DesignSpark Current Boost Regulator with Onsemi NCV4264 LDO

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This 5V regulator circuit provides up to 3A load current capability, well above the 100mA current limit of the Onsemi NCV4264 LDO component itself. This is thanks to the load sharing role of the Onsemi 2N5195G PNP bypass transistor.

For the first 30ms of the simulation, the load switch is open so the total load current flows through the fixed 100 Ohm resistor (~50mA = 5V/100Ohm, see the yellow waveform on the right). After the switch closes and for the next 50ms, the load current jumps to approximately 2.55A (i.e. the additional 2.5A flows through the 2 Ohm switched resistor). Note that the output voltage is very close to 5V under both loading conditions (purple waveform), as desired for a regulated output!

To better understand how this works, note that most of the current supply to the LDO passes through the 15 Ohm bias resistor on the left. The corresponding voltage drop, as seen by comparing the brown and green waveforms on the left, is across the emitter-base junction of the PNP transistor. When that current rises above ~40mA, giving a sufficient (&gt; 0.6V) forward bias to the transistor, it results in a large transistor "boost" current flow through the parallel path to supply the load. You can compare the "boost" current (magenta waveform) to the normal LDO current (blue waveform) under these two distinct operating load conditions. Very little "boost" current is used under light-load, but it supplies almost all of the current under heavy loading conditions.

The following RS components are used in the design:

Onsemi 5V/100mA LDO: <a href="https://us.rs-online.com/product/on-semiconductor/ncv4264d50r2g/70467199/">NCV4264</a>

Onsemi -4A/-80V PNP Transistor: <a href="https://us.rs-online.com/product/on-semiconductor/2n5195g/70099758/">2N5195G</a>

Kemet 10uF Aluminum Electrolytic Capacitor: <a href="https://us.rs-online.com/product/kemet/eev106m050s9gaa/70971233/">EEV106M050S9GAA</a>

Kemet 1uF Ceramic Capacitor: <a href="https://us.rs-online.com/product/kemet/c1206c105k3ractu/70095658/">C1206C105K3RACTU</a>

You can view the companion "Electro-Thermal" simulation of this design here: <a href="https://explore.partquest.com/node/599492">DesignSpark Current Boost Regulator with Onsemi NCV4264 LDO Electro-thermal Design</a>

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