The AS123 LED Driver from ACME Semiconductor (fictional) provides fully integrated PWM dimming and a programmable current set-point. This IC is specifically for automotive rear combination (tail/stop) lighting applications. It tightly regulates the desired string current under conditions of widely varying applied DC voltage.

The PWM dimming function, which switches the LED on and off at just over 300 Hz, is active when the line input pin is high and the "PWM_disable" pin is low (

The AS123 supports current programming using a single external resistor (see r_iset in the schematic). The resistor value can be selected to give the desired LED string current, using the following formula:

r_iset = 1.85/i_desired

The AS123 is capable of regulating up to 100mA per string continuously. Therefore the value of r_iset should be no less than 18.5 Ohms. The user can change this resistor value and run a new simulation, to see the effect of this change on the LED string current.

See a "functional block diagram" schematic model of the ACME AS123 here: https://www.systemvision.com/design/acme-as123-led-driver-schematic-model

-------------- End of Example Application Note ------------------

If you are a component supplier, this type of "Live Application Note" can help your potential customers better understand the features and benefits of your components.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to drive the Power MOSFET switches of the inverter.

There are two other versions of this design. The first, "PMSM Motor And Ideal Drive", uses continuous Clarke and Park Transform models and an ideal voltage drive to represent the main features of the field-oriented control system., Another version, "PMSM Motor and PWM Drive", it similar to this version but uses ideal switches.

This version is the most detailed and therefore simulated the most slowly. It is well suited for understanding the performance of the Power MOSFETs in the context of the system, In the waveform plot on the right, the actual motor shaft angle (orange waveform) and the A-phase current (dark blue waveform) are shown. These are very similar to the results for the other two versions of the design. But the waveform plot on the left provides insight into the performance of the C-phase inverter pull-up switch. The MOSFET current Ids (green waveform), and the average power dissipated in the device (red waveform) are shown. This design can be used to size specific parts in the drive electronics, by comparing the operating conditions to which they are exposed, relative to their rated operational limits.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to the switches of the bridge.

The waveform plot in the upper left shows the drive command (light blue waveform), with values 0 to 1, where 1 is commanding the maximum quadrature current of 10 A. The motor's response is the output shaft angle in radians (orange waveform), and shows that increasing torque command results in greater rotational displacement against the load spring. The waveform plot in the upper right shows the actual motor torque (green waveform) and the A-phase current (dark blue waveform).

In a companion version of this design, "PMSM Motor And Ideal Drive", Clarke and Park Transform models are used with a continuous ideal voltage drive.This shows the ability to develop motor control and drives at the abstract level and at the circuit level.

In yet another version of this design example, the ideal switches will be replaced with actual power MOSFET device models. This can help in bridge component sizing and performance specification.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to drive the Power MOSFET switches of the inverter.

There are two other versions of this design. The first, "PMSM Motor And Ideal Drive", uses continuous Clarke and Park Transform models and an ideal voltage drive to represent the main features of the field-oriented control system., Another version, "PMSM Motor and PWM Drive", it similar to this version but uses ideal switches.

This version is the most detailed and therefore simulated the most slowly. It is well suited for understanding the performance of the Power MOSFETs in the context of the system, In the waveform plot on the right, the actual motor shaft angle (orange waveform) and the A-phase current (dark blue waveform) are shown. These are very similar to the results for the other two versions of the design. But the waveform plot on the left provides insight into the performance of the C-phase inverter pull-up switch. The MOSFET current Ids (green waveform), and the average power dissipated in the device (red waveform) are shown. This design can be used to size specific parts in the drive electronics, by comparing the operating conditions to which they are exposed, relative to their rated operational limits.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to drive the Power MOSFET switches of the inverter.

There are two other versions of this design. The first, "PMSM Motor And Ideal Drive", uses continuous Clarke and Park Transform models and an ideal voltage drive to represent the main features of the field-oriented control system., Another version, "PMSM Motor and PWM Drive", it similar to this version but uses ideal switches.

This version is the most detailed and therefore simulated the most slowly. It is well suited for understanding the performance of the Power MOSFETs in the context of the system, In the waveform plot on the right, the actual motor shaft angle (orange waveform) and the A-phase current (dark blue waveform) are shown. These are very similar to the results for the other two versions of the design. But the waveform plot on the left provides insight into the performance of the C-phase inverter pull-up switch. The MOSFET current Ids (green waveform), and the average power dissipated in the device (red waveform) are shown. This design can be used to size specific parts in the drive electronics, by comparing the operating conditions to which they are exposed, relative to their rated operational limits.

This LED lighting example demonstrates the value of simulating both the electrical and thermal* aspects of power dissipating circuits together, simultaneously.

In this application example, a Vishay NTCS0603 Thermistor provides feedback of the enclosure temperature. This feedback is used to control PWM dimming of the LEDs, thereby limiting the internal temperature when operating at high external ambient temperature conditions.

This is a "Live" design, the user can change key parameter values and then run new simulations to see the results. These parameters include "r_mirror", the resistance of the current mirror that controls the capacitor charging rate of the 555 timer, and thereby set the PWM frequency. The user can also change "r_offset" that controls the temperature level at which the dimming operation begins. Finally, the user can set "r_iLED_set", to control the ON-state operating current of the LEDs.

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* To reduce the time needed to simulate the transition and settling at 6 different temperature levels, all thermal time constants were reduced by approximately 1000x. The actual thermal response time constant of the NTCS0603 is approximately 3 seconds (depends on mounting), not 3 msec! Also, the enclosure thermal capacitance value would more likely be 3 (J/degC) instead of 3 (mJ/degC), giving a thermal time constant for the enclosure of 10 (degC/Watt) * 3 (J/degC) = 30 seconds. This time scaling does not affect the static relationship between the outside temperature and PWM dimming.

This LED lighting example demonstrates the value of simulating both the electrical and thermal aspects of power dissipating circuits together, simultaneously.

In this application example, a Vishay NTCS0603E3103MT Thermistor provides feedback of the enclosure temperature. This feedback is used to control PWM dimming of the LEDs, thereby limiting the internal temperature when operating at high external ambient temperature conditions.

This is a "Live" design, the user can change key parameter values and then run new simulations to see the results. These parameters include "r_mirror", the resistance of the current mirror that controls the capacitor charging rate of the 555 timer, and thereby set the PWM frequency. The user can also change "r_offset" that controls the temperature level at which the dimming operation begins. Finally, the user can set "r_iLED_set", to control the ON-state operating current of the LEDs.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to drive the Power MOSFET switches of the inverter.

There are two other versions of this design. The first, "PMSM Motor And Ideal Drive", uses continuous Clarke and Park Transform models and an ideal voltage drive to represent the main features of the field-oriented control system., Another version, "PMSM Motor and PWM Drive", it similar to this version but uses ideal switches.

This version is the most detailed and therefore simulated the most slowly. It is well suited for understanding the performance of the Power MOSFETs in the context of the system, In the waveform plot on the right, the actual motor shaft angle (orange waveform) and the A-phase current (dark blue waveform) are shown. These are very similar to the results for the other two versions of the design. But the waveform plot on the left provides insight into the performance of the C-phase inverter pull-up switch. The MOSFET current Ids (green waveform), and the average power dissipated in the device (red waveform) are shown. This design can be used to size specific parts in the drive electronics, by comparing the operating conditions to which they are exposed, relative to their rated operational limits.

Permanent Magnet Synchronous Machine (PMSM) and PWM Drive circuit, with mechanical load. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate the digital PWM signals to drive the Power MOSFET switches of the inverter.

There are two other versions of this design. The first, "PMSM Motor And Ideal Drive", uses continuous Clarke and Park Transform models and an ideal voltage drive to represent the main features of the field-oriented control system., Another version, "PMSM Motor and PWM Drive", it similar to this version but uses ideal switches.

This version is the most detailed and therefore simulated the most slowly. It is well suited for understanding the performance of the Power MOSFETs in the context of the system, In the waveform plot on the right, the actual motor shaft angle (orange waveform) and the A-phase current (dark blue waveform) are shown. These are very similar to the results for the other two versions of the design. But the waveform plot on the left provides insight into the performance of the C-phase inverter pull-up switch. The MOSFET current Ids (green waveform), and the average power dissipated in the device (red waveform) are shown. This design can be used to size specific parts in the drive electronics, by comparing the operating conditions to which they are exposed, relative to their rated operational limits.

Permanent Magnet Synchronous Machine (PMSM) and Ideal (continuous) Drive circuit, with mechanical load. The drive includes a D-Q control algorithm.

In a companion version of this design, "PMSM Motor And PWM Drive", the same motor control algorithm is used but SVM (space vector modulation) provides PWM switching signals to ideal switches in an actual 3-phase inverter implementation.