LM193J/883 National Semiconductor, LM193J/883 Datasheet - Page 7

• Manufacturer Part Number: LM193J/883
• Description: IC,VOLT COMPARATOR,DUAL,BIPOLAR,DIP,8PIN,CERAMIC
• Manufacturer: National Semiconductor

Applications
* Adjust for 50 mA quiescent current.
A power lamp flasher is shown in Figure 12. It is designed to
flash a 12V bulb at about a once-per second rate. The
reverse base current of Q2 provides biasing for Q1 eliminat-
ing the need for a resistor. Typically, a cold bulb can draw 8
times its normal operating current. Since the LM195 is cur-
rent limited, high peak currents to the bulb are not experi-
enced during turn-on. This prolongs bulb life as well as
easing the load on the power supply.
Since no PNP equivalent of this device is available, it is
advantageous to use the LM195 in a quasi-complementary
configuration to simulate a power PNP. Figure 13 shows a
quasi PNP made with an LM195. A low current PNP is used
to drive the LM195 as the power output device. Resistor R1
protects against overdrive destroying the PNP and, in con-
junction with C1, frequency compensates the loop against
oscillations. Resistor R2 sets the operating current for the
PNP and limits the collector current.
Figure
quasi-complementary power output stage. Q1 and Q2 form
the equivalent of a power PNP. The circuit is simply an op
amp with a power output stage. As shown, the circuit is
stable for almost any load. Better bandwidth can be obtained
by decreasing C1 to 15 pF (to obtain 150 kHz full output
†
Solid tantalum.
14
shows
(Continued)
a
power
op
amp
FIGURE 14. Power Op Amp
with
a
7
response), but capacitive loads can cause oscillation. If due
to layout, the quasi-complimentary loop oscillates, collector
to base capacitance on Q1 will stabilize it. A simpler power
op amp for up to 300 Hz operation is shown in Figure 15.
One of the more difficult circuit types to protect is a current
regulator. Since the current is already fixed, normal protec-
tion doesn’t work. Circuits to limit the voltage across the
current regulator may allow excessive current to flow
through the load. About the only protection method that
protects both the regulator and the driven circuit is thermal
limiting.
A 100 mA, two terminal regulator is shown in Figure 16. The
circuit has low temperature coefficient and operates down to
3V. Once again, the reverse base current of the LM195 to
bias the operating circuitry.
A 2N2222 is used to control the voltage across a current
sensing resistor, R2 and diode D1, and therefore the current
through it. The voltage across the sense network is the V
of the 2N2222 plus 1.2V from the LM113. In the sense
network R2 sets the current while D1 compensates for the
V
the LM113 to 0.6 mA.
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of the transistor. Resistor R1 sets the current through
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