High Voltage and Current isolated PWM switching


I just finished doing some experiments on high voltage and current isolated pwm switching. This actually starts the need for a dc electric actuators to be installed within the heat exchanger control system. 

The need to serve the electric heater actuator, with a 300 Watt power operates at a voltage of 220VAC. In my mind, I would use an electronic method of DC chopper.  To set the pulse width is used by pwm, which will be controlled via an Arduino microcontroller ATmega 328. Finally came the other requirements of the actuator system must be optically isolated, so the ground to be separated. This is usually to avoid EMI (electromagnetic interference). For switching, there are three options are SCR, MOSFET or IGBT. While the optical isolation, I make sure to choose 4N35.

After 3 days of my designs and try it out, finally got it perfect. Through this post, I will share my experiences to all visitors who need these actuators.

How it works

This simple system without a transformer, the voltage source is directly rectified by the B1 and C1 to reduce the ripples. R1 and R2 form a voltage divider circuit, serves to provide a low voltage dc supply components for 4N35. 4N35 will be supplied with a DC voltage of 12V. However, the voltage on R2 is made higher than 12V to keep the possibility of fluctuations in voltage 220VAC. These fluctuations are usually 10 percent. So at about 200VAC voltage, DC voltage at R2 must be greater 12V.

Furthermore, components R3 and D1 form a circuit for cutting / create a stable voltage to 12V by the zener diode 12V. R3 is used to reduce the current flowing in the zener when the voltage on R2 above 12V. Voltage at the zener diode fed into the circuit R4 and C2 to eliminate riple as a lowpass filter.

12V voltage is then fed to the collector of the 4N35 as the supply voltage.  Emitter of 4N35 in series with R5, so that when the LED is not given voltage, the emitter voltage is zero. This is so when the LED is not given voltage, the output is 0 volts to MOSFET (N) or IGBT (N), and not in an active condition. In short, the input and output 4N35, not as an inverting logic. R6 is a series resistor when the transistor becomes active from 4N35, a pullup to 12V. The value of R6 is selected adjustable voltage requirements of the MOSFET or IGBT Gate.

Lastly, R7 aims to reduce the LED current of 4N35, of course, adjust your PWM peak voltage.

Value of Components

Lastly, R7 aims to reduce the LED current of 4N35, of course, adjust your PWM peak voltage. 

  1. R1 = 220K/1W, R2 = 20K/1W, R3 = 2K2/1W, R4 = 470/1W, R5 = 47K/0.5W, R6 = 47/0.5W, R7 = 100/0.5W
  2. C1 = 220uF/350V, C2 = 47uF/25V.
  3. OP1 = 4N35
  4. Q1 = IGBT HGTG18n120 / 1600V /30A



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About Bambang Siswoyo

I am a college lecturer since 1988 at UB (University of Brawijaya) in the electronics department. My experience: Applications of Microprocessor system, Applications of Control System, Applications of Field Programmable Gate Array, Computer Programming in computer instrumentations. My hobby: Music especially playing the saxophone, hiking and exploring the countryside.
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2 Responses to High Voltage and Current isolated PWM switching

  1. Med Ali says:

    Thanks for this great solution!!
    4N35 collector is suplied with DC BUS, but when switching motor there is some hight pic voltage that may be damage zener or optocoupler also can modify gate signal shape.
    i hope that supply can do it from 220v/50hz with (diode, resistor, cap and Zener).
    I will test this with HCPL3120 or TLP250 and feedback you Mr.

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