GW Instek SPS Series User Manual
Page 11
7
z Description of Circuit Theory
1) +10V Voltage reference circuit：
Start up the circuits of R306 and D302 to ensure the output voltage of OPA U301, PIN 1 is in positive status when power
is on. At this moment, the output voltage of PIN 1 will pass through R307 to maintain the voltage of both ends of
ZENER DIODE ZD301(6.2V) to 6.2V. As OPA has the character of false short circuit, so U301 PIN3=6.2V, refer to the
following formula:
Therefore, the OPA’s output voltage can be changed by adjusting the VR301 as shown in the following formula:
Vref=10V→VR301=1.14kΩ
2) Voltage Adjusting Circuit
The R311, and R313 are voltage feedback attenuating resistors while R312 is to control the output of Reference voltage.
Please refer to the following formula:
If Vref=10V R311=52.3kΩ R313=20kΩ
And the R316, R317, C313, C314, and C315 are compensated circuits for voltage frequency.
3) Current Adjusting Circuit:
The U302 is an Error Amplifier with the gain at:
For example: SPS-1820, Io=20A，R341=10mΩ
Vpin12=Io×R341ЧA=20Ч0.01Ч28.01=5.602V
10V
10k
10k
4.99k
VR301
6.2
R305
R305
R304
VR301
6.2
Vref
≅
+
+
=
+
+
=
R313
R313
R311
Vref
Vout
+
=
36.15V
20k
72.3k
10
20k
20k
52.3k
Vref
Vout
=
=
+
=
Vpin13
Vpin12
VR303
R322
R321
R321
10V
A
R341
Io
=
=
+
+
Ч
=
Ч
Ч
28.01
3.57k
100k
R342
R326
A
=
=
=