7-42
Chapter 7. PARAMETER SETUP
④
Equivalent circuit when N number of SSRs are connected in parallel
Formulas (5) and (6) must be satisfied.
V
SSR/MIN
≤
I
0
/N x Z + V
D
≤
V
0
- -(5)
V
SSR’
≤
VSSR/MAX - - - - - - - - -(6)
(V
SSR’
= I
0
/N x Z + V
D
)
⑤
Example: Using Yamatake Corporation's PGM
V
SSR
: 3 to 6 V
Z
:
260
Ω
±5%
V
D
:
0.8 to 1.3 V
• What value should
I
0
be set to when connecting one PGM?
As shown in the figure on the right, a fixed-current system is used for the
voltage output of the DCP32. The fixed current can be calculated as follows
from the input voltage range of PGM.
8.9 mA
≤
1
≤
17.2 mA
I
MIN
x Z
MIN
+ V
D/MIN
> 3
I
MIN
> 8.9 mA
I
MAX
x Z
MAX
+ V
D/MAX
< 6
I
MAX
< 17.2 mA
• How many PGMs can be connected?
A current of 8.9 mA or more must flow to a single PGM. On the other hand, the
maximum current of the DCP32 is 22 mA. Accordingly, two PGMs can be
connected in parallel.
In the case of a series connection, due to the maximum output current (22 mA)
and allowable load resistance (600
Ω
), the maximum voltage that can be applied
to a load becomes 13.2 V (22 mA x 600
Ω
).
When a current of 8.9 mA flows to a PGM, the maximum voltage at both of its
input terminals becomes 3.7 V.
0.0089 x 260 x 1.05 + 1.3 = 3.7 V
Accordingly, 13.2 3.7 = 3.56, which means that three PGMs can be connected
in series.
The above calculation assumes operation in the worst conditions. For example,
even if four PGMs are connected in series, they should operate normally if a
voltage of 3 V or more is applied to each of the PGMs in a voltage ON state.
I
(V )
0
0
DCP32
SSR 1
VSSR'
Z
VD
I /N
0
SSR n
VSSR'
Z
VD
I /N
0
VD
I
Z
PGM
DCP32
