STEVAL-ISA019V2 STMicroelectronics, STEVAL-ISA019V2 Datasheet - Page 12

• Manufacturer Part Number: STEVAL-ISA019V2
• Description: BOARD EVAL SMPS L6565 3PHASE APP
• Manufacturer: STMicroelectronics
• Type: Motor / Motion Controllers & Driversr

Specifications of STEVAL-ISA019V2

• Mfg Application Notes: L6565/STC04IE170HV AppNote
• Main Purpose: AC/DC, Primary Side
• Outputs And Type: 1, Isolated
• Power - Output: 80W
• Voltage - Output: 24V
• Current - Output: 3.33A
• Voltage - Input: 250 ~ 850V
• Regulator Topology: Flyback
• Board Type: Fully Populated
• Utilized Ic / Part: L6565, STC04IE170HV
• Input Voltage: 250 V to 850 V
• Output Voltage: 24 V
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: L6565, STC04IE170HV
• Other names: 497-6339

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Base driving circuit design
Base driving circuit design
In practical applications such as SMPS where the load is variable, the collector current is
variable as well. As a consequence it is very important to provide a base current to the
device which is related to the collector. In this way it is possible to avoid device over-
saturation at low load and to optimize the performance in terms of power dissipation. The
best and simplest way to do this is the proportional driving method provided by the current
transformer in
base to make the turn-on as fast as possible and to reduce the dynamic saturation
phenomenon. The pulse is achieved by using the capacitor and the Zener in
Figure 7.
The I
ESBT STC04DE170 datasheet, and especially looking at the storage time characterization,
it is clear that a turn ratio equal to 5 is a good value to ensure the right saturation of the
ESBT at I
Equation 20
The core magnetic permeability of current transformer must be as high as possible to
minimize the magnetization current I
only drives the core into saturation). On the contrary, a too high permeability core may lead
the core into saturation even with a very small magnetization current. To avoid saturation, it
is necessary to increase the number of primary turns and the size of the core as well. If a
core with a very small magnetic permeability is chosen, it is possible to reduce the number
of primary turns and the core size. If the permeability is too small, we may not have current
on the secondary side because almost all the collector current becomes magnetization
current. As a compromise, a ferrite material with a relative permeability in the range 4500-
7000 is the best choice.
After selecting the ferrite ring diameter, the minimum primary turns is determined to avoid
core saturation from the preliminarily fixed turn ratio N with 0.2. By applying Faraday's law
and imposing the maximum flux B
Equation 21
where B
C
/I
B
sat
ratio is fixed once the current transformer turn ratio has been chosen. From the
C
is the saturation flux of the core which depends on the magnetic permeability.
= 2 A, so that in the current transformer we can first fix:
Proportional driving schematic and equivalent circuit
Figure
Rb
Dz
V
1
7. At the same time, it is very useful to provide a short pulse to the
=
Cb
N
Ib
TP
•
dϕ
------ -
dt
Doc ID 13127 Rev 4
Lp
L
T
p
≅
max
N
TP
M
Ic
equal to B
(which is not transferred to the secondary side but
•
A
e
N
------ -
N
•
P
S
ΔB
------- -
ΔT
=
⇒
1
-- -
5
sat
N
/2:
TP
Ic
L
T
=
p
2
I
M
•
V
-------------------------------
A
1
Ip
•
e
T
•
onmax
B
sat
Is
Figure
AN2495
7.