Pentek 6230 Operating Manual page 206

ADM1024
Suitable fan drive circuits are given in Figures 9a to 9f. When
using any of these circuits, the following points should be noted:
1. All of these circuits will provide an output range from zero
to almost 12 V, apart from Figure 10a which loses the base-
emitter voltage drop of Q1 due to the emitter-follower
configuration.
2. To amplify the 2.5 V range of the analog output up to 12 V,
the gain of these circuits needs to be around 4.8.
3. Care must be taken when choosing the op amp to ensure
that its input common-mode range and output voltage swing
are suitable.
+
AOUT
1/4
LM324
R1
10k
Figure 9a. Fan Drive Circuit with Op Amp and Emitter—
Follower
+
AOUT
1/4
LM324
R1
10k
Figure 9b. Fan Drive Circuit with Op Amp and PNP Transistor
+
AOUT
1/4
LM324
R1
10k
Figure 9c. Fan Driver Circuit with Op Amp and P-Channel
MOSFET
12V
Q1
2N2219A
R2
36k
12V
R4
1k
Q1
BD136
R3
2SA968
1k
R2
39k
12V
R3
100k
Q1
IRF9620
R2
39k
4. The op amp may be powered from the 12 V rail alone or from
±12 V. If it is powered from 12 V then the input common-
mode range should include ground to accommodate the
minimum output voltage of the DAC, and the output voltage
should swing below 0.6 V to ensure that the transistor can
be turned fully off.
5. If the op amp is powered from –12 V, precautions such as a
clamp diode to ground may be needed to prevent the base-
emitter junction of the output transistor being reverse-biased
in the unlikely event that the output of the op amp should
swing negative for any reason.
R1
100k
AOUT
Q1/Q2
MBT3904
DUAL
Figure 9d. Discrete Fan Drive Circuit with P-Channel
MOSFET, Single Supply
AOUT MBT3904
R1
4.7k
Figure 9e. Discrete Fan Drive Circuit with P-Channel
MOSFET, Dual Supply
R1
100k
AOUT
Q1/Q2
MBT3904
DUAL
Figure 9f. Discrete Fan Drive Circuit with Bipolar Output
Dual Supply
–14–
12V
R2
100k
Q3
IRF9620
R3
3.9k
R4
1k
12V
R2
100k
Q3
IRF9620
R3
39k
Q1/Q2
DUAL
R4
10k
–12V
12V
R2
100k
Q4
BD132
Q3
TIP32A
BC556
2N3906
R3
3.9k
R5 R4
100
1k
REV. A