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,

• The effective voltage output is represented by Uef.
• The voltage goal or the starting point that the SMPS is trying to reach or maintain is represented by Uvst.
• It is most likely a time constant or timing component in the circuit.
• Deadtime is the dead time of SMPS switching cycles.
• The fluctuation of the effective voltage Vef with respect to the timing of the switching cycle is shown by the formula t −2*deadtime / t.
• This value is sometimes included in the scaling factor of 0.5 0.5 which modifies the actual voltage calculation.

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 a 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:

The transformation ratio for a 230V line input is calculated as follows assuming an effective voltage of 107V at the primary:

Transformation Ratio = 107V / 11.5V = 9.304

For a 12V bulb with a required 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.

The length of the leads to the lightbulb must be safe because of RF voltage and the risk of 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:

Using the instructions given in the beginning create a circuit schematic diagram.

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

Verify that a circuit board has sufficient space for all of the components so that they may be connected properly.

Transformer Construction:

Follow the transformer design while cutting and shaping the ferrite core if it is not already in the proper 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 followed 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 planning to construct or modify such a circuit.

References

Halogen Lamps Technical Specifications data