AVT735 - DC switched mode regulator. Modeler drill controller. Economical bulb dimmer
The device can be powered by a battery or DC power supply. The load can be any DC motor or bulb. Thanks to the switched-mode principle, slight energy loss is detected. The output transistor does not require a heatsink. The regulator module is ideal for use with the modeler driller. The regulator ensures that the driller is working at maximum torque even at low rotation speed.
• Used for speed control in modeler drills.
• 6-24V/100W bulb brightness control.
• Near 100% efficiency at maximum output current 10A.
• Adjustment of the output waveform with potentiometer.
• Power supply: 6-25V DC.
• PCB dimension: 36×57mm.
• Electronic Kit – soldering required.
The U1A and U1B gates work in typical two-inverter oscillator mode. Frequency determines the C2 capacitor or in a few cases the C3, as well as the potentiometer PR1 and resistances R2, R3. MOSFET T1 transistor is controlled by two gates U1C, U1D connected in parallel. If the T1 is a MOSFET, then the R4 resistor is not needed and it could be replaced by jumper. If the transistor T1 is a Darlington transistor, use R4=2.2k to limit the base current. Potentiometer PR1 can vary the duty ratio of the output waveform in a wide range from 1 to 99%. Pulses on the T1 gate switch on and turn off the T1 transistor while the average power delivered to the load connected to the Z2 connector depends on the generator duty cycle. In this way the PR1 potentiometer makes it possible to control power delivered to the load. Clamp diode D4 is necessary when the regulator supplies the inductive loads (motors in particular).
Thanks to the switched mode operation principle the power loss of the T1 transistor is low and it does not need heatsink even at currents of several amperes and up to 100W loads. It should be remembered the kit is a power regulator and not a motor rotation regulator, so the speed of motor rotation depends on how heavily it is loaded.
Power is switched mode regulated by the kit that supplies square voltage wave load. This signal can be a source of electromagnetic interferences. The cables connecting the regulator and the load should be as short as possible. The cable connection should look very much like a twisted pair of cables. Additionally, it is recommended to connect the 1000-10000µF electrolytic capacitor to the power supply connector.
The extra C3 capacitor can be connected by jumper J1. As a result of this the oscillating frequency of the generator is lowered from about 700Hz to 25Hz. This reduces generated electromagnetic interferences. Such high frequency reduction might have a negative effect on some loads (i.e. it might cause the undesired bulb flashing effect). Should this be the case, the capacity of the C3 can be selected by the user himself.
Assembly and test
The schematic of the regulator is shown in Figure 1 while the PCB layout is shown in Figure 2 in the user manual. While assembling the regulator particular attention should be paid to the polarity of the components. Once the regulator has been assembled and checked, the corresponding load. (e.g. a bulb) should be connected. Then the power supply from 9 to 15V can be connected. A device assembled without errors will operate immediately after switching on the power supply.
R1-R3, R5: 1kΩ
R4: 0Ω (black)
PR1: Rotary potentiometer 100kΩ
D1, D2: 1N4148
D3: 12V Zener diode
US1: CMOS 4093 IC with 14-pin IC socket
T1: BUZ11, STP55NF06 or similar
J1: goldpin connector with jumper
Z1: 2-pin terminal block connector
Z2: 2-pin terminal block connector