HV400MJ Datasheet, PDF (8/11 Pages) Intersil Corporation – High Current MOSFET Driver

HV400MJ/883
Applications Circuits
The HV400MJ/883 was designed to interface a pulse trans-
former to a power MOSFET. There must be some means to
balance the transformer volt-second product over a cycle.
The unipolar drive shown in Figure 3 lets the core magneti-
zation inductance reverse the primary and secondary volt-
ages. The zener diode on the primary side limits this voltage
and must be capable of dissipating the energy stored in the
transformer. The load may be connected to either the power
MOSFET drain or source.
VS
7
2
1
CS
8 R_OUT
7
C_IN
2
T1
1
C_S
8 ^ROUT
3 AND 6
4
5
HV400MJ/883
FIGURE 4. BIPOLAR DRIVE WITH DC BLOCKING CAPACITOR
3
AND
6
4
5 POWER
HV400MJ/883
MOSFET
FIGURE 3. UNIPOLAR DRIVE
A diode is added in series with Pins 2 and 7 to allow the
transformer secondary to go negative. The charge storage of
the Pin 7 diode may cause the turn off delay time to be too
long. Alternatively, Pin 7 could be left disconnected and a
second external diode connected between the transformer
(anode) and Pin 1 (cathode). In some applications the diode
in series with Pin 2 may be unnecessary but the -35V input
to output or ground maximum rating should be observed.
Sometimes the volt-second balance is achieved by a push-pull
drive on the pulse transformer primary. This is especially useful
if there are two secondary windings driving two HV400MJ/883s
out of phase such as in a half-bridge configuration.
Other times it is more convenient to achieve volt-second
balance by using capacitors to block DC in the primary and
secondary windings as shown in Figure 4. The Pin 7 diodes
provide a path for discharging the secondary side DC block-
ing capacitor. Both capacitors, C_IN and C_S, should be at
least 10 times the equivalent MOSFET gate capacitance.
The HV400MJ/883 can be used as a current booster for low
side switches by connecting directly to the PWM output. The
circuit would be similar to the switching time test circuit.
It is worth restating that some consideration (and experimen-
tation) should be given to the choice of external components,
i.e., resistors, capacitors and diodes, to optimize
performance in a given application.
8