 20 mA, even at the highest frequency and voltage
of operation, therefore low current availability is not an issue. The main disadvantage of
transformerless supplies is that they don't offer isolation from the HV line.
One down side of this circuit that it is not isolated from mains so it should not be used in
applications requiring touch of any contact from user. If any part even though +5V side is touched it
would cause shock to the user. Please be careful about touching when using it during experiments
or final applications.
Warning! An electrocution hazard exists during experimentation with transformerless circuits that
interface to AC mains wall power. There is no transformer for power-line isolation in the circuit, 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 circuit during experimentation.