Mosfet preregulator is simple and good complex which achieved the decrease dissipation on 5V the stabilizer of voltage. Simpler is from SCR preregulator, but therefore in the event of considerable inductivities of power supplies, comes to the additional smaller warm-up mosfeta (e.g. 0.3W).
Example usages. If want get 5V and 150mA exit currents in the classic example use 9VAC the source, adjuster with the electrolyte and 7805. Result is about 0,875W heatings on 7805. Usage preregulator on 24VAC the source takes his clothes off the voltage on 7.5VDC= before the stabilizer 7805. Stabilizer dissipate 0.375W, and mosfet may be and without heat sinks, if is the inductivity of source small (e.g. toroidalni trafo strengths 150W). In the practical experiment has been tried 5VA trafo, 18VAC (the substantial inductive source). Warms the mosfeta by half less than the stabilizer (0,19W). Overall warms 0.565W. When 18VAC classic would stabilize, would have on the 7805 dissipation 2,5W the code 150mA.
Follows the conclusion: mosfet preregulator gives the reduction of the total dissipation for 4,5 times when it is about the stabilization of the high entry AC voltages on the small exit voltage.
Use this preregulator may be and in cases when uses small transformers, who with the enlargement corrected voltage know enough to fall. Use preregulator will reduce unnecessary losses strengths on the regulator strengths these this will reduce burdening the transformer i.e. will reduce drop the voltage.
The additional characteristic is that the stabilizer can successfully to work and at drop the voltage for 50 % (for 24VAC the source). The this fantastic result and small dissipation, fight only switching preregulator. Aside from this, dissipation almost not at all depends on the entry voltage. The only lack of complex is that the uppermost value entry voltage must be at least 8V higher from the uppermost value of preregulator voltage (in order to the pier have the power supply). The additional complex with the capacity pump was able rješiti and necessary power supply gatea the mosfeta. Example capacity pumps see on the complex Power supply 24V / 20mA
Principle of work:
Principle of work was founded on the filling capacity on the growing edge of half-wave voltage to the moment when the voltage on the electrolyte achieves the necessary uppermost value. This regulates 13V zener diodes which starts close mosfet. When this starts will happen, voltage on the mosfetu starts let him grow, and the transistor switch closes mosfet by the end of. Time limits the unnecessary dissipation on the mosfetu. Next to second the half-wave, current for the stabilizer gives the electrolyte.
In the version for inductive sources has been added the small electrolyte 100uF who blocks the high-voltage spitz. This electrolyte empties across the mosfeta on the main electrolyte during uncorrected half-wave these in this way provoke additionally the tiny warm-up mosfeta. Because of the such way of work there is no the full-wave version for inductive sources. However because of the emptying of small electrolytes preregulated voltage has the smaller waviness and resembles full-wave are corrected.
Maximal current through mosfet has been limited indirectly limiting the voltage UGS on 6,2V. Vast majority of the standard mosfeta by this voltage no can do miss neither maximal the allowed current this this element 100 % overcurrent is protected.
If wants use predstablizator in front of the changeable stablilizatora then can will join instead zener diodes 13V e.g. zener the diode 8,2 do10V, but so that has not been joined on the mass already that her anode has been joined on the exit voltage. In this way preregulator always will leave the minimal voltage for the work stabilizer regardless of the exit voltage.
Warning: Complex has drawn from the transformer mainstream who equal exit. Therefore needs pay attention that the secondary coil has been dimensioned for this current. Warming the transformer because of losses because of the current wears out will change. Recommend that uses trafo with 12V secondary instead 24V when uses the small trafo. That is, 12V trafo same strengths has the 4 way smaller resistance wires, and thereby and 4 way smaller losses in the coil. Accident is what you losses overheat trafo these increase the probability burnings. Therefore recommend the usage of the small 12V the transformer instead 24V.
Power transformer has been needed minimal PUsec.ac.nominal= * Iout.dc. On the lower picture is the example 5V regulator with mosfet preregulator (are checked the tested version). Mosfet is out of cool down. LM7805 needs minimally will cool down because of the dissipation from 0,5W.. For the protection from the damage, when dried up 100uF necessary, parallelly with this capacity, put the tranzijentni supresor 1,5KE82 (the cathode put on the plus). Impedances of power supplies which brings on the entrance 7805 answers the substitute connection AC of source with the uppermost amplitude 8V and internal resistance equal inner resistance connected transformer. In this example 3,5 ohma.
The shown stabilizer functions on the power supply within limits 10..24Vac (on the nominal load). Dissipation on LM7805 grow when alternating voltage power supplies grow with 10 on 24Vac.
If look for the complex preregulator which would work and on yet the shorter voltage power supplies then can will use the next scheme.
In order to the complex work and shortest voltage necessary added capacitorty pump for the achieving of sufficient biases gatea. Therefore the complex rises the voltage on the capacitor from 1uF (grounded) these need pay attention that he endures more than double uppermost voltages of power supplies.
At half-wave versions were able avoid capacitory pumps the mostnim connection of entry alternating voltage.