LM34914SDX

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LM34914SDX Application Field and Working Principle

The LM34914SDX is a member of the DC DC Switching Regulators category of PMIC (power management integrated circuits). It is specifically designed for integration into LED lighting systems. The main purpose of the LM34914SDX is to regulate incoming voltage for smooth and constant LED output, however due to its highly advanced circuitry the LM34914SDX can also handle a variety of other regulated voltage levels. Given the regulator’s switching nature, its power efficiency is superior to most other voltage sources.

As the name suggests, the LM34914SDX implements a switching regulator architecture which is an incredibly efficient way of converting different voltages and can range from as low as 5V to as high as 45V. The main workings are divided into two stages: a switching stage and a linear stage.

Switching stage

The activity in the switching stage begins when an input control signal is received. This control signal determines the state in which the switch will be put in, meaning it can either be shut off or kept on. The power transistor connected to the control signal, and thus acts as the switch, moves from a conducting state to a blocking state, depending on the state of the control signal, thus drawing current from the input source. The current then flows through the primary winding of the inductor which itself produces a magnetic field, based on the current flowing through it. This in turn, generates a voltage drop across the inductor’s secondary winding. As soon as the switching transistor switches back to its conducting state, the magnetic field is released to current through the secondary winding, producing a voltage impulse. The duration of the pulse is determined by the control signal frequency. This can either be a pulse width modulation or a pulse frequency modulation. Thus, depending on the input voltage and the status of the control signal, the switching stage will supply a high frequency current, which is generated by the switching activity of the switch itself and the change in voltage of the secondary winding.

Linear stage

The linear stage is the circuit responsible for controlling and regulating the output voltage. In order to maintain the desired voltage output, the linear stage needs to operate from an isolated, effectively regulated power source. This power source is the output of the switching stage, which itself is determined by the signal of the control signal. A controller is then used to keep the output signal under regulation. This controller adjusts the frequency of the switching cycle, thus "PWMing" the frequency of the switch and linearly smoothing the output signal. This happens whenever the output voltage deviates from the specified reference. In order to monitor the output voltage and to provide feedback to the switch, an output signal is taken from the output of the linear stage and fed back into the control signal, thus completing the loop.

The LM34914SDX is a highly efficient power regulator, capable of delivering a continuous output current of up to 5A, with a minimum output voltage of just 5V. This makes it an ideal choice for LED lighting systems, where the LED’s are typically powered off of varying DC voltages. The regulator also implements advanced circuitry to provide greater power efficiency as compared to other voltage sources. It is easy to integrate into existing LED solutions and provides a highly regulated output voltage.

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