In Amateur radio practice, there are situations when 9-volt DC source you need to obtain 12, and then a higher output voltage. Bail in such cases can I designed a compact transformerless adapter. Made on the basis of two or three common chips and four transistors, it will allow first to improve the initial voltage of approximately 17 V, and then to output the desired 12 V. And stable.
The composition of the proposed development has the integrated voltage regulator type КР142ЕН5А, output 5 V used to power the oscillator to the three logical elements 2I-NOT chips К155ЛАЗ. Generated by a generator of pulses of rectangular. They are removed with inverse output 11 of logic element DD1.4. The pulse repetition frequency is determined by timing a chain of resistor R1 and capacitor C1.
Through resistors R2 and R3, these pulses are applied to bases of the transistors VT1 and VT2, forming together with semiconductor transistors VT3 and VT4 electronic switch. It induces the charge-discharge C2 — capacitor “voltage boost”.
In particular, in the presence of low-voltage (log.0) on output DD1 11.4, the transistors VT1 and VT2 are in the locked state, and VT3 in the open. Since collector current is the base of VT3 to VT4 powerful, the latter is also open, and through it, and the diode VD1 C2 is charged to Uвопьтодо6авки (almost -almost to the voltage of the power supply).
A circuit diagram of a power adapter to connect the 12-volt load to the unit the power is calculated for output voltage 9 V
With the advent of the terminal 11 DD1.4 voltage high-level (log. 1) the transistors VT1 and VT2 will open. But will be locked VT3 as its base bridged transition open VT2. Accordingly, and VT4 are closed, disconnecting the capacitor C2 from the voltage of +9 V.
At the same time will start the category C2 (in the absence of DA2) chain: open the VT1 transistor, a power source, load superalloys C3 and the diode VD2.
The power source and the capacitor C2 are connected in series. The total resistance of open VT1 and VD2 is low, so capacitor C3 will be the total voltage Andsource + Uвопьтодо6авки. Being, in essence, unregulated, it is transferred to the load or, if necessary, on the integral stabilizer DA2 type КР142ЕН8Б. The latter, mounted on a heat radiator area of approximately 20-25 cm2, is able to provide Ist = 12 V At Nagr = 280 mA. However, with increasing load current up to 300 mA output voltage DA2 is reduced to 11.5—11.6 V, but it practically does not affect the functioning of most electronic devices.
When I nest.napr. = 350 mA output voltage taken from the capacitor C3, is equal to 12 V. In this case, it is possible to do without chips КР142ЕН8Б, connecting 12-volt load directly to the unregulated output of the adapter.
A printed circuit Board,
Other options are use adapter. In particular, a voltage of 12 V at the input. The efficiency of the scheme in this case did not impair, but on the smoothing capacitor C3 formed 24, which can then be converted into various stable voltage, for example, 15 or 18th Century, So it is possible the joint work adapter and 12-volt car battery!
In establishing the device does not need, if assembled without errors on the PCB of 1.5 mm of foil Micarta or PCB from a known good parts. In the author’s version, for example, used the resistors MLT-0,125 — cheap, affordable and compact. The same can be said about the condensers K50-6 (C1), K50-29 (C2, C3). Do not fail, and transistors, if you take them with the following static coefficients of transmission current: 1400-1500 (VT1), 130-150 (VT2, VT3) and 90-100 (VT4).
If necessary, you can reduce the resistor values R2 and R4, to use transistors with a few large static coefficients of transmission of the current, to choose the optimum value of the resistance R1.