SMPS Halogen Lamp Circuit

SMPS Halogen lamps usually need transformers to work.

This post is about a new kind of transformer that uses a switching power supply.

It is simpler than older transformers and works with other light bulbs too as long as they do not use radio waves RF.

This new design also saves energy.

What is a SMPS Halogen Lamp Circuit:

A power supply circuit is designed for safely powering halogen lamps is referred to as an SMPS Switched Mode Power Supply.

Halogen lights need a constant regulated power source and generally operate at higher temperatures.

To fulfill these needs an SMPS design is often used so that it provides a regulated output voltage or current to light the halogen lamp.

Circuit Design and Working:

Parts List:

With MOSFETs arranged in a half bridge configuration the circuit is powered by the IR2153 which has an RC oscillator and a floating upper MOSFET driver.

The transformers mains generates an effective voltage of about 107V when it operates at a frequency of about 50 kHz.

Formulas and Calculations:

The voltage calculation follows the following formula:

U_ef = ( U_vst − 2 ) *0.5*√(t−2*deadtime / t )

where,

• Uef is the effective voltage output
• Uvst stand for the voltage goal or setpoint that the SMPS is attempting to reach or sustain.
• t is probably a timing parameter or time constant in the circuit
• deadtime is the SMPS switching cycles dead time.
• t −2*deadtime / t indicates how the effective voltage Vef fluctuates in relation to the switching cycle timing.
• 0.5 0.5 is the scaling factor to modify the effective voltage computation may include this coefficient.

Transformer Tr1:

The ferrite core EE or EI used in the construction of the pulse transformer Tr1 is obtained from computer switching power supply like AT or ATX.

The cross section of the core should be between 90 and 140 mm².

Depending on the particular needs of the bulb, adjustments to the number of rotations is required.

To reduce magnetic leakage a winding approach with 20 turns under and 20 turns above the secondary is used for a standard AT or ATX transformer with 40 turns on the primary.

Transformation Ratio Calculation:

To determine the transformation ratio assuming an effective voltage of 107V at the primary for a 230V line input the calculation is made as follows:

Transformation Ratio = 107V / 11.5V = 9.304

For a 12V bulb with a desired voltage of 11.5V the primary requires:

9.304 × 4t = 37t

To make sure the winding configuration is correct modifications are needed.

Output Power and Components:

Using MOSFETs such as STP9NK50Z or IRF840 without a heatsink the electronic transformer can handle outputs up to 80-100W.

Higher power requirements can be met with additional heatsinks and/or more powerful MOSFETs like STP15NK50ZFP, STW20NK50Z, STP25NM50N, IRFP460, IRFP460LC, STB25NM50N-1 or 2SK2837 with a recommended Uds of 500-650V.

Caution is advised regarding the length of leads to the bulb due to RF voltage and potential interference.

Safety Warning:

It is important to remember that almost every component of the circuit is electrically connected to the mains.

Tr1s poor design result in mains voltage at the output which could be dangerous.

Plan carefully about the awareness of safety regulations while building and using the Electronic Halogen Transformer

To ensure a safe working device it is necessary to carefully follow the many steps involved in building the Electronic Halogen Transformer.

The transformer construction guide is provided below:

Circuit Design:

Make a circuit schematic diagram using the guidelines listed in the beginning.

Add the IR2153 IC, the pulse transformer Tr1 and the half bridge setup with MOSFETs.

Make sure that there is enough room for all the components on a circuit board so that we can connect them correctly.

Transformer Construction:

Follow the transformer design while cutting and shaping the ferrite core if it is not already in the appropriate shape.

Use the recommended amount of turns and winding process such as 20 turns under and 20 turns above the secondary while winding the primary coil on the ferrite core.

Unwind the whole secondary and the top half of the original primary.

Wind the new secondary the necessary number of turns while considering the intended bulbs voltage factors

Check that the windings are properly sealed before reconstructing the core.

Circuit Assembling:

Solder the circuit boards components in line with the layout and design.

Make a half bridge connection between the IR2153 IC and the MOSFETs.

Connect the capacitive divider and diode bridge while following the circuit design .

Make sure the transformer is properly polarized before connecting it to a power source.

While looking for problems test the voltages at several locations across the circuit using a multimeter.

To get the desired output change the transformers number of turns or other settings as needed.

Troubleshooting:

• If issues arise use the oscilloscope and multimeter to troubleshoot and make necessary adjustments.

Safety Precautions

• Ensure all components are well insulated to prevent electrical hazards.
• Keep leads to the bulb as short as possible to minimize RF interference.

Conclusion:

Safety measures should be taken while constructing or operating with an SMPS halogen light circuit especially because halogen lamps can get quite hot when in use.

Its important to follow the necessary safety standards and laws.

One should follow the design rules and safety standards if you are planning to construct or modify such a circuit.

References

Halogen Lamps Technical Specifications data