The LM150 family of adjustable 3-terminal positive voltage regulators can provide more than 3A throughout a 1.2V to 33V output range. They're easy to set up, using only two external resistors to set the output voltage. Furthermore, both line and load regulation are identical to discrete designs. The LM150 is also available in standard transistor packages, making it easy to install and handle.
In addition to greater performance over fixed regulators, the LM150 series has full overload protection, which is only available in ICs. The chip has a current limit, thermal overload prevention, and safe area protection. The overload protection circuitry continues to work even if the adjustment terminal is accidentally unplugged.
Construction
Where to Use
The LM150 may be used in a wide range of applications in addition to replacing fixed regulators or standalone designs. Because the regulator is "floating" and only sees the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input-to-output differential voltage is not exceeded, i.e. the output is not short-circuited. The LM150 may be used as a precision current regulator by connecting a fixed resistor between the adjustment pin and the output. Clamping the adjustment terminal to ground, which programs the output to 1.2V, where most loads use minimal current, can provide supplies with the electronic shutdown.
How to Use
The LM150 generates a nominal 1.25V reference voltage, VREF, between the output and adjustment terminal when in operation. The program resistor R1 is impressed with the reference voltage, and because the voltage is constant, a constant current I1 flows through the output set resistor R2.
The LM150 was developed to decrease IADJ and make it highly consistent with line and load changes since the 50 A current from the adjustment terminal represents an error term. To do this, all idle operating current is returned to the output, resulting in a low load current need. The output will rise if the load on the output is insufficient.
Guidelines
When using external capacitors with any IC regulator, safety diodes are occasionally required to prevent the capacitors from discharging through low current points into the regulator. When shorted, most 10F capacitors have a low enough internal series resistance to yield 20A spikes. Despite the fact that the surge is brief, it has enough energy to cause damage to components of the IC.
When a regulator's output capacitor is linked to the input and the input is shorted, the output capacitor discharges into the regulator's output. The discharge current is determined by the capacitor's value, the regulator's output voltage, and the pace at which VIN decreases. This discharge line of the LM150 is through a big junction that can easily withstand a 25A surge. Other forms of positive regulators are not affected in the same way. There is no need to utilize diodes for output capacitors of 25 F or below.
It's a good idea to use an input bypass capacitor. For practically all applications, a 0.1F disc or 1F solid tantalum on the input is sufficient input bypassing. When adjustment or output capacitors are employed, the device is more sensitive to the lack of input bypassing, but the aforementioned settings will remove the risk of difficulties.
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