MC3423DR2 ON Semiconductor, MC3423DR2 Datasheet - Page 6

• Manufacturer Part Number: MC3423DR2
• Description: IC SENSOR UNDERVOLTAGE 8-SOIC
• Manufacturer: ON Semiconductor
• Series: MC3423r

Specifications of MC3423DR2

• Technology: Mixed Technology
• Number Of Circuits: 2
• Applications: General Purpose
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power (watts): -
• Voltage - Working: -
• Voltage - Clamping: -

variety fuse (3AG or 3AB style) which cannot be relied on
to blow before the thyristor does, and trust that if the SCR
does fail, it will fail short circuit. In the majority of the
designs, this will be the case, though this is difficult to
guarantee. Of course, a sufficiently high surge will cause an
open. These comments also apply to the fuse in Figure 11B.
influenced by its construction and the characteristics of the
The usual design compromise then is to use a garden
The value of di/dt that an SCR can safely handle is
l
di
dt
V
V
in
in
Figure 12. Typical Crowbar OVP Circuit
Figure 13. Crowbar SCR Surge Current
Figure 14. Circuit Elements Affecting
Supply
Power
DC
R & L EMPIRICALLY DETERMINED!
*Needed if supply not current limited
SCR Surge and di/dt
Supply
ESL
Power
ESR
C
DC
Configurations
out
*
Waveform
+
Output
Surge Due to
Output Capacitor
Cap
R
Sense
+
l
Lead
pk
OV
C
out
MC3423
To
L
Current Limited
Supply Output
Lead
Sense
(11A)
(11B)
OV
L
R
V
V
out
out
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MC3423
6
gate drive signal. A center−gate−fire SCR has more di/dt
capability than a corner−gate−fire type, and heavily
overdriving (3 to 5 times I
<1.0 ms rise time signal will maximize its di/dt capability.
A typical maximum number in phase control SCRs of less
than 50 A(RMS) rating might be 200 A/ms, assuming a gate
current of five times I
done this, a di/dt problem is seen to still exist, the designer
can also decrease the di/dt of the current waveform by
adding inductance in series with the SCR, as shown in
Figure 13. Of course, this reduces the circuit’s ability to
rapidly reduce the DC bus voltage and a tradeoff must be
made between speedy voltage reduction and di/dt.
Surge Current
excessive,
overheating will result. The surge capability of the SCR is
directly proportional to its die area. If the surge current
cannot be reduced (by adding series resistance − see
Figure 13) to a safe level which is consistent with the
systems requirements for speedy bus voltage reduction, the
designer must use a higher current SCR. This may result in
the average current capability of the SCR exceeding the
steady state current requirements imposed by the DC
power supply.
A WORD ABOUT FUSING
words about fuse protection are in order. Referring back to
Figure 11A, it will be seen that a fuse is necessary if the
power supply to be protected is not output current limited.
This fuse is not meant to prevent SCR failure but rather to
prevent a fire!
possess an I
a high enough continuous current rating to survive normal
supply output currents. In addition, it must be capable of
successfully clearing the high short circuit currents from
the supply. Such a fuse as this is quite expensive, and may
not even be available.
CROWBAR SCR SELECTION GUIDE
following selection guide is presented.
2N6400 Series
2N6504 Series
2N1842 Series
2N2573 Series
2N681 Series
MCR3935−1 Series
MCR81−5 Series
If the peak current and/or the duration of the surge is
Before leaving the subject of the crowbar SCR, a few
In order to protect the SCR, the fuse would have to
As an aid in selecting an SCR for crowbar use, the
Device
2
t rating less than that of the SCR and yet have
immediate
GT
I
16 A
25 A
16 A
25 A
25 A
35 A
80 A
RMS
and < 1.0 ms rise time. If having
destruction
GT
1000 A
) the SCR gate with a fast
160 A
160 A
125 A
260 A
200 A
350 A
I
FSM
Metal TO−3 Type
due
TO−220 Plastic
TO−220 Plastic
Metal Stud
Metal Stud
Metal Stud
Metal Stud
Package
to
device