SMPS Halogen Lamp Circuit

SMPS Halogen lamps usually need transformers to work.

This guide 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 SMPS Switched Mode Power Supply halogen lamp circuit is a power supply circuit designed to drive halogen lamps efficiently.

Halogen lamps typically operate at higher temperatures and require a stable and regulated power source.

An SMPS design is commonly employed to meet these requirements, providing a regulated output voltage or current to power the halogen lamp.

Circuit Design and Working:

Parts List:

The circuit is structured as a half bridge with MOSFETs and driven by the IR2153 featuring a floating upper MOSFET driver and an RC oscillator.

Operating at a frequency of around 50kHz, the primary of the pulse transformer achieves an effective voltage of approximately 107V.

Formulas and Calculations:

The voltage calculation follows the following formula:

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

where,

• Uef: This is the effective voltage output, or a parameter associated with the SMPS circuits output voltage, particularly in relation to regulating or controlling the voltage.
• Uvst: This might stand for the voltage goal or setpoint that the SMPS is attempting to reach or sustain.
• The expression Uvst​−2 indicates a particular offset or adjustment from this setpoint.
• t: This is probably a timing parameter or time constant in the circuit; it could have anything to do with the switching frequency or another aspect of the SMPS functioning.
• deadtime: This is the SMPS switching cycles dead time.
• In order to prevent shoot through current, dead time is the amount of time that both the high side and low side switches in a half bridge or full bridge system are off.​
• t −2*deadtime / t: this word may indicate how the effective voltage, Vef fluctuates in relation to the switching cycle timing.
• It proposes a scaling factor or adjustment based on the ratio of t−2 deadtime to t.
• 0.5 0.5: The scaling factor to modify the effective voltage computation may include this coefficient.

Transformer Tr1:

The pulse transformer Tr1 is constructed on a ferrite core EE or EI obtained from computer switching power supplies, such as AT or ATX.

The core should have a cross section ranging from 90 to 140mm².

Adjustments to the number of turns may be necessary based on the specific bulb requirements.

For a typical AT or ATX transformer with 40 turns on the primary, a winding technique involving 20 turns under and 20 turns above the secondary is employed to minimize magnetic leakage.

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:

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

Adjustments are made to ensure a proper winding configuration.

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 crucial to note that nearly all parts of the circuit are electrically connected to the mains.

Inadequate design of Tr1 may lead to mains voltage at the output posing potential hazards.

Careful consideration and adherence to safety guidelines are essential during the construction and operation of the Electronic Halogen Transformer.

Building the Electronic Halogen Transformer involves several processes, and it is essential to follow them carefully to ensure a safe and functional device.

Below is guide for constructing the transformer:

Circuit Design

Create a schematic diagram of the circuit based on the specifications mentioned in the initial content.

Include the half bridge configuration with MOSFETs, the IR2153 IC and the pulse transformer Tr1.

Plan the layout of components on a circuit board, ensuring sufficient space and proper connections.

Transformer Construction

If the ferrite core is not already in the desired shape, cut and shape it according to the transformer design.

Wind the primary coil on the ferrite core considering the recommended number of turns and winding technique e.g. 20 turns under and 20 turns above the secondary.

Unwind the upper half of the original primary and the entire secondary.

Wind the new secondary with the required number of turns considering the voltage specifications for the intended bulb.

Reassemble the core, ensuring proper insulation between windings.

Circuit Assembly

Solder the components onto the circuit board according to the schematic and layout.

Connect the MOSFETs and the IR2153 IC in the half bridge configuration.

Connect the diode bridge and capacitive divider as per the circuit design.

Connect the transformer to a power source ensuring proper polarity.

Use a multimeter to measure voltages at various points in the circuit, checking for any irregularities.

If necessary, adjust the number of turns on the transformer or other parameters to achieve the desired output.

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:

When designing or working with a SMPS halogen lamp circuit, it is crucial to consider safety precautions especially since halogen lamps can become very hot during operation.

Additionally, compliance with relevant safety standards and regulations is essential.

If you plan to build or modify such a circuit, it is recommended to refer to established design guidelines and safety standards.

References

Halogen Lamps Technical Specifications data