I have this transistor circuit with relay. Here the transistor input is connected to the GPIO pin of the micro controller. According to whether this relay is ON or OFF, then phase voltage is passed (as shown).
The problem is, I noticed this circuit may consumes large current.

What's the problem behind this circuit?

Is there any modification that I would make?

datasheet of relay

datasheet of transistor

enter image description here

  • 1
    \$\begingroup\$ Which part of this circuit that consumes large current? How large current did you measured? \$\endgroup\$ – Unknown123 Apr 22 at 10:43
  • \$\begingroup\$ @Unknown123 actually that my assumption that some part of this circuit consume some extra current \$\endgroup\$ – ravi s Apr 22 at 11:40
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    \$\begingroup\$ You've changed your circuit quite a bit. Which one is it that you have actually built and tested? \$\endgroup\$ – pipe Apr 24 at 8:05

Relays need a certain amount of power to operate. For a given size you can often reduce the current needed if you can select a higher supply voltage with a matching voltage relay. A 12V relay could easily consume 5/12 of the current of your current 5V relay.

The resistor in parallel with the diode and coil does not serve much purpose. As a snubber the value is too large and as a pull-up it is not needed. The relay coil already provides a DC path for any currents that are expected.

The 1N4149 diode is a small signal switching diode and the snubber diodes are often selected from the more robust rectifier type diodes if there is any doubt that the fly-back currents could exceed the current handling of the lighter duty signal diode.


Your relay appears to require 200mW to operate, so at 5V it will draw about 40mA. The drive circuit is okay, but the 10K is doing little of value.

If you consider 40mA to be too much, you have a few options.

  • You can use the normally closed contact rather than the normally open, so it will draw the same current but when in the other state.
  • You can replace the relay with a bistable type that only requires a brief pulse to turn it on, and another brief pulse to turn it off.
  • You can try to find a more sensitive relay (though 200mW is already pretty sensitive).

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