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LM322N データシート(PDF) 9 Page - National Semiconductor (TI) |
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LM322N データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 14 page Typical Applications (Continued) The average charging current through Rt is about 30 nA so some attention must be paid to parts layout to prevent stray leakage paths The suggested timing capacitor has a typical self time constant of 300 hours and a guaranteed minimum of 25 hours at a25 C Other capacitor types may be used if sufficient data is available on their leakage characteristics Two Terminal Time Delay Switch The LM122 can be used as a two terminal time delay switch if an ‘‘on’’ voltage drop of 2V to 3V can be tolerated In Figure 9 the timer is used to drive a relay ‘‘on’’ Rt Ct seconds after application of power ‘‘Off’’ current of the switch is 4 mA maximum and ‘‘on’’ current can be as high as 50 mA Zero Power Dissipation Between Timing Intervals In some applications it is desirable to reduce supply current drain to zero between timing cycles In Figure 10 this is accomplished by using an external PNP as a latch to drive the Va pin of the timer Between timing periods Q1 is off and no supply current is drawn When a trigger pulse of 5V minimum amplitude is received the LM122 output transistor and Q1 latch for the duration of the timing period D1 prevents the step on the Va pin from coupling back into the trigger pin If the trigger input is a short pulse C1 and R2 may be eliminated RL must have a minimum value of (VCC)(25 mA) TLH7768 – 20 FIGURE 9 2-Terminal Time Delay Switch Frequency to Voltage Converter An accurate frequency to voltage converter can be made with the LM122 by averaging output pulses with a simple one pole filter as shown in Figure 11 Pulse width is adjusted with R2 to provide initial calibration at 10 kHz The collector of the output transistor is tied to VREF giving constant am- plitude pulses equal to VREF at the emitter output R4 and C1 filter the pulses to give a dc output equal to (Rt)(Ct)(VREF)(f) Linearity is about 02% for a 0V to 1V out- put If better linearity is desired R5 can be tied to the sum- ming node of an op amp which has the filter in the feedback path If a low output impedance is desired a unity gain buff- er such as the LM110 can be tied to the output An analog meter can be driven directly by placing it in series with R5 to ground A series RC network across the meter to provide damping will improve response at very low frequencies Pulse Width Detector By driving the logic terminal of the LM122 simultaneous to the trigger input a simple accurate pulse width detector can be made (Figure 12) TLH7768 – 21 FIGURE 10 Zero Power Dissipation Between Timing Intervals TLH7768 – 22 FIGURE 11 Frequency to Voltage Converter (Tachometer) Output Independent of Supply Voltage TLH7768 – 23 VOUT e 0forWR1 C1 Pulse Out e W b R1 C1 forWR1 C1 FIGURE 12 Pulse Width Detector 9 |
同様の部品番号 - LM322N |
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同様の説明 - LM322N |
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