When designing a tube devices, we are often faced with a significant difference between the voltage, supplied from the power source to the anode, and the actual requirements of the scheme. Solving for this difference while using series-connected resistors has several drawbacks – voltage strongly depends on the load. The proposed system is able to provide the required voltage tolerance 4-5%, while reducing ripple.Schematic diagram of the anode voltage stabilizer shown in Figure 1.
The diode D1 is connected in series to the input protection circuit in case of incorrect polarity change. diodes D2, D3 and resistor R1 provide a reference voltage. The selection of these elements is determined by the output voltage. The reference voltage at the input will be applied to T1 and T2. The use of field-effect transistors (MOSFET) instead of bipolar due to the lack of the secondary breakdown phenomenon, which would limit the current at high voltages. The use of two transistors protects the circuit from overheating. Resistor R2 and capacitor C2 prevents parasitic oscillations. Resistors R3 and R4 are intended to overcome differences in characteristics between transistors T1 and T2. Resistors R6 and R5 and the transistor T3 to limit the output current to the set value. When the voltage drop across R6 is sufficiently large, to open T3, sources of T1 and T2 are closed gates, limiting the output voltage, whereby there is a current. Resistor R5 T3 protects the base from damage by excessive current. The capacitors C1 and C3 are designed to block the impulse noise, which is extremely undesirable in the lamp circuits.
A sample device is assembled on the single-sided printed circuit board 105 mm × 40 mm, assembly diagram is shown in Figure 2.
Using the power supply to 20 W, You can opt out of the transistor T2 and the resistor R4 installation. Before soldering resistors R1 and R6 calculate their resistance according to Ohm's law:
For the correct voltage to the Zener current needs at least 5 mA. Maximum output voltage, which can be obtained, limited drain-source voltage of transistors T1 and T2, an operating voltage of the capacitor C1 … C3 and to input and output power respectively CON1 and CON2. Its value is determined by adding the voltage at the Zener diodes D2 and D3 – in the present scheme is recommended not to exceed 300 AT, enough for preamps, and other low power circuits. Zener diodes should be installed just above the board because of the heat. It is also necessary to use diodes with a relatively high power, so they do not overheat.
For the output currents, exceeding 150 mA, Use resistors R3, R4 and R6 with higher permissible power loss. Effectively achieved output voltage and a maximum current may differ from the estimated because the tolerances of individual elements parameters. The reference board, adapted to supply about 260 AT, output voltage is about 220 AT (200 AT + 24 The diodes, connected in series), and the maximum output current is about 70 mA. Transistors T1 and T2 – if both are used, they must be identical. This channel MOSFET with N-type voltage not less than the calculated 500 AT. These requirements are met, For example, IRF820. FETs are mounted on radiators. It is also possible to use transistors with an insulated housing or similar type IRFIBC20G.
Ratings of parts utilized in the scheme presented in Table.