Datasheet

9/2/04
Page 6 of 11
© 2004 Fairchild Semiconductor Corporation
6-PIN DIP RANDOM-PHASE
OPTOISOLATORS TRIAC DRIVERS
(600 VOLT PEAK)
MOC3051-M MOC3052-M
t(delay), t(f) versus I
FT
The triac driver’s turn on switching speed consists of a turn on
delay time t(d) and a fall time t(f). Figure 9 shows that the delay
time depends on the LED trigger current, while the actual
trigger transition time t(f) stays constant with about one micro
second.
The delay time is important in very short pulsed operation
because it demands a higher trigger current at very short
trigger pulses. This dependency is shown in the graph I
FT
versus LED PW.
The turn on transition time t(f) combined with the power triac’s
turn on time is important to the power dissipation of this
device.
1. The mercury wetted relay provides a high speed repeated
pulse to the D.U.T.
2. 100x scope probes are used, to allow high speeds and
voltages.
3. The worst-case condition for static dv/dt is established by
triggering the D.U.T. with a normal LED input current, then
removing the current. The variable R
TEST
allows the dv/dt to
be gradually increased until the D.U.T. continues to trigger
in response to the applied voltage pulse, even after the LED
current has been removed. The dv/dt is then decreased
until the D.U.T. stops triggering. τ
RC
is measured at this
point and recorded.
SCOPE
I
FT
V
TM
t(d)
t(f)
ZERO CROSS
DETECTOR
EXT. SYNC
V
out
FUNCTION
GENERATOR
PHASE CTRL.
PW CTRL.
PERIOD CTRL.
V
o
AMPL. CTRL.
I
FT
V
TM
10 k
Ω
DUT
100
Ω
ISOL. TRANSF.
AC
115 VAC
Figure 9. Delay Time, t(d), and Fall Time, t(f),
vs. LED Trigger Current
I
FT
, LED TRIGGER CURRENT (mA)
100
0.1
10 20 30 40 50 60
10
t(delay) AND t(fall) ( s)
µ
1
t(f)
t(d)
Figure 10. Static dv/dt Test Circuit
+400
Vdc
PULSE
INPUT
R
TEST
C
TEST
R = 1 k
Ω
MERCURY
WETTED
RELAY
D.U.T.
X100
SCOPE
PROBE
APPLIED VOLTAGE
WAVEFORM
V
max
= 400 V
dv/dt =
0.63 V
τ
RC
τ
=
τ
RC
252 V
0 VOLTS