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so im using 2 mosfets per phase, one between 48v and phase, and the other one be...
dtorrese

dtorrese

@copilot mi error, lo que hice fue conectar una resistencia pull down entre el gate del high side mosfet y tierra en lugar de conectarla entre el gate y la fase, ya que la fase está conectada al source del mosfet del highside, mi pregunta es, que podría provocar esto ?
2y

copilot

Conectar una resistencia pull-down directamente entre el gate del MOSFET de lado alto (high-side MOSFET) y tierra (GND) podría tener varias implicaciones en tu circuito, dependiendo del resto del diseño y cómo pretendías controlar ese MOSFET. Aquí te detallo algunas consecuencias potenciales:
  1. Encendido Inadvertido: Los MOSFETs de lado alto generalmente se utilizan para controlar cargas en un rango de voltaje más alto que el del circuito de control. Conectando el gate directamente a GND a través de una resistencia pull-down, estás asegurando que el gate esté a un potencial de 0V (o muy cercano) respecto a GND. Si la tensión en el source es significativamente positiva (en tu caso, conectada a una fase), podría no ser suficiente para mantener el MOSFET apagado, porque el voltaje (V_{GS}) (voltaje gate-source) podría no ser suficientemente negativo o bajo para apagarlo.
  2. Control Ineficiente: Para un MOSFET de canal N de lado alto, el voltaje de gate-source ((V_{GS})) positivo necesario para encender el transistor debe ser mayor que el voltaje de threshold ((V_{th})), y debe referenciarse al source. Esto significa que conectar el gate directamente a GND a través de una resistencia pull-down no es útil para el control eficaz del MOSFET, ya que inhibe la capacidad de aplicar un voltaje adecuado entre gate y source para encenderlo correctamente.
  3. Interferencia en la Función de Conmutación: Si estás utilizando un driver de MOSFET o algún circuito especial para controlar el gate del MOSFET de alto lado, la presencia de una resistencia pull-down a GND puede interferir con la capacidad del driver para elevar el voltaje de gate a un nivel suficiente para encender el transistor. Esto puede resultar en una conmutación más lenta o en que el MOSFET no se encienda completamente, afectando la eficiencia y aumentando las pérdidas de potencia.
  4. Disipación de Potencia Inesperada: Aunque es menos probable dependiendo de la configuración exacta de tu circuito, si el MOSFET de alguna manera entra en una región de operación en la que no esté completamente apagado ni completamente encendido (una condición de alta resistencia), podría disipar potencia inesperadamente, lo que lleva a problemas de calor.
La forma de evitar estos problemas es asegurar que el gate del MOSFET se controle de manera que el voltaje (V_{GS}) sea adecuado para las condiciones de encendido y apagado esperadas. Para un high-side MOSFET de canal N, esto normalmente se hace utilizando técnicas como el uso de un driver de gate con bootstrap o un controlador dedicado que pueda proporcionar un voltaje adecuado por encima del voltaje de source para encender el MOSFET efectivamente.
2y
dtorrese

dtorrese

mi error, lo que hice fue conectar una resistencia pull down entre el gate del high side mosfet y tierra en lugar de conectarla entre el gate y la fase, ya que la fase está conectada al source del mosfet del highside, mi pregunta es, que podría provocar esto ?
2y
dtorrese

dtorrese

@copilot si en lugar de poner una resistencia en pulldown entre 48v y fase la pongo entre 48v y tierra para el mosfet del high side, que efecto puede tener en los mosfets? puede provocar un corto circuito o que se active sin querer?
2y

copilot

La conexión de una resistencia en configuración de pulldown se usa típicamente para asegurar que el gate de un MOSFET permanezca en un estado conocido (bajo en este caso) cuando no se le aplica un voltaje de control. Esta técnica es crucial para evitar activaciones involuntarias del MOSFET debido a ruido o cargas estáticas. Sin embargo, la ubicación y el propósito de dicha resistencia varían dependiendo de la aplicación y la topología de circuito en cuestión.
Considerando tu pregunta, parece que hay cierta confusión acerca de conectar una resistencia de pulldown entre 48V y la fase (supongamos que "fase" se refiere al gate del MOSFET de high-side en un circuito), o entre 48V y tierra para un MOSFET de high-side. Aquí desglosaré ambos escenarios:
Resistencia de Pulldown Entre 48V y el Gate del MOSFET de High-Side
  • Conectar directamente la resistencia entre 48V y el gate: Esto no es una configuración pulldown tradicional. De hecho, aplicar directamente 48V al gate de un MOSFET podría dañarlo grave o permanentemente, ya que la mayoría de los MOSFETs tienen un límite de voltaje gate-to-source (Vgs) que suele estar mucho por debajo de 48V (por ejemplo, ±20V).
Resistencia de Pulldown Entre 48V y Tierra para el MOSFET de High-Side
  • Conectar una resistencia entre tierra y el gate del MOSFET de high-side: En teoría, esto mantendría el MOSFET en estado desactivado mientras no se le aplique una tensión de control positiva respecto a su source. Sin embargo, en la práctica, esto podría no ser efectivo o seguro para un MOSFET de high-side por varias razones:
    • Voltaje negativo en el gate: Para un MOSFET de high-side, conectar el gate directamente a tierra a través de una resistencia podría implicar un voltaje Vgs negativo cuando el source está positivo (i.e., cuando el MOSFET está conduciendo). Esto es inverso a lo deseado y podría conducir a comportamientos no deseados.
    • Activación Involuntaria: No necesariamente causaría un cortocircuito directo, pero si la diferencia de potencial entre el gate y el source no se maneja correctamente, puede resultar en una activación no deseada o dañar el MOSFET.
Recomendación
Para un MOSFET de high-side, se utiliza comúnmente un esquema de "bootstrap" o un driver de gate dedicado que puede manejar adecuadamente el voltaje entre el gate y source, incluso cuando el source esté a un voltaje alto. La resistencia de pulldown se conectaría entre el gate y source del MOSFET para asegurar que se mantenga apagado cuando no haya una señal de activación.
Si quieres una configuración específica o más detalles sobre cómo manejar MOSFETs de high-side en tu proyecto, por favor, proporciona más información sobre tu configuración actual, y con gusto te asistiré con recomendaciones más detalladas.
2y
dtorrese

dtorrese

@copilot if im building an esc for a 48v 500w motor, using 2ed2184 drivers and IRFB7734 mosfets, if i fix the switching frequency to 20kHz, and have the code run going from a sequence fo phase A-B, A-C and so on using 6 step commutation, can the speed of the motor be increased by varying the pulse width of the gate of the mosfets?
2y

copilot

Yes, the speed of the motor can be increased by varying the pulse width of the gate of the MOSFETs when building an ESC (Electronic Speed Controller) for a 48V 500W motor using 2ED2184 drivers and IRFB7734 MOSFETs, with a fixed switching frequency of 20kHz and employing 6-step (trapezoidal) commutation for phase sequencing (A-B, A-C, and so on).
Here’s how it works:
  • PWM (Pulse Width Modulation): By varying the pulse width that controls the gate of the MOSFETs, you essentially adjust the effective voltage and current delivered to the motor. A wider pulse width increases the average voltage (and hence speed), while a narrower pulse width decreases it.
  • Gate Control via 2ED2184: The 2ED2184 driver facilitates efficient switching of the MOSFETs at high frequencies, such as your 20kHz switching frequency. Adjusting the pulse width modulated signal to the gates of IRFB7734 MOSFETs controlled by these drivers directly influences the motor speed.
  • 6-Step Commutation: This method helps in commutating the motor by switching the phases in sequence (e.g., A-B, A-C,...). By applying PWM within this context, you variably adjust the speed of the motor by changing how "strongly" or "weakly" each commutation step is applied.
The detailed implementation can be adjusted as follows:
  • Generate PWM signals at your chosen switching frequency (20kHz) with a microcontroller or similar device.
  • Control the PWM duty cycle (pulse width variation) to modulate the speed. For instance, setting a duty cycle closer to 100% will try to apply full power (as per the limit of your power supply and motor specifications), thereby increasing motor speed. Conversely, reducing the duty cycle decreases the speed.
Here are a few considerations for your project:
  • Heat Dissipation: High-power applications like a 500W motor can generate significant heat. Ensure your MOSFETs, especially the IRFB7734, have adequate heat sinking and cooling.
  • Driver and MOSFET Compatibility: Verify that the 2ED2184 gate driver's output can properly drive the gates of your IRFB7734 MOSFETs considering factors like gate charge and required voltage levels.
  • Electrical Parameters: Check the electrical parameters of your motor and make sure that your ESC design meets these requirements, especially regarding the voltage (48V) and power (500W) ratings.
  • Protection Mechanisms: Implementing safety and protection mechanisms (such as overcurrent protection, under-voltage lockout, and thermal shutdown) can help prevent damage to the motor and the controller.
By adjusting the PWM duty cycle, you essentially control the power delivered to the motor, thereby controlling its speed. Your approach of using 20kHz for the switching frequency is a good balance between efficiency and minimizing audible noise or electromagnetic interference (EMI).
2y
dtorrese

dtorrese

@copilot if the driver I'm using is an 2ED2184 and mosfets are IRFB7734, is it still recommended to use pull down resistors?
2y

copilot

For your project involving the 2ED2184 gate driver and IRFB7734 MOSFETs, the use of pull-down resistors on the gate of the MOSFETs can still be recommended depending on the specifics of your application and the behavior you wish to achieve. Even though the 2ED2184 is designed to actively drive the gate of the MOSFET, including both turning it on and off, there are a few considerations that might lead you to include pull-down resistors:
  1. Undefined States During Power-Up/Down: During the power-up or power-down sequences, the gate driver might not be fully operational, and the gate of the MOSFET could potentially float to an indeterminate state. A pull-down resistor ensures that the gate is held low (turning the MOSFET off) until the driver actively drives it.
  2. Noise Immunity: In noisy environments, a pull-down resistor can help to provide additional immunity against spurious turn-ons of the MOSFET by ensuring that minor noise spikes are less likely to inadvertently turn the MOSFET on.
  3. Protection During Uncoupled States: If there are scenarios where the MOSFET could be disconnected from the driver (either during testing, assembly, or fault conditions), a pull-down resistor ensures that the gate will not float and potentially turn on the MOSFET unintentionally.
The choice of resistor value is a balance between power consumption (lower values consume more power but provide stronger pull-down capability) and effective gate control (higher values consume less power but might be less effective in noisy conditions). Typical values range from 1kΩ to 10kΩ.
Given these considerations, if your application is sensitive to any of the above scenarios, adding pull-down resistors could be beneficial. You'd connect them as follows:
  • Connect a pull-down resistor between the gate and source of each IRFB7734 MOSFET. For example, for a MOSFET designated as Q1, you would connect a resistor (let's designate it RPD1 for "Pull-Down 1") between Q1:Gate and Q1:Source. Specify the resistor as follows:
    • Connect RPD1:1 to Q1:Gate
    • Connect RPD1:2 to Q1:Source
Remember, these design strategies are dependent on your specific application requirements and the environment in which your device will operate. It's always good practice to validate your design through simulation and physical testing to ensure optimal performance and reliability.
2y
dtorrese

dtorrese

@copilot so im using 2 mosfets per phase, one between 48v and phase, and the other one between phase and ground, for the low side one, i want to use a 10k resistor for pulldown connecting it between the mosfet gate and gnd, for the high side one, where should it be connected? plus which ohm resistance do you recommend for either resistor?
2y

copilot

For your setup with 2 MOSFETs per phase in an H-bridge configuration (high side and low side MOSFETs), you’re off to a good start by planning to use a pull-down resistor on the low side MOSFET. This resistor ensures that the gate is pulled to a low state when not actively driven, preventing the MOSFET from inadvertently turning on. Your choice of a 10k resistor for the pull-down is typical and generally works well to keep the gate voltage low without drawing too much current when the gate is driven high.
For the high side MOSFET, things are a bit different due to its connection to the higher voltage rail (48V in your case). The gate voltage of the high side MOSFET needs to be driven higher than the source voltage (which could be up to 48V) to turn it on, typically requiring a gate drive voltage greater than 48V. This is usually accomplished with a bootstrap circuit or a gate driver IC that can provide a higher voltage and incorporate charge pumps or other mechanisms for this purpose.
Regarding where to connect a resistor for the high side MOSFET and what value it should have:
  • High Side Resistor: This can be more complex due to the need for a higher gate voltage. However, if you're using a pull-down resistor to ensure the MOSFET remains off when not actively being driven, it should be connected between the gate and source of the high side MOSFET. This configuration ensures that the gate is pulled to the source voltage level (not ground), effectively keeping the MOSFET off. The assumption here is that you have a driving circuit able to handle the necessary voltage levels for turning the high side MOSFET on and off.
  • Resistance Value: For the high-side pull-down resistor, a value in the range of 4.7k to 10k ohms is also reasonable. This range provides a good balance between ensuring the gate is reliably pulled to the source voltage without excessive current draw through the resistor when the gate is driven high.
Example Connections:
  • Low Side MOSFET:
    • Gate Drive: Connect your gate driver output to the gate of the low side MOSFET (e.g., Connect GD1:OUT to QL1:G).
    • Pull-Down Resistor: Connect a 10kΩ resistor between the gate and ground (e.g., Connect R1:1 to QL1:G, R1:2 to GND).
  • High Side MOSFET:
    • Gate Drive: Connect your high side gate driver output to the gate of the high side MOSFET (e.g., Connect GD1:HB_OUT to QH1:G).
    • Pull-Down Resistor: Connect a 4.7kΩ to 10kΩ resistor between the gate and source of the high side MOSFET (e.g., Connect RH1:1 to QH1:G, RH1:2 to QH1:S).
Remember, the specific requirements for gate drive voltage and resistor values might vary based on your MOSFETs' specifications and your driving circuit. Always consult the datasheet of your components to ensure compatibility and safe operation. If you have any further questions or need more detailed advice, feel free to ask!
2y
2
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