Para aplicaciones en las que el aislamiento de la red de energía no es importante, se puede ahorrar el transformador, que es un componente caro, pesado y voluminoso. En su lugar se aprovecha la reactancia capacitiva de un capacitor de poliéster de buena calidad para hacer la reducción de la tensión de la red de energía.

   El proyecto que presentamos puede operar tanto en la red de 110 V como 220 V y proporciona una corriente de hasta 20 mA. La tensión de salida depende únicamente del diodo zener utilizado, quedando entre 3 V y 12 V. Tensiones menores pueden ser obtenidas con una referencia formada por diodos comunes, como muestra la figura 1.

 

Figura 1 - Referencia con diodos comunes
Figura 1 - Referencia con diodos comunes

 

   

Cada diodo proporciona una tensión del orden de 0,6 V cuando se utiliza como referencia. Así, para 2,4 V basta usar 4 diodos en serie. Un LED también se puede utilizar como referencia de 1,6 V para los tipos rojos. Para los tipos amarillos y verdes la referencia será de 1,8 V y 2,1 V como muestra la figura 2.

 

Figura 2 - Uso de un LED como referencia de tensión
Figura 2 - Uso de un LED como referencia de tensión

 

 

   Evidentemente, como se trata de una fuente que no está aislada de la red de energía, no debe tener partes expuestas ni los aparatos que van a ser alimentados. Pequeñas radios, calculadoras, relojes son algunos de los aparatos que pueden ser alimentados por esta fuente.

   En la figura 3 tenemos el diagrama completo de la simple fuente.

 

Figura 3 - Fuente sin transformador
Figura 3 - Fuente sin transformador

 

   

Su montaje no requiere más que un pequeño puente de terminales para servir de soporte para los componentes, como muestra la figura 4.

 

Figura 4 - Aspecto del montaje
Figura 4 - Aspecto del montaje

 

   

Es claro que si el lector tiene recursos para elaborar placas de circuito impreso, puede utilizar el estándar de la figura 5 como referencia.

 

Figura 5 - Placa de circuito impreso para el montaje
Figura 5 - Placa de circuito impreso para el montaje

 

   

El componente crítico de este proyecto es el condensador que debe tener valores y tensiones de trabajo conforme a la siguiente tabla. Se debe utilizar un capacitor de poliéster de buena calidad:

 


 

 

 

   El fusible de entrada es importante para proteger el circuito, ya que si el condensador entra en corto, es necesario que la alimentación se apague inmediatamente. El condensador electrolítico debe tener una tensión de trabajo un poco mayor que la deseada en la salida. Por ejemplo, para una salida de 6 V, utilice un condensador de 12 V o 16 V.

   El circuito cabe en una pequeña caja del tipo eliminador de pila enchufable en la propia red a partir de cualquier toma común.

 

 

Lista de material

   D1 a D4 - 1N4004 - diodos de silicio

   C1 - Capacitor de poliéster - ver tabla y texto

   Z1 - Zener de 3 a 12 V x 1 W - según la tensión de salida deseada

   C1 - 1 000 uF - condensador electrolítico - ver el texto

   F1 - 500 mA - fusible

   Varios:

   Puente de terminales o placa de circuito impreso, cable de fuerza, soporte de fusible, hilos, soldadura, caja para montaje, etc.

 

 

 

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