6/15/05

Page 6 of 11

© 2005 Fairchild Semiconductor Corporation

6-PIN DIP RANDOM-PHASE

OPTOISOLATORS TRIAC DRIVERS

(600 VOLT PEAK)

MOC3051-M

MOC3052-M

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

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

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.

point and recorded.

SCOPE

IFT

VTM

t(d)

t(f)

ZERO CROSS

DETECTOR

EXT. SYNC

Vout

FUNCTION

GENERATOR

PHASE CTRL.

PW CTRL.

PERIOD CTRL.

Vo AMPL. CTRL.

IFT

VTM

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

100

0.1

10

20

30

40

50

60

10

1

t(f)

t(d)

Figure 10. Static dv/dt Test Circuit

+400

Vdc

PULSE

INPUT

RTEST

CTEST

R = 1 k

Ω

MERCURY

WETTED

RELAY

D.U.T.

X100

SCOPE

PROBE

APPLIED VOLTAGE

WAVEFORM

Vmax = 400 V

dv/dt =

0.63 V

τRC

2

τ

=

τRC

252 V

0 VOLTS