βL105

The βL105 series are driving circuits for 5- or 10-LED bar-graph displays, made by IPRS Băneasa [1].

The I.P.R.S. Băneasa Full Line Condensed Catalog (1990) lists the βL105, βL106, βL107 and βL108 as driving circuits for a 5- or 10-LED bar display, with an integrated current generator adjustable between 0 and 20 mA; the light emitting diodes are connected in series, to reduce the power dissipation and to have the same current under any operating conditions, from a 12 V supply for red LEDs and 16 V for green or yellow ones [1]. The four types differ by their input thresholds (in the Variants table); an externally compensated operational amplifier included in the IC allows scaling, peak detection and/or chaining, and the internal reference may be used for biasing [1]. With the inputs of a βL105 and a βL106 connected in parallel, a 10-LED bar display with the thresholds 0.1 V, 0.2 V, 0.3 V … 1 V is obtained, and with a βL107 and a βL108 one with −20 dB, −15 dB, −10 dB … +6 dB [1].

The catalog gives an operating temperature of −25…+70 °C, a supply voltage range of 12…18 V, a power dissipation of at most 680 mW, a programmable LED current of 0…20 mA, a linear dependence between the LED current and the command current (ILED = 20 mA − 40·ICOM), a biasing current of at most 1 µA and an operational amplifier open loop gain of at least 10000; LEDs of different colours can be connected in any order [1]. Pins (TO-116, top view): 1 non-inverting op amp input, 2 frequency compensation, 3 op amp output, 4 GND, 5 LED 5, 6 LED 4, 7 LED 3, 8 LED 2, 9 LED 1, 10 bar display input, 11 V+, 12 LED current control, 13 internal reference, 14 inverting op amp input [1]. The typical application (a 5-LED chain at 20 mA) is in the Gallery [1].