I need to drive a relay, but my logic signal is limited to 3.3v with a maximum of only 2 mA. Can I use a level shifter? I have a 5V relay with a 125 ohm coil drawing approximately 40 mA. Any other recommendations? Should surge suppression diodes be used? (Using National Instruments VirtualBench digital I/O)
Drive a relay from a 3.3v 2mA max output
3.3vlevel-shiftingrelay
Related Solutions
I have used a Photovoltaic relay for this in an Arduino driven application, the IR PVT312.
It is designed to work as a substitute for a Relay, and is rated to switch up to 250V at 190mA. It is suitable for AC and DC switching.
As you can see from the diagrams below, it's an opto-isolated MOSFET switch.
When S1 is opened the capacitor charges through the relay.
When you close s1 you short out the capacitor leading to very high currents.
The one ohm resistor is in the capacitor switch path and changes it from a dead short to a resistive path.
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Best Answer
Since you only need one channel, something like a ULN2803 is overkill. A single NPN level shifter should work.
simulate this circuit – Schematic created using CircuitLab
But I have to warn you that this is quite possibly marginal. It requires that the transistor be saturated at a gain of about 25, and this is a bit iffy. If the transistor is not quite in saturation, the relay voltage will not be a full 5 volts, and it may not operate reliably. In order to fix this, you might replace the NPN with a small N-type MOSFET with a logic-level gate threshold such as (for instance) a VN0104N3-G. These are available for less than $1.