VJ1206Y224KXXAT ONSEMI [ON Semiconductor], VJ1206Y224KXXAT Datasheet - Page 3

• Manufacturer Part Number: VJ1206Y224KXXAT
• Description: Low-Cost 100 mA High-Voltage Buck and Buck-Boost Using NCP1052
• Manufacturer: ONSEMI [ON Semiconductor]

output voltage will rise up dramatically and burn the output
capacitor eventually. Hence, a zener diode Z
“dummy” load resistor is needed to consume the minimum
amount of energy as shown in Figure 1. It is also noted that
when R
condition, the output voltages at lower output current
conditions are also pulled up. Hence, the clamping zener
diode Z
as the output voltage but it will reduce some of the efficiency
at lower output current conditions.
Topology
is to step up or down a voltage. The output voltage is
inverted. The maximum duty of NCP1052 is typically 77%.
Burst-mode Operation
means the MOSFET can be completely off for one or more
switching cycles. The output voltage is regulated by the
overall duration of dead time or non-dead time over a
number of switching cycles. This feature offers advantages
on saving energy in standby condition since it can reduce the
effective duty cycle dramatically. In flyback topology, the
circuit is mainly designed for discontinuous conduction
mode (DCM) in which the inductor current reaches zero in
every switching cycle. The DCM burst-mode waveform can
be represented in Figure 4. It is similar to the pulse-width
modulation (PWM) one.
Table 1. Summary of Topology Difference Using NCP1052
Output voltage
Output current
Input voltage
Operating mode in nominal
condition
Standby ability on V
current
Transformer / Auxiliary winding
Isolation
Buck circuit is to step down a voltage. Buck-boost circuit
The NCP1052 is with a burst-mode control method. It
1
1
pulls up the output voltage at a given output current
is needed to be with the breakdown voltage as same
DESIGN CONSIDERATION
CC
charging
< 0.7 V
< 300 mA
< 700 V
Continuous
Bad. The current flows through
output even if there is no load
It is only for standby
improvement or additional
output
No
in
Buck
1
or minimum
http://onsemi.com
AND8098/D
3
Negative & < 2.33 Vin
<< 300 mA, output current is
only a portion of the inductor
current
Continuous
Good. The current passes
through inductor only
It is only for standby
improvement or additional
output
No
t 700 * V out V
t 700 V
Because of burst-mode control, the effective maximum
duty is lower and said to be 70% roughly. When a buck
converter is in continuous conduction mode (CCM), the
input voltage V
duty ratio D.
maximum output current is always smaller than the
maximum switch current in non-isolated topologies.
However, in isolated topologies such as flyback the
maximum output current can be increased by a transformer.
The relationship in buck-boost is
Another aspect on topology is the output current. The
Figure 4. DCM Inductor Currents in Burst Mode
Buck-boost
V out
V in
in
and output voltage V
+
and PWM Control
1 * D
V out
V in
D
Burst mode
+ D t 0.7
PWM
t
Depending on transformer ratio
< 10 W. It depends on operating
condition and audible noise level
<< 700 V. It depends on
transformer ratio
Discontinuous
Good. The current passes
through primary winding only
It is a must for the main output.
Additional auxiliary winding can
improve standby performance
Yes. Opto coupler can be
eliminated if isolation is not
needed
1 * 0.7
0.7
out
+ 2.33
Flyback
are related by the
(eq. 2)
(eq. 3)