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The LMHV’s specification is 0. At low output currents, current regulation is degraded since the voltage across the sensing resistor becomes quite low. Another transient condition which has been shown to cause problems is momentary loss of the ground con- nection. With this variety to choose from, pm305h is now possible to select the regulator for each application, and reduce cost significantly over competing approaches.
LM305H Cross Reference
If this is unacceptable, another solution must be found. To ensure adequate surge capability during turn-on, a diode rating of at least twice the output current is recom- mended, especially for higher current supplies where the ratio of filter capacitance to output current is somewhat higher.
Current limiting protects against short circuits fusing the aluminum interconnects on the chip. Also, the LM is packaged in standard transistor packages which are easily mounted and handled. The current from the internal ft resistor is Vs. In addition, the time-to- failure used to rate capacitors on data sheets is often 10, hours.
Notice that line regulation is measured with constant load and pulsed input voltage, whereas load regulation is measured with constant input voltage and pulsed load.
This is accomplished in Figure 7. Besides replacing fixed regulators, the LM is useful in a wide variety of other applications. The stability problem with slower pass transistors, if it occurs at all, is usually seen only on the negative regulator. The major drawback of the zener reference, poor long- term stability, can be eliminated if the zener breakdown site is placed below the die surface where it is shielded from high field effects of mobile surface ions.
Dual Complementary Supply — “Full-Wave Center Tap” four diodes The only advantages of the half-wave rectifier are its simplicity and the savings in cost of one diode.
LM, LMZ, – 1 pages datasheet sitemap ::
Band-gap references are generally chosen for the higher current devices 0. This decreases the output voltage from Insure datashret no-load Vin max does not exceed the value listed on the data sheets or in the table of Section 2. The required S a was determined in Section datashfet. LM O 0. Further, it is extremely well regulated against line voltage or load current changes so that it contributes virtually no error to dynamic regulation. When the power is first applied, Q 2 turns ON and saturates Q.
Further, improvements are made in performance over older regulators. Temperature difference between radiating and adjacent objects or space. The circuit design has been optimized for excellent regulation and low thermal transients.
Operating frequency is about 30 kHz and ripple is about mV, depending upon input voltage. The substrate is electrically connected to the negative terminal of the temperature stabilizer.
Discharge occurs when either the input or output is shorted. Q- always operates as a switch and needs no heat sinking. The LMP is also a possibility as seen from this figure, although a marginal one on the basis of Iout max. Both the regulator output transistor and each output switch are internally current limited and, to limit junction temperature, an internal thermal shut- down circuit is employed.
Considerable effort was expended to make the LM34 1 -XX series of regulators easy to use and minimize the number of external components. If the load should be “light” at “high line,” then there will be an additional rise in secondary voltage, beyond that due to the rising line voltage, caused by the decreasing voltage drop in the transformer windings.
Most 10 jF capacitors have low enough internal series resistance to deliver 20A spikes when shorted. Any voltage drop due to load current through this series resistance appears as a change in the reference voltage and degrades regulation.
The capacitor will then discharge through reverse biased emitter-base junction of the pass device, Q16, which breaks down at 6.
The circuit in Figure 7. Normally this causes no problem since, when the regulator is initially powered, the output increases as the input increases. Current limiting is included to limit the peak output current to a safe value. Resistor bypassing will not degrade regulation if, under worst-case conditions of maximum input voltage and minimum load current, the regulator is still delivering output current rather than absorbing current from the resistor.
Raising the Output Voltage above the Input Voltage: The extra diodes result in twice the diode voltage drop of a FWCT circuit so that the latter may be preferable in low voltage supplies. For those interested in a rigorous theoretical analysis, there are a number of fine references available. Internal to the LM is a diode from input-to-output which conducts the current around the device when the oppo- site regulator is active.
About the only way to insure that thermal limiting works is to power the regulator, short the output, and let it cook. More recently, simple three-terminal regulators supplying one to three amps have been placed on individual cards within a system. Output current is sensed across R6 and compared to a fraction of the 1. Special applications for the tracking regulators are discussed in Section 7, as follows: Regulation is measured at constant junction temperature.
Also using Figure 7. Included on the chip are current limit, thermal overload protection and safe area protec- tion. For output capacitance in excess of uF, a high current diode from input to output 1N, etc. All characteristics except noise voltage and ripple rejection ratio are measured: The will track the LM within mV. The first, known as a “band-gap” or AVbe reference is shown in simplified form in Figure A3.
Solomon e National Semiconductor Corporation Semiconductor Drive, Santa Clara, California TWX National does not assume any responsibility for use of any circuitry described; no circuit patent licenses are Implied, and National reserves the right, at any time without notice, to change said circuitry.