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DC-DC Converter Voltaje-Mode ControlDesign OPAMPS and Infrastructure

Reyes, Rosales, Jos

Benemrita Universidad Autnoma de Puebla

Puebla, Mxico

[email protected]

Abstract This paper presents the design of a DC-DC

converter and its internal structure, which basically for this

paper considered three main blocks (an error amplifier, a

comparator and a DC-DC converter), which will be explained

later in more detail.

This paper starts by giving a general introduction of the DC-

DC converters and their use today, then emphasizes the

converter used in this document and the reason that was used,

the output of this converter is sent as feedback error amplifier,

which is also at the transistor design, so that the output generates

a PWM signal (pulse-width modulation) that is necessary for a

good converter efficiency.

The purpose of this document is to provide the reader a broad

view about the DC-DC converter in voltage mode and observe

that there is a transistor level circuit that meets the expectations

of the error amplifier.

I.INTRODUCTION

Power electronics in general is responsible for processingand controlling the flow of electrical energy by supplyingvoltages and currents in an optimal way for the loads. This

processing can become current conversions or regulation will

be processed same parameters voltage, current, frequency, as

required by the load.

In the industrialized world, the key to any activity is

energy. However, the loads that occur in such circumstances

are largely non-linear, to help work with these charges have

been introduced into the world electrical power converters asthese significantly improve energy consumption, thereby

improving also equipment performance and preventing these

suffer any damage.

A power converter is a basic module (building block) ofpower electronics systems. The converters use power

semiconductor devices (diodes, transistors, thyristors, SCR)

controlled by electronic signals (control circuits) and energy

storage elements (inductors and capacitors). Figure 1 is shown

the block diagram of the power converter with the necessary

signal to the control.

Convertidor

DC-DC

Controlador

VoutVin

Ref

Fig. 1. Diagram of the power converter whit control.

The converters can transform the nature of the energy for it

to be used in different applications. In this way they are divided

into:

AC to DC converter (Rectifier) DC to AC converter (Inverter) DC to DC converter (Chopper) AC to AC (Ciclo-converters)

These converters are termed direct energy converters, as

used for a single step conversion.

This paper emphasizes the DC-DC converters.

There are two methods for DC-DC conversion:

Linear: Based on the use of a regulatory elementthat works in your area resistive dissipating

energy.

Switched Converters: They are based on the use ofsemiconductor elements working in switching (cut

/ driving), thereby regulating the flow of power tothe inverter output. These converters are also

called switching power supplies and have

significant advantages over linear converters.


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II.SWITCHED CONVERTER OPERATION

The principle is the same for all switched power converters

is based on energy storage and transfer in switching cycles.During the first interval of the working cycle, the drive stores

the energy in the coil, transferring the second energy range to

work this capacitor. The control governs the conduction statesand locking switches.

To introduce the basic operation of the DC-DC converters,

consider the circuit shown in Figure 2, consisting entirely of a

switch and a pure resistive load.

Vin

S

Vout R0

i0

Fig. 2. Diagram of basic operation DC-DC converter

The switch opens and closes according to a signal of period

"T" drive period called. The time during which the switch is

closed, and therefore the load is connected to the primary

power source, driving time will be called TON. On the other

hand the time that the switch remains open, leaving the load

isolation, lockout time is called TOFF . The sum of TON and

TOFF, as seen in Figure 3, gives the converter period (T).

T

T - TON

z

Vout

TON

Vin

Fig. 3. Converter period

When the switch S is closed, 0


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When the current is mild variation is said to be in

"continuous mode". Now according to the law of conservation

of flow holds:

(VsVo)DT= -Vo (1-D)T (3)

Where D is the duty cycle and T is the period, Vo is the

output voltage Vs is the source voltage.

From the above it follows that

D=Vout/ Vs (4)

To calculate the capacitor inductor, one has as a rule of

estimation.

L >= R(1-D)/2F (5)

Cmin = (1 -D)Vo/ 8VrLF2 (6)

It proposes a 10K load at a frequency of 100 MHZ with this

results in an inductor and a capacitor 30UH 3pF. As output

clipped signal is obtained, as shown in Figure 6.

Fig. 6. Vout of the Reducer Converter IdealThis result is implemented with an ideal switch, but this

was changed to a MOS transistor and its behavior is the same.

IV. GENERAL BEHAVIOR OF THE DC-DCCONVERTER CONTROL MODE VOLTAGE

In voltage mode control scheme shown in Figure 7, theconverter output voltage is detected and subtracted from one

external reference voltage error amplifier.

The error amplified produces a control voltage which is

compared with a constant amplitude waveform with a

sawtooth. The PWM comparator produces a signal that feeds

the switches that control the DC-DC converter.

ComparatorConvertidor

DC-DC

Error

Amplifier

Voltaje

Reference

Voltaje output

Control

VoltajePWM

Signal

Sawtooth

Waveform

Fig. 7. Voltage Mode Control SchemeThe design of the DC-DC converter is done. To show the

general behavior of this system is to design the error amplifier

transistor level.

This block involves placing an array of transistors single

ended configuration such that input Vin is obtained, an input

Vip and output Von, which is shown in Figure 8.

Fig. 8. Array of Transistors Singles-EndedThe proper functioning of the error amplifier depends on

the good design of transistor-level device, for this we must

ensure that all transistors are in the saturation region, so as weall know have to calculate the dimensions of the transistors for

a positive response.

The error amplifier is designed with a configuration in

differential mode, where input is obtained as the output voltage

and the reference voltage, the general diagram of this

configuration is shown in Figure 9.


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V1 V2

R1

R2

R3

R4

Vout-+

Fig. 9. Differential Amplifier idealFrom where you get

(7)

V.RESULTSThe error amplifier is designed with a block instance where

single ended configuration transistor level.

The general scheme using the above described are shown in

Figure 10.

Fig. 10.General Sheme of the D-DC Converter whitControl

The following figures show the behavior of the converter

made.

With a 1.2V reference voltage, the output is 1.4voffering.

Fig. 11.To 1.2V reference voltage With a 1.4V reference voltage, the output is 1.5v

offering.

Fig. 12.To 1.4V reference voltage With a 1.6V reference voltage, the output is 1.6v

offering.

Fig. 13.To 1.6V reference voltage

With a 1.7V reference voltage, the output is 1.8voffering.

Fig. 14.To 1.7V reference voltage

VI.CONCLUSIONThis document has allowed us to analyze the operation of a

DC-DC converter controlled chopper in voltage mode.

In the resulting signals obtained can be observed that all

this has on pulse circuit in the output voltage of the circuit, this

presents disadvantages applications when it is used by a control


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signal fed back to avoid these voltage spikes that may be

detrimental to the loads.

The results generated in this paper were satisfactory, as it

was found to design a transistor level amplifier which together

with a feedback comparator worked for a DC-DC converter.

This work was a result of learning which consisted of in-depthstudy of the transistor and its applications.

BIBLIOGRAPHY

[1] Rashid, Muhammad, Electrnica de Potencia, Tercera edicin,2004

[2] Mohan, Ned, First Course on Power Electronics and Drives,edicin 2003

[3] F. Maloberti, Analog Design for CMOS VLSI systems,Kluwer Academic Publisher, 2001.

[4] Mohan, Ned,Undelad, Tore, Robbins, William, Electrnica depotencia, convertidores, aplicaciones y diseo, tercera edicin.

[5] Garzon S. Carolina, Anlisis de convertidores de potencia DC-DC con software libre de openmodlica, 2012.

conv dc-dc paper english

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