15-20 years ago, 9-volt battery "Krona" is widely used to power portable receivers, remote controls and other portable electronics. Now this equipment is often powered by trehvalkovyh sources (two "AA" cell), and "Crown" are used only in electrical devices, rangefinders, the radioactivity indicators, portable metal detectors and other instrumentation. Unfortunately, now the industry does not produce network adapters on 9 V to power these of the devices. Anyway, I such adapters are not met. And the instruments themselves with devaluatolin the food does not have sockets for connection of external source. Therefore, for power, for example, the meter is required small source sizes comparable to the size of the "Crown".
Chip LNK501 is a generator of pulsed power source and specifically designed for building compact pulse power supplies small capacity. It is available in 8-lead DIP package (LNK501P) and 8-you-water-SMD-package (LNK501G). Both options allow you to collect miniature source. By the way, the body is actually a 7-lead, as the 6-th output no (pass), but the countdown conclusions like 6-th output.
Chip LNK501 contains a pulse-width controller with MOS-transistor. The diagram of the controller together with the MOS transistor is a scheme, included consistently load. Load is the primary winding pulse transformer T1. The pin 5 is connected to the drain of the output transistor and power circuit diagram of the generator connected together conclusions 7. 1, 2, 3, 4 - source the output transistor. Pin 8 is used to control the generator. Frequency generating a fixed, equal to 42 kHz. Filling frequency of the pulses depends on current through the pin 8. The latitude dependence of the pulse reverse current. Chip can work within the supply DC voltage (coming from primary rectifier) from 90 to 700 V.
A schematic diagram of a network Crown" shown in the figure. This source gives a stable DC voltage of 9 V at a current of 100 mA, that is able to replace the standard "Crown" even with a considerable supply of the current.
The AC voltage from the mains is fed to the rectifier bridge diodes VD1-VD4. The resistor R1 serves to limit the inrush current charging C1 and C2 in turn on the power. The rectified voltage is smoothed chain C1-L1-C2 and further goes to pin 5 A1.
The load of the output transistor A1 is the winding 1 of the transformer T1. When output transistor A1 is open, through the winding 1 T1 elapses increasing the current and the magnetic core accumulates energy. In this case, the diodes VD5 and VD6 closed as under reverse bias. After closing of the output transistor the voltage in the windings reverses polarity. Diodes VD5 and VD6 open, passing the voltage at the load.
Rectifier VD5-R3-C5 is used to obtain a chip of information on secondary the tension. The voltage on the secondary side of the circuit is determined by the magnitude of the rectified voltage of the primary winding. In the period closed state of the transistor A1 a-wave of the voltage on the primary winding T1 the capacitor C5 is charged to 50...60 V. This voltage and serves as measuring, by which the SHI scheme A1 calculates the latitude of pulses. measuring via circuit R2-C3 is supplied to pin 8 A1. Resistor R2 together with the internal resistance output 8 A1 forms a voltage divider. To adjust the output voltage by selecting a resistance R2.
Thus the stabilization of the output voltage on C4. But. change current feedback obtained by rectification of the voltage of the primary the winding in the low-load mode is only slightly dependent on the actual voltage on the secondary winding rectifier. As a result, at nominal output voltage 9 In idle and at low current consumption), the voltage jumps up almost by half. and declines rapidly in the current range from zero to 20...30 mA. Further the increase of the load current voltage drop is not so noticeable, although it also has the place, as at a current of 100 mA will already be below 9 V.
These changes will be very significant when powered portable devices with LCD indicators consuming minimum currents. Therefore, to ensure stability of the final output voltage, in the circuit taken a series of measures. First, the output from the secondary the rectifier is loaded led HL1, which makes the power supply unit to operate in the idle state. This introduces led power supply a relatively stable mode voltage at the output of the rectifier 11...13 V. secondly, after the rectifier included integral stabilizer A2, which is already the resulting output voltage maintains at a stable level 9 V.
By the way, this source can be converted to other output voltage, for example, to 5, using the appropriate stabilizer in place or A2 to make a variable voltage output, using in place of the integral A2 stabilizer with adjustable output voltage.
The transformer T1 is wound on the armature core EF12.6 data sheets. Primary winding - 130 turns of wire sew 0,09. Then a layer of the film Ferapontovo (as she is used insulation from the wire MGTF) Secondary winding - 25 of turns of wire sew 0,25. The frame of the transformer is very small, so the winding you need to tightly turn to turn, but not to pull the wire so as not to disturb the insulation.
Choke L1 - ready small inductance 100-500 µh.
The diodes of the rectifier bridge VD1-VD4, you can replace the other, with a maximum reverse voltage of at least 500 V and a current of not less than 0.3 And, for example, 1N4007, or use a bridge rectifier type DB105, DB106, DB107 (it's even it is preferable from the point of view of minimization).
Diode 1N4937 can be replaced by CDA, CDG or other silicon with time reverse recovery less than 250 NS, for reverse voltage not lower than 600 V.
The 1N5819 diode can be replaced by CD CDA CDA or another time reverse recovery not more than 500 NS and a reverse voltage of 40 V.
The secondary circuit of the stabilizer can be solved otherwise. At low currents you can use the load parametric voltage on the Zener diode and the resistor, or make anotherstory parametric stabilizer on the model scheme.
The power supply case is the case of the used battery type "Crown". You need to remove all contents, thoroughly clean the body from the oxides, and to cover its inside a good layer of insulation, which can be used epoxy varnish. Contact the socket previously removed and use it when the mounting block. In the middle of the panels between the contacts you can make a small the hole through which is visible led.
Installation of a power unit made by volumetric method "on air", tightly. but so that network chains were dangerously close to the secondary. In the process of installation stick to the geometric dimensions of the "Crown", so that the resulting "lump" freely placed in her body. Then the "lump" is checked in the work and establish, if it is necessary. After that it is placed in the body from the "Crown" and washed down with epoxy or some insulating sealant. After fill hardens completely, the unit is ready for operation.
The unit is installed in the battery compartment of the device instead of "Crown". You will need to the battery cover to saw through the groove to output the power cord out.
Author: A. A. Mokhov