Question

You are designing an LED dimmer that controls the light intensity through PWM. The LED circuit draws 500 mA when on at 12V. The normal operating condition is 60% duty cycle and switching at 10 kHz. You are between using the BCP56-16T1G BJT and MGSF1N03LT1G MOSFET (assume you are driving with 10V) as a low-side switch. Which device would be best to use from an efficiency perspective (accounting only for conduction and switching loss)? Why?

Answer 1

Comparison between IGBT and MOSFET on conduction and switching based as light controller ( IN DIMMER)

MOSFET as power switch
The MOSFETs (metal oxide semiconductor field effect transistors) are also switching power device like IGBTs. They typically characterized as faster switching but higher conduction loss during on-state compared to IGBTs. The MOSFET is majority carrier device and therefore it is not suffering from tail current that happens in bipolar power devices such as IGBT or BJT (Bipolar Junction Transistors). Consequently MOSFETs have less switching loss and are capable of higher switching frequency than IGBTs. On the contrary bipolar devices are having benefits from conductivity modulation during on-state. The conductivity of IGBT is getting lowered during on-state thanks to hole injection from additional p-type layer, and it results in lower conduction loss of IGBT compared to MOSFETs especially at high current range. A drawback of bipolar action is certain amount of voltage drop – Vce(sat) across the IGBT even with small current level.

The IGBTs (insulated gate bipolar transistors) have the ability of being turned off anytime during the phase

The operating frequency of power switch in light dimmer is line frequency. Since the switching frequency is low, IGBTs are often considered as appropriate power switch for dimmers. However, operating current is less than 4 A even with the case of 400-W dimmer. The average current through the power switch is 0.5 A when on-duty is 0.60. Typical IGBT rating for this 400-W rated dimmer is 600 V, 15 A, and Vce(sat) of IGBT is around 1.4 V at 3 A, 100°C. In this current range, MOSFET can achieve lower conduction loss. Therefore conduction loss is primary power loss and MOSFET can be selected based on on-resistance characteristics. With the latest high voltage MOSFET technologies, low on-resistance MOSFETs are widely available at affordable price.

Device operating temperature

They provide smaller footprint, easier assembly, and better performance. They provide smaller footprint, easier assembly, and better performance.