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Application Information
The ACPL-K30T automotive photovoltaic (PV) driver is a
device that is paired with MOSFETs to form basic building
block of several types of application. It consists of an Al-
GaAs LED input that is optically coupled to a photovoltaic
diode array. This becomes a voltage source with galvanic
isolation. The advantage of photovoltaic driver is its sim-
ple design which does not require bias supply.
Basic Construction
As shown in Figure 12, the input side of the PV Driver is
LED driven. A current limiting resistor is required to limit
the current through the LED. Recommended input for-
ward current is 10 mA to 20 mA. The LED is optically cou-
pled through a photodiode stack (D1 to D12) consisting of
12 photodiodes connected in series. When current is driv-
en into the Light-Emitting Diode (LED) on the input side,
the light from the LED generates photo current on the
string of photodiodes to charge the gate of the MOSFETs,
generating a photo-voltage proportional to the number
of photodiodes, to switch and keep the power device on.
Figure 12. Basic Construction of Photovoltaic Driver
Figure 14. Photovoltaic Driver + Two Back-to-Back MOSFETs
PV Driver and MOSFET Congurations
The photovoltaic driver is a device that is combined with
high voltage MOSFETs to form a solid-state relay. The pho-
tovoltaic driver can be congured with a single MOSFET
or two MOSFETS (back to back) for bidirectional applica-
tion. Pin 5 is connected to the Gate and Pin 7 is connected
to the Source. Figure 13 and 14 are sample application cir-
cuits for the two congurations.
Turn-O Circuit
The photovoltaic driver has a built in turn-o circuit,
which decreases the turn-o time. This circuit instanta-
neously discharges the gate capacitance of MOSFETs once
the photovoltaic driver is turned o. The turn-o circuit is
activated when the photovoltaic voltage is collapsing.
The sequence of operation of the turn-o ciruit:
When LED is ON:
1. Q1 and Q2 are saturated.
2. SCR (Q3 and Q4) is disabled.
3. Photodiode array is connected to Gate and Source.
When LED is OFF:
1. Q1 and Q2 cease to conduct.
2. Photodiode array is disconnected from Gate and
Source.
3. SCR (Q3 and Q4) is triggered and Gate capacitance
(C
GS
) is discharged rapidly.
Turn-O Circuit
8
7
6
5
1
2
3
4
R
LED
GND
V
S
I
F
Turn O Circuit
8
7
6
5
1
2
3
4
R
LED
GND
V
S
I
F
Figure 13. Photovoltaic Driver + Single External MOSFET
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
G (V
O
+)
S (V
O
–)
Q1
Q2
Q3
Q4
Turn-o
Circuit
Anode
Cathode
R
LED
C
GS
2
3
5
7