Calculation of the stabilizer. reference Information

Calculation of the stabilizer

Background

Calculation of the stabilizer

To obtain a more constant voltage at the load when the consumed current changes, a stabilizer is connected to the rectifier output, which can be made according to the circuit shown in Fig. 1. In such a device, a zener diode V5 and a regulating transistor V6 work. The calculation will allow you to select all the elements of the stabilizer, based on the given output voltage U_н and maximum load current I_н. However, both of these parameters should not exceed the parameters of the already calculated rectifier. And if this condition is violated, then the stabilizer is first calculated, and then the rectifier and power transformer.

The calculation of the stabilizer is carried out in the following order:

1. Determine the input voltage required for the operation of the stabilizer (U_issue) for a given output (U_н):

U_issue = U_н + 3,

Here, the number 3, which characterizes the minimum voltage between the collector and emitter of the transistor, is taken based on the use of both silicon and germanium transistors. If the stabilizer will be connected to a ready-made or already calculated rectifier, in further calculations it is necessary to use the real value of the rectified voltage U_issue.

2. Calculate the maximum power dissipated by the transistor:

Р_max = 1,3 (U_issue - OR_н) I._н,

3. Select a regulating transistor. Its maximum allowable power dissipation must be greater than the value of P_Max, the maximum allowable voltage between the emitter and the collector is more than U_issue, and the maximum allowable collector current is greater than I_н.

4. Determine the maximum base current of the regulating transistor:

I_b.max = I_н / h_{21E min},

where: h_21Emin - the minimum current transfer coefficient of the selected (according to the reference book) transistor ..

5. Select a suitable zener diode. Its stabilization voltage must be equal to the output voltage of the stabilizer, and the value of the maximum stabilization current must exceed the maximum base current I_{b max}.

6. Calculate the resistance of the resistor R1:

R1 = (U_issue - OR_Art) / (I_{b max} + I_{st min}),

Here R1 is the resistance of the resistor R1, Ohm;
U_Art - stabilization voltage of the zener diode, V;
I_b.max - calculated value of the maximum current of the base of the transistor, mA;
I_st.min - the minimum stabilization current for this zener diode, specified in the reference book (usually 3 ... 5 mA). .

7. Determine the power dissipation of the resistor R1:

P_R1 = (U_issue - OR_Art)² /R1,

It may happen that a low-power zener diode is not suitable for the maximum stabilization current and you will have to choose a zener diode of much higher power - this happens at high current consumption and using a transistor with a small coefficient h_21Э. In this case, it is advisable to introduce an additional low-power transistor V7 into the stabilizer (Fig. 2), which will reduce the maximum load current for the zener diode (and hence the stabilization current) by about h_21Э times and apply, respectively, a low-power zener diode.

In the calculations presented here, there is no correction for the change in mains voltage, and some other refinements are omitted that complicate the calculations. It is easier to test the assembled stabilizer in action by changing its input voltage (or mains) by + -10% and more accurately select the resistor R1 for the greatest stability of the output voltage at the maximum load current.

Publication: radioman.ru

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