A. Voltage Converter Principle
Generally, DC voltage converters are voltage reducers that are often found in electronic circuits through voltage dividers (voltage dividers or voltage stabilizers). In some electronic circuit needs, DC voltage facilities are needed that are higher than the source voltage (step up). For this reason, a DC Converter circuit is needed which is usually developed for various DC output voltages.
Fig.1 principle of voltage change
The input DC voltage U1 is changed by the DC-AC inverter circuit into AC voltage. This AC voltage is very flexible to be developed into step up or step down depending on the needs through the transformer. The AC voltage from the transformer secondary is rectified into DC voltage through the AC-DC rectifier. The output DC voltage is U2.
NB: It would be better if you have read the previous material >> CONVERTER BASICS
B. PWM Control Circuit
DC-AC inverter can be built with a push-pull MOS FET circuit controlled at each Gate by a square pulse that can be controlled by a narrow pulse width (PWM). The load from each Drain is fed to the transformer primary whose AC output voltage depends on the integral area of the MOS FET Drain-Source conduction angle controlled by the narrow pulse width of the PWM at its input.
The PWM control circuit as shown in figure 2 is built using the IC TL494.
Fig.2c Function block diagram
Fig.3 signal form from the pins of the IC TL 494
The PWM pulse from the PWM comparator is corrected by the pulse steering flip-flop. The error amplifier is equipped with a 0.7 mA current limiter. Each output transistor can be used as a Common Emitter or Emitter follower, either singly or in push-pull mode.
C. MOS FET DC to DC
Pins 5 and 6 of the TL 494 IC are RAMP waveform components, which when compared with a certain voltage level, will produce a PWM (Pulse Width Modulation) pulse width at the comparator output. Through the Pulse Steering Flip-Flop (in the form of a D flip-flop) in the TL 494 IC, the PWM pulse will be developed into two PWM pulses that are 180o out of phase to drive the MOS FET installed in a Push-Pull manner. The PWM pulse fed through the Gate will condition the junction (conductivity) between the Drain and Source of the MOS FET which together will produce an alternating current (AC) pulse. Each Drain of the MOS FET is connected to a toroidal transformer with a ferrite core, because the PWM pulse works at a frequency of around 50 kHz. The transformer is facilitated with a center tap primary winding and a center tap secondary winding whose output can be developed for the desired output voltage. On the secondary side it is connected to a bridge diode to obtain the desired DC voltage.
The conclusion is that the MOS FET DC to DC functions to change a lower DC voltage to a higher DC voltage as desired. One example of a bias circuit is seen in Figure 4 below:
MOS FET DC to DC Converter
Evaluation:
- Why was the switching type power supply (Switched Mode Power Supply) invented?
- What is the difference between a linear power supply and a switching power supply?
- What are the advantages and disadvantages of both types of power supplies?
- How do buck converter and boost converter switching power supplies work?
- Where are the applications of switching type power supplies mostly used?
- How does a buck boost converter type switching power supply work?
Answer:
1. In reality, linear power supplies have efficiency when transferring power/energy to a maximum load of only 50%, so that much power is lost in vain. Therefore, the discovery and development of switching power supplies is intended to overcome the energy waste found in linear power supplies.
2. What distinguishes between switching and linear power supplies is how power or energy is transferred to the load. In conventional/linear power supplies, power/energy is transferred to the load continuously, while in switching power supplies, power or energy is transferred to the load periodically according to its switching frequency (generally switching frequency applications are recommended above audio frequency for certain reasons).
3.a. Linear Power Supply
Profit:
- No High Frequency Interference.
- Low Noise/Ripple.
- Very stable.
Loss:
- Maximum low efficiency 50%
- Problem with Weight
- The physical form is relatively large
- The Price is Expensive
3.b.Switching Power Supply
Profit:
- High efficiency minimum 71%
- It is very light in weight
- The price is cheap
Loss:
- High frequency voltage and current shock disturbances
- Ripple/Noise at high frequencies is relatively large
- Tolerance/accuracy demands of switching components
- Disturbance of magnetic induction voltage
4.a. Buck Converter Working Principle
Buck Converter
- S1A closed
- L stores magnetic energy
- S1B open
- R receives charge from C
- S1A open
- L provides energy to C and R.
- S1B closed
4.b. Boost Converter Working Principle
Boost Converter
- S1A closed
- L stores magnetic energy
- S1B open
- R receives charge from C
- S1A open
- L provides energy to C and R.
- S1B closed
5. Switching Power Supply Applications,
Almost all electronic device power uses this type, for example: Television, Video, VCD, Computer, Cellphone Charger, Laptop Charger, etc.
6. Working principle of Buck-Boost Converter
is a combined converter of Buck and Boost Converter, the purpose of which is to improve the switching speed so that better efficiency can be obtained.
Netizens
Q1: How do you calculate the transformer windings? For example, if the input is 12v, the expected output is 32v ct.
Get to know the Input-Output Interface
1. DC Input Module (Current Sinking)
The Input Sinking Module is a module that flows current into the module input terminal, if the input is activated. Therefore, current flows out of the input components (sensors, switches, and so on). So the input components in this case function as a current source (Current Sourcing), where each component has a common measurement point. While the input module has a single common.
2. DC Input Module (Current Sourcing)
Input sourcing modules channel current out of the input terminal to the input component, if the input is activated. So, the input components, in this case, function as current sinking components. Therefore, the signal at the input component terminal will be channeled to ground, if the input is activated.
3. AC/DC Input Module
This module can receive/send current (current can come out or come into the input terminal), alternately every half cycle. The upper interface will work as a current source or current receiver. The lower interface is used for sensor output or switch with AC source.
4. DC Output Module (Current Sinking)
Sinking and Sourcing are terms used to define the control of direct current flow in a load.
Sinking digital I/O (input/output) provides a ground connection to the load.
Consider a simple circuit consisting of a single digital input connected to a digital output. The circuit requires a voltage source, a ground, and a load.
Sinking digital I/O provides the necessary ground in the circuit. Figure 1 shows a sinking digital output connected to a digital input source. In this circuit, the load is pulled to ground because the sinking digital input is provided.
5. DC Output Module (Current Sourcing)
This module flows current out of the output terminal to the actuator. The output component functions as a current receiver (Current Sinking). All commons of the output components are connected to the negative side of the DC power supply, while the common terminal of the module is connected to the positive side of the power supply.
6. AC Output Module
This module connects the AC voltage to the AC type actuator and is never referred to as a current source or output current receiver. The AC source is connected between the common module and the AC output component. The AC module can be used on all AC type actuators if the voltage is appropriate.
7. Relay Output Module
This module has Normally Open (NO) relay contacts for each port, which allows a larger load current to flow, which can drive both DC and AC output components. The block diagram of the relay output module interface is shown in Figure 12-8d.