Transformerless Power Supply
Compact transformerless power supply circuit provides a low-current DC output for small electronics using capacitive or resistive voltage drop methods.
Transformerless power supply:
Transformerless power supply offers a small and economical way of converting the AC mains voltage to low-current DC without the large transformer. It is usually used with small electronics, where capacitive or resistive methods of voltage drop are safely used to reduce voltage. This is suitable in the case of LED circuits, low-power sensors, or gadgets that have low power requirements. Although it is small and cheap, it is not isolated of the mains and must be treated carefully. The working principle, input to output connections, and installation can be explained in this guide, moreover, hobbyists and electronics enthusiasts can easily adopt a simple AC to DC power supply to high-power applications by implementing this guide.
5 pin relay connection
A 5 pin relay wiring diagram shows the connections for relay terminals 85, 86, 30, 87, and 87a. This relay is commonly used in automotive, lighting, motor, and switching circuits where both normally open (NO) and normally closed (NC) contacts are required.
- Terminal 85 & 86: Coil connections. When energized with 12V or 24V, they create a magnetic field to switch the relay.
- Terminal 30: Common input terminal connected to the power supply.
- Terminal 87: Normally Open (NO) contact, which connects to 30 when the coil is energized.
- Terminal 87a: Normally Closed (NC) contact, which connects to 30 when the coil is de-energized.
This relay allows switching between two circuits or controlling high-current loads with a low-current trigger. For example, in cars, it is used for headlights, horns, fuel pumps, and fan motors.
Work / Installation (Inputs → Outputs)
Input: Battery/Power Supply → Relay Coil (85, 86) → Common Terminal (30).
- Connect terminal 85 to ground/negative.
- Connect terminal 86 to the switch or control signal (positive).
- Connect terminal 30 to the battery positive or common input source.
- Connect terminal 87 to the load that should turn ON when relay is energized.
- Connect terminal 87a to the load that should remain ON when relay is OFF.
Output: When the coil (85–86) is powered, 30 connects to 87 (NO). When coil is OFF, 30 connects to 87a (NC).
Testing & Final Adjustments
After wiring, supply voltage to 85 and 86. Listen for a clicking sound, which indicates the relay is switching. Use a multimeter to check continuity:
- With coil OFF → 30 connects to 87a.
- With coil ON → 30 connects to 87.
Verify proper switching under load. Ensure wires are correctly rated and terminals are tightened. In automotive use, add a fuse between battery and relay input for safety. Label terminals to avoid confusion and prevent wrong wiring. Once tested, the relay provides reliable operation for lights, fans, motors, and automation circuits.
Frequently Asked Questions - Transformerless Power Supply:
What is a transformerless power supply?
A power supply that converts AC to DC without using a transformer.
How does it work?
It uses a series capacitor or resistor to drop voltage, then rectifies and filters DC output.
Is it isolated from mains?
No, it is non-isolated; care must be taken to avoid electric shock.
What voltage can it provide?
Typically low DC voltage suitable for LEDs or small electronics.
Can it power high-current devices?
No, it is meant for low-current applications only.
Is it safe for beginners?
With proper insulation and precautions, yes, but direct mains is dangerous.
Can it be regulated?
Yes, using Zener diodes or small voltage regulators.
What components are used?
Capacitor/resistor, diodes, filter capacitor, optional Zener.
Can it power LED lights?
Yes, ideal for low-power LED lighting.
Is it cost-effective?
Yes, it is compact, simple, and inexpensive.
