A simple powerful parallel stabilizer on transistors 12 volts 600 milliamps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The proposed article describes the principles of operation of a parallel stabilizer, and considers the possibility of using it to stabilize the power supply of powerful high-quality bass amplifiers. A diagram of a complete power supply with a parallel regulator is also shown.

Among radio amateurs, as well as in high-quality industrial audio devices, parallel regulators are widely used. In these devices, the stabilizing element is connected in parallel with the load, which is well reflected in such a parameter of the stabilizer as its speed. In fact, the speed of the stabilizer is determined by the speed of the stabilizing element. Also, the advantages of parallel stabilizers include the fact that regardless of the current consumed from the stabilizer, the current consumed by it from the power source remains unchanged. This fact has a positive effect on the level of noise emitted by the PSU as a whole (due to the fact that the consumption current deviations do not flow through the transformer and rectifier bridge), although it is the reason for their low efficiency.

Consider the above on the example of the simplest parallel stabilizer - a parametric stabilizer on a zener diode (Fig. 1).

Rice. 1. Parametric stabilizer

Resistor R0 sets the total current that will flow through the zener diode and the load connected in parallel to it. It is easy to see that when the load current changes, the current through the resistor R0 will remain constant, only the current flowing through the zener diode D1 will change. This will happen as long as condition (1) is satisfied:

I_Н<I_R0-I_st.min.   (1)
where I_Н - load current,
I_R0 - current through R0,
I_st.min. - minimum stabilization current of the zener diode D1

The speed of this stabilizer will be determined mainly by the rate of change in the value of the barrier capacitance of the zener diode [1], as well as the charge-discharge time of the capacitor C1.

However, such stabilizers also have disadvantages - in particular, in order to obtain a more or less decent stabilization coefficient (> 100), a current commensurate with the load current must flow through the zener diode. This circumstance, taking into account the fact that the vast majority of zener diodes are designed for currents up to 100 mA, makes it difficult to use parametric stabilizers in powerful devices.

To get around this obstacle, a powerful active element, such as a MOSFET transistor, is placed in parallel with the stabilizer, as shown in Fig. 2.

Rice. 2. Powerful parallel stabilizer

In this circuit, the zener diode only sets a stable voltage at the gate of transistor Q1, through the drain-source circuit of which the main current flows. Zener diode VD3 protects Q1 from breakdown due to the high voltage of this implementation. More details about the operation of this scheme can be found in [2].

The circuit shown in figure one is capable of handling high currents (limited by the limiting characteristics of the applied mosfet), but it releases more power and has a low efficiency (less than 30% - if the drop across resistor R1 is relatively large, the current through the mosfet is comparable to the current through the load, the values input and output voltages do not exceed 100 V), which is a serious disadvantage in high-power applications.

But the current flowing through the mosfet can be significantly reduced without compromising the stabilization factor if the source of instability in this circuit is eliminated. Let's dwell on it in more detail.

When the voltage at the input of the stabilizer changes, the current flowing through the resistor R1 changes, this change can be reduced by increasing the value of this resistor, but this, in turn, will require an increase in the voltage drop across this resistor, and therefore reduce the efficiency. The best solution, in my opinion, is to replace this resistor with a current source, on which the voltage drop can be set equal to the sum of the input voltage deviation + 2-3 volts for the active element of the current source to work normally.

Taking into account these additions, a power supply circuit with a parallel stabilizer was developed, shown in Fig. 3.

Rice. 3. Schematic diagram of a PSU with a parallel stabilizer (click to enlarge)

The function of the current-setting resistor here is performed by the current source on the transistor Q1. To reduce the instability of the current it produces, it is powered by another current source of lower power, which in turn is powered through an RCR filter to reduce ripple. Resistor R7 can roughly adjust the operating current of the stabilizer, resistor R4 smoothly. Resistor R8 can adjust the output voltage of the stabilizer within a small range. R6 represents the PSU load, consuming about 600 mA. (Do not connect the PSU without load!). Transistors Q1 and M1 can be installed on a common radiator with an area of ​​at least 500 sq.cm.

The main technical characteristics of the stabilizer (with input and output RC filters):

1. Output voltage = 12V.
2. Input voltage > 18V.
3. Load current - 600 mA
4. Current consumption - 750 mA (with the ratings indicated in the diagram, it changes by selecting the resistor R2, R7, R4 - in order of magnitude of influence)
5. Output ripple level - -112dB
6. Efficiency=57%

It is easy to see that the presented circuit has sufficiently high parameters in terms of efficiency and Kst, comparable with the characteristics of compensation series stabilizers, while almost completely retaining the advantages of parallel stabilizers.

At the same time, the circuit is quite simple, does not require scarce parts, and can be designed even by novice radio amateurs.

With an input voltage of up to 50V in the circuit, you can use - Q1-BD244C, Q2-BC546A, M1-IRF630. As a zener diode D7, you can use any voltage of 8,2 V, diodes D1-D4 such as SF54, diodes D5, D6, D8, D9 - for example 1N4148.

Literature

1. Zherebtsov I.P. Fundamentals of electronics, p. 40, L, 1989
2. Ryzhkov V.A. A simple parallel transistor stabilizer, audioportal.su/another/p2_articleid/65

Author: Baushev Oleg aka Olegyurich; Publication: cxem.net

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