Fig. 1

VOM1271 Photovoltaic MOSFET Driver Circuits

by Lewis Loflin

In Fig. 1 is a test circuit I used to evaluate the VOM1271 photovoltaic opto-coupler. It worked well for N-channel and P-channel MOSFETs and IGBTs. To quote the manufacturer data:

The VOM1271 is a stand-alone optically isolated MOSFET driver. Unlike conventional MOSFET drivers, which require an external power supply to provide VCC and or VDD rails to the driver itself, the VOM1271 obtains all the required current to drive its internal circuitry from the LED current on the low voltage primary side of the isolation barrier.

This saves the designer the space and cost associated with providing one or more external power supplies. The VOM1271 also integrates a turn-off circuit internal to the component itself, thus doing away with the need for additional components in order to increase the overall switching speed by decreasing the turn-off time.

These features, combined with a small SOP4 package, provide designers with a small footprint, highly integrated isolated gate driver solution for a large variety of MOSFET drive applications.

In my case I turned the test circuit on-off with an Arduino Uno. But when I connected the Arduino ground or common to the same power supply common connected to the VOM1271 output circuit the unit failed to work. The output of these photovoltaic opto-couplers is often 10uA.

So the power supply for the output circuit must be separate from Arduino.

Fig. 2

Fig. 2 is the VOM1271 internal block diagram.

Fig. 3

Fig 3 illustrates the typical MOSFET connection to the VOM1271 or similar type photovoltaic opto-coupler.

It required no other external circuitry.

VOM1271 with two power MOSFETs forms bidirectional AC-DC switch.
Fig. 4

Fig. 4 VOM1271 with two 2N7000 MOSFETs forms bidirectional AC-DC switch rated at 200mA at 60V.

Alternative Parts

The Vishey VOM1271T is available from Mouser Electronics for $2.33 each or $1.94 each Qty 10.

An alternative is the Toshiba TLP3906 $2.08 each or $1.69 each Qty 10.

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