Tachometer Application
Typical values shown above apply to a nominal value of
RPM # OF CYL.
x
= Frequency
60
2
VREG of 8.5 volts. It must be realized that trimming of RT
will be necessary to compensate for variations in regula-
tor voltage from one unit to another.
VF/V = 2.1 + Frequency x CT x RT (VREG -0 .7)
OUT
The above equations were used in calculating the follow-
ing values, where VF/V = 7.1V at =270¡ and CT = 0.01 F.
An alternative to this adjustment is to replace R2 with a
potentiometer, as shown in Figure 2.
OUT
4 cylinder: Freq = 200Hz, RT = 320k½
6 cylinder: Freq = 300Hz, RT = 220k½
8 cylinder: Freq = 400Hz, RT = 150k½
Partial schematic shown in Figure 3 represents one met-
hod for use with DC applications instead of frequency.
TRIM
IOUT/EQ
10kW
RT
CP
CP
RT
2.1V
0.7V
CT
IIN
1kW
Figure 2: Alternate Trimming Method
Figure 3: DC Application
5
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
