GEC PLESSEY HI\- O48 [SEMICONDUCTORS | ____ PRELIMINARY INFORMATION 2N423 / ZN423Z | PRECISION VOLTAGE REFERENCE SOURCE The ZN423/Z is a monolithic integrated circuit using the energy bandgap voltage of a base-emitter junction to VReF SUBSTRATE produce a precise, stable, reference source of 126V This | is derived via an external dropping resistor for supply voltages of 15V upwards The temperature coefficient of the ZN423/Z, unlike conventional Zener diodes, remains constant with reference current The noise figure assoctated Vrer with breakdown mechanisms ts also considerably reduced FEATURES | Low Voltage GND GND Mi Low Temperature Coefficient Hi Very Good Long Term Stability 2N423 (CM-2) 2N4232 (TO-92) . row ope a sistance Fig 7 Pin connections (bottom view) @ Tight Tolerance Mi High Power Supply Rejection Ratro M 2N423 - 2-Lead TO-18 Metal Can Package Re ee Mi 2N423Z - 3-Lead TO-92 Plastic Package R ABSOLUTE MAXIMUM RATINGS j ET OT Maer 1 Reference current, lper 20mA >a Operating temperature range ZN423 -55C to +125C BANDGAP REFERENCE Vs-Vrer Vs ZN423Z OC to +70C Storage temperature range ZN423 -65C to +165C ZN423Z -55C to + 155C ORDERING INFORMATION Device type Operating temperature Package Tsou ZN423 -55C to +125C CM2 ZN423Z oc to +70C TO-92 : Fig 2 Circuit diagram ELECTRICAL CHARACTERISTICS Test conditions (unless otherwise stated) Tamb = 25C, Shaping capacitor, Cg =O 1nF Value Characteristic Symbol Unit Conditions Min. | Typ. Max. Output voltage VReEF 12 126 1 32 Slope resistance Rarer 05 15 Q lnaep = 5MA Reference current ler 15 12 mA Temperature coefficient 30 ppm/C External resistor Rext 100 Q Rext = (Voc-Vrer)/trer RMS noise voltage 6 uv 1Hz to 10kHz Power supply ratio Psrar 60 dB Psrr = Rext/Rree. Veer = 1 26V. Incr =2 5MA, Veg =5 OV 2-41 ZN423/Z Reference current lare (max ) v operating temperature 12 1 i 1 | ! | | I i { < if i E f t BI | ! = | i aL 1 a * Ty | fo i | I | i I 2 1 j ! I j t ot -55 -40 -20 0 +20 +40 +60 +80 +100 +125 Operating temperature C Fig 2 Derating curve 15 "3 i . Toc 5mA Co =0 lpr q11 ! las 309 x n 07 A on ~ le Cg = pF we o5 3 | 03 01 = , | 10 10 10 102 103 10% 19 108 Frequency - Hz Fig 3 Slope resistance v frequency (lrer = SMA) 2-42 ZN423/Z +5V i 620 ZN423 4 Phra ZS170 znazap >> 6 D1 2 L 4 | 2 28170 c2 TR2 7 5p D2 2N3055 N ot cio, 3.3k TR1 2200/1 | Ri ZTX108 10V Fig 4 5V, 05A power supply APPLICATIONS 5V, 0.5A Power Supply 5V, 1.0A Power Supply The circuit shown in Fig 4 is essentially a constant current The circuit detailed in Fig5 provides improved source modified by the feedback components R2 and R3 to performance over that in Fig 4 This ts achieved by feeding give a constant voltage output the ZN423 reference and the ZN424P error amplifier from a The output of the ZN424P need only be 2V above the more stable source, derived from the emitter-follower stage negative rail, by placing the load in the collector of the output (TR1) The supply rejection ratio 1s improved by the factor transistor TR2 Current control is achieved by TR1 and R5 R1/R5, where R5 1s the slope resistance of the ZN423 This simple circuit has the following performance The output voltage ts given by characteristics (R3 + R4) Rs VREF Output noise and ripple (full load) = ImV rms Load regulation (0 to 05A) =01% and may be adjusted by replacing R3 with a 220 and a 5002 Temperature coefficient = + 100ppm/C preset potentiometer Current limit = 065A The output is protected against short circuits by TR2 setting a current limit of 1 6A R1 | 3.3k TRI 4 ZTX108 33k . 4 aw too 2 T 25V wa 2821 272 L 2 p ZN423 0 p3 A a 12 KSOS1A NO Pt | be 2$272 R3 620 1% 25V wT asv Fig 5 5V, 10A power supply 2-43 R1 22k {____ CURRENT LIMIT TRS ZTX450 TRE 2N3055 =_ Sc1 4000 OUTPUT av CONTROL 7Tx300 FINE COARSE D1 25 DS TOR R4 1 Ok o9 28278 2sv| BKSta0n I tk = c8 LO , Ft . a7 ys 4a7u fo : 201 Op N 0 |zs278 D6 zNeeet aca Pt KS091A 4 (&) T ty 100): a. R3 o, te | |B 8 Z8278 aT i141 TRI : ZTX500, R2 D4 zs278 a | 1 I Fig 6 OV to 12V, 1A power supply OV to 12V, 1A Power Supply The circutt of Fig6 provides a continuously variable, highly stable voltage for load currents up to 1A The output voltage Is given by (VR5 + VR6) Vo= aa VREF and ts controlled by VR5 and VR6 which should be high quality components (preferably wire wound) The emitter follower stages TR1 and TR2 buffer the bias and reference from the output stage The negative rail allows the output to operate down to OV The current hmit stage monitors output current through R15 As the potential across R15 increases due to load current, TR4 conducts and supplies base current for TR3. thus diverting part of the output from the ZN424P via TRS to TRS Shaping 1s achieved by the network C5, R8 together with the output decoupling capacitors which also maintain low 2-44 output resistance at frequencies above 100kHz The power supply has the following performance characteristics Output noise and ripple (full load) <100uV rms Output resistance (0 to 1A) IMQ Temperature coefficient + 100ppm/C Variable 100mA to 2A Current Source In the circuit of Fig7 the output current is set by the resistor R in the collector of TR2, which may be switched to offer a range of output currents from 100mA to 2A with fine control by means of VR3 which varies the reference voltage to the non-inverting input of the ZN424P The feedback path from the output to the inverting input of the ZN424P maintains a constant voltage across R, equal to (Vcc- Vin) and hence a constant current to the load given by (Vcc - Vin)/R ZN423/Z 20V MAX 6V MIN 0.5| |R| IR| #A- - -- R| |10 R2 ate C3 on 680 TW \ SET 2N&23 rT o CURRENT &) Oty 1 | 2 DN Lt N r soy ZN424P + 7 TR2 2N3055 O+ <) Fig 7 Variable current source 2-45